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Powering up a computer the proper way after long term storage

O

oldbeagle

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Dec 27, 2023
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Most of my computers have not been powered up since the mid 1990s when I got them. Some have worked fine like my apple //e models whereas all the power supplies have failed in my Mac II boxes. I have some even older stuff that I never powered on including a Heathkit HERO robot and a few OSI C1P computers.

What's the best way to power up old machines? I have heard use of a Variac to power up machines at a very low voltage which from what I understand helps get the electrolytic capacitors to revive (recondition) without problems.

Anyone have any guidance on this?
 
Someone would firstly identify and remove any RIFA branded plastic mains voltage caps.
Reviving old capacitors is called reforming and is mostly applicable to those the size of a drink can. To reform, the capacitors are removed and have a very slowly increasing DC voltage & current applied to them from a power supply that has current limiting capabilities.
Capacitor analysers with ESR function such as the one from Peak Electronics are very useful and inexpensive.
 
You can use a Variac providing the computer has an internal linear power supply. If it has a switched mode power supply, all bets are off...

I have just written a post on this very subject yesterday on a new HP-85 thread if you would like to go and read it.

Dave
 
Most of us just flip it on and see what happens. But please do track down the thread Dave refers to for some appropriate reminders.

Seaken
 
seaken said:
Most of us just flip it on and see what happens. But please do track down the thread Dave refers to for some appropriate reminders.

Seaken
Click to expand...
I suppose it depends on what it is. If it's super rare then I'd not just flip it on. If it's something fairly common then sure if a visual inspection looks Ok.
 
I don't suggest that just flipping it on is necessarily the best approach. I'm just acknowledging what is fairly common. I think I postponed flipping on my N* for nearly ten years because I was afraid of having to deal with a power supply or capacitor failure. But I saw so many folks just going for it that I decided it was time to take the chance. If it got damaged I'd have to fix it anyway. And a visual inspection only goes so far, especially when you don't really have a lot of experience. If you have more experience maybe you'll do some tests on the electronics and power with some specialized equipment. A lot of us casual hobbyists don't have that.

Anyway, I agree that if it's on the older side and more rare I would be more careful.

Seaken
 
Well, Yes the visual inspection would at least include verifying the voltage rails. If they're not right then it won't work at all or could be damaged. Or could partially work. I am no expert here. I do what I can with what I have. I have nothing really rare so don't worry about it too much.
 
In general, I think these days it is a good idea to do some basic research on any specific item to see if there are any general known issues that one should be careful about.

For example, some bad c64 power supplies can fry the entire machine. Also, a few cheap built-in power supplies can be damaged if they have no load. Variacs can be useful for linear power supplies, but generally should not be used with switched-mode power supplies. RFIA filtering capacitors may need to be replaced preemptively, while faulty tantalums are usually no big deal even when they make a big boom.

When possible, and where warranted, I like to test each part by itself. For example, give a power supply a dummy/alternate load and sanity check voltages. Then connect each part and see if it behaves the way I expect.
 
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