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Dell System 200 motherboard issue

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sorphin

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This is one of 2 system 200 boards I have.. it was working great until the other day when it wouldn't come on, then came on, then wouldn't.. All ram has been externally tested last night and any dodgy chips replaced.

I ran the Landmark Diags for it and it fails on Protect Mode on the CPU.
I've switched in another CPU. Same result.

Without the diag roms, no image and beep codes of 4 sets of 4 beeps. (none of which matches any phoenix codes i've found).. and with the diag roms, 6 highlow and 2 dits right before it loads the screen.

Any one have any thoughts?
 

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How's the CMOS battery and CMOS chip? One thing that folks forget is that switching from PM to real on a PC AT involves writing stuff into CMOS, resetting the CPU then reading it back at POST (tells the POST routine that it was a mode switch).
 
RE: chip.. no idea.. what this board is even using for CMOS.. it's a dell board with VLSI/CHIPS chips... battery is good.

Here's the output from the board with no issues. (aka how THIS board was until recently)...
 

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sorphin said:
I ran the Landmark Diags for it and it fails on Protect Mode on the CPU.
I've switched in another CPU. Same result.
Click to expand...
From the Landmark/Supersoft manual, the description of the failing test is:

1666909420788.png

But we have also seen this test 'freeze' when the motherboard's keyboard controller chip is faulty.
The reason will be along the lines that Chuck suggested: As part of the test, the code will be triggering a return to real mode from protected mode.
That is done by:
1. Write the reset reason into a particular RAM location in the CMOS/RTC chip (or equivalent), then
2. Reset the CPU via the keyboard controller chip.

At [here] is an example of an earlier thread where a 'freeze' of the PROTECTED MODE CPU test was caused by a faulty keyboard controller chip on an IBM 5170 motherboard.
 
modem7 said:
From the Landmark/Supersoft manual, the description of the failing test is:

View attachment 1247806

But we have also seen this test 'freeze' when the motherboard's keyboard controller chip is faulty.
The reason will be along the lines that Chuck suggested: As part of the test, the code will be triggering a return to real mode from protected mode.
That is done by:
1. Write the reset reason into a particular RAM location in the CMOS/RTC chip (or equivalent), then
2. Reset the CPU via the keyboard controller chip.

At [here] is an example of an earlier thread where a 'freeze' of the PROTECTED MODE CPU test was caused by a faulty keyboard controller chip on an IBM 5170 motherboard.
Click to expand...
It does have an 82c206. I also just switched in the keyboard controller from the working motherboard into this one. No change. By the way it's not freezing on the protected mode test it tries to do it prints a failed up top and resets and starts over.
 
This is the good board. Amusingly sitting on top of my 5170. I haven't put the keyboard controller chip back in it's actually a eprom one where is the one on the other board is not a eprom. There's a few various Pals and obviously the big chips chips. Which I'd have to figure out how to get them out of their sockets. I can't find my damn POST card, so I have a temporary replacement showing up tomorrow, but yeah..
 

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modem7 said:
See the final paragraph in post #28 of the earlier thread at [here], a thread also about the Dell System 200.
Click to expand...
Guess I'm trying the 2nd 1/2 of that message.. my chip popper wants holes in the corners.. and these sockets don't have those. EDIT: trying to switch out the 82c206 and all I'm whining up doing is bending up the corner pins. So once I get those straightened out I don't think I'll be removing any more of these giant plcc since they don't have the sockets that my chip puller works with and I don't want to damage the working board any further. I guess I'll try switching Pals around.
 
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I was at least able to take the 82c206 from the board having issues and I put it in the good board and the good board still works and passes the diags so it's not the 82c206.
 
I tried switching around all the pals between the boards. No change. I put in a postcard with the normal ROM and the diag ROM. Shows the same codes of 01 and 02. I would try switching the other PLCC chips but there's no safe way that I can remove them because the remover I have requires the two holes on either side of the top of the socket these sockets only have holes on the bottom of the four corners and using a screwdriver is how I almost destroyed the pins on the first chip.
 
sorphin said:
I was at least able to take the 82c206 from the board having issues and I put it in the good board and the good board still works and passes the diags so it's not the 82c206.
Click to expand...
Having now seen on these forums, another case of unexpected symptoms produced by a low/dead battery, perhaps, 'just to be sure', verify that the Vcc pins of the 82C206 are getting the expected voltage.
Refer to the diagram at [here], which shows you the pins and provides an indication of what voltage to expect.
 
modem7 said:
Having now seen on these forums, another case of unexpected symptoms produced by a low/dead battery, perhaps, 'just to be sure', verify that the Vcc pins of the 82C206 are getting the expected voltage.
Refer to the diagram at [here], which shows you the pins and provides an indication of what voltage to expect.
Click to expand...
I tried it with three batteries and with four batteries all brand new. With power off I get the expected voltages at that PIN of 4.75 and 6.45 respectively. With the machine on I get about 4.74 volts at that PIN and the two VCC pins. I should note that neither this motherboard nor the one that is working and testing fine has had batteries kept on it. And this board was working for the longest time. I just reset the CMOS when I turned it on because of the battery. But now it doesn't even get to show video when using a normal bios where is the good one does.
 
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