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| Bad caps on my Commodore 64? Should I replace them? |
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| furyanwolf:
Hi everyone, Introductions follow, TLDR at the bottom :) I've been subscribed to the EEVblog channel for a while now and been trying to pick up some electronics knowledge here and there in my spare time. I'm a software developer myself and I've always been excited by the idea of making and/or repairing my own hardware. I'm especially drawn to old/vintage computers and tech and I'm trying to learn as much as I can about low level programming and how hardware has evolved over the years to the levels of modern day computing. And so I thought a nice place to start my adventure might be by buying an old Commodore 64 and possibly fixing/modernizing its parts (if necessary) and following up with some BASIC programming. Fun times ahead ;D. I'm quite sure I'll be spending some time on the Vintage Computing subforum soon too. TLDR: Being a an electronics noob, I'm not sure if my newly acquired Commodore 64 is in a good, bad or "eh, will probably be fine" condition. I've inspected the board and to my eyes, the electrolytic caps seem fine (though I'm still inclined to replace 35 year old caps), however I am not sure what to make of the many ceramic capacitors on the board. A lot of them seem to be covered in a white substance and I'm not sure if this means that the caps have gone bad or if it is something else altogether that perhaps I shouldn't worry about. I've included many pictures of the board in the imgur link below. I would appreciate any help/guidance as to what the white substance on the ceramic caps is, whether I should be worried about it and whether I should replace those caps at all or regardless of the substance anyway. Any advice as to other aspects of the boards condition would also be highly appreciated :-+ Pictures of the board: https://imgur.com/a/8dOCTwV Thanks! P.S. I can not yet say whether the computer even powers on as I did not want to take any chances with the old power supply and I'm waiting for a new one to arrive in about 2 - 3 days. |
| Kleinstein:
The ceramic caps are fine. The white stuff looks like residue from cleaning the flux. The ceramic caps are pretty robust. The ones to worry are the caps in the power supply and to a lesser degree the electrolytic ones on the main board. The ones on the main board would probably not do much damage if they fail. So one could give them a chance. For the power supply it may be a good idea to slowly start it up on it's own and check if the voltages are Ok without the rest connected. If the caps short out, they may damage the transformer and so on. The caps in the supply also run pretty hot. |
| Ian.M:
I wouldn't worry too much about 'bloom' on the surface of an old disc ceramic cap even if it isn't just flux residue, as the coating on them was often wax impregnated. Desolder the worst affected one and check it for value and leakage current at its rated working voltage before considering replacement. I'd be very surprised if its actually bad. You can also take the opportunity to see if the bloom can be wiped off with IPA or can be readsorbed by gentle heating with a hot air gun to melt the wax, before deciding if either would be viable as an in-situ cosmetic treatment for the board. IIRC Commodore BASIC was quite nasty - to do anything useful at the system level you mostly had to use cryptic PEEKs and POKEs or even resort to SYS or USR() calls for stuff that other versions of BASIC either had dedicated keywords for, or a cleaner way of accessing OS commands in a human readable format. I only had a C64 for a few weeks as I found it so frustrating that I traded it for an early model Sinclair QL Unfortunately Commodore dropped the hardware GPIB port their PET had when they designed the VIC20 and C64 which makes it rather less useful as it cant control lab instruments over GPIB without an external interface. |
| furyanwolf:
Thanks for the replies! :) I will give the ceramics a chance in this case. I might still replace the electrolytics for my peace of mind, but I'll wait for the new power supply to arrive first, test it out with it's current components and then decide if it's worth changing anything at all. My concern was more of whether those components would have somehow produced the substance, hence being a sign of degradation, but if that is not the case, I will try to clean them off if possible and see what happens. As for BASIC @Ian.M, I'm honestly going into it with no expectations, most of my experience is in C# and Java, wildly different and modern languages as it is, so I'm expecting BASIC to be a bit of an experience either way. But it's interesting to know that there are better options out there, might just look into acquiring more vintage computers down the line ;D |
| james_s:
You can't visually tell anything about the condition of electrolytic capacitors unless they are *really* bad. Personally I would just leave them all alone if the machine works, but if it's getting flaky you could look at replacing the electrolytics. You can get a component tester for under $10 that can measure ESR though. |
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