Partly working keyboard

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Partly working keyboard

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?

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Just wanted to say I'm having

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:

  • The self-diagnostic (CTRL-OPEN-CLOSE-RESET) works fine and results in "KERNEL OK"
  • Disks work and I can load into games and things fine

Just no keyboard input works.

 

 

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You are correct, Ctrl-reset

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.

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Thanks for your comments and

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:

  • 3600-PRO keyboard encoder
  • 74LS123 (the only socketed TTL chip)
  • 74LS00
  • 74LS08 (2 pcs)
  • 2716 EPROM

 

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.

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Hi,

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. 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.

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.

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dc99 wrote:Hi, Yes the KR3600

dc99 wrote:
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.

 

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.

 

e wrote:

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.

 

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.

 

e wrote:

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.

 

Good suggestion. Fortunately the computer's EPROMs are available online, but throughout all these years I never thought about backing up the keyboard EPROM. I might have borrowed a buddy's Apple II back in the day in order to read/save the keyboard EPROM using my Apple II-based EPROM programmer, but those are all saved on 5.25" floppies, so at the moment it's a catch-22, and for all I know the actual disk may not even be readable by now. Oh well.

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If you had the cable around

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.

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dc99 wrote:If you had the

dc99 wrote:
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.

 

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:

e wrote:
The KR3600 decoderchip sound quite similar to AY-5-3600 but it isn´t similar at all ! But it was acommon used chip in third-party keyboards.

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.

 

 

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On a normal Apple II/IIe

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

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There's no 7404 (or 74LS04)

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?

 

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Hi,

Hi,

1. I double checked and in my early 2e version it has a KR3600-017 labelled chip in the keyboard encoder socket which is labelled on the board as AY3600-PRO so I'm fairly certain you will be fine with the AY-5-3600-PRO.

2. If for some reason this doesn't work these encoders have the same pinouts but different key mappings so the worse case is you will press a key and another one will be displayed. At least the you will be able to confirm if it's the encoder or not.

3. Perhaps you can try using your scope on a simple 74LS chip on your motherboard which is working to see if your using it properly.

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Thanks for double checking

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).

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I've received and replaced

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?

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Not a PROM issue

When the keyboard is not working at all, then I don't think it's an issue with lost PROM data. That would be more likely when some keys were not working or keys would be misinterpreted.

When no key at all is working, and you have already checked the keyboard itself, then I'd look at the mainboard logic connecting the keyboard to the CPU. The 74LS257 (B7) would be a likely culprit: that's the multiplexer/buffer which connects the upper 4-bits from the keyboard controller to the CPU's data bus. The top most bit indicates a keypress. So, when this chip doesn't work, then the CPU has no way to detect any keypress.

If you have a multimeter then check the voltage level at pin 7 at the keyboard connector (A7) (or at pin 2 at B7). It needs to toggle to 5V as soon as you press a key. When that's working, then the keyboard is OK and the issue is on the mainboard. I would suggest to replace the 74LS257 at B7 in this case. Otherwise, when you do not see 5V after pressing a key, then you need to investigate the keyboard itself.

T.

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Thanks for your suggestions.

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).

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It's normal that unconnected

It's normal that unconnected input pins fluctuate. 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.

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. 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).

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).

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The keyboard controller in

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.

 

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David_M wrote:

David_M wrote:

The reason for the eprom being there is to map those standard scan codes to the ascii codes expected by the motherboard.

 

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?

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MacFly wrote:

MacFly wrote:

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.

 

Yes, that makes sense, and good to know when testing.

 

e wrote:

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.

 

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.

 

e wrote:

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).

 

Nope. No 5V detected at all.

 

e wrote:

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).

 

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?

 

 

 

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Are you absolutely sure that

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.

 

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MacFly wrote:

MacFly wrote:

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.

 

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.

 

 

e wrote:

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.

 

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

 

 

 

 

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UPDATE:

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.

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Oh, I forgot to post photos

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).

 

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74LS02 is a NOR gate. So,

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:

Fuji wrote:

 

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!

 


 

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).

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MacFly wrote:

MacFly wrote:

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.

 

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.

 

e wrote:

 

Fuji wrote:

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!


 

Is that a typo or is A12/pin 2 really 2V?

 

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.

 

 

e wrote:

Also, C11/pin 4 ist 1V - or 0.1V?

 

Sorry about the typo. I've rechecked C11 (74LS04) pin 4 and it reads 0.1V.

 

 

e wrote:

C11/pin 4 should have the same voltage as A12/pin 2 - these pins are directly connected.

 

Hmmm.. that's strange. There's no connection between those pins. I better remove the PCB and check underneath!

 

 

e wrote:

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).

 

I'll definitely get back to this when I have more a little more time than today. Hopefully this will lead to something good.

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