My original (1983?) Commodore 64 (brown breadbox with grey function keys) has trouble powering on. Specifically, when I flip the power switch the power LED will glow dimly and the machine fails to display video. However, if I unplug and re-plug the physical power (DIN) connector (with the power switch in the on position) the computer comes right up and the LED glows at full intensity.

I know C-64 power supplies are notoriously bad, but if the power supply were the problem I'm not sure the unplug/re-plug trick would work so reliably - so I was thinking maybe the switch is janky. I'm going to try swapping the power supply for a home-brew rig I keep in storage (that I know is reliable) to see if that impacts the problem, but in the mean time:

Is there any known history regarding the C64 power switch failing on early (read: before 1985ish) models? Also, if anyone has any good suggestions I wouldn't object.

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    I've repaired a number of faulty C64s and never seen the power switch itself go bad. Usually it's either the (if original) power supply itself which are notoriously unreliable after all this time, or the solder joints on the DIN connector or power switch that go bad. Have you checked all of those? You should be able to visually see the bad solder joints, and can measure the power supply voltage with a multimetre when the LED is dim. – Dawn Minion May 28 '19 at 12:35
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    I have recently discovered that the female connectors in the DIN socket can break at the joint where they come out of the back of the housing and fold down towards the PCB; a small tuning fork-shaped bit of metal drops out. Thankfully for me it was one of the unused pins in the A/V connector. Maybe there's some fatigue there? Unplugging and re-plugging would certainly be agitating things in that area. – bodgit May 28 '19 at 13:16
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    Single data point for my pre-85 C64: the PCB connections of the power switch had dry joints and work reliably when resoldered. – scruss May 29 '19 at 12:29
  • I worked at a shop that handled a lot of C64s in the mid-eighties. Usually the bad power supplies were bad out of the box. If it's still working after all these years, it's likely the solder joints from plugging it in many times. – Cliff Hall Jun 30 '19 at 23:35

A history of failing is maybe a strong statement, but for what it's worth, I've seen a couple of failure modes of the power switch during C64 repairs.

The most typical is that solder joints become loose due to the mechanical stress on the button, which can lead to no or poor connection, similar to what you describe. This can normally be fixed by resoldering the joints.

I've also seen a failure mode where environmental conditions (presumably) had caused contact surfaces to degrade and not conduct properly. This could be fixed by repeatedly bathing the switch in contact cleaner and exercising it.

Finally, I've seen one that had a mechanical failure in it so that it could not turn on. Replacement was necessary.

I don't really have any numbers on how often these failures occur (and assume they are also a function of external factors), but I'd say that in my experience it's not uncommon.

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