Hello everyone,
Recently I've purchased the Hartke B90 from my friend for cheap and I used it at my rehearsal space. The sound was alright, but after some time a weird problem occured - one day, after 15 minutes of playing, the sound abruptly cut off and you couldn't hear anything. 5 seconds after turning off I've heard this "capacitor discharging" sound that was not there when I turned it off during normal operation.
If I turned on the amplifier after the discharge sound, it would work normally for 30 seconds or so, before shutting down again.
At first I thought that the power-amp was a chip-amp of some sort and what happened was some thermal protection shutdown, but when I touched the back of the chassis it didn't even get warm, and as you can see on the schematic, it is made of discrete components.
I also suspected a cold solder joint, but after I opened it up and took the PCB out, I couldn't find anything suspect. I did reflow most of the bigger solder joints, but the problem is still there.
I am new to amp troubleshooting, so I post here hoping that some of you could guide me or maybe someone more experienced has already seen something like this and knows what to do.
The problem with doing measurements is that the problem usually occurs after 5-15 minutes of loud playing, and for obvious reasons I cannot do this at home. I don't have any dummy load either.
Recently I've purchased the Hartke B90 from my friend for cheap and I used it at my rehearsal space. The sound was alright, but after some time a weird problem occured - one day, after 15 minutes of playing, the sound abruptly cut off and you couldn't hear anything. 5 seconds after turning off I've heard this "capacitor discharging" sound that was not there when I turned it off during normal operation.
If I turned on the amplifier after the discharge sound, it would work normally for 30 seconds or so, before shutting down again.
At first I thought that the power-amp was a chip-amp of some sort and what happened was some thermal protection shutdown, but when I touched the back of the chassis it didn't even get warm, and as you can see on the schematic, it is made of discrete components.
I also suspected a cold solder joint, but after I opened it up and took the PCB out, I couldn't find anything suspect. I did reflow most of the bigger solder joints, but the problem is still there.
I am new to amp troubleshooting, so I post here hoping that some of you could guide me or maybe someone more experienced has already seen something like this and knows what to do.
The problem with doing measurements is that the problem usually occurs after 5-15 minutes of loud playing, and for obvious reasons I cannot do this at home. I don't have any dummy load either.