Hi Folks, I'm repairing a bass amp Behringer BX3000T for my friend.
During a rehearsal, volume dropped and the bass sound was totally distorted in a "83 - Kill'em All" way.
I opened the beast and put a DMM on the power supply section :
+17v/-17v rails are OK and are powering the preamp zone.
+15v/-15v rails had a problem with T10 (mesured +6v/-15v). Changed T10 (original BC546B was dead short)
and now, I read +20v/-15v, is this due to hFE mismatch of this new transistor ?
R33 and R48 out of the board are ok. The 15v zener diodes around seem OK (reacted like a standard diode),
D10 was mesured in place, 0,65v one way, blocking the other way.
Before D10 I read +15,5v. Between D10 and R48 I read +0,63v. After R48 I read +20,5v.
Second question, VR1, VR2 and VR3 seem to be bias setting ? How to use them to calibrate the amp ?
Service manual cannot be found the schem is attached here.
Thanks for any help.
During a rehearsal, volume dropped and the bass sound was totally distorted in a "83 - Kill'em All" way.
I opened the beast and put a DMM on the power supply section :
+17v/-17v rails are OK and are powering the preamp zone.
+15v/-15v rails had a problem with T10 (mesured +6v/-15v). Changed T10 (original BC546B was dead short)
and now, I read +20v/-15v, is this due to hFE mismatch of this new transistor ?
R33 and R48 out of the board are ok. The 15v zener diodes around seem OK (reacted like a standard diode),
D10 was mesured in place, 0,65v one way, blocking the other way.
Before D10 I read +15,5v. Between D10 and R48 I read +0,63v. After R48 I read +20,5v.
Second question, VR1, VR2 and VR3 seem to be bias setting ? How to use them to calibrate the amp ?
Service manual cannot be found the schem is attached here.
Thanks for any help.
Attachments
VR1 is bias, adjust like any other solid state amp. VR2,3 are adjustments for current limiting. Just leave them alone and they will be fine.
Hi folks,
Finally got it ! Zener D18 15v was dead too !
Now reading are +14,5v/-14,5v, no hum, no shut down every 10 min due to heat.
New zeners are 5W, damn too big for the holes. I had to use old resistor legs to adapt to the correct size.
It was a long process due to lack of precious time but it works well now,
my friend will be happy to play bass again.
Finally got it ! Zener D18 15v was dead too !
Now reading are +14,5v/-14,5v, no hum, no shut down every 10 min due to heat.
New zeners are 5W, damn too big for the holes. I had to use old resistor legs to adapt to the correct size.
It was a long process due to lack of precious time but it works well now,
my friend will be happy to play bass again.
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