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Short Version (More detailed version below)
Problem: Icom 706MKiiG will not turn on.
Steps Taken So Far:
Verified that power cord works on my spare 706mkiig
Verified that the control head works on my spare 706mkiig
Tried working control head on dead radio
Opened case and...
Nomad, you were spot on! Removing the green wire at point CS restored squelch function. Now to determine whether it's the scan switch or something else causing that short.
At least, though, this radio is usable again. I wouldn't consider the scan function to be a necessity.
Here's the results of TR12:
The Base pin shows ~0v with squelch at full left. Raises to 0.66v and stabilizes as you begin turning the squelch control to the right.
However... The Collector shows 0.7v with squelch fully left and drops to near 0 as the base pin reaches 0.66v
Measured voltage at the wiper of the squelch control: Tracks cleanly 0v (Squelch Fully Open) to 1.99v (Fully Closed)
VR3 can adjust that voltage a little more, but again everything tracks fairly smoothly.
Thanks, Nomad. I'll check on it later this morning when I get a chance. Not sure that's the issue though, as I tried bypassing the squelch pot with a fixed resistor during testing and still wasn't able to squelch the radio.
I'll let you know what I come up with.
I have a Cobra 29 LX that was working fine until a couple of weeks ago when the squelch stopped working. I can turn the squelch knob all the way to the right, and the squelch never closes. This occurs whether an antenna is connected or not, so definitely not a noise level issue.
C28 was located closer to TR13 than TR15. Lifting either leg of C28 caused the receive audio to drop out, leaving only a static hiss which is unaffected by squelch. Reconnecting either leg of C28 brings the receive audio back. (I've been running my Signal Generator with a 1k hz tone on...
Thanks for the information. I'm going to hit the bench again this evening and try to narrow it down. If I have a moment, I'll take a video of what's going on with the radio. I know sometimes that will help especially in a case of, "It's making a noise."
Parts arrived and I've started recapping the radio. I had several NOS TA7222AP audio ICs, so I've replaced the audio IC for good measure as well. I'll keep the old one around.
I've got a few more caps to do (about 6) but I powered it up on the bench today and right now the hiss is still there...
Thanks, everyone for the replies. Nomad, the noise doesn't go away completely when I lift pin 4 of the audio IC, but it does get much quieter. I can still hear noise in the speaker, though.
I had already begun to suspect capacitors, especially since this is one of the cobras with the 10v...
I recently picked up a Cobra 140 GTL (Uniden PC-385 board) and was in the process of bench testing it. When I first started testing it, I thought the squelch was malfunctioning, but I'm beginning to think it is something in the audio chain instead. Here is what's happening:
Sorry for the delay in response. I was out of town for the weekend.
The antenna is a Larsen professional NMO style antenna, trunk mounted on the vehicle. I tested a different radio and it works perfectly. Hook the Yeticom up on my repair bench, and it still has no receive.. Something...
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