Quasar WP3422QW only stays on for a couple seconds

[blue lander]

Originally Posted by zeno

Good tips so far. Next step is check the 130 V line. Put meter on that
and slowly turn up variac. The 130 V must not go over 130 V. If it does
you have a regulator prob. If it shuts down on 130 V its a HVSD problem, not shown on the schematic, probably a bad zener diode.

Zeno

With the Variac set at 90VAC I measured the 130V at 124V. I raised the variac to 100VAC and the 130V was 138V. I didn't go any further than that but I guess that confirms it's a problem with 130V regulation?

Should I adjust the 130V pot? It's got some sort of goop on it to keep it from being adjusted

[zeno]

Yes its the regulator. Q801 the most likely suspect. The pot was
part of the old kit. IIRC a zener diode also. Shouldnt need to adj it,
most times its a hard failure of a semi.
BTW on these & its Panasonic cousins the front controls would freeze up. A few
drops of WD 40 lubes & cleans them.

Zeno

[blue lander]

Thanks - I'll start with replacing Q801.

I found this "Service Caddy for TS-969" on eBay but none of the part numbers seem to match what I'm looking for https://www.ebay.com/itm/204578889156

[blue lander]

I replaced Q801 but I get the same behavior - works with variac set to 90VAC but not at 110VAC. Anything else I should be replacing?

I haven't tried adjusting the 130v pot because it's been covered in some sort of epoxy or potting compound. I might be able to get it out with a dremel, otherwise I'd probably just have to replace the pot itself.

[blue lander]

I replaced C809 and C812, made no difference. I'll try replacing the 2k potentiometer and see if turning that changes the voltage or not. I'm measuring an open circuit between the wiper and either leg on that potentiometer so it's either bad or dirty.

[vol.2]

Originally Posted by blue lander

I replaced C809 and C812, made no difference. I'll try replacing the 2k potentiometer and see if turning that changes the voltage or not. I'm measuring an open circuit between the wiper and either leg on that potentiometer so it's either bad or dirty.

Before you go throwing more parts at it, you should start by checking some voltages. If you look in the schematic, you can see that voltages are called out at points around the transistors and other substantive junctions.

If you can confirm that voltages are all correct around a transistor, then you probably have a working transistor.

If the voltages aren't right, then pull the transistor and do a diode test on all of the legs to confirm it's still a transistor. If it looks good and the voltages are wrong, then you have more information about where the problem is (depending on which leg(s) of the transistor are wrong.

Then you just keep going this way until you encounter a bad part.

[Alex KL-1]

Like, if the out seems to following the output, triggering protection with full input, maybe the Q802 is defective or some part around that.

[blue lander]

I used a knife and small saw to chisel the melted plastic off the 130v adjustment potentiometer and gave it a blast of deoxit and that did the trick! Thanks for the help everyone