Hi,

I have realized that I have some clock generators that were fitting in the board, and one of them is the AV9107 - seems to fit the manual as well. I have removed the PLL IC that was there and replaced with the clock generator. The CPU clk is working but with no response from the board. I got the new debug card, and keyboard BIOS as well, still no response. I have tried it with Cyrix DX2 80MHz although I have read that it will accept CPU up to 66MHz - not sure if the issue could be here.

anyway, I will try some more stuff with the board but if anyone has any suggestion, let me know.

thank you, tomas

I can't really help you, but best of luck with that board. I have an Amptron DX-6600 which I'm lead to believe is merely a rebranding of that exact same board, although perhaps not the same revision. It's a solidly OK board once I got it tuned to the best of my abilities with AMISETUP. Got solidly average results in most benchmarks with a 486 DX2. I suppose most importantly, it just worked with a no-name VLB io multicard, VLB VGA card and an ES1868 sound card. A feat I was marginally surprised by.

Namrok wrote on 2024-04-12, 15:10:

I can't really help you, but best of luck with that board. I have an Amptron DX-6600 which I'm lead to believe is merely a rebranding of that exact same board, although perhaps not the same revision. It's a solidly OK board once I got it tuned to the best of my abilities with AMISETUP. Got solidly average results in most benchmarks with a 486 DX2. I suppose most importantly, it just worked with a no-name VLB io multicard, VLB VGA card and an ES1868 sound card. A feat I was marginally surprised by.

thank you for your answer. I am still angry on myself for damaging the board out of carelessness, I am always placing spacers on the boards but this time I was just too keen to test it and got the tin beneath it.
I have tried different CPU, bellow 66MHz, still no post or beep.
I have replaced the keyboard BIOS a few times with known good ones, still no response - I can try to replace the BIOS once more, I have saved the original ROM before I have fried the original BIOS, luckily.
Since the BIOS and Keyboard BIOS got fried together with the DEBUG card in the ISA slot I know that the tin and short was in the area but I am afraid the chipset got some damage as well in this case.

I am not sure what else to try or what to test to verify the chipset for example, could not find any datasheet to it.
The original "mod" that was there was at the keyboard controller, an resistor was between the VDD and Xin, if the pinout is the same as for W83C42. I have no idea why it was done like this. PIN 2-5 on the IC.

At this moment I need either some suggestions what to try to measure while I know that the area around the ROMs was exposed to the short or the same board to compare the results between each other.
I see that the X1 OSC next to the ISA port is not outputting 32kHz, the HEX inverter near to it has the 32KHz, however, I would expect to measure this frequency on the legs of the OSC as well. I have ordered a new HEX inverter to see if that will help, and then I will change the OSC as well if not - I guess this would work without CPU, right?

I have a few boards left to inspect and maybe fix but this one is bothering me at most 😀.

thx, tomas

I have replaced the 32kHz OSC but getting strange output on the legs (one nothing, second 40kHz sin) but 32kHz on the HEX converter, not sure if that is okay. I will wait for the HEX replacement but I do not think that would be the main issue.
Still hopping to find the cause at least...

tomas

Hi,

one small update, I have checked the ISA slot, according to the pinout here: https://upload.wikimedia.org/wikipedia/common … SA_Bus_pins.svg.
I have measured a very low resistance between ground and pin A8 (Data 1), and D 01 (MEM CS 16) and ground of about 3 ohm. The D 01 is going straight to the chipset from what I have seen. I have compared this to other 486 board I have near me, and the resistance is higher. This seems to me as a problem with the chipset at the end, correct? Now, someone with the same board would be much of a help to compare the results.

Anyway, what do you think? Any chance to get this chipset from somewhere or replace with something else?

The data line seems to be connected to a resistor array A103G, 10pin.
The resistivity is 10K and 22R (the Data 1 line). Could be one pin on the array be shorted?

edit: nope, the resistor array is fine but the Data 1 is definitely shorted.

thx, tomas

Hi all,

while waiting for the 50MHz OSC for the DTK board I was looking at this "sad pile" once more and tried to backtrace the DATA 1 PIN from the ISA slot that seems to be shorted and shows below 3ohms against GND.
I have backtraced the traces that are connected to the D1 PIN and found a direct connection to the: Chipset, KBC PIN 13 (D1) and Resistor Array - could be more but I was not able to find any. The 3ohm reading is present with or without the KBC and RA, and thus I am left with the chipset. I would guess that if the chipset would be shorted it would be dead but the surrounding the Data pins are showing activity on the scope. I am not able to find any component that could be shorted to the GND. I though to maybe de-solder this one leg form the board of the chipset to see if the short is still present or no. Not sure how to proceed now, any suggestion or thoughts?

Also, I have taken out the HEX inverter TC4069UBP which sits between the first and second ISA slot, add a socket there after. During continuity measurement I have noticed that between pins O6 - I5 is continuity (blue line) but I am not sure if it could be or not on purpose. It is present with the IC or without the IC. I do not want to de-solder the socket out to examine the area if there could be something causing the short, and thus wanted to ask what you think.

br, Tomas

tsalat wrote on 2024-04-23, 04:39:

Hi all, […]
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Hi all,

while waiting for the 50MHz OSC for the DTK board I was looking at this "sad pile" once more and tried to backtrace the DATA 1 PIN from the ISA slot that seems to be shorted and shows below 3ohms against GND.
I have backtraced the traces that are connected to the D1 PIN and found a direct connection to the: Chipset, KBC PIN 13 (D1) and Resistor Array - could be more but I was not able to find any. The 3ohm reading is present with or without the KBC and RA, and thus I am left with the chipset. I would guess that if the chipset would be shorted it would be dead but the surrounding the Data pins are showing activity on the scope. I am not able to find any component that could be shorted to the GND. I though to maybe de-solder this one leg form the board of the chipset to see if the short is still present or no. Not sure how to proceed now, any suggestion or thoughts?

Also, I have taken out the HEX inverter TC4069UBP which sits between the first and second ISA slot, add a socket there after. During continuity measurement I have noticed that between pins O6 - I5 is continuity (blue line) but I am not sure if it could be or not on purpose. It is present with the IC or without the IC. I do not want to de-solder the socket out to examine the area if there could be something causing the short, and thus wanted to ask what you think.

br, Tomas

Ok, so the "blue line" indicating the continuity on the TC4069UBP should be there, I have removed the socket and it is fine.
I have also lifted the leg from the chipset and the 3OHM resistivity was still present on the ISA slot. Soldering the leg back gave me 7OHM - a bit strange but ok. The board is most of the time dead, sometimes I got signal toggling on the ISA slot but the signal on the D1 PIN is frozen. No idea what to try next.

br, tomas

I believe I have destroyed the board at the beginning, accidentality, and just shorted out the CHIPSET, I will keep this on the side and maybe try something else later on.

thank you guys, Tomas