Having spent some time searching for an Apple ][ related forum I finally found this site, which I'm glad I did!
I'm trying to revive an old Apple ][+ (actually an Asian clone) and after cleaning it up (removing corrosion), re-soldering some cold joints and changing a 74LS74 I now have the familiar "Apple ][", the cursor and beep. However, the keyboard doesn't work -or rather: CTRL-RESET is the only thing that works! There's no reaction from the other keys.
So the big question is (before I spend a great deal of time troubleshooting in the wrong area): since CTRL-RESET works (or just RESET -there's a switch on its circuit board which allows you to choose one or the other way of doing a reset), would this indicate that the keyboard is malfunctioning, or something inside the computer? I don't know how the keyboard works, but could it be that CTRL-RESET are hardwired directly to the computer (i.e. the 14 pin keyboard connector that goes into the II+ motherboard) while rest of the keys have to go through the keyboard controller circuitry (on the keyboard PCB)?
The rest of the computer appears to be working as it should, but I really can't say for sure since I don't have a second system to compare with, and the floppy disks are all 25-30 years or more old. Just about none of them booted excpt for "Apple Cillin" which presented on the screen a number of hardware tests. So at least that should verify the disk controller (slot #6) and 5.25" floppy drive works. For all I know the issue with the other floppies could be a disk alignment issue, but I don't want to look into that before I get to fix the keyboard.
So where to start troubleshooting and how?
Just wanted to say I'm having this exact problem, too, but wanted to add a little bit more info for my situation, which may apply to yours as well:
Just no keyboard input works.
Fuji: You are correct, Ctrl-reset bypasses the keyboard encoder. If the other keys are not working I would be checking the keyboard PCB, specifically the keyboard encoder IC. Genuine apple ][+ encoders are Apple specific so a little hard to find unless someone is parting out a machine - chances are if it's a clone they will be using a generic encoder so you might have more luck finding one.
Tranicos: sounds like you have a Apple 2e - strange as CTRL-OPEN-CLOSE-RESET combitnation work. The 2e uses the AY-5-3600-PRO encoder and replacements are available on ebay etc so you might want to try a replacement.
Thanks for your comments and confirming that CTRL-RESET bypasses the keyboard encoder.
At least the computer appears OK! Good to hear that the encoders are still available. Mine is marked as follows:
KR3600-017
SMC 8301C
KR3600-PRO
So is this the same "3600-PRO" you said the IIe used?I see there's a total of 6 ICs on my keyboard PCB:
The keyboard has a caps-lock button with a red LED inside (if I recall correctly it only made a difference in 80-col. mode where I was able to switch between upper/lower case). And on the left hand side there's a 2-position switch for making reset possible with just the RESET key or with CTRL-RESET (my choice). There's no brand name on the keyboard or anything except for "KEY BOARD" on the component side and "SYKB-001H" on the solder side, but I haven't been able to find anything online concerning it, so there aren't any helpful schematics or other info to be found. I've always been under the assumption that the keyboard wasn't an Apple clone, but rather an "Apple II compatible" keyboard. Regardless, I've so far not been able to find an Apple II keyboard schematic either.
By the way, what is the EPROM for? I thought the keyboard encoder handled all the characters, and the actual characters seen on the screen handled by the keyboard generator EPROM on the Apple II motherboard. I hear that EPROMs go bad after a number of years, so if that's happened here -are these keyboard EPROMs generic, or does each keyboard have their own EPROM? I do have an EPROM programmer, so perhaps I should just pop out that 2716 and read/save its data as soon as I can.
[quote=dc99]Hi, Yes the KR3600-017 is the same as what the Apple 2e uses. You can find the encoder pinout online and check if you have activity at the input / output pins to confirm if it's actually the fault.[/quote]
I found the datasheet at an Apple II related website here. That's a good suggestion. I suppose my simple DIY hobby oscilloscope (Jye tech DSO-150) might suffice for this?. eBay has several KR3600-xx chips for sale, but none of them have the -17 suffix. Is it the same as the -PRO? Assuming that since it actually also says "KR3600-PRO" on my chip.
[quote]
It is also possible one or more of the 74LS ic's are causing the problem - they can be damaged simply by connecting the cable between the keyboard and motherboard the wrong way[/quote]
Yes, that could very well have happened -actually I'm sure I've put the cable the wrong way round, so maybe I should just desolder all the TTLs (LS08, LS00), solder back in sockets and replace them all (including the LS123). Any other component which I should look out for? I know electrolytic capacitors dry up after a while, so maybe I should replace the two I've found?I assume as long as the red caps lock/power LED lights up on the keyboard and CTRL-RESET works I have at least got the cable the right way round.
[quote]
You are correct how the regular apple II keyboard works, I'm not familiar with clones so I'm not sure what function the EPROM may be performing except perhaps remapping keys? As long as the window on the EPROM is covered it should be ok however if you have a programmer it can't hurt to take a backup. There is a few different versions of the Apple II keyboard, schematics are available online in various books such as Understanding the Apple ii.[/quote]
20191003-115251_PA030140.jpg
20191003-115453_PA030143.jpg
[quote=dc99]If you had the cable around the wrong way I would start by testing (or replacing) the 74LS ic's - try the 74LS08's first as one of those is what I found failed in a similar situation My 2e has exactly the same labelled keyboard encoder as your so you should be fine replacing it with a "AY-5-3600-PRO" if necessary. Your scope should be fine to test these components.[/quote]
Well, I successfully managed to desolder the two 74LS08 and the 74LS00, replacing them with IC sockets and new chips, but still no go. No difference from before. That leaves the 74LS123 (monostable multivibrator), the KR3600-PRO encoder and finally the 2716 EPROM (I have no idea what to program a new one with in case it's faulty). I couldn't get any output on my scope, so my guess is that the encoder is broken or I just haven't got the hang of using it properly.
I'm about to order a 74LS123, the AY-5-3600-PRO and a couple of 10uF/16V electrolytic capacitors (the only electrolytics in the keyboard) as it's not impossible these might be dried out after 35 years or so.
I'm a little confused about the encoder chip though... according to this Apple II page, the KR3600 isn't compatible with the above:
and furthermore it confuses me that my keyboard decoder is marked "KR3600-17" as well as "KR3600-PRO". If I'm not mistaken, from what I've read the "-PRO" extension means it's programmed with a standardized key-table while the other extension numbers means it's got one of a number of different customized key-tables ordered by the company who's designed the keyboard in question. So how can it be both? Can anyone enlighten me on this?
In any case it's not much of an outlay so I'm ordering the AY-5-3600-PRO to see what happens in case replacing the other parts doesn't solve my problem.
On a normal Apple II/IIe keyboard. plugging the keyboard in wrong invariably kills the 7404 that is connected to -12 volts on the keyboard socket. I'm not sure how this clone keyboard is wired, but I would expect a similar result.
regards,
Mike Willegal
There's no 7404 (or 74LS04) on the keyboard PCB here unfortunately. The two 74LS08 chips appear to be closest to the keyboard socket, and they've both been replaced with no difference.
Are there any ICs on the II+ motherboard which are directly related to all of this which I could try replacing?
Thanks for double checking the encoder. Seems like it's the same one as I have!
Yes, I'm thinking the same about the encoder -at least something will come up on the screen when I press the keys, so I can confirm that the encoder needs replacing.
Good idea about checking a simple TTL chip with the scope -I'll give it a go. So next off is ordering the AY-5-3600-PRO (I found sellers of these on eBay in case someone else is in need of the same).
I've received and replaced all the ICs (including the encoder) but the keyboard still doesn't work. So next I replaced the two electrolytic capacitors (it wouldn't surprise me if they had drived up after all these years) but that made no difference either.
The only componets left are a bunch of diodes (I've checked most of them in-circuit with a multitester set to diode-testing and they appear fine- I should probably test them all though), a few condensers and the EPROM which is still a big mystery (what it's for and what it contains).
I have heard that EPROMs can lose its information after many years, which is what I suspect, but I really have no way to know. Having read its contents with an EPROM programmer I think I'll upload it here and ask if someone more knowledgeable than myself can see if its data makes any sense. Is there anything else I can try?
Thanks for your suggestions.
I've checked the voltage on pin 2 of the computer main board B7 (74LS257) where something strange is going on (I also replaced the IC but with the same result):
When I power on the computer, pin 2 reads +5V and stays that way when pressing many of the keys.
However, when pressing some other keys it reads around 0V! The voltages stay that way until I press a different "group" key (i.e. the "+5V group" or the "0V group". I don't know if there's a pattern to this, but here's which keys show which voltage when pressed:
0V when pressed
entire top row keys (all number keys, colon/asterisk, hyphen/equals)
ESC
RETURN
Left arrow
Right arrow
; + (semi-colon/plus)
, < (comma/less than)
. > (period/greater than)
/ ? (slash/question mark)
Spacebar
+5V when pressed
all letter-keys (A-Z)
No voltage change when pressed
CTRL
RESET
REPT
Left-SHIFT
Right-SHIFT
NOTE: for the "no voltage change" group I've tried both pressing the "+5V" group and the "0V" group prior to pressing, but the voltage didn't change regardless.
So some good news as there's some response!
Next, I unplugged the keyboard and checked the pin 2 (B7) voltage again and it reads around +1.5V but fluctuating. Seems like a capacitor discharged or some other unstability.
Back to the EPROM: I posted separately on the keyboard EPROM where I also uploaded its data (hoping someone can see if it looks garbled/damaged or not, and if they can identify it or determine its use).
The keyboard controller in the 2+ and the 2e are the same chip, I have used the chip from a 2+ to repair a 2e before.
Somebody mentioned thast were a custom chip just for Apple... no they aren't The manufacturer offered a few standard configurations and a full customisation option. Apple went with one of the common standard options.
The reason for the eprom being there is to map those standard scan codes to the ascii codes expected by the motherboard.
[quote=David_M]
The reason for the eprom being there is to map those standard scan codes to the ascii codes expected by the motherboard.[/quote]
Are you referring to the II+ and //e you have repaired? Do they also have an EPROM in the keyboard circuitry, or are you only referring to my II+ clone?
[quote=MacFly]
The voltage is driven by the keyboard. Also, only "normal" keys trigger a keypress - the modifier keys (shift, cltr, ...) do not trigger a "keypress event" themselves. They are reported differently.[/quote]
Yes, that makes sense, and good to know when testing.
[quote]
However, looking at the schematics again, I did mix up the pins. The interesting pin to check is pin 5 at B7 (not pin 2). This is "a normal key's keypress is pending" signal. This should rise to 5V when you press a key. It gets cleared to 0V as soon as the CPU has acknowledged the keypress. So normally, when the CPU is able to read, the 5V is only visible for a few microseconds - so impossible to see with a simple multimeter. [/quote]
I do have a simple single-channel oscilloscope. I'm quite new at using 'scopes so I might be doing something wrong, but there appears to be a memory function on it which stores the last peak signal. But there's no response when measuring pin 5. Checking the voltage it stays at around +0.12V regardless of a keypress or not.
[quote]
However, when you can see continuous 5V at pin 5/B7 after a keypress, then there's an issue with mainboard being unable to address the keyboard register (guaranteed not to be a keyboard issue then). [/quote]
Nope. No 5V detected at all.
[quote]
Also check the voltages at the keyboard flipflop at B10 (74LS74) at pins 11 (strobe input signal from the keyboard) and at pin 13 (keypress reset, must be 5V).[/quote]
Pin 11 read around 0.12V (regardless of key pressing or not) and pin 13 reads around 0.11V, also regardless of having a key pressed or not.
How should I interpret the results? Obviously the keyboard is sending something out (hence the B7 pin 2 readings), so can I assume the problem is (first of all) related to the II+ motherboard?
Could the 74LS257 (B7) be at fault? I don't have any new replacements but seeing that B6 and C11 are of the same type I swapped them around without any difference in booting the computer or reading the B7 pins -can I safely assume they're (74LS257) all OK?
Are you absolutely sure that pin 13 of B10 (the 74LS74) is low (almost 0V)? If so, then it's obvious that no keypresses can be detected. That would confirm a mainboard issue.
Double-check B10/pin 13. When you confirmed this to be low, then check pins 1,2,3 of A12 (a 74LS02) and also pins 3 and 4 of C11 (74LS04). They should have the voltage levels as shown in the attached picture (H=about 5V, L=about 0V). These voltages should be constant (they'd only change for a microsecond or so, when the CPU accessed the keyboard).
When B10/pin 13 is really low, then one of mentioned ICs seems to be not working (B10/A12/C11). Should be easy to tell which is at fault, by checking the pin voltages.
AII+Keyboard.png
[quote=MacFly]
Are you absolutely sure that pin 13 of B10 (the 74LS74) is low (almost 0V)? If so, then it's obvious that no keypresses can be detected. That would confirm a mainboard issue.[/quote]
Yes, I just checked it again.
On a slight sidenote: B10 turned out to be the culprit when the computer didn't work (can't remember if the screen was all garbled and stayed like that without a beep or just a black screen), but replacing that 74LS74 returned the familiar "Apple ][" along with the beep.
So could the problem be somewhere else which had then lead to a damaged B10? A cold solder or otherwise bad contact etc? just thinking out loud.
[quote]
Double-check B10/pin 13. When you confirmed this to be low, then check pins 1,2,3 of A12 (a 74LS02) and also pins 3 and 4 of C11 (74LS04). They should have the voltage levels as shown in the attached picture (H=about 5V, L=about 0V). These voltages should be constant (they'd only change for a microsecond or so, when the CPU accessed the keyboard).
When B10/pin 13 is really low, then one of mentioned ICs seems to be not working (B10/A12/C11). Should be easy to tell which is at fault, by checking the pin voltages.
[/quote]
Here are the readings of all those pins:
B10 (74LS74)
pin 10: 4.47V (high)
pin 13: 0.1V (low) should be high!
A12 (74LS02)
pin 1: 0.1V (low) should be high!
pin 2: 2V (low) correct!
pin 3: 0.01V (low) correct!
C11 (74LS04)
pin 3: 4.5V (high) correct!
pin 4: 01.V (low) correct!
Should I interpret this as B10 and A12 not working, or that some other circuitry before it leading to those wrong readings?
I'll try to see what happens if I replace A12 and again B10:
replacing A12 (74LS02):
Same readings with 4 different replacement ICs
replacing B10 (74LS74):
same readings with 3 different replacement ICs
UPDATE:
I don't know if this is significat or not, but back in the day I built a "keyboard beeper" for my Apple II clone. It plugs into the B10 socket (74LS74) and has a "through socket" for the B10 IC itself. Whenever a key is pressed a short "beep" sound is heard through its piezo buzzer. Just for fun I plugged it in as I have nothing to lose and it actually beeps every time I press a key! I tested every key and all (the "normal" keys) emitted a beep, so obviously some information is sent to the computer from the keyboard!
Regarding the EPROM I also burnt a new one using the new EPROM data someone kindly posted in my other thread, where someone else also confirmed that my current EPROM was most likely intact, but even with the new EPROM it made no difference (the keyboard beeper works the same with the old, original EPROM). So it's probably like you say an issue with the computer itself.
Oh, I forgot to post photos of that keyboard beeper (there's no way to edit existing postings here -perhaps it's a limitation to new members of the forum).
20191202-122548_PC020008.jpg
20191202-122600_PC020009.jpg
74LS02 is a NOR gate. So, when pin 2+3 (inputs) are low, than pin 1 (output) just has to be high. If that wasn't the case, then A12 is broken (but you already replaced it). Otherwise, I see only two other options: either there is an issue with the power supply to A12: check pin 14, Vcc, should be 5V. Also check the resistance of pin 7 to ground (with the system switched off). When these were also ok, then the only option left would be a short cut of pin 1 to ground.
However:
[quote=Fuji]
A12 (74LS02)
pin 1: 0.1V (low) should be high!
pin 2: 2V (low) correct!
pin 3: 0.01V (low) correct!
C11 (74LS04)
pin 3: 4.5V (high) correct!
pin 4: 01.V (low) correct!
[/quote]
Is that a typo or is A12/pin 2 really 2V? Also, C11/pin 4 ist 1V - or 0.1V? C11/pin 4 should have the same voltage as A12/pin 2 - these pins are directly connected. When you measure different voltages than this clearly indicates a connection issue between these two pins (bad soldering, broken track on the circuit board or a bad contact at one of the two IC sockets).
[quote=MacFly]
Otherwise, I see only two other options: either there is an issue with the power supply to A12: check pin 14, Vcc, should be 5V. Also check the resistance of pin 7 to ground (with the system switched off). When these were also ok, then the only option left would be a short cut of pin 1 to ground.[/quote]
Regarding A12: pin 14 reads approx 5V so that's good.
And I read full continuity between pin 7 to the power supply's GND (tested when powered off).
I also checked the resistance between pin 1 and GND which measured around 10 Mohms, so apparently no short circuit there.
[quote]
[quote=Fuji]
A12 (74LS02)
pin 1: 0.1V (low) should be high!
pin 2: 2V (low) correct!
pin 3: 0.01V (low) correct!
C11 (74LS04)
pin 3: 4.5V (high) correct!
pin 4: 01.V (low) correct!
[/quote]
Is that a typo or is A12/pin 2 really 2V? [/quote]
I just checked it again and indeed it reads around 2V.
Actually it reads either around 1.95V or 1.65V depending on which 74LS02 I try. Strange, but perhaps there are some brand differences.
[quote]
Also, C11/pin 4 ist 1V - or 0.1V?[/quote]
Sorry about the typo. I've rechecked C11 (74LS04) pin 4 and it reads 0.1V.
[quote]
C11/pin 4 should have the same voltage as A12/pin 2 - these pins are directly connected.[/quote]
Hmmm.. that's strange. There's no connection between those pins. I better remove the PCB and check underneath!
[quote]
When you measure different voltages than this clearly indicates a connection issue between these two pins (bad soldering, broken track on the circuit board or a bad contact at one of the two IC sockets).
[/quote]
I'll definitely get back to this when I have more a little more time than today. Hopefully this will lead to something good.
I've started tracing the PCB tracks between those ICs and I noticed that some of the vias (including one track from one of the above ICs) don't look very good. I believe they're corroded. It's hard to say before cleaning them properly and doing some extensive continuity testing (it takes time tracking down which PCB trace goes where -paper tape and a pen for marking stuff comes in handy!).
In any case there's no contact between those two IC pins, and simply melting solder into a couple of those vias didn't help. So I think I'm going to get myself one of those abrasive glassfiber pens to remove the corrosion then try to apply some solder into those holes again. Failing that I might need to scratch off a little protective layer from the traces and solder a small wire-strand between the upper and lower layers.
Other suggestions on how to repair vias?
[quote=Fuji]
I've started tracing the PCB tracks between those ICs and I noticed that some of the vias (including one track from one of the above ICs) don't look very good. I believe they're corroded. It's hard to say before cleaning them properly and doing some extensive continuity testing (it takes time tracking down which PCB trace goes where -paper tape and a pen for marking stuff comes in handy!).
In any case there's no contact between those two IC pins, and simply melting solder into a couple of those vias didn't help. So I think I'm going to get myself one of those abrasive glassfiber pens to remove the corrosion then try to apply some solder into those holes again. Failing that I might need to scratch off a little protective layer from the traces and solder a small wire-strand between the upper and lower layers.
Other suggestions on how to repair vias?
[/quote]
I've poked a bit of wire through the via then soldered both sides and clipped off the excess. Doesn't take much. Just like the excess lead from a resistor or capacitor will fix several vias.
I've got pretty much the same problem. It beeps and can boot to the Apple ][ screen. The cursor will not respond no matter which keys I press. If I press the reset key, it beeps again but the cursor would move the bottom of the screen. If I press the reset key again, there will be one more line of the prompt and the cursor turns into a blinking vertical bar. The more I press the reset key, the longer the vertical bar goes.
It works! It works!!!!
I can't believe it, but all of a sudden my keyboard is working again.
Here's the culprit:
20191216-114740_PC160003.jpg
I started "fixing" open vias by soldering through those open holes, and in the process I used a glassfiber pen to scratch away corrosion, dirt, flux etc. That's when I noticed the broken trace (as shown above) which I easily fixed with a single strand of wire soldered as a "bridge" on top of the trace (using the glassfiber pen again to get to the copper trace).
That reconnected C11 (pin 4) and A12 (pin 2) .
A MILLION THANKS to McFly in particular for leading me through this! I would never have figured it out on my own.
Neosunrise: it wouldn't surprise me if you had some broken connections as well. But it could also be one or several broken ICs. I've found other Apple II problems I've had using a book which listed typical symptoms and which IC/ICs could be the cause of this. I can't remember the name of this book off-hand, but will post back when I find out. Actually I think it's available online as well now. I'll let you know if I find the link.
I found some info like that here for starters. And here's a chart named Which IC does the job?.
Oh, I just found out which book I've been using for my previous issues: "How to repair the Apple computer" which you can download from this page along with numerous other Apple II related books (also several repair related books apparently).
This is the direct link to that specific book (if you don't want to browse through all of the other books as well). I found the troubleshooting charts from page 38 and onwards very useful and highly recommend it for simple problems (broken ICs). Hope this helps.
Thanks so much Fuji for sharing the resources. I really appreciate them. Congratulations on your working Apple II! I am going to replace the chips on the keyboard and will see how it goes. I suspect that there are some damages caused by the liquid poured onto the PCB, as shown in the pictures. Anyway, will check it out in case the replaced chips still cannot bring the keyboard back to life.
IMG_2720.jpg
IMG_2729.jpg
Thanks and you're most welcome!It's the least I could give back here, after getting all that help :-)
I hope you don't spend too much money getting replacement ICs in vein, which I did (oh well, now I have a nice collection of spare parts at least). The technical advice I received here was invaluable in tracing down the problem instead of just guessing and swapping ICs by qualified guesses as I would have continued doing if I didn't have anywhere to ask.
I hope you soon succeed. These are nice machines, and unlike today's computers can actually be repaired. My next step is plug in my expansion cards, try out my floppy disks and see if they're readable and basically refresh my Apple II skills. Exciting times.
[quote=Fuji]
It works! It works!!!!
[/quote]
Thanks for reporting back. And Congrats, well done! :-)
A systematic approach always pays off. And with these machines, looking at the schematics and using a simple multimeter often is enough to narrow down any issue. And it's also more fun, than just randomly swapping parts. ;-)
Thanks, and yes -it's more fun, and you might even learn a few things along the way.
On the subject of keyboards; a few keys are double-triggering and only trigger when pressed from certain sides. I assume it's a matter of opening them up and spraying some contact cleaner/cleaning them with a Q-tip, but is there a common procedure for opening them up? It doesn't look obvious to me and I don't want to break anything (guessing it's a matter of prying them open with a scredriver from each side), or do I have to desolder the actual switch and open it from the under-side?
Any ideas anyone on how to open up those keyboard keys (so I can spray in some contact cleaner)?
I mentioned (and showed photos of) my keyboard beeper add-on board and have just written a DIY (Do It Yourself) "how to" on that which I posted here for those interested.
I had luck on my double-repeating keys and unresponsive keys by just (powering off the unit and unplugging it) then removing the caps and using an eye dropper to drop in some 90% isopropyl alcohol along the stem (several drops) and then repeatedly striking the key a couple dozen times, then letting it dry overnight in a warm place before turning it back on. I had several malfunctioning keys on my 2e when I first got it and this fixed all of them and none have stopped working since then. There are diagrams on the net about how to actually open them up after desoldering them, but looks like lots of tiny parts and springs.
Good suggestion which I'll definitely try out!
So you're saying the keys have to be desoldered first to be open from (I assume) underneath? Mine's a clone keyboard and I haven't seen any markings on the key buttons giving away the brand/model (it might be underneath and seen after desoldering now that I think about it), but then again the method you've read about might be a common, general way to open most keyboard keys...
My vote for the simpler method first.
OK, tried the isopropyl method, but it didn't completely solve my problem (though some keys worked a little better). I will now attempt to desolder a key to see if it can be opened from underneath, and cleaned within with a contact cleaner.
A quick question: how is the REPT key supposed to work?
If my memory is correct you hold down REPT and a key, that key is repeated, right? And if you hold down REPT on its own, then nothing happens?
But on my keyboard, pressing down REPT on its own repeats the last key you pressed!
Oh, here are some photos of the key buttons I've just desoldered:
20200107-113135_P1070021.jpg
20200107-114053_P1070042.jpg
20200107-114029_P1070039.jpg
At first they look all the same, but upon closer inspection they have different numbers imprinted upon the stems:
20200107-113548_P1070030.jpg
Strangely, there's a different number underneath (here from the same key as the one pictured above with "38" on the stem, but with "31" underneath:
20200107-113756_P1070033.jpg
Out of the 4 keyboard switches I removed, they all have different numbers on them (despite being in the same row (A,S,D.....) I can't explain this to the different angles of the keys either).
The don't appear to be serviceable as it looks like some sort of epoxy sealing underneath. Dripping isopropyl alcohol did better the condition of some switches, but one appears completely "dead" while another still has intermittent contact. I might give that one a new go with the alcohol.
Does anyone recognize these keyboard switches and know where new ones can be purchased?
I don't know of a replacement, but consider drilling 2 very tiny holes along 2 sides of the side of the case body and injecting isopropanol or contact cleaner with a diabetic needle, (as example) then working the switch vigorously and injecting dry air to remove the cleaning fluid. Consider this a last ditch effort to clean the contacts. Just a suggestion.
Good suggestion as a last resort.
Actually I managed to get some of the alcohol into the most problematic switches as well by pressing the stem to the side while puring a few drops along the other side of the stem. That appeared to have fixed them all, but it's all a little strange...... read on.
With all 4 problem-switches removed I decided to see how the keyboard would work with the Apple II powered on. You guessed it! The REPT key problem was gone!
So I soldered back one key at a time to see if that would change anything when powering up again. Two of them appear to work fine again without disrupting the rest of the keyboard while the other two cause the problems to come back again. I've tried to trace the PCB for a broken track or cold solder joint but haven't found anything yet. There's definitely some erratic behaviour but it doesn't make sense as the switches now work as they should (according to my multimeter set to continuity mode).....
I should probably swap switches around, or use some completely different momentary pushbuttons for testing but I haven't done that yet, but... could it be that some isopropyl alcohol might be still trapped inside and causing some electrical contact even when not pushed? Is it electrically conductive? I've used chemically pure isopropyl alcohol (more than 99.5% purity according to the bottle). Drilling a small hole would as you suggest would solve a lot of things but something I want to save as a last resort.
I bet you could still hgave some liquid in them. I know when I did mine, I thought Id wait an hour or two and it would be dried out, but powering it up resulted in continuous typing of a few letters over and over, so I turned it off again and set the whole computer on top of a radiator in the house overnight - a hot water type, not a steam type, and the next day all issues were gone and its worked perfect ever since. I think I used 90% which means 10% of something else (water usually for example), so Id imagine even a .5% water would be enough to make contact in that tiny space.
Yes, that sounds plausible. Thanks for confirming.
I think I'll follow your suggestion and see what happens after a day or two near a radiator. I did measure some (fluctuating) MegaOhms of resistance with those switches not pressed down. I assume it should be zero, but it's hard to compare with the fully working ones as I haven't desoldered them from the keyboard PCB. Time will tell....
[quote=dc99]My 2e has exactly the same labelled keyboard encoder as your so you should be fine replacing it with a "AY-5-3600-PRO" if necessary. Your scope should be fine to test these components.[/quote]
Yes! I can confirm that the AY-5-3600-PRO that you suggested works fine as a replacement (for the KR-3600-PRO)!
I've written more about it and other interesting related findings in a separate thread .
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Oh, while I'm at it (in case someone with the same keyboard is wondering), the two-way switch on the upper left hand side's purpose is to define how to do a reset: either by pressing the RESET key alone, or by holding down CTRL and RESET together (I prefer the latter to avoid mistakingly resetting the computer).
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I almost forgot to say.... the keyboard now works again!
Thellmer: your encouragement and suggestion really helped! Drying the keyboard and removed keys in a (slightly) heated (and dry) environment solved the issues I had, so apparently there was a little conductivity between the key-switches, and with multiple key-switches acting that way, no wonder I got some strange results.
NeoSunrise: how's your keyboard repairs going? Hopefully some of my experiences and the help I've been given here will get you on your way.