I have a non functional CDM750 in VHF, no front paned lights no functions of any kind, interestingly enough, the mic with this radio has the green/red led in the upper corner which does illumintate to indicate power on & transmit but the radio does not function. I have checked all the obvious possibilities, and still can find no reason for no power up. When power is applied it appears to have a slight current draw, barely measurable. When attempts are made to read the radio it also fails to communicated with radio. Any suggestions? I have no service manual to troubleshoot further.
Thanks
Doug
DEAD CDM750
Moderator: Queue Moderator
Re: DEAD CDM750
Since you have power and a 'function' light of sorts, get out the test gear and check for reference oscillator signals. (16.8 mHz)
You can also check for the 2nd Osc. as this will also be a good indicator for receiver operations.
No receive, no receive audio...
Aside from this, there's not much to look for with the cover on as the CDM is a pretty tightly shielded radio(single board).
Current draw is only a small indicator, but small current draw in RX mode is far better than 10A and letting the smoke out.
Tune the monitor to 44.645mHz. and connect a sniffer and probe from the holes in the chassis front.
The case does not allow a weak signal out, so you will have to enter through the holes to 'sniff' for the 2nd Oscillator.
Once you determine/find out if you have signal, and it's on frequency, you can begin to dig deeper and remove the cover to look for the obvious problem....burned traces or components, corrosion from spilled liquids,....Etc.....
Step by step analysis will yield results and a possible answer.
You can also check for the 2nd Osc. as this will also be a good indicator for receiver operations.
No receive, no receive audio...
Aside from this, there's not much to look for with the cover on as the CDM is a pretty tightly shielded radio(single board).
Current draw is only a small indicator, but small current draw in RX mode is far better than 10A and letting the smoke out.
Tune the monitor to 44.645mHz. and connect a sniffer and probe from the holes in the chassis front.
The case does not allow a weak signal out, so you will have to enter through the holes to 'sniff' for the 2nd Oscillator.
Once you determine/find out if you have signal, and it's on frequency, you can begin to dig deeper and remove the cover to look for the obvious problem....burned traces or components, corrosion from spilled liquids,....Etc.....
Step by step analysis will yield results and a possible answer.