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486 not booting anymore

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First post, by Boohyaka

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Hi guys,

I've dismantled my perfectly working 486dx2-66 to adapt and clean a few things in the case. After mounting it back, it powers up but I get no picture at all...nor any POST error beep or anything (this already existed back on AT computers? it's been so long...)

The mobo is a Soyo SY-025K2. It has 4 30 pins and 2 72 pins slots (4x2MB + 2x2MB).
Video is a Cirrus Logic VLB card. I have another VLB gfx card, but never had a chance to try yet, so I can't be sure it works...

Haven't troubleshoot such computers in a very long time, it's all rusty in my head. My idea would be to get to minimum configuration, but have a few questions:
- Not sure which RAM slots needs to be filled at minimum. Next to the 30 pins on the mobo is written BANK0(2), first 72 pins is BANK1(0) and second 72 pins is BANK2(1). I suspect that either BANK0(2) or BANK1(0) needs to be filled?
- Is the VLB I/O controller compulsory for boot or should I be able to get to BIOS without it?

Any other tips or ideas?

Thank you guys.. 🙁

Reply 1 of 6, by Baoran

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If the motherboard has multiple VLB slots, it might matter which slot the video card is in. You could try the VLB video card in all slots without the VLB I/O controller to see if you can get picture in any of them.

Reply 2 of 6, by Boohyaka

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Thanks Baoran, yes I'd tried that but no luck. At this stage I believe I may have damaged a trace when removing the motherboard by being careless with an annoying plastic fixing pin that wouldn't come out 🙁 I have discussed it with a friend that is an expert with this stuff and I will send it to him for analysis/repair. Bleh 🙁

Reply 3 of 6, by Horun

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It is always a good policy to never remove a working motherboard from a case unless it is being replaced. I have seen some get slightly warped over time that shows when removed because of the years of heat and mount stress. It can cause breaks in solder joints around SMT parts that never would happen if left mounted. Is rare but have seen it happen, also have seen what a dropped screwdriver can do to a good board ;p

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 6, by CoffeeOne

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Boohyaka wrote on 2020-02-21, 14:41:

- Not sure which RAM slots needs to be filled at minimum. Next to the 30 pins on the mobo is written BANK0(2), first 72 pins is BANK1(0) and second 72 pins is BANK2(1). I suspect that either BANK0(2) or BANK1(0) needs to be filled?
- Is the VLB I/O controller compulsory for boot or should I be able to get to BIOS without it?

Good idea to try with the minimum configuration:
Try with only one (!) 72 pin RAM module (you can try both slots) and the graphics card, skip everything else.

Reply 5 of 6, by Boohyaka

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Horun wrote on 2020-02-23, 21:40:

It is always a good policy to never remove a working motherboard from a case unless it is being replaced. I have seen some get slightly warped over time that shows when removed because of the years of heat and mount stress. It can cause breaks in solder joints around SMT parts that never would happen if left mounted. Is rare but have seen it happen, also have seen what a dropped screwdriver can do to a good board ;p

Oh man, please don't tell me. if it's not broken don't fix it, right? I wanted to redo the whole cabling, exchange the CPU cooler with a brand new one I received recently (with a better fixing mechanism), and try to find a solution so the whole motherboard doesn't bend every time I remove or add a full-size VLB card as there was no support under the outer edge of the motherboard...
One of the plastic fixing clips in the middle of the board was a nightmare to remove (what a stupid idea that was seriously, why didn't they simply use screws) and I didn't notice how close some traces were to this middle hole. I damaged one of them and only noticed when I carefully checked the whole board. I've been messing with computers since the 80's and not once did I damage anything (except a burnt AMD K6 😁 damn those things cooked quickly!) but this time I really did one hell of a dirty job. I blame it on getting older - less vision, less patience 😀 But I learnt a lesson.

CoffeeOne wrote on 2020-02-23, 21:45:

Good idea to try with the minimum configuration:
Try with only one (!) 72 pin RAM module (you can try both slots) and the graphics card, skip everything else.

Yup I tried of all that, but there's definitely something wrong 🙁 as said, it's going to be shipped to a good friend of mine that should be able to assess the damage and probably fix it, let's hope. It's a cool motherboard. I would feel really bad if I killed it.

Reply 6 of 6, by Horun

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Was not saying that infamous line. Older 2 & 3 layer boards are less prone to warping than the newer 5+ layer ones. Sounds like your board was not secured to firmly anyway so probably no issue with warping, too bad you scratched the traces, been there/done that (my screwdriver hint). Google 'warped motherboard' and check the images sometime, you will see some very good examples of what happens with lots of screws+heat+time.
Your board should be fixable.

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