When or should we expect our 8-bit motherboards to fail due to the capacitors?

Question

I would assume that most people who have been trying to keep these old micros working are well aware of the finite life of components, which is the idea that age will eventually cause things to fail. Though the components in our 8-bits seem to be a bit higher quality than those that fell ill to the Capacitor Plague, I do wonder how much time is left before some things won't work anymore.

The question here is more that I haven't really seen anyone suggest that their computers have died because of capacitor failure on the motherboard; by this I mean that if the power supply fails, it not only prevents the machine from working but could also take down the rest of the machine with it due to incorrect voltages... but to my question, I haven't seen any reports really of people saying that their machine (with a healthy power supply) is not working because of a capacitor failure in the logic parts of the motherboard.

I suppose it differs by manufacturer and model, but I'm not really sure what to expect and when for some of this kit. Being proactive about the power supply is one thing, but is that enough? That being said, should I be worried as long as I have the power supply covered, i.e. as long as the supply voltages are in spec from the PSU then nothing can really fry in the rest of the machine but perhaps just fail logically?

I'm curious how diligent one should be about this.

Answer 1

As someone who owns around 70 vintage computers (8/16 bit), leaky caps are a big concern for me.

In my experiences, batteries leak far more often than capacitors. Obviously, electrolytic capacitors can, and often do, leak.

Companies like Commodore didn't exactly use high quality parts. So the shelf life for those electrolytic caps isn't long. Yet, I have Commodore's (Atari's, Apple's, etc.) that have never been recapped but still work great with no leakage.

I keep almost all of my collection in my basement which is climate controlled. Heat can drastically shorten the life of those caps.

With ceramic capacitors, they typically last a very long time and there is nothing to really leak with them.

But, there is just no way of knowing when they will fail.

If the computer is important to you, then re-cap it with good quality caps like Panasonic.

One thing I want to mention, is that unless you know how to professionally solder/de-solder and work on boards, then you may cause more damage than just leaving the caps alone. If you don't know how to properly solder, then farm it out to a professional.

Especially if they are surface mount caps.

Answer 2

This clearly needs a "depends" answer.

There are known places where I wouldn't even dare to switch on a computer without replacing caps first - The Sinclair ZX Spectrum series is such a candidate - It features an analogue voltage step-up circuit for the memory supply voltage generation that is known to be able to simply fry all of your otherwise perfectly working memory at the first power-on when some of the caps in the circuitry have lost capacity. Those caps are a must to replace before doing anything else.

Others, I'd just keep an eye on - I have some Atari STs that I tend to open every three years or so for a check and never had any problems with the large caps in the PSU circuitry. No need to fix anything that isn't broke here.

Batteries, especially of the rechargeable type, are a different story. I generally replace them with off-PCB battery holders as outlined in another question

Edit:

Because comments have asked for it: The ZX Spectrum's memory power supply (generated on the main logic board) is an ingenious piece of circuitry that is able to generate +12V, -12V and -5V supply voltages for the memory chips (and other CMOS logic on the main board) from a +9V DC and a +5V DC (generated from a straightforward 7805 linear regulator) input with just a handful of components. Part of its ingeniousness is an oscillating circuit based on TR4, a small transformer and a couple of capacitors (and is a perfect example how Sinclair managed to sell computers at revolutionary low prices)

The downside of this ingeniousness is that it has an in-built capability to self-destruct: in case the oscillation doesn't start (for whatever reason, typically caps that have lost capacitance), TR4 and/or TR5 will die of over-current, and the circuit may deliver 9V to the -12V inputs of the memory chips which can't really stand that for long...

Answer 3

“Now” might be a fair answer, given that I've had to replace capacitors on two compact Macintosh motherboards (Classic and Classic II). Failed caps can prevent booting if the conductive electrolyte shorts critical connections. Leaked electrolyte is decidedly sticky-looking. Similarly, failed display capacitors in 68K Macintosh PowerBooks might not stop the machine from booting, but will stop you seeing anything on the screen.

I don't know if it was a particular symptom of the surface-mount electrolytic capacitors that Apple used, or just a general eventual failure mode of all electrolytics. Any equipment 20 years old or older with electrolytics may be suspect. The effects can be reduced by cleaning the circuit board, but ultimately any leaking capacitors will need to be replaced.

Answer 4

I would not worry too much. old capacitors were of good quality, not like the now-days junk. I have plenty of ancient components and I did not had to change any capacitors on them (unlike for newer ones) and they still function perfectly.