General HP40W, Weird combination of component failures..

[radio429]

Got this one working fine this evening. Had the typical full power tx with no modulation failure. AM Amp regulator TR-51 was shorted. That immediately fixed that issue. Then noticed weird RF output power levels and lack of stability. Found both VR10 & VR11 were open. Neither of them look diddled with, replaced and reset biasing on the IRF520's. Then found signal meter would not deflect at all on TX. VR8 was open! Then on RX just the little bit of receiver noise floor had the meter deflecting half scale. Pumping just 10uv or less into the RX would peg the S meter! moving VR1 had no effect. Found VR1 open! I guess what I can't quite believe is that all of this is coincidental or because someone diddled with all those VR's and burnt them. Didn't any look worn or messed with. After replacing them all and calibrating the meters with the service monitor, all is well! Just suspicious that some underlying event took all them out. Maybe a stray induced voltage from a nearby lightning hit?? If so I would expect finals gone. None of them are bad! Weird stuff. Anyone else have a similar type of parts failure combination on a non screwdrivered radio?? Just wondering!

 

[Eldorado828]

Curious, by chance did you try to clean the vr's before replacing them. Just wonder if everything was coated in that varnish looking crap that's left after they clean the boards before assembly. I've seen that stuff almost seize them up before.

 

[radio429]

Curious, by chance did you try to clean the vr's before replacing them. Just wonder if everything was coated in that varnish looking crap that's left after they clean the boards before assembly. I've seen that stuff almost seize them up before.

Didn't bother, but I still have those VR's and might check them for that. The RCI-69 radios have been absolutely terrible for that crap!! I nearly always replace any when they start doing that, I don't trust they won't do it again. Thanks for that thought!

 

[nomadradio]

Sure makes it sound like an oxidation/contamination issue. Base radios with a perforated top cover will get this way after a few decades. Trimpots toward the front end of the circuit board won't have any environmental dust/schmoo on them. But the same type trimpot at the rear will be visibly rusty or crusty or both.

Any chance it rode in a dump truck just a bit too long?

73

 

[radio429]

Sure makes it sound like an oxidation/contamination issue. Base radios with a perforated top cover will get this way after a few decades. Trimpots toward the front end of the circuit board won't have any environmental dust/schmoo on them. But the same type trimpot at the rear will be visibly rusty or crusty or both.

Any chance it rode in a dump truck just a bit too long?

73

Nope, this radio looked nearly new. Don't think these HP40W's have been around all that long anyhow. Did get around to looking at the pots a little closer, black powdery and comes off easily on your fingers. Didn't do any more investigation and trashed them. Puzzles me, really looked like they were just made that way and not really any burnt smell coming from them. Anyhow, they are long gone. If I ever see another one like this it would really prompt me to investigate a little further! Me thinks just factory defective pots that didn't have the resistor carbon path baked on correctly? Never seen such before nor seen the manufacturing process of these little pots but really do suspect they were just not made right in the first place. I am not knowledgeable in potentiometer manufacturing but my guess is that these parts skipped a finishing process at the manufacturer. Might seem like a far fetched explanation but is as good a guess as I can come up with now.

73

 

[towerdog]

My guess would be exposure to moisture over a very long time. I had a rusty old Kenwood HF rig like this, worked great when it worked but always something burning out, vco not locking or relay not clicking. Resins, various varnishes, flux all break down and change over time too, vco was an easy fix but it was everything from knobs to caps until I finally gave up and sold the cursed thing

 

[radio429]

My guess would be exposure to moisture over a very long time. I had a rusty old Kenwood HF rig like this, worked great when it worked but always something burning out, vco not locking or relay not clicking. Resins, various varnishes, flux all break down and change over time too, vco was an easy fix but it was everything from knobs to caps until I finally gave up and sold the cursed thing

Hard to say, looks hardly used and it's back in the customer's hands. Thanks for the replies!