Radio keys up constantly (with or without a microphone). Besides that, everything works. A quick check of PTT pin 3 does NOT show a short to ground.
What info can I provide for further help?
What info can I provide for further help?
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Cobra 29 Constant Key Up
- Thread starter Chris Lawrence
- Start date
I believe this is the schematic https://web.archive.org/web/2019071...ra/29ltd_chr/graphics/cobra_29ltd_chr_sch.pdf
Aligning Cobra 29, stuck on the TX part
https://web.archive.org/web/20170329045752/http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29_ltd_classic_sch.pdf The notes by Rick Jackson on the left side of the schematic (above) suggest this: Check C117, I (personally) have seen this capacitor go bad or even...
Simply unsoldering the center lead of TR21 so it can't touch the rim of the hole will reveal if it's forcing transmit mode.
73
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I would check C117 first, TR21 is forced into Transmit mode if C117 is shorted, or even partially shorted, just enough to turn TR21 on. I have seen it quite a few times. Rick Jackson of Euroradio has seen it enough to put in the notes along the left side of the schematic.
In the Cobra 25 LTD series, C114 is the same capacitor in the same (general) place.
In the Cobra 25 LTD series, C114 is the same capacitor in the same (general) place.
Thanks. I’ll be checking all these things the first chance I get today. Will let y’all know.
Update: I was in the correct area yesterday as I was trying to trace down the issue. TR21 has 7.24/7.93/8.05 volts to each leg. Unsoldering center leg unkeys the radio.
Today: Replaced C117 w/ new and no change. Lifting r95 also unkeys radio.
Today: Replaced C117 w/ new and no change. Lifting r95 also unkeys radio.
Thanks. I replaced c117 w/ new. TR21 still receiving ~8vdc
Thanks Nomad. Middle leg is receiving 8 volts. Desoldering center leg unkeys radio. Trying to trace down the short.
Thanks Nomad. Middle leg is receiving 8 volts. Desoldering center leg unkeys radio. Trying to trace down the short. Lifting r95 also unkeys radio. I guess it feeds tr21(?)