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Thank you guys. This site is so helpful when I get stumped. The other techs on here are the most knowledgeable people I've ever had the privilege of speaking with, very detailed to learn from. They don't just tell you what to do, they explain how the circuit works so you'll learn from it. I...
Got it guys. Transmit back up to par.
Culprit?
R123 was open, showing no ohms in circuit. Yanked it out and checked it, still no ohms. Replaced with new 1 ohm 1/4w 1% and bingo, output is back.
Thank you guys for helping me out.
R62 left side lead voltage in receive is 2.72v.
R62 left side lead voltage in transmit is 2.07v.
If I'm counting the pins right, IC1 (PLL) pin 15 voltage is 2.40v.
Radio receives great on all channels.
Removed R56 from circuit. The bead wasn't cracked, it was that glue on it that made it look like it was cracked. Replaced it with another one anyway, along with the resistor (resistor tested at proper ohms), still no output, same results.
TR16:
Voltage chart calls for GDS from TR16, but doing a...
Almost every 142 I have ever repaired, aligned, tuned would backswing with the deadkey around 5w. After alignment, I normally set the deadkey to 3w and it will swing forward up to 5.5w in average, and around 12w to 15w peak.
I would say old dried up caps may be the issue. Or it could be that...
Thanks Brandon, you got darn good eyesight. I checked in that area time and time again, never even noticed that. I'll swap that out and get back with you.
Would this also keep the base and emitter of the driver at 0v in both receive and transmit?
Here are a couple shots of the results when I tested the driver and final in my tester.
Final:
Driver:
Here are shots of the entire board, topside and bottom.
Bottom:
Topside:
A few more shots:
Haven't checked the voltages in the transistors mentioned earlier by others, but I will...
I do have an oscope (100mhz). It's a digital scope though.
I have an old analog scope too, I unhooked it cause I'm rearranging my desk around.
I can use the digital scope to snoop around that area right, or would the sniffer probe be better?
These are the only surface mount components on this one.
Left side of board (radio facing you), near audio IC. And no, that's not a solder joint touching the 2 traces, it's that sticky flux.
Center of board and around VCO.
No those are not solder balls, that you may see here and there...
My bad,
Collector of both driver and final in receive mode is 13.26v.
Base of DRIVER in receive mode is 0.06v.
Emitter of DRIVER in receive mode is 0.00v.
In transmit the collector of the DRIVER is 12.45v.
In transmit, both the base and emitter of the DRIVER are 0.00v.
Collector of FINAL in...
Got one of these brand new Cobra 29 LX Max radios on the desk today with a no transmit issue.
Collector of Driver in receive mode is around 16v, hmmm...
Collector of driver in transmit mode is 13.4v.
Collector of Final in receive mode is around 6v.
Collector of Final in transmit mode is around...
So, to clarify all that's been done to this radio:
All 10v, 16v and 25v caps have been replaced, except the 50v caps.
FL1 455 Filter replaced.
FL3 SSB filter replaced.
TR52 replaced.
L8 replaced.
L13 replaced.
L14 replaced.
10.240mhz crystal replaced.
10.695mhz crystal replaced.
C67 replaced...
It's all good shadetree, I get mixed up on these radios and posts at times myself.
I think I got it.
Replaced C37 (I missed that one earlier when recapping), touched up alignment. I now have meter movement on SSB as well, when there are stations rolling in. Gonna leave it as is.
I noticed that before I replaced TR52 and C193, if I touched the front face chassis edge with my arm and also grabbed the PL259 of my coax, I would feel a DC tingle in my finger and arm. After I replaced those two parts, I don't get that tingle any more. That's an improvement.
And for...
Replaced FL1 (455 filter), no change.
Replaced C89, no change.
Aligning the SSB receive with the RF generator goes smoothly, everything goes great, but not when hooked to an antenna. Antenna is the same antenna I always use with no issues ever, SWR is 1.1, all jumpers and coax are tuned...
I know TR18 is one of the FETs you're referring, but which is the other FET?
TR18 voltages are correct according to voltage charts. And it's placed in the same orientation all these export radios have TR18 placed, backwards from what the silkscreen on the board shows.
Changed a few more parts that seemed suspicious this morning.
Changed L8 with a known working one of the same value. No change, I had to almost bottom this one out to for receive to peak.
Changed C17, very little improvement in SSB receive.
Changed C67. No change in results.
Replaced TR52...
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