Recently, I got a very nice but non-working HP 3335A, with a defective power supply.
After a little wait, the spare PNP power darlington transistors arrived. 2N6052, pretty general purpose power transistors.
The look very shiny and heavy chromium plated, I got 4 pcs, and two had some marks of screws, and 1 had irregular connection wires. Doesn’t look like a genuine Motorola, but well, it is no rocket science anymore to make PNP darlington transistors.
After installing the transistors (I checked the contacts on the board, they seem to be good), some quick test with the load transistor showed perfect regulation of the power supply both on the -15 V and -5 V rails.
With the module assembly connected, unfortunately, the -15 V rail goes up to about -3 V, by current limit regulation.
No other way to find out than by checking module by module. The 3rd last checked turned out to be the faulty one – A7 assembly, mixer.
A little shorted 2.2 uF cap…
At the far lower left.
Replaced it with a 10 uF ceramic multi-layer capacitor.
To check the quality of the transistors, I sacrificed one piece, and cut it open – seems very solid inside, with copper heat spreader, well-mounted die, good bonding wires. So even if it has not been made by Motorola, it seems like decent quality.
Now… doing a proper test…. several hours on, to see if there are other weak links. The attenuator at least is working, and the output is good!