Thanks for the responses:
Don T wrote:Ok, what kind of trimpots are installed in the the thing? I've honestly never seen any that look like that.
hehe, if you don't know I sure don't; but they are 1kΩ variable resistors that appear to do the job when tested. I even switched two around to see if I had missed something and problem persisted on the +5V supply.
I've learned to never assume anything, therefore: Check for AC voltage across the two green wires coming from the transformer. Then check for DC voltage at the Anode end of CR15 or CR16 (which should be negative), and at the Cathode end of CR18 or CR17 (which should be positive)
Yeah I feared that it may be a problem with the transformer itself. I'm getting an AC voltage of ~25V across the blue and grey pairs and ~10V across the green pair. Is this correct? I can't seem to find any reference in the service manual.
It's quite awkward for me to probe the 4 big rectifying diodes when the unit is connected but I think I'm getting a small negative voltage on the cathode end of CR17 and CR18 contrary to what you said. I beginning to think I should just whip those out - a basic diode test indicated they were ok but I'm running out of components to blame here!
It may be worth replacing CR19, it's a 1N4748A zener diode, 22V, 1W. Zeners are a PITA to test.
Yep this was something I thought of too but I put in a new one and the problem persists.
Take Q7, Q6, and Q5 off the board and test them out of circuit. Be sure to also check them "backwards" for leakage using the diode test function on your DMM.
Let us know how those turn out! Good Luck!
I think they came out alright but I'll check them again.