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Cobra 2000 Mod Meter Not Working

HavaV10

HavaV10

Active Member
May 24, 2023
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Lake Havasu City, Arizona
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.
 

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
 
Last edited:
nomadradio said:
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
Click to expand...
Yes the mod meter on the right will work in SWR mode. I just got done with a full re-cap of the 2000. Took forever! I will have a look and check C190. I will check for a solder bridge, I sure hope I didn't put that cap in backwards. Thanks so much for your time. You are always a very big help.
 
looked over the radio a little tonight. C190 is installed correctly. I see a brown wire in that area I need to trace back to the switch panel to make sure it's properly connected and I need to check for a short on the solder side as you mentioned.
 
nomadradio said:
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
Click to expand...
ok this what I found. This is right underneath VR7 and near C190 some kind of a mod with a jumper and a cut trace. Any ideas what this could be?
 

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That modification is called "Volting the (AM) Final". (or the RED Wire MOD)

It puts power supply voltage (13.8v) to the final while in the AM mode
by-passing the AM regulator's (TR41) lower voltage of just under 7v .....
This forces the radio to put out more power while in the AM mode.

The Final is meant to use the 13v while in SSB mode.

I would take the jumper wire out and let the radio use the radio's regulator (TR41) while in the AM mode.

73
 
Dr. Frankenstein said:
That modification is called "Volting the (AM) Final". (or the RED Wire MOD)

It puts power supply voltage (13.8v) to the final while in the AM mode
by-passing the AM regulator's (TR41) lower voltage of just under 7v .....
This forces the radio to put out more power while in the AM mode.

The Final is meant to use the 13v while in SSB mode.

I would take the jumper wire out and let the radio use the radio's regulator (TR41) while in the AM mode.

73
Click to expand...
thanks I'll remove the jumper and solder the cut area back together. Anything else I should check?
 

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