Let's say you have an older power supply you want to repair, upgrade or just keep running reliably to protect all that irreplaceable vintage hardware in your vintage computers. I know they can be re-capped, but what else can and/or should be replaced with better quality components if possible? Are there any components which CAN'T be upgraded or replaced?
I’d love to know myself!
I’ve got a mid-90’s Aptiva that’s an AT PSU with two 3.3v 6pin cables and a 3 pin for standby/button power.
It’s nothing too off the wall and I’ve seen workarounds for the 3 pin cable. I also imagine splitting a 3.3v to two six pins is a sound idea. However, it be nice to keep the one I’ve got running as it’s still as solid as it was in 1997.
Things you can upgrade/repair beside caps:
You can also upgrade the capacitors on the input line filter with safety rated caps if the PSU uses generic caps there.
What is usually very difficult to replace is custom made parts like transformers, so unless you take one from another identical PSU I wouldn't suggest trying to mess with those. But transformers don't fail very often unless there's some sort of catastrophe. Inductors/coils are also typically difficult to replace if you don't know the values, you can use an inductance meter but I don't think they're precise enough.
What I take into account when deciding whether I should attempt to repair a PSU is:
In general I recommend refurbishing older power supplies of good quality instead of buying new >700W monsters to use in retro PCs. The learning curve is not very steep, if you have basic soldering experience it will be very easy to work with single sided PCBs.
Also, I find many inconveniences to buying modern high-power units such as: price (not just the PSU but also the SATA->Molex/Floppy and ATX->AT adapters you need to buy), high current output that could cause trouble in the case of a short, bottom fan placed upwards ends up being blocked by the top of a baby AT case, and finally I personally feel they look completely out of place in an older case.
TheMobRules wrote on 2023-04-02, 00:11:Things you can upgrade/repair beside caps: […]
Things you can upgrade/repair beside caps:
- Bridge rectifier
- Switching transistors on the primary side
- Rectifier diodes on the output, especially if the original ones are undersized
- Fan, if you want a more silent one or the current one breaks
You can also upgrade the capacitors on the input line filter with safety rated caps if the PSU uses generic caps there.
What is usually very difficult to replace is custom made parts like transformers, so unless you take one from another identical PSU I wouldn't suggest trying to mess with those. But transformers don't fail very often unless there's some sort of catastrophe. Inductors/coils are also typically difficult to replace if you don't know the values, you can use an inductance meter but I don't think they're precise enough.
What I take into account when deciding whether I should attempt to repair a PSU is:
- Is it at least of decent quality? You can't really fix things like poor design (no OCP/OVP, wimpy heatsinks, and so on) so I don't bother with those
- Was there any catastrophic failure? If there are holes in the PCB or some major damage I wouldn't risk trying to fix it
In general I recommend refurbishing older power supplies of good quality instead of buying new >700W monsters to use in retro PCs. The learning curve is not very steep, if you have basic soldering experience it will be very easy to work with single sided PCBs.
Also, I find many inconveniences to buying modern high-power units such as: price (not just the PSU but also the SATA->Molex/Floppy and ATX->AT adapters you need to buy), high current output that could cause trouble in the case of a short, bottom fan placed upwards ends up being blocked by the top of a baby AT case, and finally I personally feel they look completely out of place in an older case.
Excellent info, thank you! I need to step up to the learning curve with this as I've never done PSU repair and I am not an electronics engineer, but I would like to keep the old PSUs alive as much as possible because like you, I do not like to use newer PSUs in old PCs. I do pick up NOS high quality PSUs on ebay when they're reasonable.
Some basics, it's old info, but we're working with old parts..
https://www.repairfaq.org/sam/smpsfaq.htm
Despite it recommending replacement on a cost/bother basis for PC PSUs there's a lot of what is said that applies to them there.
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From my experience, it's mainly the caps and diodes that fail. An 1N4001 diode can often be substituted by a stronger 1N4007, for example.
Beware of Z-Diodes, however. They may look like ordinary silicon diodes like 1N4148, but are voltage dependent.
Whatever you do, please make photos before the repair.
And make notes about were each component was located. A little drawing may help, too.
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TheMobRules wrote on 2023-04-02, 00:11:In general I recommend refurbishing older power supplies of good quality instead of buying new >700W monsters to use in retro PCs. The learning curve is not very steep, if you have basic soldering experience it will be very easy to work with single sided PCBs.
I agree with you.
Since it have (partially) recapped several mainboards, this is actually my list of fully recapped old PSU devices:
#1 K6-2/500, #2 Athlon1200, #3 Celeron1000A, #4 A64-3700, #5 P4HT-3200, #6 P4-2800, #7 Am486DX2-66
I have a lot, though the latest one still needs some adjustments. 5vsb still shows 9v despite replacing the caps, so I figure one of the smaller ones must've gone bad.
It's a CWT ISO 500PP if anyone wonders.
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