another 2000gtl problem

[dirtyjob]

have this cobra 2000gtl, theres voltage on the chassis, if you touch a mic, say a turner plus 3 or any metal mic to the metal faceplate of the cobra it arcs !!!, What is causing this and what is the fix please, anyone.

[Bluerunner]

Is it arcing just with the key down or even while just listening?

Check the mic wiring and its ground to chassis

If only with the key down it could be Common Mode Antenna (CMC) Currents. A coax choke might fix it.

Read the voltage between the mic frame and radio chassis. If it is around 12 VDC it is probably the mike wiring. If you read low voltage AC that changes with the volume control it is probably the mic wiring part that interrupts the audio to the speaker on transmit shorting.

If it is around 110AC, check the 110AC chassis plug & wiring to the primary of the radios power transformer, chassis and maybe too long circuit board screws that might be touching. check any of the small bypass capacitors on the 110 AC side. Sometimes a bent chassis can touch something hot on the circuit board too.

Static electricity can be picked up by the antenna and the coax can act as a very long linear capacitor and build up quit a charge. When I worked on a offshore oil platform we had a TV antenna (A Gerold direct 75 ohm connection, no 300-75 ohm transformer at the antenna (about 300ft above the waterline & maybe 200ft of coax from the antenna to the TV distribution amp in the quarters). I bumped the coax connector with my arm. The shock knocked me down and left my arm jittery & numb for 20 min. I found that I could burn my initials in a metal tabletop with the arc from the center pin of the coax connector. There was a storm on the horizon, but clear blue skies where I was. Ok when hooked up to the distribution amp, something in it would bleed off the charge. Just a little strange but true story.

Just some suggestions. I have experience all of the above when fixing problems on different radios.

[MDYoungblood]

I'm guessing no toy's like echo or a RB are installed. With what is happening something is shorting positive voltage to ground. Does it do this with any mic or just the Turner?

3's

Greg

[dirtyjob]

any mic or anything metal for that matter, ya its strange for sure, its not on keydown, its anytime anything metal touches this radio, also i noticed if i turn down the volume and turn up the dynamike i hear a local am radio station "broadcast station" through the speakers, I also hear myself when i modulate through the speakers and this radio has no talkback installed, i looked to see if someone had bridged the speaker/pa jacks and there is nothing.
I will check all that was suggested, ty for the ideas. I will post my findings when i can.

[nosaj]

As soon as you can tell us the voltage between the mic and the chassis it will clue us in.
If 110Vac could be caps in the picture attached[Please login or register to view this link]
Nosaj
KN4UCQ

[dirtyjob]

will do just had to replace my multimeter, i'll take the voltage readings and report back

[dirtyjob]

oh and i just noticed for some reason c71, parts list says it should be a 0.001uf 50 volt mylar is now 2 ceramic caps in series. Hate used radios sometimes