Cobra 139 Repair Help

[Wraith]

Hello, i know that this post is quite old, but i recently got myself a cobra 139 and the transmit does not seem to work on it, the main 13.8V drops to approximately 0.3 if not less, i’ve been trying to fix it, but to no avail, should i also attempt to replace all capacitors? Or could the problem be hidden somewhere else?

MODBREAK_HEADBozo

Since the other topic was older, I have created a new topic since it is a new question. The other topic was based on a previous user inquiry on the forum.

[Bozo]

Welcome to the forum, @Wraith

The issue you're facing with your Cobra 139's transmit function sounds like a tricky one.

replacing capacitors could potentially fix the problem, it's also possible that there's another underlying issue causing the voltage drop.

Before jumping into capacitor replacement, have you checked the wiring and connections thoroughly? Sometimes, a loose or faulty connection can lead to voltage drops. It might be worth inspecting the wiring and ensuring everything is securely connected.



Keep us posted on your progress, and don't hesitate to reach out if you need further assistance!

[Wraith]

Ah, thanks a lot, Bozo, i am pretty sure that there’s no wiring problems as i have studied the station many times and didn’t notice much except for the PA switch packed full of olive oil (i did clean it out though).
I was suspecting that i might’ve blown up the final or uh… Output transistors? (Sorry for not being aware of proper names of those parts of the station, i’m still very new to this) but i have pulled them out, checked and they seem fine.
Been checking all components that would dump the voltage to the ground if shorted but it didn’t result to much except me questioning my life choices.

[Wraith]

So, i got the 3.5 volts on after finding a dead zenner’s diode but now i noticed that the s/rf pwr meter does not budge when the station is in the receive mode which is… Weird because previously it did jump up when turning on the station.
I’m quite tired of this station and trying to fix it…

[Swanman]

I know this is an older thread. One little trick I learned working on computers and radios. Look at the little round barrel shaped capacitors. On the top, most of them have a tri-pointed star like a Mercedes emblem. Look for obvious leakage and if any are bulging or split. Sometimes visual inspection can beat testing of components. If you find one showing signs of malfunction, fins a replacement out of a junk box or radio. When you desolder a bad one, make sure you note the polarity for the replacement.

Years ago a Chinese manufacturer made thousands of them that were never up to par and would fail at odd times. I've found a lot of LCD TV's that have been put by the curb only to find that one or two bad capacitors.