VOGONS


First post, by jheronimus

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Hi, all. Recently got my hands on a board that went through scrappers and unfortunately has a lot of stuff missing. Kind of my first experience with a task like this, so I wanted to ask a few questions:

nCf3mPD.jpg

Here are some photos of the motherboard on Amoretro, for reference.

1. Two missing VRMs.

Am I correct to assume the top VRM (U22) is LT1085 and the bottom one (U55) is LT1084?

(all images are clickable)

9bVl6lbm.jpg

8EN9wIxm.jpg

2. What is this thing?

zqpeV22m.jpg

gGJFYdXm.jpg

I assume it's a cyllindric 32,768 kHz oscillator with a ceramic capacitor underneath? Does anyone have any ideas what specific parts could work here? (links to Mouser would be really helpful).

3. Unknown missing IC next to missing BIOS — any ideas what could this be?

mGZPK4ym.jpg

4. BIOS image.

Couldn't find any appropriate one so far. Maybe someone could dump it for me?

Sorry if some of the questions might seem silly — my knowledge of electronics is fairly limited. Basically I don't have any engineering background whatsoever, and basically started soldering a bit just this year. But I'd really love to finally get a working Socket 5/VLB motherboard.

Last edited by jheronimus on 2021-04-05, 09:45. Edited 1 time in total.

Pentium 166 MMX Overdrive, 32 MB RAM, Ark Logic ARK1000VL, Tekram DC-680C, Turtle Beach Tropez, Gravis Ultrasound Max
Pentium III 1000, 256 MB RAM, Matrox G400 MAX, Adaptec 19160, Yamaha YMF740B

Reply 1 of 9, by Deksor

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There's a bios for a motherboard using the same chipset as yours. Maybe you can give it a try ? http://www.win3x.org/uh19/motherboard/show/2047

Trying to identify old hardware ? Visit Ultimate Hardware 2019 - Project's thread The Ultimate Hardware 2019 (UH19) project- a stason.org/TH99
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Reply 2 of 9, by quicknick

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2. You're right, 32.768kHz crystal for the RTC. Should be really easy to find.
3. I'm 99% certain that the socketed chip is the PLL clock generator. On AmoRetro's pic I can see it's made by Macronix but it's really hard to tell the part number. Luckily you're not missing the other socketed IC (the PAL).

Reply 3 of 9, by Horun

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quicknick wrote on 2020-12-25, 01:09:

2. You're right, 32.768kHz crystal for the RTC. Should be really easy to find.
3. I'm 99% certain that the socketed chip is the PLL clock generator. On AmoRetro's pic I can see it's made by Macronix but it's really hard to tell the part number. Luckily you're not missing the other socketed IC (the PAL).

#3: mx8315pc (if same as on my similar but diff model Biostar). Yes very lucky the PAL chip is there !
Wondering why the the VRM trannies and resistors were removed, only guess is to fix similar but the removal of the resistors seems odd as they do not break down or burn up....

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 4 of 9, by Deksor

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Maybe it was used for parts ? I've seen this before

Trying to identify old hardware ? Visit Ultimate Hardware 2019 - Project's thread The Ultimate Hardware 2019 (UH19) project- a stason.org/TH99
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Reply 5 of 9, by jheronimus

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Deksor wrote on 2020-12-24, 23:16:

There's a bios for a motherboard using the same chipset as yours. Maybe you can give it a try ? http://www.win3x.org/uh19/motherboard/show/2047

Thanks! Will try that.

Horun wrote on 2020-12-25, 03:33:

#3: mx8315pc (if same as on my similar but diff model Biostar). Yes very lucky the PAL chip is there !
Wondering why the the VRM trannies and resistors were removed, only guess is to fix similar but the removal of the resistors seems odd as they do not break down or burn up....

Is there an alternative for that mx8315pc part? I can't find a chip to buy online, but I'll look at my other boards later for a possible replacement.

quicknick wrote on 2020-12-25, 01:09:

2. You're right, 32.768kHz crystal for the RTC. Should be really easy to find.

Is there a ceramic capacitor underneath it?

Pentium 166 MMX Overdrive, 32 MB RAM, Ark Logic ARK1000VL, Tekram DC-680C, Turtle Beach Tropez, Gravis Ultrasound Max
Pentium III 1000, 256 MB RAM, Matrox G400 MAX, Adaptec 19160, Yamaha YMF740B

Reply 6 of 9, by Horun

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jheronimus wrote on 2020-12-26, 01:25:
Horun wrote on 2020-12-25, 03:33:

#3: mx8315pc (if same as on my similar but diff model Biostar). Yes very lucky the PAL chip is there !
Wondering why the the VRM trannies and resistors were removed, only guess is to fix similar but the removal of the resistors seems odd as they do not break down or burn up....

Is there an alternative for that mx8315pc part? I can't find a chip to buy online, but I'll look at my other boards later for a possible replacement.

Quest Components has them, that is where I bought some Dallas RTC a few months ago that work perfectly.
They have over 200 in stock, the part is discontinued but will be NOS and when gone there be no more....
https://www.questcomp.com/part/4/mx8315pc/279851702
at $2.60 each plus shipping. If you need any Dallas RTC they still have some, type DS12887 and DS12c887 into search box for a list.
I will double check Digikey and Mouser as they have Euro distributes too. I may order a few of those myself.
Edit: nope only found at Quest so far. The UMC9515 is an equal part according to mkarcher but cannot find any in stock.

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 8 of 9, by jheronimus

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Wow, missing resistors next to the VRMs are a nasty surprise. What kind of resistance should they have?

Here's what I found for LT-1085CT (upper, responsible for providing 5V to ISA) and LT-1084CT (lower, responsible for providing 3.3V to the CPU).

Am I correct to assume that both should work with 0.25W resistor for 120 Ohm and a 0.25W for 360 Ohm?

Pentium 166 MMX Overdrive, 32 MB RAM, Ark Logic ARK1000VL, Tekram DC-680C, Turtle Beach Tropez, Gravis Ultrasound Max
Pentium III 1000, 256 MB RAM, Matrox G400 MAX, Adaptec 19160, Yamaha YMF740B

Reply 9 of 9, by jheronimus

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So I came back to this project, ordered mx8315pc from eBay and found a guy that will (hopefully) be able to fix the board, but he will only be able to start in May at the earliest. He already fixed a Supermicro P54VL-PCI for me, so I figured that it's a better idea than trying to fix the Biostar board myself.

Meanwhile I'm still trying to find the original BIOS. So far I have only figured that the BIOS string should be 2A5UMB01 and be 128KB in size. I have contacted Biostar for a BIOS, but they replied that they don't have anything on this board anymore. FGB, the author of amoretro, says he doesn't have the board anymore.

So I'm bumping the thread in hopes that somebody notices it and could provide me with a dump of the original BIOS 😀 If that doesn't work, I'll of course try the BIOS from another board using Opti 546/547 chipset, but from my experience with an Opti 596/597, an alternative BIOS might not be too stable.

Pentium 166 MMX Overdrive, 32 MB RAM, Ark Logic ARK1000VL, Tekram DC-680C, Turtle Beach Tropez, Gravis Ultrasound Max
Pentium III 1000, 256 MB RAM, Matrox G400 MAX, Adaptec 19160, Yamaha YMF740B