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2SA733 TRANSISTOR HELP

dss56

Well-Known Member
Sep 27, 2010
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121
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What is a good replacement for this 2SA733 TRANSISTOR What have you used.

thanks HAPPY NEW YEAR TO ALL
 

Its a cobra 29ltd the transmit is on all the time without the mic and suspecting tr21
to be shorted
 
Most likely culprit is C117 next to L3 is shorted. But, can be any of the other red circled items, too, these are either tied directly to, or low resistance to the PTT line of the Mic socket. last time I helped someone with a Cobra 29 a few months ago, that had TX all the time, it turned out to be a cracked (shorted) C121 up by the mic plug area.

C29 TX C117.jpg


C29 LTD Classic PTT path.jpg

C29 Board Layout TX all the time.jpg
 
Last edited:
yep, could be any of a few things.

here is what I would check..

with the mic out of the radio, measure the voltage at
TR21-base. it should be "high" about 8 V
if not, then find out why. maybe C117 is bad as mentioned.
And it sounds like you have about 8 V a TR21-collector if it is
in TX all the time.

if TR21 is bad, cut it off board, to be able to receive again.

..
 
Well
thanks guys I will try in next few days to look at it.
Dont have much time as scheduled for January 7th triple bypass surgery here in Boston Ma. Hope all will go well and then back to my daily routine.

HAPPY NEW YEAR TO ALL IN THE GROUP
 
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