Not that I need more gear but I just put together a deal with s fellow AKer for an AU-20000 that needs repair.
First off, this is the earliest AU-20000 I've ever seen referenced - it could be the 4th one ever made with S/N 215100004 - Oct 1975.
He brought it to a local tech who said everything looked good except for the power supply PCB (F2508).
I don't have complete confidence in that conclusion since he was unable to power it up but so it goes.
The guy does have a huge amount of experience but is also a bit quirky - locals likely can guess who I'm referring to.
But the PS board certainly does need attention as the power resistors have melted their solder joints.
I plan on completely redoing that board and would like to install larger wattage power resistors off the board (those gold chassis mount resistors) to prevent heat damage.
Looking at the service manual R11 & R14 are listed as 150Ω/5watt but the actual board (and other pictures I've seen) have a 120Ω and 150Ω in series (for 270Ω total). Mine also has a 1200Ω/5watt Carbon resistor on the back side which results in 220Ω total value.
The next curiosity is that there are 3 diodes mounted on the back of the board - not sure what's going on there.
Due to my work schedule this project may be a bit drawn out (plus I first have to finish up a friends Marantz 2270).
I have fixed a AU-20000 before so I'm comfortable working on it and the modular design with boards that unplug will make this less of a challenge.
First off, this is the earliest AU-20000 I've ever seen referenced - it could be the 4th one ever made with S/N 215100004 - Oct 1975.
He brought it to a local tech who said everything looked good except for the power supply PCB (F2508).
I don't have complete confidence in that conclusion since he was unable to power it up but so it goes.
The guy does have a huge amount of experience but is also a bit quirky - locals likely can guess who I'm referring to.
But the PS board certainly does need attention as the power resistors have melted their solder joints.
I plan on completely redoing that board and would like to install larger wattage power resistors off the board (those gold chassis mount resistors) to prevent heat damage.
Looking at the service manual R11 & R14 are listed as 150Ω/5watt but the actual board (and other pictures I've seen) have a 120Ω and 150Ω in series (for 270Ω total). Mine also has a 1200Ω/5watt Carbon resistor on the back side which results in 220Ω total value.
The next curiosity is that there are 3 diodes mounted on the back of the board - not sure what's going on there.
Due to my work schedule this project may be a bit drawn out (plus I first have to finish up a friends Marantz 2270).
I have fixed a AU-20000 before so I'm comfortable working on it and the modular design with boards that unplug will make this less of a challenge.