VOGONS


First post, by 90skidJohnny

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Ok. So long story, not so long.

Been working on this 486 Frankenstein for months. Lots of things were wrong with it. But I finally got it generally working and such.
Last step was fitting it into the power supply cuz .. ugh issues. Anywayssss.....

I went to go fire it on after adding this new PSU, not. PSU fan would kick on , but no post or anything like that. Left it at that as I was done for the day.
Well, then the next day went to go put the testing PSU I had been using in. accidentally nudged the table and for whatever reason I deduced to keep it right on the edge. Mobo hit the floor.
ISA VLB video card was in the slots when it hit. got it hooked back up. PSU fan would kick on but the CPU felt cold, and the motherboard sounded dead. got frustrated walked away.

Today Ive been going over the board with a fine tooth comb (well, magnifying glass). found some .. "minor scratches". on the bottom, but using my multimeter everything seemed ok. no broken caps or anything.
Blew everything out with air. Plugged it back in.

Now PSU Kicks on. And the motherboard "Sounds" like it has power. CPU is getting warm... but still... for the life of me. won't post.
No Beeps. Just Turns on, keyboard flashes, and away we sit.

Any ideas?

Prior to this, sometimes I would have to turn the system on and off a few times while it was on my test bench, but I thought this could be cuz it was on a bench and my VLB card might of come loose. This mobo has no onboard video.

Reply 1 of 7, by HanJammer

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Do you have a POST card? If not - get one ASAP. It's quintesential piece of equipment for every retro PC owner. Also try some simple ISA video card - 8 or 16 bit... no fancy VLB stuff.

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Reply 2 of 7, by 90skidJohnny

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Not sure what a post card is. But ill check it out. Sadly, the 8bit card I got doesn't work.
But I can't get this to post even without the cards in. or even memory

Per my work log, it would beep even when memory wasn't plugged in.

Reply 3 of 7, by 90skidJohnny

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Also I noticed, this board has those funky tantalum capacitors. They all appear to have the same rating... However...

They all seem to look the same. But a few seem shorter / skinnier than the rest??

Reply 4 of 7, by rasz_pl

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so you either cracked one/few solder joints, or even a component (not tantalum, you would know if one was dead 😜)
this is very difficult to fix, either patiently with loupe and needle poking every single solder joint, or shotgun method resoldering everything (with fresh flux+solder)

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Reply 5 of 7, by treeman

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can try flexing it a bit and pressing down on chipsets and certain spots, might fire up then you can backtrack which section you flexed/moved then try to see if any cracked solder joints etc, looking for needle in a haystack.

It seems a common story with old electronics, they flex and warp over the years leaving some section not conducting signals or cutting out

Reply 6 of 7, by HanJammer

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POST card: https://pl.aliexpress.com/w/wholesale-post-card-isa.html it will show you the POST code output from ISA or PCI bus and will help to narrow the search area…

If it's a broken solder joint then you can try baking the motherboard in the oven. Remove as many chips as you can, Cover the plastic parts with kapton tape (or at least tin foil) and put it in the oven for several minutes…

Watch this video first if you never did that before: https://www.youtube.com/watch?v=yLVwtBgS_Ac

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Reply 7 of 7, by 90skidJohnny

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I picked up a POST Card. Pretty cheap. Just gotta wait for it to ship from overseas.

The board does have some flex to it. Noticed that as soon as i got it, but it was working prior to the drop.

I really dont wanna let this board die. I got a good chunk of change invested in it currently.
Ill def go back and re-inspect everything. The shotgun method seems like an option, Im not too terrible at soldering. it just seems "expensive" to replace everything, exspecially if it is just one part. Gonna get my magnify glass and check the underside again for any cracked joint. This board originally had 2 bad traces (From original battery leak) which i repaired.

I just picked up another neat system, and I guess the first thing i should do is drop in the CPU from the other machine (pretty sure they are compatible) just to rule out something going out in it.

Thanks all.