Weird SWR amp problem.

[ChrisW]

SWR California Blonde crackle

It's just the same as those other Workingman combo's with the cracked legs on the output transistors. Probing with a meter on a California Blonde I was touching the soldered portion connected to the board showing voltages. Then I started doing continuity checks since other voltages were missing in places. At that point I tested for voltage high up right on the pin of the transistor and 0v is what I got. Got out the magnifying glass and sure enough hairline cracks just above the joint on the board right through the legs.

Also, there is a crossover board in the back and I imagine something could be loose in there too. There is a drawing diagram of the California Blonde crossover attached to one of the schematics out there, but it was different than the unit I repaired.

Hi

Hi I have a similar problem here, but the crackle happens after about 5 minutes of warm up... so I am looking for cracks in transistor legs. To do this, I would like to remove the power transistor clips but it looks almost impossible to put back in place... any advice here? Second thing, there is a component below the board labeled D6 (guessing rectifier bridge) but there is an airgap between it and the heatsink. Is that ok, or should I get it in thermal contact with paste and pin height adjustment?

Thanks!
Chris

[glebert]

I remember the heat sink clips seeming like a bigger deal than they actually were. IIRC you can work them on slowly and lift up the legs a little to get them to slide up onto the transistors.

[ChrisW]

I remember the heat sink clips seeming like a bigger deal than they actually were. IIRC you can work them on slowly and lift up the legs a little to get them to slide up onto the transistors.

Thanks for the feedback. I cut the HS into sections with my dremel and it worked like a charm. No cracks in the transistor legs, but this seems like a thermal thing so I redid the thermal interfaces. But otherwise, could the transformer be the thing heating up and starting to crackle?

[ChrisW]

fixed thermal issue SWR California Blonde

Just to follow up on this thread... here is a summary for those repairing a SWR California Blonde with a thermal issues. In my case, the crackling behavior was certainly thermal and always started happening after 5 to 10 minutes of warmup. There were no cracked transistor legs visible. I found two adjacent TO220 transistors (appearing to be part of the preamp stage on the front board) with heat sinks that were not in good contact with the components. Removing the heatsinks revealed no thermal compound. Added thermal compound. While testing, these components get very hot. For good measure added new thermal compound to the output transistors. Amp reassembled, problem appears to be solved (at least no crackle after 2 hours at moderate volume).