Bad C64 PSU?

[freddy]

Folks,

I have two different C64 PSUs, one is from C64 (whose box is hosting 4x v1 SIDs) and a C64-II PSU. When powering either 4x v1 SIDs or 4x core v2 MB6581 with the old C64 PSU, everything works as a charm.

When using C64-II PSU, for the 4x v1 SIDs I get _lots_ of humming in the resulting mixed channel (but the SID modules do work, actually), v2 MB6582 even doesn't power up properly - the 4x20 backlit LCD gets lit, first and third line are blacked out and I cannot get any further, no CS LEDs lit, but the humming can be heard.

When I measure the voltages, +12V for SIDs is okay in both cases, but instead of 4.99V I'm getting with old C64 PSU I only get +4.45V for PICs, 5V fan, HC595, LC256, etc. When I measure unloaded PSUs, for the C64 (old one) I'm getting +5.22V, for the newer C64-II barely +4.03V.

I suppose this humming is caused by low voltage, as is the "unability to boot" (because of higher load of v2 MB6581), but can someone audio-skilled confirm this before I start opening the C64 PSU? Any similiar experience (i.e. to what to look at inside the C64 PSU)?

Thanks.

[Natsirt]

i.e. to what to look at inside the C64 PSU)

I would hazard that you'd probably be disappointed by what you found, were you to open one.

AFIK, most of these supplies aren't really serviceable; All of the electronics are housed in

this icky resinous goo, and I've found that the plastic case likes to eat fingers for breakfast...

[Goblinz]

I would hazard that you'd probably be disappointed by what you found, were you to open one.

AFIK, most of these supplies aren't really serviceable; All of the electronics are housed in

this icky resinous goo, and I've found that the plastic case likes to eat fingers for breakfast...

I was very pleased with what I found in my broken C64 CPU ... A burnt out fuse :D