Few notes from my experience with a 517 Protection Trigger Fault - may be of use to someone out there.
Amp was handed to me with a "Fault". So, dummy loads went on first. No problem. 1Khz Sine wave, clipped nicely, warmed up, seemed pretty stable. Opened it up, saw the usual issues with cap leakage and the glue, so replaced as required. Tested again, all good. Connected some speakers, a CD player and...... protection cut in at 40% volume level. So changed all the caps in the PSU and trigger board.
Same fault. The amp is so well built for maintenance, I simply swapped amp modules. The fault moved. So it was the Amp module. Removing wire to the protection circuit from the emitter resistor sense, the protection did not fire. So it had to be the DC across the emitter resistor. Oh how I was SO wrong.
I started to replace parts throughout the amp, assuming that the fault was some complex transient DC shift, triggered by music transients - as don't forget, during all this time the amp worked fine with a sine wave.
Hours and £££ later, having replaced almost everything, I decided to do something I should have done far earlier - listen to the amp when the transient triggered. If there was something untoward I would hear it. I attached a spare 400w 12" (but of course I could have used a small speaker with series resistor across the dummy load ! ). Total silence when the trigger fired (I connected the speaker prior to the relay using clips - so simple on this amp). Clearly no DC. I (yet again ) investigated the sensing circuit, removed parts etc, and it became clear that owing to the high impedance of the sensing trigger circuit (other board), it was actually being triggered by music transients transferred to the trigger wire by cross talk and leakage. I double tracked all the PCB tracks around the sensing circuit and it now all works fine. Clearly the transistor was simply floating and the net average signal from a sine wave not going to drag the 6v trigger down with the cross talk.
So I guess the lesson learned is 1) listen to the amp, 2) look for the simple things first (as they are cheap to fix) 3) remove elements of these "add on circuits" to amps to see what changes (I would have quickly realized that there was no DC across the emitter resistors triggering the circuit).
Hope this helps someone !
Amp was handed to me with a "Fault". So, dummy loads went on first. No problem. 1Khz Sine wave, clipped nicely, warmed up, seemed pretty stable. Opened it up, saw the usual issues with cap leakage and the glue, so replaced as required. Tested again, all good. Connected some speakers, a CD player and...... protection cut in at 40% volume level. So changed all the caps in the PSU and trigger board.
Same fault. The amp is so well built for maintenance, I simply swapped amp modules. The fault moved. So it was the Amp module. Removing wire to the protection circuit from the emitter resistor sense, the protection did not fire. So it had to be the DC across the emitter resistor. Oh how I was SO wrong.
I started to replace parts throughout the amp, assuming that the fault was some complex transient DC shift, triggered by music transients - as don't forget, during all this time the amp worked fine with a sine wave.
Hours and £££ later, having replaced almost everything, I decided to do something I should have done far earlier - listen to the amp when the transient triggered. If there was something untoward I would hear it. I attached a spare 400w 12" (but of course I could have used a small speaker with series resistor across the dummy load ! ). Total silence when the trigger fired (I connected the speaker prior to the relay using clips - so simple on this amp). Clearly no DC. I (yet again ) investigated the sensing circuit, removed parts etc, and it became clear that owing to the high impedance of the sensing trigger circuit (other board), it was actually being triggered by music transients transferred to the trigger wire by cross talk and leakage. I double tracked all the PCB tracks around the sensing circuit and it now all works fine. Clearly the transistor was simply floating and the net average signal from a sine wave not going to drag the 6v trigger down with the cross talk.
So I guess the lesson learned is 1) listen to the amp, 2) look for the simple things first (as they are cheap to fix) 3) remove elements of these "add on circuits" to amps to see what changes (I would have quickly realized that there was no DC across the emitter resistors triggering the circuit).
Hope this helps someone !
Hello, I have the same problem with a 517, in the dummy load test bench, with 100Hz, 1KHz, and 10 KHz, the failure does not occur. Neither with music, but connected speakers, when increasing the volume and in the saturation zone, the trigger of the protector appears. I'm thinking that maybe this is fine, by design. I did not recap, I am not very fond of that, (unless necessary) hoping that simply by replacing all the capacitors, the equipment will work as when it was new. The glue in this case doesn't seem to have corroded anything around it. It only occurs to me to decrease the sensitivity of the current detector on the emitter resistors, but I don't want to compromise the safety of the final transistors in the face of a real overload.
Has anyone found any other solution?
Thank you
Has anyone found any other solution?
Thank you
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.