Cobra 2000 Mod Meter Not Working

[HavaV10]

Hello all. I have older late 1978 Cobra 2000. Works good. The modulation meter isn't doing anything when I key up and the switch is in the mod position on AM. Just curious if there is a transistor that switches this circuit on that might be bad? I have good audio out but the mod meter just doesn't do anything when I key up on AM. I checked and sprayed with contact cleaner VR7 with no success. There is a roger beep board in the radio but I don't think that has anything to do with that. Thanks for any help.

 

[nomadradio]

You didn't mention if the meter works in SWR mode. It's common for a meter that old to become mechanically seized on the inside. If the meter is free and moves okay, I'd suspect C190, a 0.47uf 50-Volt electrolytic cap. If all the radio's electrolytic capacitors are original, this is more likely. Running a radio that old with original electrolytic caps can become a game of electronic whack-a-mole as they fail one or two at a time from age and use. A radio that's meant to be dependable at that age routinely gets all of that type part changed at once. But there are factors. Mileage is hard to judge, but it's important. If that cap proves to be bad, I would contemplate re capping the radio. Or you could just use it until the next one causes mischief.

Not a small job.

Had a radio that had been recapped in the shop because the modulation meter wouldn't move. Turned out there was a tiny glob of solder shorting across the new capacitor in the modulation meter circuit. Removing the short fixed it.

73