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PC crashing in BIOS help?

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Reply 20 of 29, by AppleSauce

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red-ray wrote on 2022-04-18, 18:14:
Heat shrink to provide electrical insulation. The SIO chip now sees -5 […]
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AppleSauce wrote on 2022-04-18, 17:59:

what are the blue tubes next to the resistors?

Heat shrink to provide electrical insulation. The SIO chip now sees -5

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What value are the resistors btw?

Reply 22 of 29, by Cuttoon

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If you know your way around voltage regulators, use those.
A resistor does the job for a particular use case. By Ohm's law, it will reduce 12 V to 6 V as long as it's in line with the equivalent of exactly the same resistance. But since semiconductors are very much not an ohmic load, you'd basically have to determine that resistance on the fly of for a certain use state. Which can be done by simply using a multimeter by simply measuring the resistor's voltage (difference between its legs, which should be around 7 V).
So, really not an exact science, but since load on -5 should be simple and negligible, it should be easy enough to placate the bios at least.

I like jumpers.

Reply 23 of 29, by AppleSauce

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Right well ill keep the resistor fix in mind then.
The other thing that bothers me is that the +12v rail seems a bit high.
It seems to be at about 13.8 or 13.9 volts.

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Reply 24 of 29, by Doornkaat

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If the value is right this PSU is probably not suited for your system.
Some PSUs are group regulated meaning they can't regulate voltages on all rails indivudially. Since modern PSUs are focussed around the +12V rail it is assumed that this is always the rail with the most load on it and therefore the one most likely to be low under heavy load. Since older systems draw more on +5V the PSU has to increase the voltage on +12V to keep +5V stable.
I don't think you should keep using this particular PSU for this system.

Reply 25 of 29, by AppleSauce

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Doornkaat wrote on 2022-04-19, 10:40:

If the value is right this PSU is probably not suited for your system.
Some PSUs are group regulated meaning they can't regulate voltages on all rails indivudially. Since modern PSUs are focussed around the +12V rail it is assumed that this is always the rail with the most load on it and therefore the one most likely to be low under heavy load. Since older systems draw more on +5V the PSU has to increase the voltage on +12V to keep +5V stable.
I don't think you should keep using this particular PSU for this system.

Well that sucks, its not really a new supply either its a DELL NPS-250KB B
similar to this one.

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Reply 27 of 29, by shamino

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Onboard sensors are unreliable, sometimes they show things that are wildly incorrect.
Best to check with a multimeter to find out what the voltage really is. If it really is 13.8V then that's dangerously high, but it might be a false alarm.

12V and 5V are easy, just probe them from a 4-pin drive connector (yellow wire is 12V, red is 5V, black (or the case of the PSU) is ground).
3.3V can be measured by backprobing the ATX connector on an orange wire, the probe should be able to go in far enough to make contact and give a reading.

Reply 29 of 29, by AppleSauce

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So far so good , I've managed to get win98 running