cobra 29 classic, whats wrong?

Sounds like its times to get the SWR set.Check the connections and coax.

Did you get the new mic and it is still sticking on transmit?
How are you checking SWR? The radios internal meter is not very accurate.

 

Hiya. Sorry, I've been gone a week, or I'd have weighed in earlier.
By changing the mic, you've already pretty well eliminated the mic's PTT switch or cable as the problem. But rattling the radio to fix it probably eliminates the mic, anyway. BTW, as has already been noted, if you've got an original Telex mic, PLEASE keep it and get it repaired rather than junking it. I stumbled across a couple attached to junked radios and was happy to get them for the cheap price I paid for the dead (but repairable) CBs; the mics alone were worth what I paid for the clunker radios.

You mentioned that after you changed the mic, the SWR was high (how high, BTW?) Had you checked it before the mic change? I saw that you said the antenna was fine, but how had you determined that? Although it's unlikely that a bad antenna system would cause your TX to hang, unless the braid connection in the radio's end of the coax were open, or the braid inside the cab were horrendously leaky. But even then, the 29's case is steel and pretty well shielded, so it's unlikely that RF spraying around the outside of the radio would get into the guts of the radio and spoof the TX/RX switching circuit with rectified RF.

However, TR-21 is the TX/RF switch transistor, and transistors *do* get leaky, as can the peripheral components (capacitors, resistors change value, etc.) and improperly affect TR-21. My suggestion to isolate the problem would be to hook the radio to a decent dummy load, disconnect the microphone, and just momentarily jump the PTT pins in the mic jack, then remove the jumper. If the TX still hangs, then the problem is definitely inside the radio itself. You can also try plugging the mic in just far enough to make contact, key the transmitter, let go of the switch and then, if the TX is still hanging, just slip the connector back out of the jack. If the radio unkeys, it *might* be an intermittent short between two of the pins on the inside of the mic jack, but using a jumper instead allows for a somewhat cleaner test; a screwdriver tip or paper clip to short the pins removes the mic and/or mic cord from the equation.

If that test confirms the radio as the problem area, and you've got decent troubleshooting skills, I'd suggest looking at TR-21 and its supporting components. If you don't have a good DMM with some degree of RF immunity (can be as simple as an RF choke inline with the test leads), then I'd get the radio to a shop. A shop will probably want one of the mics you've got just so they can rule that out as the problem in the interest of thoroughness (and cuz lotsa shops don't necessarily take the word of a user as gospel; I know I'd prefer to have the whole unit as used because of that same reason myself).

Hope that helps, and that you haven't already gone down too many expensive roads with empirical testing yet.

73

 

Boomer,
You may be having two problems at once: an open (or shorted) coax, yielding that SWR of over 3:1, AND the TX holding in. TR-21 is the switch transistor to turn on the transmitter, and the control line to its base has a pretty big (big value) electrolytic transistor, labeled as "C-117". That sort of capacitor, called an "electrolytic", is prone to getting leaky. If yours has, then it *may* be taking a few seconds to charge up high enough to turn off the base of TR-21. If it were on my bench, I'd put a dummy load on the output of the radio to eliminate the antenna system as part of the problem, then put a voltmeter on the base of TR-21 and see if it stays low (where it goes to let the radio transmit) after letting off the PTT.

I'm currently in a orthopedic rehab facility for a leg injury, or I'd be happy to help. The HMFIC for my case estimates 6-8 weeks before they'll let me hobble out of here.

-- Stu --

 

Best wishes on recovery Handlebar! Hang in there bud!
Try not to chase those pretty rehab Nurses too much.....lol!

 

Yea Handlebar get done with that quickly, I will be thinking of you while I'm in recovery mode.. I will be in the operating room Friday morning at 5:30AM they tell me I won't be able to use my shoulder at all for 6 weeks. I hope I will be able to at least type so I can harass you all on the forum..And Hello to you to EZ..

 

Thanks to all for all the good thoughts. And Vintech, just keep in mind that, at 0530 on a Friday, your anesthesiologist and surgeon will probably have their minds on how they're gonna be spending their weekend. Part of my job as a surgical technician (during college and for awhile after) was to keep stepping on the surgeon's foot to keep him awake, and make sure the gas-passer wasn't diverting the anesthetic to a handheld mask for himself to kinda kill the time when he'd rather be asleep.
(Yes, I'm j/k.)
My "smarter half" is in charge of reeling in the better-looking nurses for me. Only two of my legs will bear weight, and the one on the far right is not one of them.... FWIW, the wife rolled her eyes and mumbled something about "keep dreaming, fella" at that one.

73

73

 

I can't begin to tell you how much better I feel now.. How can I ever repay you for this wonderful information.. I think I will double my prozac and take a shot of whiskey just before they cut me open..Thanks again Hbar!!!

Vintech 73's I think?