User Port voltage at recommended maximum

[pquinton]

The USER PORT voltage comes directly from the 5V output from the power supply.  So, if you see 5.25V there then it will also appear on all of the logic ICs too.  5.25V is about the maximum you want to see.  I am surprised it is this high though.  What power supply are you using?  Typically, the Commodore "brick" power supply outputs >5V when it is about to die!  When they die the voltage can go over 20V, killing all of the chips.

Thanks for the info, it's a Commodore White brick PN: 251053-12 and I've just checked and it's measuring 5.25v at the plug. The PSU came supplied with a C64C I recently purchased (incorrectly as a donor.. long story.. didn't realise it had a short board in it)

Any recommendations on an alternative PSU?

Thanks,
Phil.