G7 B+ Voltage problem

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seavote

Well-known member
Joined
May 31, 2006
Messages
1,085
Location
Long Beach,New York
i'm having some trouble getting my G7 up and running. repaired some problems but ended up frying my psu pcb. i jumped all the traces . they look good. i get continuity where i should. my transformer is running hot however and i'm only getting 145Vdc without the mic attached. if i burned out or damaged the rectifier would i still get power (low voltage)? or when a rectifier goes does it just stop passing all voltage? i have another rectifier and just want to know if i'd be wasting my time swapping it out. thx
 
while swapping out the rectifier i noticed a trace branching off one of the damaged pads that i did not notice befor . the pad was not making a connection to the trace. repaired it. now voltages are good for heater(5.8V) and B+ (163V , 67V to capsule) with no heating up of the transformer. the pcb looks like hell but the connections are solid and working. tonight i'll give the mic a listen. thanks for any help and for putting up with my rambling and constant need for reassurance.(see other posts, better yet just take my word for it) i'll try not to be such a wussy with future projects.
 
Good catch!
Sounds like the open connection was letting something run wide open, somebody lost their bias.
I wish Jesse Jackson would lose his bias.
 
just tried to test my mic. while connecting the 3 pin xlr to the audio "out" on the power supply the xlr sparked.(unit was plugged in but the power switch was off) now i have no B+ voltage to speak of (mv.s) and another trace on the psu is fried. pretty soon my psu is going to be point to point!! the trace was fine befor i secured the psu on the stand offs and all voltages were fine. i thought the entire problem was the fried traces but now i suspect that the traces are just the result of the problem not the cause. i've been able to locate some previous problems and repair them. this one has me stumped. why would the audio out arc like that with the power switch off? is there a problem between my ac ground and the 3 pin xlr? the 3 pin xlr definitly has continuity to the ac ground(the psu case) should there be no ground from the ac ground lug to the psu case? please help i dont understand whats going on in my psu
 
you had a ground loop, and the two chassis were at different potential, which got connected thru the xlr.
check the pin numbers on the xlr jack, they are confusing and hard to read.
if everything is right, i believe the pins 2 and 3 should have no connection to ground because of the xfmr.
 
cj thanks for the fast reply. i'll jump the fried trace tomorrow and check the xlr connector. i'm 99.9% i hooked this up correctly but...?
in the mean time i may have found the problem. the mic psu and the mic pre are plugged into different outlets. i tested the outlets and the mic pre outlet has reversed polarity. this would cause the "different potential" yeah?? to repair this i would just reverse the wires to the outlet, is that correct?
 

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