3 ms·

I have a boxed C64 that hasn't been turned on for over 20 years I thought I'd try to turn it on but got spooked by the requirements for the PSU I understand i

by lmpdev 3y ago

I have a boxed C64 that hasn't been turned on for over 20 years I thought I'd try to turn it on but got spooked by the requirements for the PSU I understand it needs ripple free 5VDC 2-4A+ through a 7 pin din Am I really going to blow the unit up with a switch mode, does it really need linear regulation? What's stopping me using 2-3 LM7805s in parallel? [Background] former burnout frontend dev working at an electronics shop

unwind 3y ago
You are probably aware, but replacement PSUs are fairly widely available [1]. I am no EE but I would be very surprised if they are linear. [1]: https://www.c64psu.com/ https://www.c64psu.com/
dusted 3y ago
You can do it with a linear supply, a common mod that people do is actually to replace the lm7805 regulator with a pin compatible switching replacement for less power draw and heat generation. I think ripple-free is by 1982 standards ;)
HPsquared 3y ago
Can't you just use some filtering caps? (spoken as a non-EE)
lmpdev 3y ago
Edit: Do NOT use LM7805s in parallel, they don't load balance evenly
jwr 3y ago
The PSU also supplies 9V AC (this is not a mistake). The C64 is quite sensitive to over-voltage, so your switching supply might work, or it might kill it because there are voltage spikes which modern equipment doesn't care about, but the C64 will. The PSU situation isn't great: building your own is difficult (see https://www.c64-wiki.com/wiki/Power_Supply https://www.c64-wiki.com/wiki/Power_Supply), and using an old "real" PSU is risky, because they tend to produce >5V as they die, taking the C64 with them. That's why I ended up using the Ultimate 64 rather than a real C64: just supply it with 12V DC from basically anything, and it will be fine.
biggieshellz 3y ago
Why would you blow it up with a SMPS? I built a PSU for mine with a 5V switch-mode wall wart that originally powered a USB hub and it works fine. There's a 100uf filter cap on the 5V rail inside the machine already that will smooth things out. The real danger is letting the 5V rail get too much over voltage; that's what happens with the original power supplies, and it will cook the RAM chips in a hurry.

by lmpdev 3y ago

unwind 3y ago

You are probably aware, but replacement PSUs are fairly widely available [1]. I am no EE but I would be very surprised if they are linear. [1]: https://www.c64psu.com/ https://www.c64psu.com/

dusted 3y ago

You can do it with a linear supply, a common mod that people do is actually to replace the lm7805 regulator with a pin compatible switching replacement for less power draw and heat generation. I think ripple-free is by 1982 standards ;)

HPsquared 3y ago

Can't you just use some filtering caps? (spoken as a non-EE)

lmpdev 3y ago

Edit: Do NOT use LM7805s in parallel, they don't load balance evenly

jwr 3y ago

The PSU also supplies 9V AC (this is not a mistake). The C64 is quite sensitive to over-voltage, so your switching supply might work, or it might kill it because there are voltage spikes which modern equipment doesn't care about, but the C64 will. The PSU situation isn't great: building your own is difficult (see https://www.c64-wiki.com/wiki/Power_Supply https://www.c64-wiki.com/wiki/Power_Supply), and using an old "real" PSU is risky, because they tend to produce >5V as they die, taking the C64 with them. That's why I ended up using the Ultimate 64 rather than a real C64: just supply it with 12V DC from basically anything, and it will be fine.

biggieshellz 3y ago

Why would you blow it up with a SMPS? I built a PSU for mine with a 5V switch-mode wall wart that originally powered a USB hub and it works fine. There's a 100uf filter cap on the 5V rail inside the machine already that will smooth things out. The real danger is letting the 5V rail get too much over voltage; that's what happens with the original power supplies, and it will cook the RAM chips in a hurry.