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@Speedy check your mail. I'm sending some pictures with voltage readings for the
transformer.
One set of measurements was taken with a Fluke 79 DMM. The specifications say the meter is
good to 20KHz and is averaging.
The second set is taken with a Fluke 87 true-RMS DMM. Specifications say it is good to
about 200KHz.
I also made a 3rd set of measurements with the 87 for frequency. This is with no cards
plugged into the chassis. I had it powered up (with the Apple II+) for about 1 hour to
allow things to stabilize.
Q2
54.33KHz
Duty Cycle 39.8% and 60.2%
Q1
54.19KHz
Duty Cycle 44.2% and 55.8%
Page 29 of the Fluke 87 user's manual talks about how this is measured.
I am not able to get any reliable resistance measurements. Not at all surprising. They're
all fractions of an ohm, and certainly not repeatable with any kind of precision with
these handheld meters.
I have a small signal generator on hand that can make sine/square waves. 1 to 15KHz I
have a 6.3v and 12.6 VAC power supply. I bet we could calculate the inductance by hooking
up a series resistor and and doing the half-ass technique where you monitor frequency and
current. I can do that with the DMMs I have on hand and the math is simple. Let's just see
how many microhenries are spinning around in that coil!
I wouldn't mind desoldering the transformer from my other expansion chassis, as the board
needs minor cosmetic work anyhow. This would be no problem. And furthermore, we can see
just how much it steps up and down.
Next time I'm on extended vacation I'm bringing my lab with me!
Ok.. I'm building a signal source to make a sine wave and some volts!
Then I'm going to hook a resistor in series with the inductor and then connect it all
together and see what happens.
I intend to use something like L = R * sqr(3) / (2 * PI * freq)
I figure if we know the frequency and fling it around in a couple of circles and divide it
into resistance boosted by 3rd square root we can get some sense of the mess and figure
out how many Henries are in each winding! What say hava'go at it?
I'm going to work in millivolts because I can get stable readings and precise readings
down there(!) Beside my inductance meter/generator is going to have to work off of 1 or
2 AA batteries.
Hello Keatah,
that won´t be neccessary....
with the datasheet of the inductioncoilcase
the measured millivolts and volts - the rest is pure math...
the frequency is known by the frequency-generator ( the 4 2N2222A transistors )
2 each make the squarewave generator and drive one of the MOS-FET´s
and you got the duty-cycle:
we have 2 square-wavegenerators each working on one primary coil
at the moment it´s just a guess, but in fact the 24 volt regulator delivers the voltage for both generators...
each generator works with resistor and capacitor network ( frequency determined by R/C ) so with the uncovered voltage of 24 Volt
the operating frequency is also only mathwork....
the measured output voltages are approximately a intermediate
between squarewave from input and sinewave as result of loss by induction - at the output on secondaty side -( which can also be calculated by mathwork )
the loss by transduction can be read from tables of the datasheet that comes along with the coilcase...
and most other data can be taken from datasheet or datasheet from similar coilcases....
in general we can say: inputvoltage at primary side is 48 volts
( resulting from 2 halfwaves opposite out from 2 squarewave branches )
and 4 output branches : one for plus 5 volt, one for minus 5 volt, and similar
is valid for the 2 times 12 volt branches ( one for positive and one for negativ ).....
so we can calculate them by the ideal transformationfactor and add the loss caused by transmission )
( i.e. - if i want to get 5 Volts and i know that 20% loss is in that branch i just have to calculate to get
in ideal case 6 Volts, but due to loss of 20% the true output will be only 5 Volts )
of course that´s just the simple explanation... i´d have to subtract also the loss calculated by the fact that
the duty-cycle of the squarewave causes less display in true RMS-measurement compared to sinewave....
if i measure sinewave true RMS displays factor 0,74532 of true value ( or 1,41 if i calculate other way around )
and with the calculated values i can take the tables and calculate the values in mHenry and the resulting windings....
the only thing that would help to get more precise calculation would be precise knowledge of the thicknesss of the used wires....
so if i can get:
how thick is the wire used for the primary windings at the MOS-FET side....
how thick is the wire used for the windings on the secondary side....
( the reason : if i use thicker copperwire i need less winding but more current -
or alternate - with thinner wire i need more windings with less current
to get in result equal value in milliHenry )....
@ Keatah:
so if you have a instrument to measure precise diameter of the used wire on primary side
and at secondary side this will help us for better calculation....
sincerely speedyG
Yep, that all makes sense.
Back home I have access to equipment that would give fractions of a mil for the diameter of
the wire.
But in the meantime I made some measurements with a homebrew DMM -to- LCR converter, and a
signal generator built of discrete parts. It's always nice to compare calculations against
the actual circuit.
Hello Keatah,
such simple experiments always make sense ! I would never have learned how to use my math knowledge without doing experiments too...
the experiments teach us that there is allways a slight shift of true values away from ideal values.....
to tell the truth - i´ve often made the experience that brief guess of calculation with some
kind of brief subtraction of a kind of "offset" by experience gets better results, than math on paperwork only....
for example in this very case i could make long math to determine how many percent of squarewave survives the coil
and how much will have "transformed" to sinewave.... but my first simple guess would be:
at secondary side the wave will be about 45% from original squarewave and abour 55% altered to sinewave....
i´d bet that this guess will be closer to reality than paperworkmath... and i know that, because of the
experimants i´ve made with all kinds of transformers.... i have several tube-amplifiers and i calculated the
outputtransformers from several hundreds of volts and only few milliampere to average output of 65 to 70 Volt with
current of about nearly 4,5 ampere ( so output results to 250 Watt at 4 Ohm speakers from 15 Hz ro 25 kHz audiofrequency ) for my stereoamps... and after having calculated 3 of them, i made guess for the 4th amp and in reality i found out:
when i made 2 kinds of transformers that the ones made upon guess sounded better than those resulting from math, because
i added a kind of "offset" due to loss by experience to my guess... the bass sounded better and sharper at edge at the guessed transformers...
similar experience i made with experiments at switching power supplies.... it turned out, that those working with higher frequencies above 50 khz had better performance ... but it also turned out to be true, that there will be no better performance above 80 khz..... working with frequency above 80 kHz rises loss of efficiency....
this has to do with factors like drop of inductive loads above that frequency....
the transformers get larger and reqire more current, but at the same time output does not rise by same factor but instead turn out to be less effective....
if you view moderm switching powersupplies, there is not much difference in size of the transformer at primary side , betweeen output of 350 watt or 550 Watt... the difference is not the size, but rather more the wires used , their diameters, and of course using 6 coilwindings with thinner wire parallel have better performance instead of 2 coils with less windings but thicker wire...
such things can only be found out by experience and by experiments...
by the way make one experiment with sinewave and one with squarewave at the same transformer - and compare results...
and become amazed from the results.....
so happy experiments....
sincerely speedyG
I sent you out the measurements. Check them with your super math. I'd like to see how they
hold up against my ghetto test equipment.
I was able to determine that the frequency of this transformer is indeed optimized at
54.02KHz. It is there it seems to operate most efficiently.
Hello to all AF-members,
so this is one of the last missing bricks in the wall...( remembering and hearing at the moment Pink Floyd )...
in the table there are 2 relevant columns - i marked one in red, because due to the function this will be the
better version. please also recognize the way the coilwindings have been layed out... ( marked by different colors )
this colors will also be added to the circuitplan for better identification .....
and of course this page will also be added in the manual....
@ Keatah:
the variable values result from position of layer within the coil....
winding layers closer to the inner circle have slightly higher values ( of µH ) than those located more to the outer side....
"broken values" as result from math have been rounded up due to transduction-loss....
sincerely speedyG
Ok Everybody,
My part of this is on hold for a bit.
My last try was this evening with the following:
1. Apple II+ (Vader) with 16k Card in Slot 0
2. A single Disk II Controller Card.
3. A Single Disk II
4. All of Speedy and Keatah's instruction down to the "nth" degree.
5. I double and triple checked everything.
6. Switched out 3 74LS138 Chips, just to be sure.
7. Placed the MEC Adapter Card in Slot 4 of the Vader.
8. Plugged in the MEC Power Supply.
9. Turned on the Vader...No Green Power Light on the MEC.
10. The Disk II did not Run, or try to find the DOS 3.3 Disk I placed into it prior
to start.
11. I pressed the "Engage/Disengage" Button and nothing happened.
12. Powered everything down because when I ran the back of my hand over the area where
the internal power supply is, It was radiating (what I think) was excessive heat.
13. I did not pull the fuse...yet. I want time for the Caps to discharge.
14. This is where I am right now.
I have just finihed placing everything off of the workbench and cleaning up the area before I tear this thing down to parade rest again. I want to go over the MB again with a fine tooth comb. Perhaps I made a mistake soldering the Caps...I don't know.
I do know I need to put it away for just a bit so I can get my head screwed on straight.
I have been trying all this week to come up with some practical reason that it refuses to
cooperate...and operate.
So as of right now I'm on hold.
If anyone has any ideas that either myself, Speedy, or Keatah have not thought of, they
would certainly be appreciated by all of us.
Steven
Hello Steven,
you caught me right before entering my bed... stay cool... i have been allready analyzing the
problem from different views....
to avoid misunderstanding due to different timezones ( i´m 8 hours ahead of your local time... so here is now 01:00 short after midnight - while in your place it´s still 17:00 afternoon ): i´ll try to reply tommorow after also checking
some of the pictures....
just one question:
the pictures with the large capacitors on the mainboard... did you make them after or before carrying out the exchange ?
could you please just take 1 or 2 pictures ( at least ) or even more if you like ( the more the better ) from the box in current status ? It would help me a lot to check several things...
don´t bother distorsion - only impportant : good light - best daylight and good focus and as high resolution as possible
( if you can change that with the camera ) that would permit me to zoom in when viewing them....
and if you could mail them to me now or within the next hours so i could examine them tommorow morning
(at breakfast) when i try to figure out chances to find mistake.... send them to the gmail-adress... there is no limit for the attachments...
sincerely speedyG
Speedy, Keatah, and all,
I'm going off the grid for a few days to try and get my mind and a portion of my life in order. I just have to set this project aside for a few.
Speedy> Received your email.
Keatah> Received your message. I am seriously considering your offer.
Thanks Guy's,
Steven
Hello to all AF-members,
while waiting for a reply on a email i revised the mainboard circuitplan -
added the external components and labeled several controllines for better tracing....
so here is now the very FINAL REVISED VERSION OF THE MAINBOARD CIRCUITPLAN:
and of course you may now download the hires-version of this final circuitplan here:
http://www.harrowalsh.de/Upload/MainboardCircuitPlanFinalLarge.gif
the size of that plan is more than 4 MB, so maybe the time for loading it might require some time,
if you have slow internetconnection....
sincerely speedyG
Ok...
I have my workbench cleared away.
Life is moving forward again.
I am going to bring out the MEC and take it down to parade rest again starting tomorrow.
I will start taking pictures of the case also, with measurements.
Then we'll see what we can see.
Steven
OK Ladies and Gents!
The MEC adventure is starting once again.
I have the board removed from the case.
I have an Apple II with Disk II connected to it for initial testing.
Once that is completed I will onve again place the MEC Adapter Card into the Apple II and the Disk II Card with Disk II Drive into the MEC.
Nice and Scientific. lol
Once I get everything running (hopefully) and operational, I will take pictures and dimensions of the case parts so Speedy and all can look at them.
This starts tomorrow.
Steven
HELP!
Everything is hooked up to test my Rev 1 II.
When I start it up (with or without Disk II card) I am getting a screen full of question marks.???????????? with one line at the bottom of the screen waiting for input.
Anyone have an idea of what is going on and what to do?
Speedy... Corey...You out there?
(There is never a phone booth around, when you need to change into a blue union suit, lol)
Steven
Hello Steven,
just entered in a bypassing because i am roughly working on the Mimeo at the moment....
all question marks but a prompt?
If possible its better to get little more precise for diagnostic.....
If there is a prompt .... are you able to enter a command?
for example a "Home" followed by enter ? and does then the screen clear up ?
are the voltages from the internal poweersupply O.K. ?
dependent to the answers it might be a powerpeonlem
or a RAM problem.....
Normaly for diagnostic it´s best to startup with a system
with nothing else but keyboard 16kB RAM ( so called minimum configuration )
and Monitor.
If system ends up at propt with clean screen and promt and
entering at keyboard is possible ( keep for the next tests this "minimum configuration" by just swapping in another RAM-chip rom after each other....)
then change that first row with the second row in the first row position and repeat....
if that test again runs without fail then change in the 3rd row at position of first row and repeat test.
this permits to detect if one RAM-chip in one of the rows is bad....
then after all 3 rows performed perfect startup ending at the prompt you may then add 2nd row and repeat startup till prompt, then add 3rd row till ending at clean prompt.
then finally you can add up the 16 Card and test again for clean startup and then finally you might add in diskcontroller for booting from disk.
speedyG
Thanks Speedy. I'll give it a shot.
OK, here is what I've got.
A II plus (Vader).
A Disk II Card.
A Disk II.
The disk II card and disk II connected to the Vader. Fully tested with diagnostic disk.
Everything works well.
I removed the disk II card and placed it into the MEC Last Slot.
Placed MEC Adapter Card into the Vader (Slot 4).
Plugged in the MEC.
Turned on the Vader.
I get a set of vertical lines on the screen,but nothing else happens.
This tends to tell me that I have a problem with the Adapter Card.
All Comments welcome.
Steven
Hello Steven,
the question above i added due to the fact that slot 0 in the MEC does not have all signals like the rest of the slots...
i therefor would recommend a test with the diskcard in slot 5 or 6 of the MEC....
and by the way just a final question: the switch at the frontpanel of the MEC is in the position "select" ?
meanwhile i am checking along with the circuitplans...
as far as i remember you have already checked and exchanged the 74LS138 chips which do the slotdecoding....
could you please send me 2 pictures ( from the 16pin flat cable in the vader )
so i can see how it is plugged in the IFcard and how it is plugged in the Vader ?
sincerely speedyG
Speedy,
I will take the pics, but I can tell you that the cable is connected correctly on both ends.
On the adapter card the Red Sripe is facing Down, to Pin 1.
On the MEC Board the Red Stripe is facing the Front of the box, to Pin 1.
Just like the instructions say.
I am going through another check later this evening.
I am also getting the list of chips from the Adapter card so I can replace all of them.
Couldn't hurt.
Hello Steven,
i trust that you have connected it the right way...
by the way when you tested the booting of the vader,
did you also test booting the vader from slot 6 with the IFcard in slot 4 or 5 inserted - but without beeing activated
( MEB shut off ) ? Did the system also then lockup ?
partlist is here:
http://www.harrowalsh.de/Upload/MCEB.doc
sincerely speedyG
No Speedy, I did not do that, but now that you mention it I will try it.
All of the chips on the adapter card have been removed, cleaned, and reseated.
Speedy, Corey, and all,
Right.
It's got to be the Adapter Card.
I removed it from the Vader.
At start-up, the Vader beeped and went straight to the prompt in the HOME position.
Just like it's supposed to.
Placed the Adapter Card into the Vader at Slot 5. No Cable.
At start-up, No Beep and the screen went straight to Vertical Bars.
Turned off the Vader, removed the Adapter Card, checked all the chips.
Everything as it should be.
Did everything again in the same order to be sure.
This time I placed the card in Slot 6.
Same results. Vertical Bars.
I checked the card over for any broken leads from parts.
Everything looks good. No breaks or cracks.
Looks like I'm going to be changing out all the chips.
A chassis is *required* to be attached and plugged in. Both power and 50-pin.
The interface card used by itself will cause these symptoms.
ADDED:
The pattern looks something like this, doesn't it?
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
??@@??@@??@@??@@??@@??@@??@@??@@??@@??@@
Corey,
Nope.
When I said Solid Vetical Lines, that is exactly what they are.
Solid 1 inch bars across the screen.
That is with the card by itself, unplugged from both the large and small connectors.
When the card is attached to the MEC and Vader, I get a screen with nothing but question marks (?).
There are no ampersand (@) symbols.
I have all the chips sittng on the workbench right now.
I am just going in to replace them all.
Able to discern if it's hires or lowres?
Hello Keatah and Steven,
solid bars are allways in lowres and indicate a lockup within the first 4 kB of startup ROM.
so there are only 3 choices remaining:
lockup because of the adressingbus or lockup because of the databus or a pulldown of the NMI-line or RESET-line or one of the phase-lines PH0 or PH1 or PH2( i.e. clocklines ).
sincerely speedyG
I've seen my chassis lock up in hi-res when I had everything all hooked up, but failed to plug in the AC mains. A normal expectation. White jail bars, maybe 6-10 of them, and a few random dots here and there. Definitely hi-res. Sometimes mixed mode, hi-res and 4-lines text.
It can also be noted that if you reverse the 50-pin cable, nothing explodes and smoke doesn't escape. Manuals says so and I verified this on my scrap chassis.
Keatah and Speedy,
Ok...
Switched out all the chips and tried card with and without cables.
Same result.
1" vertical bars across the screen.
I'm going to place all of the original chips back in this evening with the exception of the 74LS138 chips.
Keatah, am I supposed to get all the question marks and ampersands?
What does that indicate?
Steven
Hello Steven,
just sent now email....
sincerely speedyG
I've never studied the exact activity when the ??@@??@@??@@ text bars are displayed. I
couldn't tell you why that happens. I suppose I should study it someday.
But, could it be that your Bell & Howell console is at fault?
Does your B&H computer have a raised or recessed power indicator on its keyboard?
Are there any chips or a small board that connects the paddle controllers to the motherboard?
Part 1: Recessed
Part 2: No.
Well, I'm back to the vertical bars across the screen. They seem to be about 1/2 inch black and white all the way across.
I am no longer sure it's the Adapter Card.
I'm not sure what it is.
Keatah, when you were starting to make headway into getting your MEC working, what indications were you getting when you were finally going in the right direction?
Back in my prototyping shop days in the 80's we had a chassis we kept blowing up, using
too much of the power supply. Mountain had made it too convenient and accessible, if you
get my drift.
Man those were the days. We had some A/D & D/A cards controlling high power optics.
And we thought we were the shit! We used a chassis just for accommodating all the boards.
Any lab rat can testify to the glory of such a rig.
So when we'd done and gone blowed up the supply, and the system would not start, we were
presented with the ??@@ bars in text mode. It was our unofficial way of saying the box
blew. When logic on the box was bad we had the hires bars with some random dots. When
we had the ??@??@@?? we knew we had a supply problem. Well, we knew the interface
card was ok and to begin our troubleshooting efforts in the box. We knew what kept
exploding - when some of the lasers would overheat and short and surge their supplies,
some of that came back in through the cards in the chassis.
Eventually we made our own ZIF-sockets for the transistors and stuff and this made for
easy swap out, easy like a fuse. And then we better isolated the cards themselves.
But as a technical troubleshooter here, now, today. I would want you to hook everything up
and measure the power section of your box with a DMM. You can get one at a hardware store
for dirt cheap. About the cost of a fattening meal at Olive Garden or Portillos. You don't
need a Fluke or HP or anything exotic to do this.
You turn the DMM to DCV, touch the BLACK test probe to GND and hold it there.
Then touch the RED lead to various points and report back the readings to us.
You measure +5, -5, +12, -12. Each result should be close to each number respectively.
And while your at it, you can test the AC power brick and the integrity of the 50-pin &
16-pin connector with the DMM too.
Testing the supply is really that simple, and it cuts the chassis mainboard in half. Power
problem? Logic problem? This will tip the scale one way or the other. And I hope it's a
logic problem. Easier to fix.
This is my approach, and other people will have other ways of going about this. And that's
absolutely fine because there's multiple techniques and different insights. The more the
better. Even with a simple thing as this.
And remember don't get all flustered. This is FUN stuff. It's a puzzle! And it will
be working soon enough.
I just received Speedy's email, printed out the email and the picture (drawing).
I'm not going to work on this thing anymore this evening.
I wish sometimes that I had not stopped drinking. lol
Thats ok. I refuse to give up.
This MEC WILL be operational. period.
A wise man once said:
It may have been a MasterChief I knew. lol
If someone can forward that to me, I want to follow along.
Hello to all AF-members here,
this is just the repeating of the mail i sent to gsmcten.
i repeat it here for better understanding of the troubleshooting mission:
Hello Steven,
the bars happen if 1 of the 3 conditions is fullfilled:
1) if one of the cables is pluged wrongside in at MEC or IFcard,
2) if cables are correct but MEC without power
3) if IFcard is plugged in system; but not connected by cables to MEC
to understand better the function:
if IFcard is in the Apple ( or Vader ) it is supposed to get signals from the MEC to
"unlock" the Vader or Apple and permit booting.....
if the IFcard does NOT SEE the correct signals it locks the Vader because it waits
for the signals from the MEC to decide if the Boot is to be performed
a) from the MEC box
or
b) from the Apple !
This is handled by the Interrupt Request signal, Reset , NMI signal or by the Device Select signals.
---------------------------- this is inserted for further information ----------
this is realized by some inverted AND gates.
if one of the lines from the box, that is determined to turn "high" in normal operation
IF the box is deselected but with power and cables are correct
AND the controlline remains "low"
( because
one cable is plugged in wrongside
or
wrong or no power is in MEC box
or MEC box is selected
then the AND gate in the IFcard has different signals
and keeps the Apple in "shutoff" position by keeping either RESET or NMI in "low" position
-------- end of inserted explenation ------------------
A) If the MEC is connected correct but deselected
the IFcard turns up this mentioned signals ( RESET and NMI ) and permits the Vader to boot
and search for the diskcontroller and the drive and boot from it
or
B) if the MEC is selected it prevents the Vader from searching its own slots
but instead forces the Vader to search in the MECbox for the controllercard and
boot from that card and ignore any diskcontrollercard in the Vader !
So if the system hangs up - it´s because the IFcard does not get the
correct signals from the MECbox !
It believes it must lock the Vader and wait for the correct signals from the
BOX to determine HOW TO CONTINUE the booting process....
The card can´t recognize if it is to force the booting from box or Vader....
and therefor locks up !
I hope i explained this functions in a way that permits you to
understand whats going on n the IFcard......
i add as attachment the plan from the box and i marked those IC´s in blue,
which control most of the signals.
Those marked red are only important IF the box is SELECTED
(- so if IFcard is in Vader AND diskconbtrollercard is in Vader and box is NOT selected
- this IC´s are not required and the Vader should boot and IGNORE the box ) !
( of course this still assumes that cables are correct connected ! )
sincerely speedyG
Speedy, Keatah, and all,
Well then, I still have a problem.
That's ok because I now know what I should be looking for.
I cleaned and/or replaced all the chips in the MEC.
Hooked everything back up.
Now I have the Vertical Bars, plus 5 lines of question marks(?) and ampersands(@).
I beleive that this may be progress. lol
Keatah: I'm going tomorrow to get a DMM.
I'll start taking some readings.
I must have power, or the interior Power Supply area would not be getting warm when I start things up.
Speedy: I understand what you are telling me to do and I'm trying my best to do it.
I'll get this thing to operate, but it may take a little finagling (maybe a 3 lb. hammer instead of a 6oz.) lol
If it is locking up we know something at least is happening.
Yes. Thats progress.
Steven
Went up to Jameco this morning and ordered a DMM, a magnifying workbench light and a pair of magnifying glasses.
I want to be sure I can see what I'm looking at. lol
I figured that while I was going over the MEC board that I'd check the traces to ensure no cracks or splits.
In the mean time I'm going to fade back ten yards and punt.
I've had this Vader that I'm using sitting for a while and she needs some TLC. So I figured while I have it out I'd give it a once over and clean her up a little.
Steven
Speedy, Keatah, Corey, and All,
A bit of difference...
I just received an Apple II Plus yesterday.
I removed the vader and set up the II Plus with the IF Card.
Everything looks good.
Powered up and received a screen full of....
Question Marks (?) and Ampersands (@)!
No more Black and White Vetrical Bars!
What does this mean?
Hello Steven,
this sounds very much like the explenation from Keatah in Posting #173 and #182 above about a blown
power source in the MCEB. So at this point it´s probably the best turn to wait for feedback
from Keatah, because he has expertise on that topic and he probably can troubleshoot that better.
It would be good idea to check voltages as explained by Keatah in his posting #182, because there
are 4 branches : +12 V, +5V, -5V and -12 V - and dependent to which branch has wrong value measured
it will point to the damaged part.
After in earlier posting Keatah has spotted out that he had performed
several repairs on that kind of symptoms he probably can even spot out the damaged part.
sincerely speedyG
Speedy, Keatah, and all,
The DMM came in, along with my extendable Lamp and the close in goggles.
I will be learning to use the DMM over the next few days, then I'll have a go at taking readings from the MEC board.
Don't expect perfection first time out.
I am in learning mode.
Steven
Hello Steven,
i´m glad to see you back again.......
I hope Keatah is able to assist you with advice after you have taken the measurements.
As he explained in a prior posting, it seems he has quite some experience with blown parts in the powersupply of the MCEB.
Just besides, when taking the measurements i will be pleased, if you check out the values printed on the 2 capacitors
that are marked red in the bottom left corner in the last drawing..... i´m still missing the values for the partlist.
I wish you good progress....
if Keatah can´t reply fast, then you can of course also add the values in the drawing and mail it back to me.
sincerely speedyG
@speedy What are the capacitor C# or designations?
@gsmcten
It is now summer and as I mentioned earlier in the thread I will be busy. And my indoor
computing activities are on their seasonal downswing. But I will help as much as I can.
Begin by looking at these three pictures.
One of the pictures indicates voltage levels.
Another shows orientation of the 50-pin cable.
And another shows the interface card installed in my beater (experimenter) Apple II+.
https://picasaweb.google.com/114688480094930960522/May72013
So, Connect up the chassis. Both ribbon cables. AC power to chassis, AC power to Apple
II+. Interface card inserted in slot 2. No disk drives anywhere in the chassis or Apple
II+. Turn on the Apple II+. The green light on the chassis should come on. And you should
get a ] prompt. Pressing the button on the chassis should toggle the red light on/off.
Report back what happens.
Now we begin some basic power supply measurements. Set the DMM to DCV and connect the
leads to V and GND.
Connect the black lead of the DMM to a GND test point on mainboard. I have used TP1 GND in
this example. Then go through each measurement point and verify they are what I marked on
the picture.
Since this is a power supply you will not want to go shorting out things out. That would
be disastrous causing more damage.
Report back what the values are.
You may also test the wall adapter in a similar fashion. Except here, you turn the DMM to
ACV. I expect the AC adapter to output about 28V AC.
Report back what the actual output is.
BTW, what model DMM did you purchase?
And to gain confidence with the DMM, test some batteries and wires and discrete components
to see how it all works. That's how I learned. I thought continuity testing was the
hottest thing since sliced bread! I could now test wires and bad connections!
Hello Keatah,
they are close to the location of the 4 small signal transistors in the front left corner
and are labeled C3 and C4 ( ceramic capacitors ) and they are responsible for the switching frequency
of the 2 MOS FET Powertransistors.
sincerely speedyG
I would classify C3 & C4 as mylar capacitors. Polyester film & foil.. Reference DSCN1162.JPG
if you still have it.
The numbers printed on them are 102K100. And this means 1,000pF +/- 10% 100Volts
Hello Keatah,
1000pf equals to 1 nF. Thanks a lot for helping me complete the partlist.
I´ll update the relevant documents this evening.
sincerely speedyG
Speedy, If I can't troubleshoot for the next day or two.. You may need to carry the torch.
Here's my line of thinking:
But before we get into it, can you check the -12V output on the diagram? I don't see
anything to indicate what parts generate it. Wouldn't the node of C10+, R20, D6, D7 be the
best place to consider as the -12V output? For it is there I measure -12 to -14 depending
on load. And it is there it is closest to the power supply.
I still have not gone over the circuit plan in detail. But soon I hope. Nice job.
Now..
I'm asking Steven to check all the power supply outputs, AC adapter output, and 12V sense
line from the Apple II+ to the chassis. This 12V sense line is essentially a remote
on/off. This goes to Q7. I'm also looking for some activity on Q1 and Q2.
If all that stuff checks good. Then we can assume the chassis primary excitor side of the
supply is powering up simultaneously with the computer. A good thing to be sure. If
Steven's DMM has Hz functionality, we could check for 54KHz on the casings of Q1 and Q2.
Next we would check why the Green Power-On LED isn't lighting up. This is why I'm strongly
suggesting power supply is inactive, shorted, or just plain bad. Maybe some other part on
the 5V rail is shorting things out. Or the coil could be bad, so could anything connected
to L1 like D2, D3, and D4. C7 and C9 could be electrically leaky.
The 16 pin cable need not be connected to the computer for the chassis supply to power up.
The chassis has a 12V sense line. Which incidentally can be modified with a switch to
allow the chassis to be turned on independently of the II+. But I don't recall us ever
doing such a thing. That's what the three empty holes are for, for a switch connector.
And passive resistance (power off and all discharged) between GND and +5 and -5 is about
200ohms. -12V resistance to GND is about 550ohms. And +12V to GND shows the typical charge
and discharge action as the semiconductors reach threshold and fire off, so to speak,
basically indicating 3Mohm down to 8Kohm or so. Anyhow, none of these resistance
measurements should indicate 0 ohms, which would indicate a shorted rail.
Maybe we'll get lucky and find the power adapter is bad!! Wouldn't that be an easy fix.
I'm also asking Steven to check that too. I was going to get into testing the bridge, but
I figure we'll start with supply outputs themselves. A reasonable 50/50 starting point.
In the course of thinking about all this I might have discovered an easy way to make the
chassis work on a //e and platinum //e. I have to measure and test later. 1 step at a time.
Carry on
Steven.
All measurements will be made with the DMM black COM/GND lead attached to either a
standoff screw hole or TP1 GND on the chassis motherboard. The red lead is what you will
use to probe things and grab the measurements.
My makeshift graphic shows actual live voltages. You may or may not get similar readings.
Since this is a circuit that could be malfunctioning, anything could be happening. So be
sure you're using the DMM right. Gain confidence by measuring some batteries. If you can
measure a 9V battery or your car battery, then you can do this.
It is important to always use volts readings and connections. You must not do anything
with Amps or Current. Just volts for now.
It may help to use a chart like so..
Select DCV and grab these readings first.
DCV READINGS
Test point +12VEN =
Test point +12VAC =
Test point +12V =
Test point +5V =
Test point -5V =
Top of diode D7 =
Metal Case of Q2 =
Metal Case of Q3 =
Now select ACV on the DMM and get these.
ACV READINGS
Test point +12VAC =
AC adapter output =
And to measure the power brick adapter output, just connect both leads of the DMM to the
output of the brick.
Hello Keatah,
to me it sounds a lot like the syptoms you have explained earlier in the posting related to the busted supply....
in such a case i would first have suspense against one of the Shottky diodes to be blown....
another point if the voltages are good - might be the NE555 at location U1.
It´s the part that gets the value from sense of the 12 Volt and lights up the LED for the frontpanel and
besides it also leads the info on the sensed voltage as well as the select/unselect switch position back
to the logic up at U11 to U9 ....
from there the sensed signal and the switchposition is sent back to the logic on the IF-card to permit unlocking the NMI and the IRQ lines in the Apple itself....
anyhow - if your for extended period offline - just drop a note and i´ll continue the diagnostic with Steven...
i just know you have more experience with the box.itself. I don´t have one and therefor i must depend to my analysis as engineer for microprocessors
and from the circuitplan and the pictures.... ( i have them all together in one large folder..... )
and we all know well by experience there IS a difference between theory and practical behaviour .....
that´s the reason i stepped back and left this task up to the very point in your hands...
sincerely speedyG
Hey Steven. Am I right in reading that you ordered and replaced the standoffs in your
chassis? Are they a good fit and replacement for the original ones?
If so, I'm too lazy to research now and would like to get the part numbers from you for
these. I want to replace mine, The plastic seems a little stiff and ratty, and while they do
their job, I'd like new ones. I could steal from my other chassis, but then.. So you see?
And with any restoration project I do I keep the old fasteners and all replaced material.
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