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If you know anything about the Commodore 64 (and other Commodores, really) you know that Commodore really went the cheap route and produced some awful power supplies. The Commodore 128 PSU isn't quite as bad as the C64 version, but it's nowhere near perfect.

If you open up the PSU for a C64, you will see that the insides of the brick are completely filled with epoxy. There is no way to salvage the parts or repair them.

My assumption is that Commodore didn't want average folks repairing their own PSU when they went south (which happens a lot). And, Commodore would much prefer you buy a new PSU. But was that really the reason? Or, did Commodore think they were making them safer by doing that?

cbmeeks
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    It stops humming from the transformer. – Jan Mattsson Aug 07 '17 at 16:34
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    It was handy when my C64 power supply failed and I kept it going by putting it in a bucket of icewater. When my mom found out, she made my dad buy me a replacement, saving me $50 in precious allowance money. – Ben Jackson Aug 08 '17 at 06:53
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    @BenJackson How in the world did that work? I didn't think putting any electronics in water would ever "kept it going"... – Nelson Aug 08 '17 at 08:35
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    @Nelson Potting is one of the most effective ways to keep water out of electronics. As for how it fixed it, it likely had a fault causing overheating. – SomeoneSomewhereSupportsMonica Aug 08 '17 at 09:40
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    Over 30 years later I still have a scar on the second knuckle of the first finger of my right hand from trying to open a C64 power supply. That epoxy is sharp in places. – Tim Locke Aug 08 '17 at 15:08
  • I'm sure it was to make it space-worthy. Electronics intended for space use at that time were typically embedded in epoxy to protect them from hazadous environment or space. – SF. Aug 08 '17 at 17:39
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    Being a young computer dork with a C-64 and living in the middle of nowhere - when my C-64 power supply fried my Dad fixed it for me. He carefully cut away the epoxy, reverse engineered the circuit, built a new one, and put the whole mess in an old chassis left over from some earlier (read: 1960's) project. I still have that power supply, and it still works perfectly. It's not impossible to salvage or repair a potted C64 power supply, it's just really hard. – Geo... May 24 '19 at 16:24
  • @Geo... that's awesome to hear! Yeah, not impossible but super difficult and not worth it for most people at the time (replacements were easily obtainable). I'm glad you kept it. While my dad didn't know anything about C64 PSU's, he did make me a steal grappling hook when I was a kid (I wanted to be a ninja LOL). However, I lost it. – cbmeeks Jan 06 '20 at 13:43
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    Acorn did this with their real time clock dongle which was really just an anti piracy device as the server software (L3 Econet) would not run without it. I do still have pics of one I dismantled once to discover the chip numbers were removed too to discourage any copy attempt. Funny thing was although not really widely known at the time ( well I never heard or saw anything about it ) it was not difficult to circumvent said protection as the clock was not essential for its operation! – AndyF Jan 13 '20 at 14:49

2 Answers2

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Epoxy offers two advantages -- it is an electrical insulator, and it conducts heat better than air. Transformers and inductors are generally potted with epoxy for this reason. [ref] Perhaps the cause of the high failure rate is that Commodore engineers decided they could use cheaper components to build the power supplies, depending on the epoxy properties to balance out any deficiencies.

In 2012 Bil Herd (Commodore engineer) speculated:

They were made for CBM by the boatload, they got warm and were not rated for things like the CBM cartridge [Bil probably meant CP/M cartridge], etc, though they would continue to make voltage they would just run hotter reducing their life. Potting them was probably to protect CBM as it's hard to start a fire from within a pound of epoxy. The potting would have made the hottest components slightly less hot and everything else too hot.

Remember that the VIC 1 had started at least one fire, I think something like 3. The case used to melt and sag over one of the heat sinks. Supposedly a programmer tried to design apiece of the power supply without really knowing heat and wattage calculations. So a good reaction would be a supply that never caught fire, was impervious to static and even water, and was a bitch to air ship.

Dale Mahalko
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RichF
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    That is an excellent answer. And, it makes total sense. I guess Commodore wasn't as stupid as I thought they were. Too bad they didn't design a better PSU before they potted it. :-) – cbmeeks Aug 07 '17 at 17:22
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    The explanation I remember hearing at the time was it was done for safety reasons, maybe even specifically to get certification, and that the usual failure mode was that expansion and contraction would eventually crack the voltage regulator or break one of the connections. –  Aug 07 '17 at 17:43
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    Even without overloading those C64 PSUs died regularly. I used to fix them by piggy-backing a new 7805 on and replacing the removed case bottom with a generous heatsink - did at least two dozen of them. – Zac67 Aug 07 '17 at 19:27
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    FYI, "CBM" is Commodore Business Machines. – RBarryYoung Aug 08 '17 at 14:10
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    @RBarryYoung Thanks, but I know. If you are responding specifically to my internal quote note where I referred to "CP/M", I believe in that one instance Bil meant "CP/M cartridge" and not "CBM cartridge". The Z80 processor and other components within that cartridge would have added a noticeable load on the power supply, which in context is exactly what is being discussed at that point. FYI, Bil Herd is the lead engineer for the C= 128, and the one who decided to add the Z80 to its motherboard. So it makes sense that he would specifically reference the C64's CP/M cartridge. – RichF Aug 08 '17 at 16:41
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    @RBarryYoung I edited my answer to include the word "cartridge" within my note. Hopefully that clarifies my meaning. – RichF Aug 08 '17 at 16:47
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    Maybe some safety standard for toys was met that way, given the target market included very young segment.... – rackandboneman Aug 09 '17 at 15:49
  • So maybe the decision also had to do with trying to avoid lawsuits from potential fires. Anyway I used my C-64 quite a lot back in 80's in Sweden (I had 3 of them at different times) and I don't remember any issues with the power supplies ever. Made me wonder if they were better made on the European market. – x457812 Feb 21 '20 at 23:09
  • Every time I read stories about CBM I'm more appreciative of the level of engineering Atari, and later Apple, put into their products. – Maury Markowitz Jul 01 '22 at 15:03
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Electricians some times (or used to) do similar techniques when configuring wiring -- once the wires were in place, they would fill the cavity with a non-conductive resin or epoxy, so that the chance of any movement or shift in the wiring would cause a short or a disconnect is greatly reduced. I've seen this in numerous situations myself, including air compressors, where there is quite a lot of vibration.

Personally I think it was a cheap way to make their power bricks last longer because people move those things around, they get kicked a lot (I had a C64 for a very long time), and probably had to hold up the weight of many-a-12-yr-old when they stepped on it, because well, they're 12 and they can.

Tim S.
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    I would also assume that the design was more to avoid mechanical than electrical damage - A power supply of that time had to consists of some pretty heavy components (transformator, large capacitors, large inductors) that were hard to mechanically fix with the solder joints on the PCB only. – tofro Aug 08 '17 at 10:25