Can’t win with 486 boards!!! Keyboard error on AT keyboard.. \ VOGONS

Can’t win with 486 boards!!! Keyboard error on AT keyboard..

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First post, by 9646gt

Posted on 2025-06-20, 23:00

9646gt Offline

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Well here we go again. Third 486 board I have bought that has an issue. One had an incompatibility but this makes two that have hardware problems.

Board is a Biostar MB-1433 50UIV Ver3. When I boot I get a keyboard error and keys don’t work. I do briefly see the light flash very quick on the keyboard. Keyboard works on another computer.

It did have a NICAD battery that had literally just started to show the smallest leak starting. Green area about the size of a pen head but NOTHING else shows any corrosion signs. Battery was replaced with external battery pack on JP8

A fuse labeled F1 has good continuity. There are two parts labeled L1 and L2 next to the connector. I’m not an electrician by any means so maybe diodes? L1 measures good continuity and with power on shows 5v on it. L2 shows good continuity but shows 0v with power on. I used deoxit on the keyboard connected with no luck. It’s a bid loose when connected but not seriously so and moving it around changes nothing.

What to do from here? I did check that it’s outputting 5v and continuity is good from all internal pins to their solder connections on the bottom of the board

Reply 1 of 9, by henneberg

Posted on 2025-06-21, 07:31

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To visualize the progress of the boot procedure , a board like this is nice: https://vi.aliexpress.com/item/1005005871082476.html

It is used in this Biostar MB as well: https://www.youtube.com/watch?v=Fw-975rV70E

Reply 2 of 9, by weedeewee

Posted on 2025-06-21, 08:43

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looking at photos of the board, I can't help but wonder if the keyboard controller chip is missing, and maybe the RTC chip as well.
and yeah sure, the photo on TRW doesn't show those chips, but that doesn't mean that that board was working.
then again, other photos also show those chips lacking... maybe it's integrated in the chipset, tricky to say with there not being a datasheet available.

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Reply 3 of 9, by 9646gt

Posted on 2025-06-21, 12:45

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weedeewee wrote on 2025-06-21, 08:43:

looking at photos of the board, I can't help but wonder if the keyboard controller chip is missing, and maybe the RTC chip as well.
and yeah sure, the photo on TRW doesn't show those chips, but that doesn't mean that that board was working.
then again, other photos also show those chips lacking... maybe it's integrated in the chipset, tricky to say with there not being a datasheet available.

It’s my understanding that the controller is integrated into the chipset on this board. The other blank spots are for real time clock and such

Reply 4 of 9, by 9646gt

Posted on 2025-06-21, 12:46

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I think the black parts installed at L1 and L2 ferrite inductors if I am reading right. The one at l2 doesn’t show voltage while powered on but L1 does. Is this a clue of anything?

Reply 5 of 9, by weedeewee

Posted on 2025-06-21, 13:05

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9646gt wrote on 2025-06-21, 12:46:

I think the black parts installed at L1 and L2 ferrite inductors if I am reading right. The one at l2 doesn’t show voltage while powered on but L1 does. Is this a clue of anything?

Yes, they likely are.
Is the lack of voltage a clue? It could be.

What you could do, since I get that you can measure continuity, is take your multimeter, set to diode mode reading, and measure the clk & data pin of the keyboard connector to ground, both with the red probe on the signal and black on ground and the other way around, black on the signal pin and red on ground.

Right to repair is fundamental. You own it, you're allowed to fix it.
How To Ask Questions The Smart Way
Do not ask Why !
https://www.vogonswiki.com/index.php/Serial_port

Reply 6 of 9, by 9646gt

Posted on 2025-06-21, 22:40

9646gt Offline

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weedeewee wrote on 2025-06-21, 13:05:
Yes, they likely are. Is the lack of voltage a clue? It could be. […]
Show full quote

9646gt wrote on 2025-06-21, 12:46:

I think the black parts installed at L1 and L2 ferrite inductors if I am reading right. The one at l2 doesn’t show voltage while powered on but L1 does. Is this a clue of anything?

Yes, they likely are.
Is the lack of voltage a clue? It could be.

What you could do, since I get that you can measure continuity, is take your multimeter, set to diode mode reading, and measure the clk & data pin of the keyboard connector to ground, both with the red probe on the signal and black on ground and the other way around, black on the signal pin and red on ground.

What reading would I be looking for? I have seen a good guide for checking the connector with a meter. I did verify continuity from the pin in the connector to the solder joint on the board

Reply 7 of 9, by 9646gt

Posted on 2025-06-22, 17:18

9646gt Offline

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weedeewee wrote on 2025-06-21, 13:05:
Yes, they likely are. Is the lack of voltage a clue? It could be. […]
Show full quote

9646gt wrote on 2025-06-21, 12:46:

I think the black parts installed at L1 and L2 ferrite inductors if I am reading right. The one at l2 doesn’t show voltage while powered on but L1 does. Is this a clue of anything?

Yes, they likely are.
Is the lack of voltage a clue? It could be.

What you could do, since I get that you can measure continuity, is take your multimeter, set to diode mode reading, and measure the clk & data pin of the keyboard connector to ground, both with the red probe on the signal and black on ground and the other way around, black on the signal pin and red on ground.

The clock pin shows nothing in diode mode either way around. The data pin does show voltage with probes both ways around

Reply 8 of 9, by TheMobRules

Posted on 2025-06-22, 17:52

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Can you check a trace that seems to come from the keyboard connector and crosses diagonally near the negative battery terminal? Due to the quality of the original picture I'm unable to tell, but it seems dubious so there may be a break in the section where I circled in red:

The attachment image.jpg is no longer available

Reply 9 of 9, by 9646gt

Posted on 2025-06-22, 18:14

9646gt Offline

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TheMobRules wrote on 2025-06-22, 17:52:

Can you check a trace that seems to come from the keyboard connector and crosses diagonally near the negative battery terminal? Due to the quality of the original picture I'm unable to tell, but it seems dubious so there may be a break in the section where I circled in red:

The attachment image.jpg is no longer available

You eagle eye!!!!!!!!! You’re right!! I did my first ever trace repair on that spot just now and it works perfectly!! I can’t thank you enough for looking so closely and catching what I missed!

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