tsalat wrote on 2023-10-21, 10:08:

Hi, […]
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Hi,

I was recently repairing an old 486 board with embedded CPU damaged by battery leak, and ended up with "Keyboard Error" message. The board is labelled as ZEON 94V0 but I couldn't find any information about it. Visually, the A-Trend ATC-1411A appears to be the exact board (https://theretroweb.com/motherboards/s/a-trend-atc-1411a). The board has no dedicated IC for the keyboard. I have repaired the traces that were broken, the one I have found, and replaced the keyboard connector as well. The board will boot up to the BIOS error message, debug card no error, claiming an issue with the keyboard.

- The keyboard will blink at the beginning.
- The GND, 5V are fine, NC is not connected.
- The DATA in has 5V without the connector plugged, connected to the UMC UM8496F
- The CLK pin has 0V without the connector, and 5V after the keyboard is connected
- The fuse is just a wire, from the production, all good here.

I went through the board a few times, found two issues on the way of looking for the keyboard error but nothing solved the keyboard issue. The keyboard is fine, I have tried another PS2 with the same outcome.
The broken traces next to the battery were not connected to the keyboard plug, the DATA line went above that area and is fine. I have added some pictures about how it was looking before and after.

The CLK trace is going from the back side of the board to an inductor and from there to a capacitor next to the SIMM slots. From this moment I have no idea where it goes, the capacitor seems to be there only as a filter, nothing is going away from him and the other leg is GND, make sense. The trace from the CLK is beneath the SIMM slots and I cant find where it goes further - I have been beeping for an hour with no positive location of the trace behind the location I can see from the back side of the board.

I am not sure now about both the CLK and the DATA of course.

Does the CLK should be 0V without the keyboard plugged in? Does it make sense that after plugging the keyboard the voltage goes to 5V on the CLK pin?
What is generating the CLK for the keyboard connector? This could help me to find the trace I am missing and maybe locate the issue. I do not have an OSC at this moment so can not check if any CLK is reaching the keyboard. Is the clock coming from the clock generator? - the peripheral output? - I would assume that even the ISA slots would be dead in this case but they are getting 2,5V on the OSC pin.

ahhh, I am so lost at this moment and need some advise 😀.

any help and advise would be appreciated, thank you Tomas

Web searches indicate other boards marked with Zeon as being by San Li (the 94V-0 is a standards mark for PCB manufacture)

PC Hoarder Patrol wrote on 2023-10-21, 10:39:

tsalat wrote on 2023-10-21, 10:08:

Hi, […]
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Hi,

I was recently repairing an old 486 board with embedded CPU damaged by battery leak, and ended up with "Keyboard Error" message. The board is labelled as ZEON 94V0 but I couldn't find any information about it. Visually, the A-Trend ATC-1411A appears to be the exact board (https://theretroweb.com/motherboards/s/a-trend-atc-1411a). The board has no dedicated IC for the keyboard. I have repaired the traces that were broken, the one I have found, and replaced the keyboard connector as well. The board will boot up to the BIOS error message, debug card no error, claiming an issue with the keyboard.

- The keyboard will blink at the beginning.
- The GND, 5V are fine, NC is not connected.
- The DATA in has 5V without the connector plugged, connected to the UMC UM8496F
- The CLK pin has 0V without the connector, and 5V after the keyboard is connected
- The fuse is just a wire, from the production, all good here.

I went through the board a few times, found two issues on the way of looking for the keyboard error but nothing solved the keyboard issue. The keyboard is fine, I have tried another PS2 with the same outcome.
The broken traces next to the battery were not connected to the keyboard plug, the DATA line went above that area and is fine. I have added some pictures about how it was looking before and after.

The CLK trace is going from the back side of the board to an inductor and from there to a capacitor next to the SIMM slots. From this moment I have no idea where it goes, the capacitor seems to be there only as a filter, nothing is going away from him and the other leg is GND, make sense. The trace from the CLK is beneath the SIMM slots and I cant find where it goes further - I have been beeping for an hour with no positive location of the trace behind the location I can see from the back side of the board.

I am not sure now about both the CLK and the DATA of course.

Does the CLK should be 0V without the keyboard plugged in? Does it make sense that after plugging the keyboard the voltage goes to 5V on the CLK pin?
What is generating the CLK for the keyboard connector? This could help me to find the trace I am missing and maybe locate the issue. I do not have an OSC at this moment so can not check if any CLK is reaching the keyboard. Is the clock coming from the clock generator? - the peripheral output? - I would assume that even the ISA slots would be dead in this case but they are getting 2,5V on the OSC pin.

ahhh, I am so lost at this moment and need some advise 😀.

any help and advise would be appreciated, thank you Tomas

Web searches indicate other boards marked with Zeon as being by San Li (the 94V-0 is a standards mark for PCB manufacture)

thx for the information

Those fix wires look nice and tidy so far 😀

The CLK signal should I think be generated by the keyboard controller rather than the keyboard.
The pinout for the UMC chipset doesn't seem to be known but since it's got an unpopulated space for an 8042 keyboard controller that probably has the KB CLK and KB DATA lines hooked up to it. See this datasheet for a similar generic keyboard controller: https://tvsat.com.pl/PDF/W/W83C42P_win.pdf
Pin 37 is usually KB-CLK and Pin 38 is usually KB-DATA which seems to be standard for most 8042 chips as far as I'm aware.

See this page for information on what the signals should look like: http://www.ue.eti.pg.gda.pl/fpgalab/info_kbd/ … nfo_kbd_en.html
It describes that the KB-CLK and KB-DATA have pull-up resistors on them which pulls the signal up to 5v which is the signal's off state to reduce noise / unwanted state changes. When the clock signal is generated it overpowers the pull-up resistor and pulls the signal to ground instead.

You're seeing 5v on the pin only when the keyboard is connected - so the keyboard itself is pulling up that signal correctly. However you should see 5v or another voltage that the multimeter could interpret the clock signal as, when there's no KB connected - because that's not there I am guessing that the KB-CLK pin isn't connected to the board anymore since it's not going to the pull-up resistor (pulling it up to 5v when on) either.

Check whether the KB-CLK pin connects to pin 37 on that empty "8042" footprint, I doubt that it does currently. If it's not connected then you can trace that around to see where it goes and either fix the break or just run a jumper wire from KB-CLK to pin 37 to see if that works 😀

edit: check whether L2 measures 0 ohms resistance across its two legs, that looks like where the CLK signal should be but might be routed internally?
Check whether either leg of L2 is connected to the KB-CLK pin. L2 is an inductor that filters some noise but corrosion can break them, you can safely bypass L2 with a piece of wire to test. Make sure that the top leg of L2 is connected to the KB-CLK pin
Check whether you can measure voltage on either side of L2 between that leg and Ground - from your pictures that looks like the most probable area of damage given how corroded that KB-CLK pin was with the DIN connector removed.

hi, and thank you a lot for your answer!

The CLK signal should I think be generated by the keyboard controller rather than the keyboard.
The pinout for the UMC chipset doesn't seem to be known but since it's got an unpopulated space for an 8042 keyboard controller that probably has the KB CLK and KB DATA lines hooked up to it. See this datasheet for a similar generic keyboard controller: https://tvsat.com.pl/PDF/W/W83C42P_win.pdf
Pin 37 is usually KB-CLK and Pin 38 is usually KB-DATA which seems to be standard for most 8042 chips as far as I'm aware.

thank you for sharing this, really helpful. The explanation about the readings are highly appreciated. Learned something new 😀

Check whether the KB-CLK pin connects to pin 37 on that empty "8042" footprint, I doubt that it does currently. If it's not connected then you can trace that around to see where it goes and either fix the break or just run a jumper wire from KB-CLK to pin 37 to see if that works 😀

You were right, the KBCLK was not connected to the CLK pin of the connector but was high at 5V after turning the PSU on. I have quickly jumper-wired the pin 37 to the CLK pin of the DIN5 connector and the keyboard is working! However, I am getting still the keyboard error but apart of this the system was able to proceed to BIOS etc... I have attached a few pictures about the connection and where the KB-CLK from the pin 37 goes or from where the CLK is coming.

edit: check whether L2 measures 0 ohms resistance across its two legs, that looks like where the CLK signal should be but might be routed internally?
Check whether either leg of L2 is connected to the KB-CLK pin. L2 is an inductor that filters some noise but corrosion can break them, you can safely bypass L2 with a piece of wire to test. Make sure that the top leg of L2 is connected to the KB-CLK pin
Check whether you can measure voltage on either side of L2 between that leg and Ground - from your pictures that looks like the most probable area of damage given how corroded that KB-CLK pin was with the DIN connector removed.

I have wired the pin 37 to the L2 in a way that the CLK goes through the inductor. The inductor seems to be fine. The damage was quite extensive but the L2 takes the traces from the bottom of the board: the pin CLK goes to the L2 and from the L2 it proceed under the SIMM slots. I could not identify any traces on the surface that would be run from L2 on top of the board.

The traced KB-CLK from the 8742 goes to the UM8496F but there is no alternative trace that would be run directly to the keyboard connector or anywhere else. Hence, I am puzzled how and from where the CLK could be coming if not from the same source as the PIN 37 of the 8742. Since the system complains still about the keyboard I am missing something.

br, Tomas

best regards, Tomas

Hi,

so, I have looked for some reference images of the board, couldn't find the exact brand but found close ones. It seems that the L2 was connected to the resistor right next to it. The resistor is fed by 5V and goes to the 1 PIN of the 8042 which is the K/B Clock Input. This pin is connected then to UM8496F, next to the pin from where the KB-CLK goes. This pin is however always low, no idea why. Hence. I have decided to stick to the pin 37, steal the KB-CLK turn off the keyboard error message in BIOS etc... Board is working, iam happy.

thank you for your help!

Tomas

Huh I wonder how it's still giving an error - great news that it's working though 😀
Maybe it's only working in one direction perhaps? Try toggling the caps lock to see if there's a problem there.
The KB CLK pin both from the KB-CLK at the DIN connector and the 8042 footprint, probably routes to the UMC498 chip next to where the KB-DATA pin is. That resistor going from 5v to the CLK is probably the pull-up resistor so it's good that's reconected.

Otherwise though it's great that you can now get into the BIOS and actually use the computer.
I knew I recognised that tablecloth from somewhere as well, your repair of that other board with grafting a new clock generator onto it looks really cool.

Thermalwrong wrote on 2023-10-22, 11:19:

Huh I wonder how it's still giving an error - great news that it's working though :) Maybe it's only working in one direction pe […]
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Huh I wonder how it's still giving an error - great news that it's working though 😀
Maybe it's only working in one direction perhaps? Try toggling the caps lock to see if there's a problem there.
The KB CLK pin both from the KB-CLK at the DIN connector and the 8042 footprint, probably routes to the UMC498 chip next to where the KB-DATA pin is. That resistor going from 5v to the CLK is probably the pull-up resistor so it's good that's reconected.

Otherwise though it's great that you can now get into the BIOS and actually use the computer.
I knew I recognised that tablecloth from somewhere as well, your repair of that other board with grafting a new clock generator onto it looks really cool.

Not sure about the error but I am not much concerned about that since it can be turned off in BIOS - problem solved.
The KB-CLK from the 8042 goes to UM8496F, next to the DATA and the K/B Clock Input pin, all are next to each other on the UM8496F. My assumptions was that the L2 was connected to the resistor next to it where the path goes to the UM8496F and from there to the 8042 K/B Clock Input pin (1) - according to the data sheet of the 8042. Since there was no original path to the pin (37) of the 8042, I did not wanted to connected the L2 both to the pin (37) on the 8042 and the resistor that goes at the end to pin (1) of the 8042 - no idea what would happen. Hence, I have decided to not connect these together and only keep the DIN5 connector connected to pin (37) on the 8042 that goes to KB-CLK. I hope it make sense. I could not find a trace between the L2 and the resistor and the reference images could be misleading here. Heh, so to keep it simply, connecting to pin (37) and disabling within BIOS the keyboard check did the job.

Heh, yes, the famous tablecloth. The replacement for the clock generator was fun at the end, and the adaptor works at the end like a charm. I was lucky to find some of the MX8315MC in the SOP package at the end - although I have found some in DIP as well but quite expensive, this was more fun to do 😀. I have enclosed the gerber files for that as well, maybe someone will use it at the end.

thank you again for the help, hopefully I will find more damaged board to keep my mind busy during winter.

thank you, Tomas