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C64 power supply. Do NOT use 1 unless you check the output.

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C64 power supply. Do NOT use 1 unless you check the output.

by mons2b » Tue Oct 04, 2016 11:36 pm

I pulled my favorite C64 out of its dusty box and I have read of issues with the factory power supplies going bad in their age and in so doing upping the DC 5v output line to ram chip destroying levels. It would seem to me that using a factory supply without something between it and your elderly precious is Russian roulette. Of course you can measure the pins from the power supply and confirm if its currently ok.. I measured one of mine at random. A darth vaderish black wedge power supply and it is currently reading 5.7 volts from the two pins concerned (9v AC output not known to fault).

So in getting to my point there are various solutions now being pushed online. One is a "c64" saver (lets you know if the volts go out of spec) which goes between the supply and your c64, others include varieties of bodges including two separate new supplies for your 5v and 9v ac requirements or online schematics to make your own new one. Now Im always one for thinking of the "third way", there's always one. My idea is to insert inline a adjustable voltage step down circuit, and ill put two din plugs/sockets on each end. This will stop the supply getting its way and feeding anymore than 5v dc in. This will let you keep using the power supply you have and not have to open it to attempt self repair or toss it out (or pick away at resin) if its one of the majority resin filled ones. Im going to order the parts and will let you know the results. :)
Last edited by mons2b on Mon Oct 17, 2016 10:43 pm, edited 1 time in total.
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Re: C64 power supply. Inline regulator to save your SID!

by mons2b » Mon Oct 17, 2016 10:41 pm

I believe there are still many people using a Commodore 64 in some part time retro capacity at least. So some first some free advice which some of you might already know but if I share this maybe it will save a few C64s from being parted out.

Pretty much most original c64 power supplies have aged to the point they are putting out too much voltage on the 5v line. In my case its showing 5.7 volts in worse cases it could be 7 volts or worse. This might not seem like much but your C64 doesnt like it at all particularly if your chips are not heat sinked. So pull out a multi-meter now and check the 5 volt pins. From what I have researched 5.5 volts is the max you really want to feed in your computer. If you see more I suggest you stop using that power supply.

Unlike most micro computers a C64 power supply puts out TWO voltages which makes them tricky to replace. Theres of course 5v dc but theres also 9v AC! Theres two or three options for you currently that vary by cost and time required. You can buy two power adapters and wire them to your old c64 plug, which is kind of messy. You can buy aftermarket power supplies EX USA and ship them over. If your real lucky you will have one of the rare power supplies that haven't been sealed in block of epoxy and you can repair it yourself. Thats OK but you will still have a crude unregulated 5v line going into your delicate sid chip etc. They didn't like ripple current when new and they like it less now they are 30 years old.

I'm going to hand assemble a very small run of adapters (five) that you can plug inline between your original adapter and your C64. Whatever dodgy output coming out of the power supply will be cut down to 4.8 to 5v (depends on what the regulator is getting fed) and it will be regulated. The 9v AC will pass through unfiltered as that line comes straight off the transformer and rarely goes wrong. It will be made in best traditions of Jack Tramiel and will do only what it needs to do. So no fancy displays or anything like that. A box with a C64 power input socket for you to plug your old power supply into and a output cable to then plug into your C64/c . If anyone here would like to buy one of my constructions let me know. Im only making five as test to see if theres any interest in this device. No pictures or price yet but that will come. No kick starter here just me myself and I. If you want dibs on one let me know!
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzswift » Tue Oct 18, 2016 7:21 am

I'd be keen unless it's mega$$$$
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by tezza » Tue Oct 18, 2016 7:50 am

Depending on price, I would also be interested in one of these.
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzoomed » Tue Oct 18, 2016 8:45 am

Yes ive been reading about this and some guy in the USA has made a SAV64 which is supposed to regulate the voltage.
http://www.lemon64.com/forum/viewtopic. ... sc&start=0
They are jolly damn expensive for what they are, plus shipping to NZ...

Im worried now after checking my voltage, its reading about 5.8V from memory and measuring across the 9VAC pins, this gives me about 10V.
:(
But i dont know how accurate my cheap multimeter really is, but i hope i have not caused any damage...

Does anyone actually know what goes wrong on these power supplies over time to cause a voltage increase?
I suspect a bad capacitor?

Either way, I want to do something, because ive been using my C64 (for short periods only thankfully) on this "dodgy" power supply before i was aware of the issue.

Anyway, would it not be too difficult to just simply use a 7805 regulator to regulate the 5v rail?

Perhaps my multimeter is wrong if i get 10VAC on the 9V pins? If its straight from the transformer, then there is nothing to worry as you say.

Either way im interested in one, another good feature would be to add a power switch to the box, and that way, it will save wear and tear on the switch on my C64 ;)
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by mons2b » Tue Oct 18, 2016 6:48 pm

Was thinking of a switch but the spirit of Jack frowned at me. lol. Still ill consider it. Ive seen the schematic and the 9v ac seems to come straight off the transformer, some power supplies might have a cap there to smooth the ripple but its not known for causing problems being left as is. What causes the 5v dc to grow is aging of the caps inside the power supply. The problem is if you have a heavy weight power supply its most likely a solid block of epoxy so you need a ice pick or chemicals to try to dissolve it. Or you can heat it (200 degrees) and wear a gas mask. Im not keen on those plans.

Maybe I should call the box the Jackulator accessory. Ive seen the common overseas options. A good but expensive power supply and a voltage warning gadget the later is great but kind of pointless these days as I think theres few C64 PSU's still within the safe spec. With the Jackulator the PSU can do its worst upto 23v whatever comes out will be lowered to 5v so as your supply ages and gets worse it just wont matter.
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzoomed » Wed Oct 19, 2016 10:03 am

mons2b wrote:Was thinking of a switch but the spirit of Jack frowned at me. lol. Still ill consider it. Ive seen the schematic and the 9v ac seems to come straight off the transformer, some power supplies might have a cap there to smooth the ripple but its not known for causing problems being left as is. What causes the 5v dc to grow is aging of the caps inside the power supply. The problem is if you have a heavy weight power supply its most likely a solid block of epoxy so you need a ice pick or chemicals to try to dissolve it. Or you can heat it (200 degrees) and wear a gas mask. Im not keen on those plans.

Maybe I should call the box the Jackulator accessory. Ive seen the common overseas options. A good but expensive power supply and a voltage warning gadget the later is great but kind of pointless these days as I think theres few C64 PSU's still within the safe spec. With the Jackulator the PSU can do its worst upto 23v whatever comes out will be lowered to 5v so as your supply ages and gets worse it just wont matter.


yeah, thats a good idea.

I suspect the caps being at fault, but other forums suggest its the regulator itself that gives out because the epoxy is an insulator and does not allow the regulator to cool down, in turn causing damage.

What do you plan to use as a regulator?
I see a 7805 needs at least 7 volts input to work, so this would only be suitable on a really bad PSU.

Would be good if it was possible to open the brick but its all sealed and not easy to get at as you say with all the epoxy, let alone trying to open the jolly thing up.
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by mons2b » Wed Oct 19, 2016 10:12 pm

Hi NZ :)

Yes it could be the regulator too. Its just often said to be the caps. Bit hard to tell when they are "Frozen in carbonite" like Han Solo. Ill just take the DC output and feed it into a circuit that will drop the voltage down and regulate it. So completely external to the existing supply. You will be able to unplug and use the "Jackulator" as I am calling it with any C64 power supply. It will not increase the amps you can get out of the original power supply so hardware hackers loading down their C64 with many accessories will probably need a new power supply with a higher spec. Also 128 users it wont work for that machine as it is at the moment.
Given feedback ive spent a few hours trying to find a cheap double pole switch so you can save your C64 switch. Loads of single pole switches. Gets harder to find a cheap one when you go to double pole which is a must because of the dual voltage output! :). So a switch is in. Still considering a power led but im trying to make this cheap and each little thing adds up to a higher parts total plus longer for me to assemble it.

I hope to have a rough prototype to show you guys soon. Still waiting on more parts. I cant wait to have it working as I cant currently run my own C64 breadbins that I want to diagnose IC issues. Cant do that with the high volts coming out now. Commodore specs say no more than 5.1 to 5.5v. I will set my device to aim for 4.8 to 4.9 to keep the ICs cooler. Ie the hard to replace SID!
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by mons2b » Wed Oct 19, 2016 10:16 pm

nzswift wrote:I'd be keen unless it's mega$$$$


Wont be mega dollars. Computers for the masses not the classes. - Jack Tramiel. :)
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzoomed » Thu Oct 20, 2016 10:05 am

mons2b wrote:Hi NZ :)

Yes it could be the regulator too. Its just often said to be the caps. Bit hard to tell when they are "Frozen in carbonite" like Han Solo. Ill just take the DC output and feed it into a circuit that will drop the voltage down and regulate it. So completely external to the existing supply. You will be able to unplug and use the "Jackulator" as I am calling it with any C64 power supply. It will not increase the amps you can get out of the original power supply so hardware hackers loading down their C64 with many accessories will probably need a new power supply with a higher spec. Also 128 users it wont work for that machine as it is at the moment.
Given feedback ive spent a few hours trying to find a cheap double pole switch so you can save your C64 switch. Loads of single pole switches. Gets harder to find a cheap one when you go to double pole which is a must because of the dual voltage output! :). So a switch is in. Still considering a power led but im trying to make this cheap and each little thing adds up to a higher parts total plus longer for me to assemble it.

I hope to have a rough prototype to show you guys soon. Still waiting on more parts. I cant wait to have it working as I cant currently run my own C64 breadbins that I want to diagnose IC issues. Cant do that with the high volts coming out now. Commodore specs say no more than 5.1 to 5.5v. I will set my device to aim for 4.8 to 4.9 to keep the ICs cooler. Ie the hard to replace SID!

Will the chips still work OK on 4.8v?
I know most chips requite 5V.
I want to test my supply under load to know for sure what the voltage is.
Either way, i want one of these, as im scared of frying my c64 after learning about this issue.
Im thinking it would be good if i can actually find a "rougher" example and leave my one in its box, because its a real "minter. :)

Speaking of switches, this is the cheapest double pole switch i can find on rs:
http://nz.rs-online.com/web/p/rocker-switches/0322029/
No real need for an LED, ad the c64 has a power LED to say its on :)
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by mons2b » Fri Oct 21, 2016 7:56 pm

Hi NZ Zoomed.

Ive found a nice switch that looks like it will do the job. Prob will skip the led but considering adding a fuse to protect the circuit regulator. I believe the c64 will work ok on 4.8. The reason I said that as a low point is that if your power supply is perfect then the regulator add on will possibly lower it to 4.8 as theres a unavoidable slight voltage drop. Unlikely but had to mention it. Ill try to tune them for 4.9 so unless your power supply was blessed by the Pope it will likely be putting out more than 5 volts so everyone should be ok. Everyone being 5 people. :). If people like them I may make a few more. I hope people like them. Below is a pin out so anyone can check with a cheap multi-meter and see what their supply is putting out. Ive found some official commodore notes that say 5.1v is too much.. but I would say definitely put that supply away if its reading more than 5.2. Just not worth it with the age of the chips now. Apparently high 5 volt lines also kill your ram chips which are a pain to replace. Both rare and unsocketed in most cases. I made another dive in my garage and found a rare 64 power supply. No epoxy, has screws and with open vents, tested it and it was sitting on 5.16 or so. This will be my fav supply for sure. I have a few of the sealed modern bricks but they are the Han Solo editions. LOL.

commodore_c64_psu-pinout.gif
commodore_c64_psu-pinout.gif (2.47 KiB) Viewed 2611 times


7 PIN DIN ‘C’ FEMALE at the computer.
Pin Name
1 GND
2 GND (5V negative pole)
3 GND
4 nc or +5V in
5 +5V in
6 9VAC in
7 9VAC in
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by bhabbott » Sat Oct 22, 2016 11:47 am

nzoomed wrote:other forums suggest its the regulator itself that gives out because the epoxy is an insulator and does not allow the regulator to cool down, in turn causing damage.
Often it's not the regulator itself, but a 'dry joint' between the regulator's GND lead and the PCB. This is caused by expansion and contraction of the joint as the power supply heats up during use and cools down again when turned off. I think the epoxy causes the fault by preventing the regulator body from moving freely with expansion, so the leads expand through the PCB and break the solder joints.

With no ground reference the regulator puts out the maximum voltage it can, typically over 7V. This was the #1 cause of fried C64s back when I was repairing them in the early 90's.

Dry joints are often intermittent. If you have a potted power C64 supply it's best not to use it at all (even it tests OK) until the joints have been examined, and preferably resoldered. The PCB is usually only covered with a thin layer of epoxy, so you may be able to see the regulator terminals just below the surface. The epoxy can be softened with heat from a soldering iron, then pried off to expose the joints. Reflow the joints with fresh solder and you will probably find the power supply works properly again.
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzoomed » Sun Oct 23, 2016 9:51 am

bhabbott wrote:
nzoomed wrote:other forums suggest its the regulator itself that gives out because the epoxy is an insulator and does not allow the regulator to cool down, in turn causing damage.
Often it's not the regulator itself, but a 'dry joint' between the regulator's GND lead and the PCB. This is caused by expansion and contraction of the joint as the power supply heats up during use and cools down again when turned off. I think the epoxy causes the fault by preventing the regulator body from moving freely with expansion, so the leads expand through the PCB and break the solder joints.

With no ground reference the regulator puts out the maximum voltage it can, typically over 7V. This was the #1 cause of fried C64s back when I was repairing them in the early 90's.

Dry joints are often intermittent. If you have a potted power C64 supply it's best not to use it at all (even it tests OK) until the joints have been examined, and preferably resoldered. The PCB is usually only covered with a thin layer of epoxy, so you may be able to see the regulator terminals just below the surface. The epoxy can be softened with heat from a soldering iron, then pried off to expose the joints. Reflow the joints with fresh solder and you will probably find the power supply works properly again.



OK interesting, Im reading under 6V on my power supply, but thats not under load.
My C64 is near new and had little use, so thats probably one reason its not so bad as others.

How do you open these bricks anyway?
The whole thing looks a sealed unit, there are no screws that i can see anywhere.
Would be good if they could be opened without showing any signs of saw cuts round the edge...
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by nzoomed » Sun Oct 23, 2016 9:53 am

mons2b wrote:Hi NZ Zoomed.

Ive found a nice switch that looks like it will do the job. Prob will skip the led but considering adding a fuse to protect the circuit regulator. I believe the c64 will work ok on 4.8. The reason I said that as a low point is that if your power supply is perfect then the regulator add on will possibly lower it to 4.8 as theres a unavoidable slight voltage drop. Unlikely but had to mention it. Ill try to tune them for 4.9 so unless your power supply was blessed by the Pope it will likely be putting out more than 5 volts so everyone should be ok. Everyone being 5 people. :). If people like them I may make a few more. I hope people like them. Below is a pin out so anyone can check with a cheap multi-meter and see what their supply is putting out. Ive found some official commodore notes that say 5.1v is too much.. but I would say definitely put that supply away if its reading more than 5.2. Just not worth it with the age of the chips now. Apparently high 5 volt lines also kill your ram chips which are a pain to replace. Both rare and unsocketed in most cases. I made another dive in my garage and found a rare 64 power supply. No epoxy, has screws and with open vents, tested it and it was sitting on 5.16 or so. This will be my fav supply for sure. I have a few of the sealed modern bricks but they are the Han Solo editions. LOL.

commodore_c64_psu-pinout.gif


7 PIN DIN ‘C’ FEMALE at the computer.
Pin Name
1 GND
2 GND (5V negative pole)
3 GND
4 nc or +5V in
5 +5V in
6 9VAC in
7 9VAC in

OK, thanks, I want to be the first to try one, I cant be without my C64, ive only been using it for short amounts of time, but im afraid of damaging it!
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Re: C64 power supply. Do NOT use 1 unless you check the outp

by mons2b » Mon Oct 24, 2016 9:28 am

Ill put you as the first to try one NZ Zoomed. I went through some old C64s i have and one breadbin had a chip hot enough to fry an egg. I think a victim of a bad power supply. I plan to give one Breadbin the full delux spa treatment with new caps and heatsinks everywhere. I will also put a new cap in the one C64 power supply Ive found that can be repaired. The regulator 7812 in the power supply is attached to a huge heatsink so it should be ok but its more than 30 years old so a new one might be good especially as I can get to it.

Something I belatedly realized.. The 1541-II disc drives have a very similar power supply that is also usually sealed and could also be now putting too much voltage into your disc drive. Those who use those SD card replacements no worries for you. But if youre like me and you like using a real drive check that power supply too. On the large original drives the power supply is INSIDE the drive. I am going to try to look inside the one i have at some point and see what voltage its feeding out.

All power supplies should be checked really at this point. So your Vic 20 , c16, plus 4 etc. Be careful with mains voltages.
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