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DistantStar001

I'm Getting My First C64, And I Have Questions

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Thanks for the help so far. I was reading the Retro 64 Bog, and one of the things that stuck out to me was the information regarding the 9v line. In testing, I noticed my PSU was giving irregular readings (between 6 and 12v). I assumed that meant that the supply was simply unregulated, but now I'm wondering if the PSU was providing appropriate power to the board? I can't really test any of the internal components of the brick as they're entombed in a solid block of epoxy, so now I'm wondering if there was something failing on that line? These questions are of course rhetorical, as I've already started to dismantle the PSU, so I can rebuild it with something safer, and more reliable. The big question is now, how do I get this solid block of 30-year-old epoxy out of my brick without destroying the case? After all, if my computer can't have all the original parts, I'd like it to at least look original on the outside.

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I actually did manage to empty it! I know that it would probably be easier to simply buy a modern replacement PSU, but the whole point is to learn new things. That's half the fun.

 

As I said, I already have a 9v brick somewhere that I can gut for a transformer. I'd try to use the original, but 1) it's encased in a solid brick of epoxy, and 2) the 9v line was giving me funny readings, so I think I'm better off just replacing it with something more reliable. The 5v line is the bigger question. It needs to be at least 2 amps and that's proving a little harder than I thought, as the last supply I found was only 1.5.

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I actually did manage to empty it! I know that it would probably be easier to simply buy a modern replacement PSU, but the whole point is to learn new things. That's half the fun.

 

As I said, I already have a 9v brick somewhere that I can gut for a transformer. I'd try to use the original, but 1) it's encased in a solid brick of epoxy, and 2) the 9v line was giving me funny readings, so I think I'm better off just replacing it with something more reliable. The 5v line is the bigger question. It needs to be at least 2 amps and that's proving a little harder than I thought, as the last supply I found was only 1.5.

9V is a AC, not DC, maybe that's why your readings fluctuate.

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9V is a AC, not DC, maybe that's why your readings fluctuate.

Actually, it was both. The 5v DC line was creeping up, topping out at about 5.4v before I stopped using it, and the 9v AC line was fluctuating between 6 and 12v. The last time I tested, my C64 was giving me a black screen. I was worried that the 5v might have spiked and fried something along the line, but when I looked it up (thanks to rpiguy9907 for the source: http://retro64.alter...ired-to-fix-it/ ), I learned that a dip in voltage on the 9v AC line can give a black screen on an otherwise good board. Maybe it was a failing fuse or something? It's kinda hard to tell since it's all entombed in epoxy. In any case, I am now hopeful that my board might be alright after all, and all I have to do is rebuild the PSU (and get a new bread-box case, replace the cardboard rf shield with something that isn't falling apart, apply some new heat sink compound to the VIC chip, and get some software...) and then I'll have a fully rebuilt, and functional Commodore 64!

 

To that end, I have found a new 5.2v 2.0 Amp DC power supply (that actually fits inside the original brick), and am in the process of choosing which 9v brick will make the ultimate sacrifice to save my C64. The real question is: How to mount all of it? I hate the idea of more epoxy (since removing a solid brick of it form my PSU was so much fun), but I really can't think of any alternative. I also want to reinforce the original PSU casing since the plastic is really thin. Needless to say, I'm going to put this whole Frainkinstonian monstrosity through a bunch of tests long before I ever plug it into my C64.

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In testing C= bricks, I've found the 9vac line can fail suddenly on a power up. That gives a black screen, but machine will still work fine on another supply. Most focus on the 5vdc lines as that one is the main chip fryer. I dumped almost all of those except a few white ones. The CBM vented version was good enough, otherwise, the new ones from Ray Carlson or a repro from europe are best bets.

That epoxy inside was what contributed to their earlier death than intended.

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That epoxy inside was what contributed to their earlier death than intended.

I kinda figured as much. Epoxy isn't that good at bleeding heat. If anything it probably acted as an insulator, slowly cooking the 7805. There's only so much a heat-sync can do, especially if it too is entombed in a solid block of epoxy.

 

I'm still trying to build my own rebrick, but I was curious if anyone knew the exact power specs for the 9v line (volts, amps, and watts)?

 

My other idea, because it might be cheaper, would be to build an adaptor for adaptors. Basically, instead of having a single brick, I was thinking of building a dongle that I could plug any 5v or 9v brick into the appropriate line, and from there into my C64. I've seen similar two-brick solutions, but the problem is that they're hardwired, and I would be sacrificing two AC adaptors that would no longer be useful for anything else. This way I could use them for my C64 when needed, and other things the rest. Not that much of an issue for the 5v, but almost everything else I have uses 9v. Any thoughts?

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Atari 8bit line used 9vac power supplies for a number of things, some with higher amperages.

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I'm still trying to build my own rebrick, but I was curious if anyone knew the exact power specs for the 9v line (volts, amps, and watts)?

 

The original power supplies were rated for 1.0 A on the 9V AC line, and between 1.5 - 1.7A on the 5V DC line. The C128 a.k.a. C64 REU PSUs were rated for up to 2.5A on the 5V IIRC.

 

I don't know if any of the modern replacement power supplies are rated higher on the 9V. I believe it is most important to have a beefy 5V as that is what is mostly used.

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... between 1.5 - 1.7A on the 5V DC line.

The 5v supply I found is rated for 2.0 amps, however, it's 5.2v, not 5v. Do I need to bring that down, or am I within specks?

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The 5v supply I found is rated for 2.0 amps, however, it's 5.2v, not 5v. Do I need to bring that down, or am I within specks?

 

I was always taught that 5.2vdc was the high limit for IC components. So, you should be fine. The 5.4 you mentioned earlier is a killer.

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Is that 5.2V under some kind of load? I suppose a resistor or perhaps a diode would be enough to drop it a little if required.

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Is that 5.2V under some kind of load? I suppose a resistor or perhaps a diode would be enough to drop it a little if required.

I haven't tested yet, as I was just reading it from the label, but I suppose I should before I start wiring it up.

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Well, I'm very glad I tested it. Turns out that the 5v supply I bought was completely dead. The capacitors had bulged, and I was getting a whopping 0.0v!

 

I think I'm going to go with an alternative plan, using a USB (5v 1.5 amp) from a shattered tablet, and a 9v AC brick that will both fit inside the original case, but they won't be grounded, which makes me nervous. I was thinking of soldering the plugs together, and then to the power line and splicing the respective outputs to the original Commodore out cable, but I would still like to ground the whole thing, and possibly add a fuse.

 

The nice thing about this is that there will be plenty of room to reinforce the original housing and add some plastic blocks to the corners. That way drill some screw holes into the bottom and make it serviceable if it ever fails. Any thoughts?

 

post-63947-0-87943400-1546588837_thumb.jpg

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1.5 Amps will just be enough, don't add any expansions to the C64 or you will quickly exceed it.

Would that include a floppy or cassette drive?

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The floppy drive has its own power, the cassette recorder though is powered by the computer and probably should fit within the power requirements. More like don't add a RAM Expansion Unit (REU) as it eats a lot of power.

 

However it should be noted that Commodore themselves gradually increased the spec on the C64, at least in Europe - not sure about the USA:

 

VIC-20 and early C64: 5VDC @ 1.5A + 9VAC @ 1.0A

C64 breadbox c:a 1984-86: 5VDC @ 1.6A + 9VAC @ 1.0A

C64C c:a 1987 and later: 5VDC @ 1.7A + 9VAC @ 1.0A

 

Perhaps 0.2A doesn't seem like much (1 watt to be exact) and I don't know if the innards of the PSUs are that much different or if they just measured they could cram more out of the existing designs until those broke down completely but if you're desiging your own PSU it generally would be a good idea to try find a 5V source rated for 2A at once when you're at it. Ideally a bit more of course, but 2A doesn't seem like a lot.

Edited by carlsson

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The floppy drive has its own power, the cassette recorder though is powered by the computer and probably should fit within the power requirements. More like don't add a RAM Expansion Unit (REU) as it eats a lot of power.

 

However it should be noted that Commodore themselves gradually increased the spec on the C64, at least in Europe - not sure about the USA:

 

VIC-20 and early C64: 5VDC @ 1.5A + 9VAC @ 1.0A

C64 breadbox c:a 1984-86: 5VDC @ 1.6A + 9VAC @ 1.0A

C64C c:a 1987 and later: 5VDC @ 1.7A + 9VAC @ 1.0A

 

Perhaps 0.2A doesn't seem like much (1 watt to be exact) and I don't know if the innards of the PSUs are that much different or if they just measured they could cram more out of the existing designs until those broke down completely but if you're desiging your own PSU it generally would be a good idea to try find a 5V source rated for 2A at once when you're at it. Ideally a bit more of course, but 2A doesn't seem like a lot.

I'm going to rethink this then, as it doesn't make much sense to sacrifice a perfectly good wall charger if the finished PSU proves inadequate.

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I'm going to rethink this then, as it doesn't make much sense to sacrifice a perfectly good wall charger if the finished PSU proves inadequate.

 

You don't have to sacrifice the wall charger, if you don't want to. Put a compatible jack on the other end of the c64 power cable and plug the charger into that as with any normal device.

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You don't have to sacrifice the wall charger, if you don't want to. Put a compatible jack on the other end of the c64 power cable and plug the charger into that as with any normal device.

I don't mind sacrificing the charger, although "sacrifice" is probably too harsh a word. My plan is to solder the plugs together and then to the AC in line that leads out of the brick. Then splice the USB and 9v to the appropriate out lines that plug into the C64 (using the same cables that were part of the original PSU). Likewise, the whole assembly will be contained in the original PSU housing. The idea is that (from the outside) it will look like an original C64 PSU, but be a lot safer, and more reliable, and serviceable should any one component fail.

 

To that end, I did find a 5v 2.0 amp USB charger that will work. I'm sticking with the same overall design pictured above, but I'm swapping one component that might not meet my power needs with one that will. The question is now, how do I gound the thing? I'm still working on that, as the adaptors I'm using are not grounded, but the original PSU was. I'd rather not have a free-floating wire in the thing, and it's my understanding that grounding is just safer for older electronics in general. Any suggestions?

Edited by DistantStar001
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So this is what I've worked out. I was thinking of just securing the AC ground temporarily to the case with some glue since I'm not sure what to do with it. Unless anyone has any suggestions?

 

The Ground is that little green line. I'm afraid it's not very clear in the jpeg. Sorry.

post-63947-0-58378500-1547114058_thumb.jpg

Edited by DistantStar001

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So this is what I've worked out. I was thinking of just securing the AC ground temporarily to the case with some glue since I'm not sure what to do with it. Unless anyone has any suggestions?

 

The Ground is that little green line. I'm afraid it's not very clear in the jpeg. Sorry.

 

 

That looks great. Be sure to drill some holes in the power supply for heat dissipation. Do not refill it with epoxy, those little USB chargers will get quite hot running a C64.

Edited by rpiguy9907

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All my hopes are dashed... At least for the moment.

 

 

I finally got my PSU rebuilt (at least to the point where I can test it), all the voltages are good, but I'm still getting a black screen. The good news is that I'm getting correct 5v on the cassette port, but no picture so far. It's just a solid black screen, no flashing, just black, then it goes to snow when I cut the power. I guess this is means that my 5v line must have spiked and fried something, the question is what?

 

Worst case sinerrio, this is a parts machine, but I'm not giving up just yet!

Edited by DistantStar001

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While it may not universally be true, given that the computer gave up the ghost from one day to the other with the original PSU (whether or not it spiked, I didn't follow if you measured it afterwards), I would first suspect the PLA chip for which there are both newly programmed PLA chips and modern replacements such as PLAnkton, realPLA, SuperPLA etc.

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