Cobra 148NW ST- No TX

[DesertDog]

Hey, guys. Git a bit of a problem here with this 148. Radio powers up and receives just fine(although channel display is a bit dimmer than I think it should be), but when the mic is keyed, S/RF meter jumps to max right, then drops back down. No modulation or carrier. I haven't opened it up yet as I wanted to check here first for suggestions as to where to start. I only have a VOM for testing, so I didn't want to go poking around in there without any direction. Thanks.

[ramblingman]

hi there,,sounds like to me,the voltage regulator has shorted......
does it have the ept0148-11z pc board

[Rick]

Is the TX LED (Light) on when you key-up?
Try the radio in SSB and AM to see if you have the same fault?

Rick.

[DesertDog]

Yeah. I did that. should have mentioned it before:oops:. TX light is on when mic is keyed both AM and SSB. I also checked the TX with a hand-held, it does transmit, but the signal is very weak and low modulation.

[Rick]

It sounds like the Final has gone south this is TR36, but maybe worth checking as below and let know what you find.

What is the voltage on the Collector of TR36 and TR38? and what is the voltage at each side of R166? all test in AM Mode TX.

Rick.

[DesertDog]

Ok. Here's what I got from the test, Rick: R166 shows 0.80 output side, 2.56 input side. TR38 -0.05 on collector, TR36 0.0. all tested on TX like you said. Looks like, yeah the final is DOA. I have another radio I can cannibalize( President Adams). Might I be able to use the finals from that radio?

[Rick]

Before you change the final, check the voltages around TR41 and TR42, the collector should be about 13 to 13.8 volts and the emitter should be about 12 to 13 volts if check the mode switch on 13 volts.

Rick.

[DesertDog]

Gotcha. I'll get to it later in today. Thanks.

[148]

mine did the same thing everytime it did it it was the final