486dx board, no power, psu good, but no startup \ VOGONS

486dx board, no power, psu good, but no startup

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First post, by tattmann

Posted on 2014-07-31, 17:41

tattmann Offline

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Joined: 2014-07-31, 17:23

Hey all, I have a problem here. I have a genoa systems turboexpress vl-3 motherboard and system I am trying to get up and running. Let me start by telling you what I have. It has a 486dx 50mhz cpu, a cirrus 512kb video card and some ide boards. Now, that's the basics. The psu is an atx style with an at adapter. I had the motherboard in my case, (an older 386 case with plastic standoffs to hold board in case) and had everything hooked up. I turned the power key switch, and........ nothing. I unhooked the psu adapter, crossed the black and green wires, and voila! the psu turned right on. yet with the psu hooked to the motherboard, nothing. I am at a complete loss............ I hooked another motherboard to the psu with the adapter, and still nothing, but I have no clue if the other board is good or not, so I cant rely on that as a test. Shouldn't there be signal power to the keyswitch wire pins on the motherboard? some kind of signal I can test for to see where the power break problem is? also, should the motherboard itself be grounded anywhere to the case? I have built MANY computers post win 95 era, and never had this problem. I have not had to deal with a pre win 95 computer in 24 years, so I am a little rusty 🤣. Any help is greatly appreciated. I can add lots of pics if needed. The bios battery has NOT leaked, and the battery is very low but NOT dead. It showed 1.5v on my multimeter. so, any ideas where to start?

Reply 1 of 6, by smeezekitty

Posted on 2014-07-31, 17:57

smeezekitty Offline

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The problem is almost certainly the adapter. AT boards have no concept of turning on a PSU
and obviously it isn't getting turned on. Either the adapter has to have a switch or the PSU needs to be perminately on and unplugged to turn it off

Reply 2 of 6, by tattmann

Posted on 2014-07-31, 18:07

tattmann Offline

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Okay, thank you for your reply. I put the adapter on another atx psu, no mobo attached. the psu instantly came on. only way to turn it off is by hitting the power switch on the psu, or by interrupting the short between green and black wires on the adapter. I will cut the shorted wire on the adapter and run the keyswitch\power switch there and see if I have power. Strange though, with the p8 and p9 plugs on my mobo, and the green to black shorted, I had no power on the psu. any idea there?

Reply 3 of 6, by smeezekitty

Posted on 2014-07-31, 18:09

smeezekitty Offline

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tattmann wrote:
Okay, thank you for your reply. I put the adapter on another atx psu, no mobo attached. the psu instantly came on. only way to turn it off is by hitting the power switch on the psu, or by interrupting the short between green and black wires on the adapter. I will cut the shorted wire on the adapter and run the keyswitch\power switch there and see if I have power. Strange though, with the p8 and p9 plugs on my mobo, and the green to black shorted, I had no power on the psu. any idea there?

Make sure the P8 and P9 and in the right order. The blacks should be next to eachother in the center.

But it does sound like a short circuit then. Try the board out of the case without anything else on it and see if it works

Reply 4 of 6, by tattmann

Posted on 2014-07-31, 18:14

tattmann Offline

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I definitely had p8 and p9 correct, blacks together in the center of the 2 plugs, and I tried it out of the case too. no power there either. That's when I decided to post here and get some help. without the mobo hooked up to the adapter, the psu comes right on. once I hook it up to the mobo and plug it in, nothing. No psu fan spin, nothing.

Reply 5 of 6, by tattmann

Posted on 2014-07-31, 18:18

tattmann Offline

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okay, new info...... the problem is definitely on the p8 side. I hooked up p9, the psu spun its fan. whatever is on the p8 side, is the problem as it acted dead with p8 hooked up.

Reply 6 of 6, by tattmann

Posted on 2014-07-31, 18:53

tattmann Offline

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Rank: Newbie
Posts: 15
Joined: 2014-07-31, 17:23

Problem sorted. I used my spare atx psu with the adapter, and hooked up p8 and p9. Plugged in the psu, and power was had, and joy by all.... 🤣. Anyway, I thank you for your patience and help. Thanks again.

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