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Old 27th Apr 2009, 8:35 pm   #45
geofy
Retired Dormant Member
 
Join Date: Jun 2006
Posts: 1,798
Post Re: Roberts RT7 - problem

While you are checking voltages elsewhere the two OC81's should have their collectors or emitters lifted out of circuit if these are still drawing excessive current, of course this can cause an additional problem of having to unsolder them. But they can't be left in drawing excess current and overheating, something is biasing them on far to hard. The base driver stage of the output stage should be checked, this is the other (driver) transformer and its components on the board.

What should have been mentioned earlier is to monitor the battery current rather than wait until things get hot, by putting the milli Ampere meter in series with the battery lead. The current should only be around 10 milli-amps or so, if the needle shots off the scale then this is why the things are getting hot and draining the battery.

(With a good radio at normal volume this current with increase and fluctuate in time with the signal)

Geof
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Last edited by geofy; 27th Apr 2009 at 8:49 pm.
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