Nice dude!
You can start selling them for big bux or what?!
Did we ever learn if iss20 boards are also defective after time or if that's a bit of a fluke?
I'm interested: I'm not sure if I should keep or move my TSL. It's the one amp that I've had to put the most into. But it's also a beast.
I just want to play, not fix amps.
It makes more sense to just replace the issue 20 board with a new one.
If you repair an old issue 20, all the filter caps still need to be changed, making it less practical more time consuming.
Yes the issue 20 board develops bias drift. The circuit tracks are too close together.
The issue 20 also burns between pin 2 and pin 3 of the output tube socket.
(check for a black spot between the pins)
The burned part should be cut out of the fiberglass. I used a dremel tool.
The bias adjust pots should be replaced every 3-5 years.
One more thing we missed before:
The 16 ohm speaker jack might be toasted / may need to be replaced.
Look and see if the plating on the switch contacts is discolored and test the switch contacts with an ohm meter.
(you knew the speaker jack has 2 sets of switch contacts, right?)
These switch contacts die from heat and it screws up the speaker impedance....
Anyway, that's what I found. A toasted 16 ohm speaker jack. Replaced that puppy too.
But overall, fixing the old board takes too long and eats up a huge amount of effort.
