Just checking in and saying hi....

[Cable Guy]

I have seen this on a different chassis, in that instance it wasn't an active device experiencing a thermal problem, it was a pad that was pulled away from the board slightly and the trace would make contact while cool, but pull away just enough to kill the circuit when it got to normal operating temperature.

 

[guitar_199]

I have seen this on a different chassis, in that instance it wasn't an active device experiencing a thermal problem, it was a pad that was pulled away from the board slightly and the trace would make contact while cool, but pull away just enough to kill the circuit when it got to normal operating temperature.

Thank you for that!!!!!!!!!
I will give that area a good "eyeball" with my magnifying hood.....and maybe my phone camera (shoot the shot as closely as I can focus and then "pinch spread" it out...). Thanks again!

Bob

 

[Cable Guy]

Thank you for that!!!!!!!!!
I will give that area a good "eyeball" with my magnifying hood.....and maybe my phone camera (shoot the shot as closely as I can focus and then "pinch spread" it out...). Thanks again!

Bob

Apparently someone was fingering around the radio wiggling and pushing on components, I imagine that's what it was that caused a separated pad/ripped trace. Just so you know, a cold solder joint can do the same thing. Sometimes you can't see the cold joint. I hope you get it figured out Bob.

Greg

 

[brandon7861]

Investigate circuit trace 10, the white wire. I don't have the schematic, but it looks like that wire serves to disable transmit. The PLL could be falling out of lock and providing this line with voltage to disable TX.

If cable guys loose joint theory doesn't pan out, I might temporarily remove the white wire and see if the keying circuit comes back to life while taking the opportunity to monitor the output frequency. Be quick on the key, there's a chance for a mismatch at the final/filter if the VCO frequency did change..

 

[Cable Guy]

Another point, I often find shorted/leaky electrolytic caps in radios this vintage. When I narrow it down with voltage measurement to the area affected, check the continuity from the point missing voltage to ground. If the schematic shows no paths to ground except through a cap, but you read a low resistance, and the active device is okay, check the caps. Since you have no modulation or PA, I would consider checking capacitors around that circuit also after verifying Brandons pll lock advice. There are a number of possible faults, these seem to be most common.