Subj : Re: C128 and C64 OS
To   : Robert Roland
From : Adam Sampson
Date : Tue Aug 20 2024 12:38 am

Robert Roland <[email protected]> writes:

> Do you have any references for this? I mean, actual facts.
> Have you ever seen an overvolting C64 PSU?

I found one earlier this year -- an Ismet-made wedge PSU that came with
a breadbox C64. The output was approaching 5.2V at the C64 end of the
cable under load.

Having dismantled it, the reason was that it uses a 7805 regulator with
a resistor divider to lift its ground reference pin a bit, and the
resistor values had drifted considerably. The PSU runs quite hot (not
helped by the heatsink and 7805 being buried in potting compound), so
this isn't terribly surprising after 40 years.

Initially I just replaced the resistors, which worked fine, but I later
found timperi's replacement PCB that uses a modern switching regulator:
 https://github.com/timperi/c64-wedge-psu-pcb
I've built a couple of these now (using boards from an eBay seller) and
they run much cooler than the original.

Thanks,

--
Adam Sampson <[email protected]>                         <http://offog.org/>

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