HanJammer wrote:I inspected the motherboard carefully and I don't see ANY mechanical dammage, not a single scratch. Soldering points are all shi […]
Show full quote
I inspected the motherboard carefully and I don't see ANY mechanical dammage, not a single scratch. Soldering points are all shiny too. When I bought it few months ago it already had the blue barrel of cancer removed so it never had any chemical dammage as well. There is just a light dust, but nothing that would cause the shorts.
Pics: https://imgur.com/a/WY6ylYP
Also here is the full list of the POST codes logged by the diag board (I just bought it and I wasn't sure how to use it when I recorded videos yesterday) from the last one (when it throws the A20 error, to the first one which according to the manual is just a code that the diagnostic board always shows when it starts). Video is initialized when the code 19 is shown. At 22 BIOS message is shown. Also like I said earlier sometimes the POST is stuck on the code 04. And sometimes it doesn't even show that - just ---- is seen on the diag board):
...
None of the tables from http://www.bioscentral.com/postcodes/amibios.htm have the exact same list of codes…
Sometimes LEDs on the keyboard are all lit up after poweron (sometimes they just give me a short blink like they should). I suspect keyboard controller is shot, too bad it's soldered on (it has only a few pins connected to the board on the solder side, I don't know if these PCBs were just two layer or multi layer). I do have shot 386 board with Jetkey keyboard controller (but it may differ from this one slightly, it has v.5.0 marking on it).
No obvious sign of mechanical damage is not 100% proof that things will work, sadly. I picked up a 486 board that I couldn't even get to show anything on the screen. Except for briefly flashing the keyboard lights it never seemed to do anything at all. I know the ISA video card I used wasn't broken because I tested it on an old P3 Gateway board and it worked okay (albeit with some odd jitter/artifacting?). And that was before I smashed a glass diode trying to snip through the battery leads. I'm not sure what's wrong on that one, because it could as easily be the CPU, BIOS, keyboard controller, ram, or some other support circuitry.
Unfortunately without more intimate knowledge of 286 board design and ICs of the era. especially those on your board, plus proper test equipment like an oscilloscope and a logic analyzer, determining the exact problem or even completely ruling out possible ones is going to be nearly impossible. Without either trial and error is basically what you're left with. In any case electrical flow can be a funny business and wires, traces, joints, etc can oxidize. And honestly there might be something wrong with one of the other ICs resulting in unexpected behavior that isn't correct.
The reason the tables vary is likely that information is incomplete, but they also refer to different versions of the BIOS which may have dropped some codes and/or included new ones. I was looking primarily at the first table with numerical codes and they seemed to line up ok (19 is "Attempting to pass control to video ROM at C0000h" and 22 is "The power-on message is displayed"). Presumably some codes are common across the entire line of AMI BIOSes, but I don't know if there is a list out on the internet for your specific version. Unfortunately I have no idea what codes your board should or shouldn't show, but the ones that do are a lot better clue than just describing what happens.
http://www.dewassoc.com/support/bios/errors/k … roller_fail.htm
The above link suggests the same troubleshooting as the other guy, swap keyboards if possible. It also points out that the keyboard and controller chip (on motherboard) talk via serial and implies that a poor connection might also cause problems. It seems likely, but not a guarantee that the keyboard controllers are compatible, particularly if they are the same brand. If you wanted to go with trying to swap them, I'd say try reflowing the solder on the connections to the old one first to see if that helps any as getting it out is going to be a fair bit of work. Ultimately you can certainly try a swap if sure it's shot, but without knowing how it failed you might just be dooming the next chip you connect up too...
Do you have any way to verify that your keyboard works?
Is this what you have?
http://www.btc.com.tw/pdf/5140.pd
https://deskthority.net/wiki/BTC_51_series
I don't see an AT/PS2 switch anywhere, so I'm not sure what distinguishes an AT connector version from a PS/2 connector version or if the protocols/behavior are equivalent.
Any chance of a full picture of the rear and maybe a close up near the keyboard port (on the back side)?
P.S.
If you can work out what how the keyboard controller is connected to the other circuitry, you might be able to test some of the traces' for continuity with a multi-meter. It may also be worth checking the voltages at chips when powered (not sure where to stick the ground probe, so maybe someone else can help you there) to make sure they are getting the correct voltages. The supply pin (Vss, Vdd?), which you can find on a datasheet, should probably be somewhere between 4.5 and 5.5 volts on most of the 74xxx logic.
Also since talking to the keyboard controller happens to be a read/write on the main system bus from/to a particular address, at least afaik, it may well be that some chip in between has bitten the dust and/or isn't working right... I have no idea how you'd test it, but it's definitely worth a check if you can find a way. The 74x245 (DM74LS245N) there right next to the keyboard controller seems like a good place to start looking since it's an octal bus buffer/transceiver and it appears to be connected to the keyboard controller on the top side of the board.
Just looking closely at your pics makes me think this is mostly a 2-sided board, but I wouldn't swear to it since I'm very much not a pcb designer/electrical engineer/etc.