Advice and suggestions for resources to learn more detailed troubleshooting and repair steps for motherboards \ VOGONS

Advice and suggestions for resources to learn more detailed troubleshooting and repair steps for motherboards

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First post, by NHVintage

Posted on 2024-06-01, 16:09

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Hi all - So as I posted on another thread I am currently working on three different older motherboards, all of which have the same behavior - turning on the power, my boot diagnostic card in the ISA slot (trying all of the slots) produces the 4 power indicators steady, and the frame and other lights settling into the same post-power up steady state (clock and frame steady, Reset off, etc) but I get zero boot codes at all. I confirmed the diag card works on a known working P55 system, codes galore as expected.

One 486 board has a good CR2023 battery, the second 486 board has no battery, the third board is a 286 board and has a battery that isn't leaking but only putting out about 1.5V (checked with multimeter) rather than 3.3V.

I boot them with no cards except the diag card in slots, with and without memory simms on them, no change in behavior. Tried pressing down all the chips too in case of bad solders. Tried booting with a vid card in, in case the boards just don't put out boot codes or my diag card can't read them. Used just one memory SIMM that works in other machines and tried it in different SIMM slots.

All the tests are being done with the board out of the chassis sitting on antistatic bags. The AT (P8-9) PS works on an SBC computer I have where P9 plugs into the SBC itself. It's a 300W PS I picked up recently, new.

Rather than give up and toss them, or just say 'dead board' like so many youtube vids and postings do, I'd actually like to learn what steps next I should try. I need to get an oscilloscope but I have a soldering station and multimeter already. So, I'm reaching out for suggestions where I can learn some additional tips and suggestions - any youtube vids, blog posts etc that might help.

And of course I'll take suggestions here.

These are the boards:
https://theretroweb.com/motherboards/s/kla-tencor-kt3052
https://theretroweb.com/motherboards/s/trang- … -headland-ht12a
https://theretroweb.com/motherboards/s/pcchips-m912-v1.7-486

I've been considering searching for a repair person that actually does this stuff, even if that would be expensive, and it might come to that, but I'll never learn if I don't try. Thanks again.

Reply 1 of 13, by NHVintage

Posted on 2024-06-01, 16:42

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The attachment 20240601_124027.jpg is no longer available

Omg I got a response from the 286! Lol. Perhaps it needed paired memory simms or it disliked the other keyboard. . Hmm.

Reply 2 of 13, by NHVintage

Posted on 2024-06-01, 16:54

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so, this board is from a CNC machine. I am guessing that it has a custom bios. there is no disk drive. I tried putting my XT IDE card in and it won't boot with it installed. but it's alive...

Reply 3 of 13, by Horun

Posted on 2024-06-01, 17:03

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Great ! Yes you do need two matched SIMMS. Can you try the post card in it now to make sure works on 286 boards ? Try the ISA slot closest to the CPU....
Board has 2 banks: DIP 0, SIMM 0 and SIMM 1 and is 16bit wide. If DIP ram is onboard then SIMMS go into SIMM 1 slots. Board is similar to my Protek DH12 / PM12.
Unfortunately there is no BIOS at TRW for it but you may be able to try a Generic 286 HT12A bios....

added: here is a similar board Re: 80286 BIOS image collection
I have a Protech DH12 that is also nearly exact....

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 4 of 13, by NHVintage

Posted on 2024-06-01, 17:41

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Wow cool! So I guess I'd need to flash the high and low onto the paired chips with the ATLO and ATHi labels right? Seems a dumb question but I want to be sure. I'll have to get a chip programmer first.

EDIT - almost forgot - tried the xt-ide on slot 1. no joy. but my floppy/parallel card did work on there, and I can see it interrogate the USB Flashfloppy (and rejecting the disk in it).

think this chip programmer will do it https://www.amazon.com/Programmer-Programmabl … 17264263&sr=8-3

Reply 5 of 13, by Horun

Posted on 2024-06-02, 03:15

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Yes the Xgecu T48 TL866ii Plus is a good programmer. That one is a clone, some brand Vikye, the real Xgecu have their logo in the plastic on top.
added: Try to find the "Vikye" website for an update 🤣
I own a older Xgecu TL866ii Pro and it has worked great, the kit I chose has 13 adapters.
Some may say the clones are ok but I chose to buy a real one and support the company that started them...https://xgecu.myshopify.com/ and https://www.ebay.com/str/xgecuofficialstore
FYI Xgecu software is update about once a month with new eeproms added. http://www.xgecu.com/en/TL866_main.html

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 6 of 13, by kingcake

Posted on 2024-06-02, 04:45

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Highly recommend this youtube channel: https://www.youtube.com/channel/UCFX1Z9N6aPWu … KR8UZ2vg/videos

Rich does great videos on how to repair ATX Power supplies, motherboards, graphics cards. And he does real troubleshooting but teaches fast and simple methods for doing so. So many channels that do teach repair blindly replace mosfets and if that doesn't work they trash the board (cough northridge fix cough)

Reply 7 of 13, by rasz_pl

Posted on 2024-06-02, 11:57

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Back pre internet we learned from 'Upgrading and repairing PCs' by Mueller, Scott
https://archive.org/details/upgradingrepairi0 … muel_2ndedition
https://archive.org/details/upgradingrepairi0000muel_d4h1
https://archive.org/details/upgradingrepairi0 … uel_17thedition

older editions have more info about older pc generations.

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

Reply 8 of 13, by NHVintage

Posted on 2024-06-02, 19:30

NHVintage Offline

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Horun wrote on 2024-06-02, 03:15:
Yes the Xgecu T48 TL866ii Plus is a good programmer. That one is a clone, some brand Vikye, the real Xgecu have their logo in th […]
Show full quote

Yes the Xgecu T48 TL866ii Plus is a good programmer. That one is a clone, some brand Vikye, the real Xgecu have their logo in the plastic on top.
added: Try to find the "Vikye" website for an update 🤣
I own a older Xgecu TL866ii Pro and it has worked great, the kit I chose has 13 adapters.
Some may say the clones are ok but I chose to buy a real one and support the company that started them...https://xgecu.myshopify.com/ and https://www.ebay.com/str/xgecuofficialstore
FYI Xgecu software is update about once a month with new eeproms added. http://www.xgecu.com/en/TL866_main.html

Oops, well I picked up the clone and it'll be here quite soon, so Amazon says. So, hopefully it'll be good enough for light duty work 😁

Reply 9 of 13, by NHVintage

Posted on 2024-06-02, 19:33

NHVintage Offline

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Rank: Newbie
Posts: 99
Joined: 2023-07-31, 13:55

rasz_pl wrote on 2024-06-02, 11:57:
Back pre internet we learned from 'Upgrading and repairing PCs' by Mueller, Scott https://archive.org/details/upgradingrepairi0 […]
Show full quote

Back pre internet we learned from 'Upgrading and repairing PCs' by Mueller, Scott
https://archive.org/details/upgradingrepairi0 … muel_2ndedition
https://archive.org/details/upgradingrepairi0000muel_d4h1
https://archive.org/details/upgradingrepairi0 … uel_17thedition

older editions have more info about older pc generations.

This is an excellent idea, I remember these books, I'll have to find some used copies from back then. Thanks for the suggestion! 😀

Reply 10 of 13, by NHVintage

Posted on 2024-06-02, 19:35

NHVintage Offline

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Posts: 99
Joined: 2023-07-31, 13:55

kingcake wrote on 2024-06-02, 04:45:

Highly recommend this youtube channel: https://www.youtube.com/channel/UCFX1Z9N6aPWu … KR8UZ2vg/videos

Rich does great videos on how to repair ATX Power supplies, motherboards, graphics cards. And he does real troubleshooting but teaches fast and simple methods for doing so. So many channels that do teach repair blindly replace mosfets and if that doesn't work they trash the board (cough northridge fix cough)

I've actually watched a couple of this channel's videos tho they didn't come up searching for the specific topic. I blame the YT algorithms. 😁 Thanks, I'll search thru the channels videos for what I need.

Reply 11 of 13, by NHVintage

Posted on 2024-06-02, 20:32

NHVintage Offline

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Posts: 99
Joined: 2023-07-31, 13:55

The programmer arrived and after choosing the right chip I try to program the new bios and get :
ERROR! Address:0x000000 Buffer Data:0xAA Verify:0xA0
Programming ...Failed

I pulled the old bios before it but didn't erase; blank check is disabled. The old bios (and new) seemed to be a bit gibberish but I don't know if that's normal, here's the new LO off the HT12.zip.

Reply 12 of 13, by NHVintage

Posted on 2024-06-02, 21:48

NHVintage Offline

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Joined: 2023-07-31, 13:55

Pretty sure the errors are due to old chips or that these are single use, so I ordered some fresh chips that'll get here in a week or so. always something 🤣.

Reply 13 of 13, by NHVintage

Posted on 2024-06-10, 22:45

NHVintage Offline

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Rank: Newbie
Posts: 99
Joined: 2023-07-31, 13:55

Horun wrote on 2024-06-01, 17:03:
Great ! Yes you do need two matched SIMMS. Can you try the post card in it now to make sure works on 286 boards ? Try the ISA sl […]
Show full quote

Great ! Yes you do need two matched SIMMS. Can you try the post card in it now to make sure works on 286 boards ? Try the ISA slot closest to the CPU....
Board has 2 banks: DIP 0, SIMM 0 and SIMM 1 and is 16bit wide. If DIP ram is onboard then SIMMS go into SIMM 1 slots. Board is similar to my Protek DH12 / PM12.
Unfortunately there is no BIOS at TRW for it but you may be able to try a Generic 286 HT12A bios....

added: here is a similar board Re: 80286 BIOS image collection
I have a Protech DH12 that is also nearly exact....

Welp, unfortunately I only got BIOS-ROM Checksum errors when I tried other BIOS, so unless someone has other ideas this board's a goner. sucks, because I get the board to start but then that, so its not like its totally dead.

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