[DaleHCook]

What make and model of power supply are you using? Is it regulated? Have you tried measuring the current drawn by the radio?

[462ron]

Hi R3, just glancing over the schematic,if C1 and C2 are good and they appear to be by the voltage you are getting on TP 18&19, then I would check X6, the output transistor next, the big one probably mounted on a heat sink. It would appear that if it were shorted, it’s the only transistor that would pull enough current to melt wires as it only has a .68 ohm resistor on the emitter and the output transformer on the collectors to limit current draw, so if shorted would have the ability to put a heavy load on the 12.6 volt supply. The other transistors appear to have a decent amount of resistance in their circuits. Not saying you shouldn’t test those but X6 would be my first one to test and they are known to short.

Ron

[morzh]

Is your power supply adequate? Perhaps it cannot source the current required.
Or...bad transistors.

[DaleHCook]

Perhaps I am missing something - which volume (AR-28 or AR-33) has the 6TPZ?

[R3Sons]

Thank you all so much. First the power supply: "KORAD KA3005P - Programmable Precision Variable Adjustable 30V, 5A DC Linear Power Supply Digital Regulated Lab Grade". I've done a lot of things with this power supply, electroplating, battery charging, prototyping projects. Always been very reliable. I thought it might be the problem, so I tested it on a few things with a lot of draw. Rock steady. I limited the draw to .5A. When I raise the limit the radios will draw much more. Not instantly, but gradually.

Thank you ron. I can't fit this into my transistor tester, so here's the multimeter diode test results:
B-E OL
E-B 0.14
B-C OL
C-B 0.13
E-C 2.6
C-E 2.8

Dale, I will try to visually confirm which one.

Thanks again.

[R3Sons]

Here's the readings from the AR14 (No markings on the one from the 5TPO) on the 6TPZ:
B-E OL
E-B .14
B-C 2.9
C-B .13
E-C .15
C-E 2.9

[morzh]

1. Have you tested out of circuit?
2. If yes, any transistor not showing E-C as OL is bad.

From your measurements, all your transistors you showed heea, are bad.

Best way to test:

analog meter. Set on Ohms x1.
N-P-N transistor:
Red is plus, black is minus.
EB - RED-BLK - open, no movement at all
EB-BLK-RED - conducts well.
CB - RED-BLK - open, no movement at all
CB - BLK-RED - conducts well.
EC, CE (colors don't matter, but test both ways) - open, no movement at all.