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Trouble shooting a 286.

M

Moogle!

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Dec 14, 2008
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No name discrete logic board, believed to have been made by Everex.

Bought it, would only occasionally turn on and 'post'. This was a message complaining saying, depedning on which keyboard controller I put in there, would say '8042 error' or 'Gate A20 error'.

Replaced about 40 10uf caps.

Turns on every time but just says 'CMOS inoperational SYSTEM HALTED'. DIscoivered RAM voltage is 4.28 on the power pins.

Suggestions? I am looking at replacing those two yellow resistor 'chips'. Any other thoughts?
 
It is indeed too low. 4.5 to 5.5 is what my ram requires as well. I am baffled as to how the board is even giving any kind of message at all. At any rate, I believe those resistor arrays have failed and are putting a load on something and that is dragging down the voltage for the Ram chips.

That is my current theory. I am sort of new to this level of troubleshooting and I haven't had a lot of time to poke at it. I could be entirely wrong.
 
In my experience, resistor arrays are very reliable.

Have you ruled out the power supply as the cause ?

If yes, do you see 4.28V when the motherboard is the only device powered by the power supply? Is it the case that you see 4.28V at the RAM, but something significantly higher elsewhere (e.g. the connector where the power supply connects to the motherboard) ?
 
Yeah, it is pretty much right on 5 volts in the other three corners. And it has had all the major 10uf tantalum replaced, about 40 in total. And I have tried 2 different PSUs. Made sure the crystals worked and tried a few different RTC chips.

Did remember one thing. The RTC socket is only getting 4.9 volts as opposed to five on the surrounding chips.
 
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Argh, I swear I'm getting dumber by the day. After getting random readings, I took another look at the data sheet and pin 8 is power, not pin 1, which is A8. I do indeed have 5.06 volts on the ram chips, so those are probably working. That would at least explain why I was still able to get a message on the monitor, the aforementioned 'CMOS INOPERABLE'.
 
So, 'CMOS inoperational SYSTEM HALTED' always appearing at power on.
That certainly sounds like the POST's test of the 'CMOS/RTC' chip (per [here]) is failing.

Moogle! said:
Did remember one thing. The RTC socket is only getting 4.9 volts as opposed to five on the surrounding chips.
Click to expand...
Had the subject been an IBM 5170 motherboard, then I would have pointed you to the diagram at [here] and said that the '+5V switch' drops a little voltage. I expect that clone motherboards have the same or similar switch.
 
Yes it does. The card in question being an ET4000 based Diamond Speedstar. The one that works is a Headland VGA VRAM, which was I initially intending to use with the board any way. I also tested a Trident based card, which also worked.

I think the Speedstar might have some code that requires a 386.
 
Maybe the ET4000 based card is faulty, faulty in a way that makes its I/O ports appear at multiple areas, with one of those areas being the same area used by the CMOS/RTC chip.
 
Oh well, we've moved onto more interesting problems. Like how you can enter 47 as a hard drive type, but not actually enter any parameters... ;)

Thanks for the help everyone.


Just discovered Gsetup won't go past 32.
 
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