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Cobra 25LTD Classic

Smokinone

Smokinone

WDX-3820
Jun 24, 2020
778
965
103
Southern Nevada
My neighbor brought me over a Cobra 25 that has no receive and no transmit. I get sound from the speaker when I touch certain parts of the circuit board. I have nothing out of the PA as well although I do hear scratchy sounds when keying the mic. I have tried other known working mics.
No transmit or wattage perceived when keying the mic. I do have 10.240 at the crystal, and do have the correct voltage at the VCO.
I am at a loss from here on.
If someone could give me a few clues on what and where to look I would appreciate it. I do have multimeter, freq counter and scope.
This is a virgin radio as well. I have looked for TSB's but find none for this radio
Thanks for any help I can get.
73's
 

Just another note, I do have the correct frequencies at the below test point for channels indicated.
TP3 by the RX 1st mixer FET should have
16.270 in RX on CH 1, or
16.710 in RX on CH 40.
 
Hmmm.. I have one like this, been a little over a year since I looked in it, so I don't remember details of troubleshooting it. Mine is a newer one, with the "Cobra" I think it says on it PLL chip. The PLL chip is dead. Rest of the radio is great condition. I just kept it around for parts or when I get an ugly radio in with a good PLL chip for it...I tried swapping in an older non "Cobra" PLL chip, no workie. If I remember right it was kind of common to see dead PLL's with the "Cobra" stamped on them (all newer radios, not the old shool real Cobra 25 Classics).
 
I didn't really pay attention to the china manufacture. I have to admit that it does look pretty new, and has a 2000 manufacture date. I had a Cobra 148 front mic that was junk, china made. Went to a shop and couldn't be fixed.
I'll see if I can find some voltage charts maybe and look at the voltages on the PLL. It is the Cobra marked PLL. Don't know if I'll spend too much time on it other than dusting off my equipment;)
Thanks for the info 443.

cobra25pll.jpg

These are the voltage readings from the cobra marked PLL. Highlighted are the inconsistent voltages according to the chart from cb tricks, not the older version as they have 2

cobra_voltages.jpg

Now included all IC voltages, which all look good except the PLL readings
 
Last edited:

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