I have a Black Star HT Club 40 on my bench that keeps blowing fuses and traces . The short is all related to where spades #1 and #2 are . If i left ether spade, the short goes away. But I have replaced the bridge asso. with that circuit , D22-D25. Still, the short is there. I have replaced Caps C144-C147 which are 0.01 uf ceramic caps which i bought from Digikey. Maybe these caps arn't compatible with this amp. Also checked the ESR on Eletrolytic caps C138-C141. Which turned out to be fine. I snipped the anode of D36, because it eliminates any other influnances from any other circuits . And the short is still there ,as i use a ballest lamp in series on the 120 volt AC line, with this amp as not to cause further damage. Theres not much left to check in this amp as far as that circuit. Which is the High Tension circuit or B+ to the tubes. If anyone has any ideas please let me know. Thanks.
You need to divide and conquer to find where the short is.
Pull out one leg of caps at a time to see if the short goes with a DMM.
Resistors don't go short, or at least I have never seen one in 40 years !
Check bridge again as if the short wasn't fixed it could have blown again.
I am assuming its not as simple as an electrolytic reversed ?
Power supply electrolytics tend to go first and can go short.
Pull out one leg of caps at a time to see if the short goes with a DMM.
Resistors don't go short, or at least I have never seen one in 40 years !
Check bridge again as if the short wasn't fixed it could have blown again.
I am assuming its not as simple as an electrolytic reversed ?
Power supply electrolytics tend to go first and can go short.
The caps across the rectifiers? There is no compatibility issue.
FIlter caps? Your ESR meter I bet took those readings at a volt or two from a meter. But the circuit pits hundreds of volts on them. They could easily be shorted at their working voltage. But don't pull them yet.
SP4 is the center tap of the output transformer. I would disconnect that guy first, eliminating the OT and tube circuits.
I don't understand why you cut D36, one end is grounded, and it is in parallel with a 1 ohm resistor in the cathode return of the power tubes. I don't see how that would affect anything.
If pulling SP4 stops the fuses blowing, then the OT may be shorted, or pins 3 of the tube sockets. One can test that by replacing SP4 and pulling off SP16,17.
If SP4 is no help, LEAVE IT OFF. I would then lift one end of R200. That would isolate just the main rectifier and filter. Just because you don't find any "bad parts" doesn't mean the problem is not in that area. A tiny bead of solder is enough to short two traces together.
FIlter caps? Your ESR meter I bet took those readings at a volt or two from a meter. But the circuit pits hundreds of volts on them. They could easily be shorted at their working voltage. But don't pull them yet.
SP4 is the center tap of the output transformer. I would disconnect that guy first, eliminating the OT and tube circuits.
I don't understand why you cut D36, one end is grounded, and it is in parallel with a 1 ohm resistor in the cathode return of the power tubes. I don't see how that would affect anything.
If pulling SP4 stops the fuses blowing, then the OT may be shorted, or pins 3 of the tube sockets. One can test that by replacing SP4 and pulling off SP16,17.
If SP4 is no help, LEAVE IT OFF. I would then lift one end of R200. That would isolate just the main rectifier and filter. Just because you don't find any "bad parts" doesn't mean the problem is not in that area. A tiny bead of solder is enough to short two traces together.
Blackstar HT Club 40
Hey Enzo . i thought lifting D36 would isolate it from the rest of the circuit but i was wrong. I will take spade4 off and try the things you said to do. I still think ive got a short in one of those electrolytics. But thanks again Enzo. I will try those things come monday.
Hey Enzo . i thought lifting D36 would isolate it from the rest of the circuit but i was wrong. I will take spade4 off and try the things you said to do. I still think ive got a short in one of those electrolytics. But thanks again Enzo. I will try those things come monday.
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