VOGONS


First post, by SSTV2

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Continuation from this dumpster find thread post. To my surprise, PCB looks OKAY, no rotten traces, pads or vias, but most of the soldering alloy, used on it, had rotten off, taking with itself some passive SMD components. All of the resistor packs were also heavily corroded as its legs were made from iron... Some of them fell off just by touching them. Main chip is held only by one pin row, it's possible to lift it up now, though badly corroded, all legs seems to be rigid. Cache chips are legit, made by UMC (UM61256FK-15), CPU did not fare well at all 😢

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resistor packs
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In conclusion, it's restorable, but to do that, motherboard needs to be stripped off of every component on it, cleaned of corrosion and reassembled.

Reply 1 of 20, by SSTV2

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I think I'll just salvage CPU socket for this motherboard, it's been waiting for socket transplant for a few years now.

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Reply 2 of 20, by Deksor

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Make sure the pins in the socket are still ok, which I kinda doubt looking at the CPU's pins ...

Weird that they did put legit cache chips and didn't socket them, that's what they do most of the time. Maybe they're still fake ?

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Reply 3 of 20, by SSTV2

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I had removed top plastic off the socket while washing MB, all of the pins were fine, except one, that was pushed in. Overall, CPU socket and ISA slots had preserved phenomenally. I also do find it strange, that legit cache is soldered in, probably they were trying to save every cent in manufacturing process.

Reply 5 of 20, by Deksor

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Probably nothing of interest, PCChips often did that in the 486 era, underneath there's just a single digit number and that's it. However the chipset of these m912 is really a UMC chipset. But they often put other stickers there.

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 7 of 20, by SSTV2

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Restored memory modules from this:

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To this:

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4 Megs total, tested good.
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Interestingly, these modules are using ICs with ZIP through-hole type case, which are converted into surface mount type.

Also, removed chipset, but both chips had cracked at the underside, due to vapor pressure from absorbed moisture in the plastic... I hope that crystal didn't move when case poped and bond wires are still intact.

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Chipset ICs after restoration:

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I've also desoldered and tested SRAM ICs, now I know exacly why they've soldered BIOS and cache in. "TAG" and ICs at "BANK 0" are legit, but ICs at "Bank 1" are all fakes 😀

Can you visually tell apart which are which?

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Fakes are just plastic with legs, measuring resistance between Vss and the rest of the pins, shows infinitely large resistance.

Reply 8 of 20, by Deksor

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For the cracked chip you can simply replace it with a regular UMC chip, because this is what these are.

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Reply 10 of 20, by Deksor

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Well it does, look at this https://www.ebay.fr/itm/UMC-UM8498F-Baby-AT-3 … 4.c100408.m2460

Mustn't have been very popular though

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Reply 11 of 20, by SSTV2

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I've decided not to waste time trying to make PC Chips MB post and just salvaged its socket 😀

The recipient is prepared for socket transplant:

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Reassembling socket after days of trying to whiten it:

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Wasted nearly a week trying to whiten that socket. Kept it in hydrochloric acid for few days - no go, hydrogen peroxide and UV for at least 3 days - no go, only scrubbing it with hard tooth brush and polishing paste did help. Any ideas how could that chipped VLB slot be patched nicely?

Reply 12 of 20, by Bullmecha

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I think I may have that exact PCChips board here somewhere 🤣 Need to do another clean up of all my hardware and see where it is.

Just a guy with a bad tinkering habit.
i5 6600k Main Rig
too many to list old school rigs

Reply 15 of 20, by treeman

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I desoldered a umc chip with a soldering iron only but the pins and excess solder make it look like a xmas tree, in my case it wasn't a problem because I replaced with a new chip which wasn't as rare as yours

Yours turned out perfect, did you use any new solder or just alot of flux and hot air?

Reply 16 of 20, by SSTV2

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Hot air and flux alone wouldn't do it, the oxide layer was just too thick for pins to tin, basically layers of lime had formed on them.

Pins had to be cleaned off thick layers of tin/lead oxides first, used diluted hydrochloric acid for that purpose. Once thick layers of solder alloy oxides had fallen off the pins, I've removed ICs from acidic solution.

After that, pins were still covered in very thin layer of oxide, so acid based flux had to be used to tin them properly, as tacky "Amtech" flux was not good enough. Used regular soldering iron in the tinning process, as some scrubbing was needed.

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Etched DRAM on the left, prepared for tinning.
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Reply 17 of 20, by looking4awayout

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You're being very brave to restore such a piece of garbage of a motherboard. 😵
This is one of the infamous PCChips motherboards with fake cache and counterfeit chipsets. According to the Red Hill guide, the M912 was available not only with the UMC "sticker", but also other ones, including Intel. So basically they just used a chipset (or ripped off an already existing one), put a sticker on the chip according to what the customer wanted, and sold the M912 with any chipset they wanted, as if the fake cache chips weren't enough...

More info here: http://redhill.net.au/b/b-bad.html

I hope the traces of the fake chips actually lead to somewhere, otherwise you'll end up with a quite crippled 486 motherboard, if it ever comes to life. Oh, assuming the cache actually works. On fake cache motherboards, the BIOS was modified in order to keep the L2 cache feature disabled regardless of the user's choice. That's why they soldered the BIOS chip: not only to save costs but to also avoid that someone would discover the scam. Perhaps the motherboard might even POST without any cache at all, even though the option in the BIOS would be set to yes!

Ironically enough, when PCChips motherboards worked properly and used legitimate components, they were some of the fastest motherboards available on the market. But their shady practices and low quality construction just made them utter rubbish.

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Reply 18 of 20, by SSTV2

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Yes, I know the history behind 486 PC Chips motherboards and company's practices of using fake cache and false chipset marking, IMHO that makes these motherboards somewhat unique and interesting in a way. For now I'll postpone the PC Chips MB restoration as I don't even have a CPU socket to test it. The funny thing is that I've previously bought a slightly newer version of the same PC Chips motherboard (M912 V1.7) as non working in an attempt to salvage its CPU socket. It turned out that MB was 100% fine, except 3.3V VRM transistor had blown, probably because of wrongly inserted CPU. Gah, I really wanted to pull out a ZIF socket out of it 🤣

Reply 19 of 20, by SSTV2

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Success:

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This motherboard has a huge flaw in PCB design around CPU socket. It definitely doesn't meet power integrity requirements for 100MHz+ CPUs.

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Any suggestions how could this be fixed W/O resoldering the whole thing?