The Big Score! Mountain Expansion Chassis!

@Speedy:

I disagree. Consider this - If we take out Q8 (which is what Steven is to do next, right?)
and the voltage climbs to 60V this means the Bridge Rectifier is acting as the step-up
multiplier. Or something else in the very front end of the supply. But there isn't much
else. Then we must order a bridge and regulator. And investigate why we're getting 60V
when we should get 34V.

If the voltages stay at 30-35, then we can just get a regulator. And the chassis will work at this point.

I tested this on my junk chassis. I took out the regulator, and the capacitors charged to
34V as noted in msg 242. So in a functioning circuit there isn't a need to get a higher
rated part. There was zero load on the rectifier and capacitors.

Well, when the regulator is out of circuit the only parts seeing power is the power brick
connector, fuse, 2 capacitors, and bridge. Everything else is out of circuit.

I also recommend that Steven does this 34V or 60V test without the Apple II connected at
first. This ensures no ground loops in case of partly isolated (failing power brick). Then
repeat the test with the Apple hooked up to check the brick isolation. Since I'm not there
in person to make subtle observations and impromptu measurements I'm leaving no stone
unturned.

I re-emphasize that my junk test chassis does not pump up above 34V. And my good chassis
doesn't go above 34V either, Apple II+ on or off. No difference. And with Apple II off, there
is minimal load anyways. Certainly not enough to decrease 60V to 34V.

Practical real-life testing (and theory) says we'll see a max of 34V with the regulator
out. If this is not the case in Steven's chassis, we'll have found the failure and likely
the cause of regulator damage.

Note:
With risk of getting ahead of the situation; I wonder if the spank'n brand-new caps didn't
apply too much of a surge current to the bridge, thus damaging it. It is 30 years old, and
we don't know the prior history. Well That's all speculation and may not apply here at all.
We'll see with the new set of measurements.

Good day gentlemen!

During the week of June 2 through June 9 I might not be available for commentary and
friendly debate and troubleshooting.

And for certain my chassis will not be available for measurements or comparisons.

Something's still bothering me here: And I might have found it. I awoke screaming about burning electrical stuff, not an unusual thing for sure. And now in organizing my MHEC
pictures and notes folder I looked at these pictures again and got to thinking if the
metal standoffs could have shorted the 5V rail at the indicated points?

Not so much the bottom edge one, there's some room there. But the one in the middle? Was a
standoff placed there? It comes perilously close to shorting 5V to GND.

Originally I didn't think so. But on Steven's board, here, the trace looks a bit wider and
closer to the hole center than on mine. Of that there is zero doubt. I'm talking fractions
of a mil here, but could it be enough to cause a problem?

None of the via holes connect to anything except ground. Which is why I downplayed the whole idea of metal standoffs shorting something. But could a standoff have "overstepped" its bounds during reassembly and pulled 5v low? On my chassis, not likely. On Steven's chassis, more likely.

Not all chassis had even plastic standoffs in that location. In fact, my later revision
junker chassis didn't have any there at all.

Maybe we need to revisit this as the root cause?? If this is the smoking gun it sure as
hell smoked the power supply!

In msgs #201 - 205 we discussed this possibility. While all the holes and vias are indeed
at ground potential. And in theory they shouldn't cause a problem. But if we are changing the
design specification, on purpose or inadvertently, something might go wrong. It might have
started with the standoffs. One thing leads to another and failures cascade.

Is it at all possible that the center standoff nicked the trace insulation and held down the 5V
rail? You did say you placed one in the center. Right?

If so, we need to consider a new mode of failure here. Since each rail is somewhat independently
derived, the other ones, +12, -12, and -5, would continue operating for the moment. Depending how
quickly (if it did) the 5V section blew, the +12V would have "backfired" itself through the drive
controller card and powered up the disk. Especially after you pressed the "chassis enable button".

Since we never really used disks in the chassis we regularly blew up in the laser shop, I hadn't
seen this exact failure mode before. But I see how it could happen.

Now with the supply containing partly fused semiconductors - it was enough to continue working.
When you killed the power (to try again) all the micro-arcing (so to speak) within some supply
parts (we have yet to determine which) stopped. And, now, today, the process doesn't start again!

Using layperson's and mechanical engine terminology: you could say that an engine had undergone a
severe overload. And while it would continue running while running, it would never start again
after being shut down. This fits with the green light behavior too

In this situation, changing the specification of the mounting hardware to something other
than the designer's choice might have blown up the whole shebang!

While further investigation is warranted I feel this is the root cause.

When 5V supply is shorted to GND, the cascade failure happens backwards here. The Power FETs
spike in frequency in attempt to maintain power, reaching way above 54KHz, up to 125KHz and
drawing immense current that the capacitors are all too happy to provide! We're talking hundreds
of amps at 35 volts!! No ordinary regulator is going to be kosher here. And when the regulator
blows, the oscillator stops and the transformer EMF collapses and backfeeds all that power it
sucked during the high-current ramp-up. Everything is blasted back all the way to the Bridge
Rectifier. A surge of 90 volts or greater. By now the current is being converted to heat by the
melting junctions. The bridge, by nature, stops the power adapter from smoking out. Putting a
protection & discharge circuit in at the capacitor point would only serve to save the Bridge. And
as a side effect, resulting a more certain destruction inside the regulator Q8.

As for the condition of the parts on the secondary side of T1, I don't know. I would need more
measurements. They might be alright. Depends on how long they were under load and if any
junctions had time to heat and fuse before the regulator gave up the ghost.

Why didn't the fuse blow? All of this crap happens within microseconds. And the fuse is a
slow-blow type. And it's on the wrong side of things anyhow. It just sits around protecting the
Bridge Rectifier from an incoming AC surge. And at the same time if the internals of the supply
gets too hot, the low melting point solder blob will liquefy and stop power. So it serves to
protect from incoming current spikes (when AC is on the upswing and at the same time the bridge
is under spec due to wear and age). It prevents the power brick from overheating if the bridge is
shorted internally. This fuse does little to protect the chassis electronics overall. Except
thermally.

All the fail happens between the caps and the T1 primary. You've got this huge blast of current
ping-ponging back and forth if the regulator stops!

Is this chassis repairable? Absolutely! I've fixed worse.

One time, I recall back in the day, a similar surge reflected off the capacitors, arced across
the -5 and -12 sections and blew everything to smithereens. We threw that board out after 2
repairs. I suspect even more power came in from outside the box that time. Quite the sight to be
sure!

Hello Keatah,

again i do agree with all the points you explained..... i had mistrusted the metal standoffs from the very beginning that Steven mentioned them... from the point the box did work, to the point the box stopped working only 2 things happened: first he changed the "big caps" and second he changed the standoffs....
so if the "big caps havn´t been faulty right from the beginning the standoffs would be the very next "candidates" of causing harm to the box. That also would fit to the symptoms, that the Q8 has been blown away and therefor the entire following part of the cuircuitay functions have been disabled by the fact, that the oscillator get´s wrong voltages and can´t start up swinging....

that was the very reason i noted up the possibilty that this went wrong....

just a note on my behalf about the SG340-24 : if you examine the inner part of the cuircuit within the IC you will see
that at the output there is a "big power Transistor" that delivers the mainpart of the current. In case of a shortcut this part would be the first to become damaged..... if that part is damaged, then there are stll enough transistors inside the regulation part, that might have kept intact - but act without the big transistor as a "oscilating pump" and probably load up the "big caps".

This is why i am rather sure that this is the cause for misbehaviour of 60 Volts.

At the other hand - if the rectifier would have been damaged as you did suspect... then we would have seen more AC voltages in the later measurements. This did not happen.
Therefor i do believe that the rectifier is not damaged.

So because of that reason, i agree first to make the "no load" measurement with the Q8 removed. I´m rather sure that
if the Q8 is removed - we will see "normal conditions" below 40 Volt !

If this is fact - then it´s time to order the replacement for the Q8. If the measurement after removel of Q8 still shows up values beyond the 40 Volt - then headache rises ahead and we have to trace deep inside to find the reason ( starting at the possibly faulty "big caps" .... - but only if we see unusual values - not before....
If we see unusual values then we also get headache for hunting of a replacemnt for Q8....

So lets first get the measurement of the "no load" condition before we give advice on ordering and on spending money - otherwise our recommendations might lead to spending money without use or result....
sincerely speedyG

Excellent. I would like for Steven to stick a naked standoff in the hole and twist it around and
see if it can rub against the trace I outlined.

IIRC Steven replaced the caps prior to him powering up the box. Since these are exact replacements
I see little problem here. They were broken off and were bouncing around in the box. Yes.

The regulator needs to be replaced regardless of where the voltage is coming from.

If the regulator is pumping up the caps to 60V then it is bad as you say. It needs to be replaced.
If the rectifier is somehow making 60VDC from 28VAC then, still, the regulator input has been
exceeded by 10V and should be replaced.

No swelling headaches. It's either one or the other. I can sell Steven the old SG340K-24
from my junker chassis. It's tested and working. I then take money and buy new NTE1924 for
10 bux!

Doesn't matter where the 60V is coming from.
In any situation to follow we need to make measurements and replace Q8.
Since measurements are free, they should be done first.

I don't see how the big caps could be bad unless there's some funky cavitational resonance
occuring between the plates inside them, which I've only read about in some obscure paper years
ago. Naw...

Hello Keatah,
hello Steven,
hello AFmembers,
again full agreement - with one remark:

to the "big caps": we don´t know at which conditions they have been stored.....
usualy manufacturers of capacitors label their products by the calculus of:
issued label of operation + 50% =(equls to) voltage that causes damage to the product....
so 40 Volt limit by specs + 20 Volt ( = 50% from 40 Volt = safty margin ) = 60 Volts......
the values we have seen reach up to exactly the limit where harm might start....

if caps is connected to wrong polarity they blow up with smoke and explosion spitting Bor acid around - that happens very fast ( in general within few seconds ) ....
- but if they are exposed to values near or close to limit of total capacity ( spec + 50% ) and that voltage is not realy much higher ( at least 10 Volt more ), then they won´t start that soon lifting the cuptop, but instead get
microcracks in the inner isolation, that will expand by time and lead after a longer period to internal shortcut...
If the time is too short to produce shortcut - the first symptom will be a drop of capacity ....
in this case : nominal 3300µF drop down to 3100MF continueing to decrease to 2800µF and so on till after the
longer period you will see 0µF = ( equal to ) shortcut..... If the damage has reached more than 30% of the former original capacity, they start leaking at the output of the wires....

I believe they might have been damaged within the first 10% of the capacity and if that happened they would
silently "die" within the period of the next 100 hours of operation.... so i propose it to be good idea to check if they still have full capacity.... if they have, then the damage might not have happened up till now because the time of exposure might have been too short... in such case we could leave them in the box..... but if measurement shows that they have less than 3000µF, then i would start to worry and give advice to replace them....

but lets first wait for the measurements from Steven....

sincerely speedyG

This is the load bearing circuit within Q8 that Speedy is talking about. The red stuff is what
handles the power. The other stuff [i]controls how much[/i] power the red stuff handles.

Raw variable power comes in on Vin. And unadulterated virgin power leaves the device on Vout. A
smooth DC level that doesn't vary much unless device limits are exceeded. Then anything can
happen, including making it vibrate up and down and pumping the "big caps" up.

If current is sinked slowly (relatively speaking) through the device, then look and see that the
thermal shutdown can come into play. But pre-pumped capacitors - courtesy of the bridge
rectifier - can allow for a big surge demand by the Power Fets and blow the output stage (marked
in red). When the Apple II is turned on.

How do the capacitors have time to charge up? Doesn't the current draw of the shorted power
supply prevent the capacitors from charging in the first place and make the fuse blow? [u]No it
does NOT![/u]

Remember the bridge is working hard 24/7, always on, and at full speed immediately within 8
milliseconds of chassis plugin!

Now when you turn on the Apple II, Q7 is a traffic police and tells the oscillator to
start up. When oscillator starts up. The Power FETs start swinging and pull everything
through the regulator, specifically the parts outlined in red. They pull extra hard and
stretch Q8 output, because the rest of the circuit cannot be excited hard enough, because
the T1 secondary is tied to ground by metal standoff which should be plastic!

There's a smaller school cop circuit like with R2, D9, C11, R1, and Q7, that looks for movement
on T1 primary (via frequency and balance polarity). In theory this is supposed to stop the
oscillator or move a bias point slightly up or down to re-balance the end output on T1A1 or T1B1
via pushing Q1 or Q2 a little harder. Depending on the load imposed by what you have installed
in the chassis.

While there is no complete direct connect between the Primary and Secondary side, the imbalance
is detected indirectly by school cop sensing the common connection of Primary side winding
connections (2) & (3). R2, D9, C11, R1, and Q7 do all that. I say school cop because it is a
small circuit that does many things. It watches 24VDCout, ~54.02KHz coil frequency, and power
on/off from Apple II. And it turns on/off and biases and tunes the main kicker oscillator.

Magnetic coupling in T1 makes sure Primary = Secondary, within reason of T1/T2 ratio.

EMF collapses in uncontrolled fashion sending shockwave backwards giving poor old Q8 a double
whammy in the ass. I only hope the swinging FETs aren't damaged either. Big expensive to
replace! And caps can dispense hundreds of amps!

I consider this a 1.5x insulated circuit in the big picture. 1x isolation happening at the
powerbrick transformer. And the other "0.5" isolation at T1. You will note that ground
propagates from the bridge rectifier (-) all the way to the ground pin on the Apple II power
supply AC cord. For it is the Apple II that creates ground reference.

Now, to properly rearguard this circuit. A fuse should be placed between Q8 and caps. For extra
bonus points we put fuses at the FETs. And saved all sorts of bux deluxe at repair time.

I also agree with msg #257. The importance of potency within the capacitors must not be
overestimated or underestimated.

A small circuit will have to be constructed to charge or discharge them at a known rate.
And by a careful DMM surveillance as they go from full power to zero across a resistor.
There are other observances like if they can hold a charge in free air with no
connections. Or if there is internal resistance.

We can calculate a discharge curve and use the 8 constants rule and all that happy stuff.

But why not test them under load. Once the chassis is fixed, check the AC ripple. With no
load, Apple II off or not connected. There should be about 7mV ripple. We can put some
cards in the chassis and look at ripple and sag.

It isn't worth it for Steven to go and buy a capacitor tester, especially one that will go
to 3000uF and do ESR and all that stuff.

I could test them, or he could take them to an electronics shop and have them do a
one-time courtesy test. Or just buy new ones. Or take a chance and just watch for fluid
leakage next year! Stick a piece of paper under them to test for leaks without taking them
out.

Why 60V? why why why.. Why not? The capacitors would act as a series resistor once you get
far enough past their tolerance. But hopefully before breakdown begins. And if the current
wasn't too much, there wouldn't be a problem at all. The capacitors themselves would be
inherently self-limiting the maximum voltage potential. When a capacitor nears full charge
it "pushes back" and current goes up.

I suspect that any oscillator born out burned out parts isn't going to be back-filling
the capacitors with any significant force. And the +50 spec you mention might very well be
the limiting factor.

Or, maybe, these are bad caps to begin with? They seem to be new old stock, mfg in the
39'th week of 1993. Maybe they have electrolytic failure, and the bridge rectifier punched
right through them? And there is no filtering whatsoever? Just a half-assed guess.

But in any case be thankful they don't have that capacitor plague disease that was popular
in computers in the early and mid 2000's. I had a Pentium III CPU catch fire because of
that!

As electronics continue to evolve - it is ever important that specification and vigilance
for quality be maintained.

I also did an impromptu test to see if anything related to the front panel button could
short against the chassis frame, and therefore GND. I didn't observe anything on my switch
assembly and the LEDs & switch are isolated good.

If Steven all of sudden got disk motor spinup with button press, maybe there's a problem
there. Just thinking outloud till we get concrete measurements.

Maybe his box has a switch that is grounded by default of having different mfg. part?

Hello Keatah,
thanks a lot for the additional expenations and adding the relevant part of the datasheet.
i agree that a extra measurement instrument to capacity is tooo much of the efforts invested in
the task..... the riplemeasurement is a quite reliable index to the function of the "big caps".
If there is any kind of damage inside, there will be a remarkable change in the riple detected -
in other words the amount of AC at the "big caps" rises with acknowlegable amount.

In the following i just treat with 4 pictures the other topic discussed above about getting
some kind of easy and cheap protection into the box against voltages that might exceed permitted
limits of the inputvoltage of the voltage regulator Q8 of 40 Volts and thereby also protect the
following parts of the box behind the regulator.

This solution acts in the following way:
unless the voltage exceeds the 39 Volt nothing changes in behaviour of the box.
At the moment the voltage rises above 39 Volt to 40 Volt or above the zenerdiode only lets 39 Volt
pass to the following stage of the box and truncates the voltage above ( or to say in other words:
it demands the voltage above 39 Volts to branch away from the mainpowerline and pass the zenerdiode
and the powerresistor in direction to the groundline - you may see that as a kind of "controlled"
shortcut of the exceeding voltage to the ground leaving the normal amout pass by to the backpart of
the box. When this happens the amount of power passing the fuse will start rising beyong its permitted
limit and force the fuse to blow within few second while the box behind the protection only recieves
the controlled and limited voltage. The powerzenerdiode can standup the load for several seconds and
the fuse will be blown before the zenerdiode will die by overheating and to heavy load.

The cost of such protection is nearly rediculous, compared with the damage that might happen without protection.

so here now the pictures how this can be realized:

In the meantime lets wait till we get the measured values from Steven....

sincerely speedyG

That could work. I'd probably rec' a subsurface zener for longevity. Actually several in
series to add up to the desired voltage. No walkout. This *is* equipment likely to be kept
and passed down through the ages.

A TVS might be even better. It instantly converts electricity to heat, handling 1500W
transients. Using several in parallel to bring the voltage down to size shoudn't prove to
be a problem. This type of protection device is made to short the 12V & 5V in PC power
supplies should it exceed limits. These parts are in every HDD!

Lots of options.

I would even advocate doing up a crowbar circuit, or buying a pre-made overvoltage
protection module.

Trivia: A capacitor can dump all its energy into a flash-tube far faster than it takes a
.357 Magnum to travel the thickness of 1 piece of tissue paper.

Capacitors discharge at near lightspeed. They are electrostatic - unlike batteries which
are snail's pace slow moving chemical reactions. Capacitors don't have to wait till
chemistry takes place. Everything in a capacitor happens at once.

It's measurement time! Q8 has to come out, and we need to asses the voltage across the caps.

Hello Keatah,
there are several good options you listed and proposed ....
but bear in mind:
Steven is not like us electronic engineer - so he has limited equipment and
less experience than we have.... we´ve spent years with the soldering iron
developing electronic equipment, i even have designed and made also the PCB´s
by myself for the prototypes...

So i took respect to Stevens experience and tried to make it very simple,
easy to assemble and cheap and easy to order the needed items....
so this is -up to my guess - the best option within the given limits to
make a proposal.... and it can be performed step by step following the
instructions of the pictures....

there are no restrictions here - any other solution to publish is welcome....
it just might be little more difficult for the readers to realize....
don´t forget : also newbies and amateurs follow probably the thread....
but of course advanced solutions should be published too.....
just my 5 cents....LOL

remark to msg 261: I have hugh amounts of pictures from Stevens box and first thing i did,
when i recieved pictures from you - was to compare both boxes hunting for diffences....
the components in both boxes are nearly identical, the only difference are some minor
differences at resistor values that change slightly the frequency of the oscilation of the
4 pieces of 2N2222A transistors....
sinceely speedyG

Absolutely right. How about a look here, for example to read about these little TVS diodes.
There's way too many to pick from for me to go through it right now. But they have them in
the 20 to 50 volt range. -- http://www.littelfuse.com/products/tvs-diodes.aspx -- Maybe we
can make it even easier by using a single component solution which can be tacked on the
bottom of the board.

The thing I like is that they respond in picoseconds. Which is fast enough that the wires
conduction power to the protection device can become an inductive issue!

We can get carried away very easily and sidestep all the troubleshooting we're supposed to
be doing.

Anyhow.. Let's prepare some measurements to move forward from here.

Hello AFmembers,
hello Steven,
@Steven: i redirected the mail with the doc-file to Keatah....

while wsiting for the measurements i proceeded with the analysis of the Mainboard and
diveded the Mainboard in to functional sections and made symbolic schematic drawing
and added the grouping of the functionblocks to the mainboardplan too......
this will help by "search & diagnostics & repair" .... it enables the user to find fast
the components on the board related to the different functions of the electronics.....
in case a later repairmanual might be made it also would be usefull to realize the dependencies
of the funtionel blocks to each other.......

the first picture shows the functional blocks ( i will extend some parts later in detail )
in general the functions of the mainboard are devided to the powersupply ( with light blue shading )
and the functions related to the slots and their management ( with the light green shading )
the functional blocks are numbered and the numbers are repeated again on the mainboard at the related components
@ Keatah: I know that at the output of the negative voltages must be corrected in minor parts.....
The databus id represented by violet shading
the adressingbus is represented by pupur shading
the controllines bus is represented by light red shading
and the slot selection lines are shaded in light yellow
the slot-shematic at the right upper left side displays the grouping again....

here in the mainboard plan the componentgroups are repeating again the same numbers
and the same shading colors....

so enjoy the results from todays work....

sincerely speedyG

Ohh that looks nice. Unfortunately I have unexpected (but routine as usual) stuff to take
care of. So I will read but not reply.

@Steven:
Use this "chassis fix'n time" to learn about the basics of electronics. Enjoy the time and
learn about how all these old computers work! Only consider sending me the board for repair
if we've replaced 10 parts and it isn't getting any better.

I wish I knew what happened to the other 1,994 chassis out there! Where are they? Who has them?

Hello Keatah,
you already announced to be absent several days, so i´ll take the tourch for a while till your back....
Hello Steven,
in the time from 1999 to 2004 i had beside been teaching pupils PC electronics and prepared them to
solve for the A+ certification as PC technicians.... and leaded at highschool several classes of pupils
basics of electronics .....
i assume that my explenations are rather well to be understood due to the fact, that i´m a fan of the statement:
picture tells more than 1000 words...
i´m confident that we´ll solve the task successfull together....
just advice for the preparing of the requested measurement:
when removing Q8 ( the SG340-24 ) first untighten the screws and remove them then
while desoldering - first remove as much solderingmaterial as possible with a vacuumpump...
then remove the rest with desolderinglace....
then the IC together with the coolingsink should get loose and drop out....

sincerely speedyG

Just an FYI to GSMCTEN, Keatah and SpeedyG,
I just acquired a card-less, disk-less, and documentation-less Mountain Computer Expansion Chassis from eBay that I'd also like to get working.

Obviously I need an interface card for it, but for the time-being, once received I can take voltage measurements or wherever you think would be helpful to get yours going too.

Hello Macnoyd,
first congragulations - i´ve been watching that offer....
second: if you can´t wait by searching for the interface card... i did the entire reverse engineering...
so i´m able to send you the entire files missing including the manuals and other stuff....
the upmost important... i can send you the gerberfiles that resulted from the reverse engineering...
that would result to a interface card in which by autorouting the traces might not be all absolute
copy from the original interface - but at least the layout and the population will be 100% same....
so with the gerberfiles - you could pass over a order to a pcb-manufacturer - and by that get a working
interface card that would permit you to operate the box....
i´ll send you pm within the next days.... i guess transport of the box to your place will take anyhow
some days to till it arrives....
sincerely speedyG

Thank you speedyG !!

Greets Macnoyd. Don't worry about any disks. I don't ever recall (nor is there mention in the manual) there ever being any.

This was not a consumer product, it was pretty vertical and niche and less than 2,000 were ever made.

To make yours functionally complete, you'll need to get:

1- an interface card
2- powerbrick
3- owner's manual
4- 16-pin ribbon cable
5- 50-pin ribbon cable

Hello to all AFmembers,
hello Keatah,
hello Macnoyd...
@ Keatah,
i´ll send to Macnoyd entire Documetation.....
- and the Interface card...? well i´m still waiting for the CFFA1 card to arrive.... that will be the very moment, i will complete testing the entire bunch of my Apple-1 expansioncards also with the CFFA1..... at the moment my planning is, to collect the orders for the Apple-1 expansioncards end of the month or first week of July - and then oder the PCB´s....and perform the entire shipping in August...
maybe i can integrate a order for some 2 or 3 Interfacecards for the MCEB to that ordering bunch of PCB´s - if it does not raise the cost of the Apple-1 cards....
otherwise i can send the gerberfiles to Macnoyd and he or you could manage a collection of orders in the USA resulting in far less transportation fees within the US....
@gsmcten and macnoyd:
in such a case it would be also far less difficult to just only populate and solder a ready PCB....
believe me wirewrapping can become an awfull job with that many chips.....
sincerely speedyG

Thank you SpeedyG,

I'm 100 percent behind populating a PCB far over a wire wrap or point to point board project.
If you already have a PCB maker you deal with, I would
go with that and request gold plating on the edge connector too.

I'm "in" for Qty=1 of all the Apple 1 boards you've been designing, and if you can get a low quantity of the Mountain Computer boards
made up along with the lot, I'm all for that too. I'm set up well here for building those boards.

Let me know if that's a possibility with your final PCB order and what you'll need to fund it.

As always, your efforts are GREATLY appreciated!

I would suggest that someone build a proof-of-concept or prototype interface board using
only the information available, then test it on the appropriate revision chassis.

It looks like all 3 chassis being discussed in this this thread are of the same revision.
But I wonder if the adjustable pots and extra capacitors on this last one were a factory mod
or customer mod?

The kinds of customers that bought these things were generally knowledgeable enough to do
stuff like this.

Now, once a card is built up, and if it doesn't work, I'll be happy to go through and
correct any mistakes. While the logic is simple, there's just a lot of connections and opportunity for mistakes to be made.

I strongly prefer to provide information and answer questions. With summer here my classic computing time is limited.

Hello Keatah,
up to my knowledge the Interface card didn´t change at any version.....
Changes of population have only occured at the mainboard ... correct ?
mentioning the time... of course we take repect to the fact that you prefer to
favour summer activities outdoor and therefor want to limit time upfront of the computer in summer....
the same is valid to me tooo...
up to the point of decision if ordering IFcard PCB´s can be handled together with the order of the
Apple-1 cards is still several weeks ahead....
i´ll mail the gerberfiles to you in the beginning of the next week, so you can view them....
that will give you at least 2 weeks time to examine them and if required propose corrections....
thats up to my opinion the best option to handle that...

sincerely SpeedyG

Ok thanks for the files.

There are two versions of the interface cards. One card, like we have discussed in this thread is the older card.

The newer card has a bank of dip switches which allows forced selection/deselection of individual slots, regardless of the chassis enable button.

Hello Keatah,

could you please - if you have some spare time - mail me some pistures from that card with the switches ?
thanks in advance

sincerely speedyG

It's packed away. In fact I'm not even at home. This would have to be something of a
fall/winter project. The 1981 manual talks about it briefly and there is a simple view of
it. Certainly nothing to reverse engineer.

There is a small logic difference in the motherboard too, IIRC

Hello Steven,

if you have 5 Apple II spare mainboards and some clones, that should be enough to have a fine stock of chips....
in such case it might be recommended to search instead of further boards for some material for the best possible
storage of the stuff, like: good antistatic foam.... good fitting antistatic bags ( probably you can pick such stuff
for free from a local computer shop if they assemble computers for customers... and if it´s an old store you probably
might even have the chance to find some old keyboards in the "antik spare parts box" for keyswitches...

and besides while the box is transported to Keatah and you are waiting for the box to turn back, you might even have
the chance to visit the local library and find some neat little books to topic of measurements and basic electronics
that might cover additionel info´s, that would be worth spending some time on reading and performing some small
experiments with your new equipment...

not to talk about the chance of recharging your "life batteries" by spending some
time outdoor for strawling/relaxing around and catching some sun....

sincerely speedyG

I've been playing with ADT for years and years now. And I'm still quite thrilled everytime a
disk is transfered or read. These are things we could only dream of back in the day. It's
like magic!

I'll have my lab prepped and ready to work on vintage equipment.

The dungeon lab, yes. It is brimming with stuff and projects in various stages of completion.
The bra part, I don't think so.

And if I make a redhead, on accident, I'll turn her into a witch because I have an
assignment.

Anyhow I anticipate the first day of troubleshooting to take place mid-week. I will keep you
updated every step of the way.

Box opening and shipping inspection underway.

Nicely packaged, no damage.

Looks like the problem(s) are all on the primary side of the transformer circuit so far!
This narrows it down to the front end of the power supply.

After the big capacitors, and before the transformer.

Looking like 1 or both of the mosfet drivers are bad. Excessive heat and current draw. Main
regulator is getting hot and possibly being pulled down to 5V.

I'll take these parts out (Q1, Q2, Q8) and test them on the bench tomorrow. Although only
one of the 3 *MIGHT* be bad I would prefer to replace them all as a set.

D2 through D7 are fine, passively. Capacitors and Bridge Rectifier look ok. Power sense
transistor looks alright too.

I will be testing the oscillators late tomorrow too.

That's all for this evening.

Hello Keatah,
i do fear that the high voltages might have damaged the 4 transistors ( 2N2222A )in the Oscilator too...
new datasheets: 2N2222 limited to 60 Volt, 2N2222A claim to be limited to 75 Volts.....
as far as i remember the old ones are also limited to maximum voltage of 60 Volts...
maybe they are the reason the the Power MOSFET´s get hot.... if they are "shut down" at the Gate
the powerdisaption might get very high and they are withoout coolingsinks to absorb higher powerdisaption....
maybe the powerdisaption drops the very moment they get input from the Gate and perform in "normal operation mode"

sincerely speedyG

I will keep this post #295 in mind as I work through the circuit today and
friday. There will be little or no work on thursday.

Then I will prepare a parts list for review. And place orders over the
weekend. That's the plan anyhow.

I am absolutely not opposed to replacing parts that may have been pushed
beyond their limits or are/have overheated. I'm thinking about doing this
with the Bridge Rectifier.

I tested the 50pin cable, the interface card, 16pin cable, and power brick.
A functional test only on my chassis. I was able to boot a game and access
the Super Serial Card. I think it's safe to say those components are working.

Once we get the power section rolling again I'll run it for several days
with a few cards in it. And 'scope out the address and data lines for clean
activity. Shit like that. You know..

Significant and Major progress has been made in a brief 5 minute
early morning troubleshooting session.

Q1, VN64GA, one of the N-Channel MOSFETs that swings the transformer
back and forth is shorted. The resistance between Source and Drain reads about
240 Ohms. It should read 2M Ohms one way and 30+M Ohms the other way. More or
less. But you can see the massive difference.

Once this component is replaced your chassis will come back to life.

Then we can assess the rest of its health and see how everything is working.
Figure out why it blew up.

Another round of good news. I have your chassis running on life-support right
now! This means I'm using stuff from my junk stash to make a temporary repair.

The box is powering up. And it is able to boot from a floppy (duo-disk)
configuration. It is also working with my Super Serial Card and has
successfully transfered images with ADTpro. I have had it running all
afternoon.

It has been an absolute pleasure working on equipment in such nice condition.
Typically by the time I see some classic computing paraphernalia, it is all
grungy and needs more work than initially planned.

We now wait for new parts to arrive by end of next week.

More later..