In , tomagain
wrote:

On Tue, 07 Oct 2003 19:45:08 -0700, Frank Gilliland
wrote:

In , tomagain
wrote:

A friend of mine was cleaning his mobile radio. When he went to plug
the power back in, the middle pin (offset) was loose and pushed back
into the radio, allowing him to put the connector in backwards. (hot
to ground) This killed the radio. (he had no inline fuse at the time)

Not to chastise you, but to everyone reading this, NEVER, EVER run a radio
without the proper fuse for just this reason!
Yes, I know, and agree wholeheartedly....but really it's not my radio

I told him I would look inside of it for him. Once inside I found
nothing burnt. After fixing the dummy pin, and connecting power with
the correct polarity to a D.C. power supply on my bench, the radio
still wont come on. When I started checking for voltage, I found that
I had 12 volts on the chassis.

This is interesting. When you measure voltage, to what are you measuring it
against? IOW, where are you putting your probes?
Digital voltmeter set on D.C. Neg lead on power supply negative
post. Positive lead checking everywhere mentioned above

It is on both sides of the on/off
switch with the switch off. The 12 volts is everywhere. Does anyone
have any ideas about what to check next? It is hard to use the meter
when everywhere shows 12 volts.... Thanks, Bill

Turn the radio off, hook the negative lead of your meter to the chassis, then
measure the two pins of the power switch. What do you get?

aproximately 1 volt give or take a tenth

I also reversed the leads and get the same readings with the negative
sign on the meter. IOW hot lead to negative post on power supply, with
negative probe checking gets the same results with negative numbers.

The negative power lead is fused somewhere between the point it connects to the
power supply and the PCB ground (which, BTW, is -not- the same as chassis
ground). It may even be a cracked or fused trace on the PCB itself. Start doing
continuity checks from the negative power lead of the radio to points inside the
radio that should be connected.

Thanks for replying

Not a problem.





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