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Unidentified XT Clone m/b

Hmmm, I suppose that confirms my card has an issue. I'll see if there is physically anything obviously wrong with it.
 
After gently retrobriting the front plastic part outside in hazy sun and clouds for 3 days, the empty case now looks like this. There is still a slightly lighter patch where there was once a sticker, but I didn't want to over-do it and I'm very pleased with how it came out. For direct comparison, the first pic is the seller's pic, as purchased. The rest are from just now.
 

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Did you use cream or liquid for the retrobrite?

Liquid, after dilution probably only about 6-9% H2O2. In a plastic tub big enough to submerge the whole piece, weighed down with a glass jar full of nails resting on it, tub covered over with clear plastic and the whole thing on a black base.
 
BTW, looking at the picture of your board, if you notice, your board seems to say "p2164-20 or hm50256-20" next to the ram, which suggests it should be able to take 256k ram chips in the first bank as-is. (Just set the dip switch the same as you would on any other IBM or clone. If I am reading the on/off marking right, mine are set to 1:ON 2:ON 3:ON 4:ON 5:OFF 6:ON 7:ON 8:OFF, I don't recall what video card I had in there last).

Also, your u39 socket (next to the dip switches) is empty. On mine it is filled with a SN7407. At a glance it looks like U39 has connections to the dip switch - might be part of your problem here.

My board also says "OEM/PC REV B1" on the back.
 
BTW, looking at the picture of your board, if you notice, your board seems to say "p2164-20 or hm50256-20" next to the ram, which suggests it should be able to take 256k ram chips in the first bank as-is.

That was my thinking too. I only have 16x 256k chips at the moment. The U39 chip was showing as bad in my MiniPro so I ordered an NOS one - which also showed as bad so I assumed for now that the MiniPro is unable to test them and put the original one back in. I suppose they could both really be bad.

Switches 3&4 relate to RAM. With both on I only ever get 64k showing. With both off I get 256k max, and then if I e.g. remove a chip from bank 4 then it counts to 192k and with a chip from bank 3 also missing it's 128k as expected.

I tried debug but it shows everything above 4000:0 as being FF and it cannot be changed, so as if there was nothing there - both with or without the RAM card fitted. I also tried other higher addresses and it's all just unchangeable FF's.
 
I discovered a failed 74xx logic chip on my RAM expansion card. I replaced it and I think I was getting somewhere until parity errors kept appearing after I played with a jumper I probably shouldn't have. Even with no RAM chips in the card and all related switches turned off, if was very unstable (but fine without the card attached) - another 2 74xx's had failed. Hmmm, wonder if something is causing them to die or perhaps due to heat because of all the battery repair bodges. The other card functions are fine with the dead chips removed. I've ordered replacements. Will see how that goes.

And something more pleasing - I made up a logo for the blank badge space on the front of the case, based on the original DTC logo. Looks great.
 

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I located my ST10 card. I put it into my IBM 5160 (IBM XT). No cables connected to it. Shortly after the 5160's POST completed its memory count-up, the ST10 displayed "ST10 v2.4", then about 45 seconds later, the ST10 displayed "1701 (04)". I was then prompted by the 5160's POST to press the F1 key to continue.

If you still have it handy modem7, what is the resistance between gnd and 5v on your ST10 card? My multimeter shows it as a short, when in actual fact it's 45ohms. Seems very low!
 
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45 ohms?

That means a 111 ma draw on the 5 volt line--that's not unreasonable for a hard disk controller.

Thanks for the clarification. I'll get out my oscilloscope and see if anything is stuck. Am a bit lost with it ATM.
 
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