CDM1250 blowing fuses

SD70MAC · Post by **SD70MAC** » Sat Dec 31, 2005 12:30 pm

I have aquired a CDM1250 VHF that as soon as you plug the power cable in it blows the fuse,any ideas what is wrong? It is a firmware verison 2.00 but it looks like new inside and out.

MetroMan · Post by **MetroMan** » Sat Dec 31, 2005 12:54 pm

Check the polarity reversal diode. It's right across the input power connector and deisgned to blow the fuse if hooked up backwards and in many cases shorts out. Try lifting one side to see if your problem clears. Can't give you circuit designation now. don't have schematics.

SD70MAC · Post by **SD70MAC** » Sat Dec 31, 2005 6:49 pm

That sound like something good to try ! I will tear it back down tomorrow.

Will · Post by **Will** » Sun Jan 01, 2006 12:53 pm

Also check the solder on the RF PA transistor's colector, many times the PA overheats and the solder melts shorting the main battery A+. The two or four capacitors on the PA colector have been known to leach the connections due to excessive heat and melting solder.

MassFD · Post by **MassFD** » Mon Jan 02, 2006 9:27 am

Are you using a real Motorola power cable or one of the auto store "trailer connectors".

While they may look the same they are sometimes wired backwards. If you look at the end of the cable that plugs into the radio, the uninsulated pin should be on the black wire (12v neg) and the insulated pin should be on the red wire (12v pos).

I have seen a few radios damaged by the wrong cable, the reverse protection diode may be trying to protect the radio from a reversed power supply.

SD70MAC · Post by **SD70MAC** » Wed Jan 04, 2006 5:31 am

I don't know the whole story on this. The radio was given to me,but I beleive it was installed by a dealer. The board has no visible damage and I tried the fuse and that did not work but it sounded like the problem.