Yesterday I received a donation of #Commodore hardware from a childhood friend, including this lightly used #Plus4 in its original box, with perfectly preserved manuals.
In spite of its excellent conditions, this #Plus4 does not power up at all
The AC fuse in the PSU and the DC one on the motherboard aren't blown, so my next suspect is the "wedge" power-supply.
These PSUs made by #Commodore in the '80s are known to fail often. Sometimes, they even output higher voltages on the +5V line which powers ALL the chips on the board!
But this isn't the case: the power LED is steady off, and I measured near 0 volts on VCC pins.
Last night I carefully opened the #Commodore wedge PSU with flat screwdrivers, but the interior is filled with a potting resin which is stuck to the box.
I measured +5V after the regulator, but it drops as soon as I connect the #Plus4 board.
If the board was shorted, the fuse would have blown. So I guess the regulator is unable to source more than a few milliamps.
I couldn't make further progress without tools. I'm literally working from my mother's kitchen!
I detached the #Plus4 keyboard to test the power LED with a battery: it works.
I cleaned the contacts with isopropyl and plugged the flat cable back on the board and now... IT WORKS!
Was it just an oxidized contact? I'm not sure.
Anyway, the tuner video signal is very noisy. I wrote this short program to test sound output.
First time I play with the BASIC V3.5 multimedia commands, and it's awesome!
@codewiz what do you measure on the power plug? Careful not to short out the pins! :)
@codewiz another candidate is a corroded power switch. Can lead to „no power“ symptoms.
@root42 Aha!
By the way, I found schematics and service manuals for the Plus 4, but couldn't find gerbers or pictures to help follow traces on the board. Know where to look?
@codewiz no, you go by the silkscreen on the board. :)
@codewiz yeah I guess the regulator is borked. Ditch the old PSU, buy a round DIN socket for the Plus/4 and use a modern C64 PSU. Sad that the PSUs are all potted. Otherwise one could easily repair them.
@root42 Even these C64 -> Plus4 adapters cost a lot, like 15 EUR + shipping.
Ok ok, I guess spending 2 hours repairing a PSU would cost more, but... isn't it more fun?
@codewiz if the PSU weren‘t potted: go for it! That’s why I love the original 1541. You can repair the whole PSU section easily.
@codewiz Check for anything in the Plus4 that's hot - it's possible the PSU is delivering the 5v to something that isn't quite a short; I had that recently in a PoE switch.
@codewiz what exactly did you clean now? Power supply socket / plug?