Bad caps on my Commodore 64? Should I replace them? - Page 1
Forum section: electronics / beginners

author: furyanwolf
author_rank: Newbie
timestamp: August 04, 2019, 01:14:32 pm
content: Hi everyone,Introductions follow, TLDR at the bottomI'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. 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 appreciatedPictures of the board:https://imgur.com/a/8dOCTwVThanks!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.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 04, 2019, 02:01:05 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2019, 02:22:06 pm
content: 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 QLUnfortunately 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.

author: furyanwolf
author_rank: Newbie
timestamp: August 04, 2019, 04:49:28 pm
content: 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

author: james_s
author_rank: Super Contributor
timestamp: August 04, 2019, 04:58:56 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2019, 05:38:45 pm
content: Quote from: furyanwolf on August 04, 2019, 04:49:28 pmBBC BASIC (originally on the BBC computer and Acorn Atom and later the Archimedes) was particularly well structured and nice to use. SuperBasic on the Sinclair QL was well structured, had better string handling than BBC BASIC, and was also user extensible.You don't need to use retro hardware to get the classic BASIC experience, which is a good thing as vintage hardware, especially storage peripherals, is getting rare and unreliable.BBC Basic has a fair bit of cross-platform support nowadays and can be run natively under RiscOS on ARM SBCs like the Raspberry PI. SuperBASIC is far less widely ported but can be run under a QL emulator on most platforms.

author: james_s
author_rank: Super Contributor
timestamp: August 04, 2019, 08:08:09 pm
content: Heck you can run BASIC on a $13 FPGA board. Check out Grant Searle's 'multicomp'.

author: Peabody
author_rank: Super Contributor
timestamp: August 05, 2019, 04:29:47 am
content: furyanwolf, you must be a glutton for punishment. Do you have an analog monitor for the C64? What about floppy drives? How about a modem, or some way to transfer files to and from Windows? And then there is 6502 Assembler, which is actually quite nifty. Well, it should be fun putting everything together, but having done that, there may not be much to do with it even if it works.

author: james_s
author_rank: Super Contributor
timestamp: August 05, 2019, 06:27:57 am
content: Oh there's tons of stuff to do with a C64. There is still an active development community along with decades of existing software. It was a revolutionary machine at the time which was enormously popular.

author: Peabody
author_rank: Super Contributor
timestamp: August 05, 2019, 05:44:35 pm
content: Quote from: james_s on August 05, 2019, 06:27:57 amOh yes, and I was devoted to mine. Even wrote an assembler for it so I could write other stuff. And the only time I've ever been "published" was an article in Transactor (anybody remember that?). But I think times have moved on. And it seems a lot of the development work involves giving the C64 new hardware capabilities it never had, and I don't quite see the point of that.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 05, 2019, 05:56:53 pm
content: Quote from: Peabody on August 05, 2019, 05:44:35 pmThe point is the same as with any other hobby with no financial gains: to have fun and learn things along the way.

author: furyanwolf
author_rank: Newbie
timestamp: August 05, 2019, 06:11:52 pm
content: Quote from: james_s on August 04, 2019, 04:58:56 pmYea I've decided it looks decent enough to give it a chance once my new power supply arrives tomorrow, and hopefully it will all work. I might replace the electrolytics at some other time.Quote from: Ian.M on August 04, 2019, 05:38:45 pmQuote from: james_s on August 04, 2019, 08:08:09 pmThanks for the infoI do know that I could've run BASIC without any old hardware, I just wanted to get into vintage computers partly for the experience/romanticism of it. Being able to actually code on it was a bonus.Quote from: Peabody on August 05, 2019, 04:29:47 amFair points, I might in fact get more accessories for it assuming it works and I enjoy my time with it. Speaking of which, I did get it with a handful of games and a datasette 1531, so I'm hoping there will be some interesting entertainment to come.Quote from: james_s on August 05, 2019, 06:27:57 amI've also heard about this, I think I heard The 8-Bit Guy mention it, insanely cool that people are still making software for the C64 these days.

author: Peabody
author_rank: Super Contributor
timestamp: August 06, 2019, 03:39:40 am
content: I can send you this program, but can't get it on a Datasette for you:MLMON64 is a machine language monitor program for the C64.It can be used to perform low-level operations on thecontents of the computer's memory, assemble and disassemblecode, and issue disk commands. All numerical values areentered and displayed in hexadecimal.The program is generally similar to, but better than, theMonitor program found in the Plus/4. But this program canbe installed starting at any location from page 08 to pageC8, and fits exactly into 8 pages (2K) of RAM, plus a fewbytes of zero-page memory.Included here are:1. MLMON64.PRG - The executable. Load and Run.2. MON64HLP.ASC and .PET - Manual for the program in ASCIIand PETSCII.3. This ReadMe file.

author: plazma
author_rank: Frequent Contributor
timestamp: August 10, 2019, 07:38:35 am
content: Check the PSU. It's known to give over voltage to the 5V pin. Depending on the PSU model it may be easily modified with a SMPS module.There is a lot of DIY electronics project for Commodore 64. Here are some of what I have made:SRAM PCB for later modelsSwitchless JiffyDOS (Kernal selector without external switches)http://pasilassila.blogspot.com/2014/06/switchless-jiffydos-for-c64.html?m=1Under voltage, over voltage, over current protector which fits inside the DIN connectoretc.Sent from my GM1903 using Tapatalk

author: Kahenraz
author_rank: Contributor
timestamp: August 10, 2019, 08:34:36 am
content: I bought model UA6013L Auto Range Capacitor Capacitance Tester off of eBay for my own sanity check when replacing capacitors. Works great.https://www.ebay.com/itm//263536242432However, I've only ever tried this with electrolytic capacitors. This video suggests that this is the wrong tool for ceramic capacitors:I agree with what's already been said. Ceramic capacitors are pretty darn robust. They're basically a bunch of thin metal sheets suspended in epoxy. No moving parts and no electrolytic to dry out:See here for more information:https://www.sparkfun.com/news/1271

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2019, 05:43:38 am
content: Ceramic capacitors from the era of the C64 were even simpler than that, just a slab of ceramic with metal electrodes on each side. I don't think multilayer ceramics came out until much later.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 11, 2019, 09:51:00 pm
content: Quote from: james_s on August 11, 2019, 05:43:38 amAlthough MLCC was an Apollo era innovation, it was not a cheap device throughout the growth of SMD of the 1980's - especially with a consumer product like the C64 which was very cost sensitive.I think the cellphones were the ones that created demand enough to reduce their price to acceptable levels. (just like with many other things that became affordable with the advent of these ever-available mini intercoms)Despite this, the SMD MLCCs can be quite sensitive to the dramatic thermal expansion subjected during soldering - they can develop small dielectric fractures if not carefully controlled.