If the mosfets are out, I would leave them out considering they are hard to replace.
You can sort out the driver problem without risking the output devices.
Just need to attach two the gate resistors to the output and try to get close to zero volts at the output. Better to pull the resistor for the output zobel though.
I have done that a few times when dealing with bad driver boards. No need to take out mosfets you cannot easily replace.
You can sort out the driver problem without risking the output devices.
Just need to attach two the gate resistors to the output and try to get close to zero volts at the output. Better to pull the resistor for the output zobel though.
I have done that a few times when dealing with bad driver boards. No need to take out mosfets you cannot easily replace.
Here is a pic of the back of the board. maybe you can spot something......Frank
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since you've replaced many transistors and the symptom still there therefore I thought maybe one of the 2SK135 MOSFETs oscillating
Here is a pic of the board now. I changed the 3 electrolytics on channel 2......I am at full rail voltage on the output of the speaker terminals for that channel. 70VDC ...........that happened after changing the caps......i did not change 25uf bypass cap at the front of the board. channel 2 is the one with the problem. I forgot to mention that initially cr10 and cr11 diodes were shorted.
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Hi Patrick. the added capacitance would be to compensate for something going bad with the mosfets? ...This amplifier is a well known amplifier with a great track record of being bullet proof. ......also, you have pointed out some gate resistors that are for the working channel. i really donot wanna mess with that channel..........but ok, I may have those capacitors or the higher ohm resistor for channel 2 . I need to check my stash. and will report back. ...it will probably be later since i have to go to work. bye for now. thanks Frank.
I don't know which channel so that I just point out the location of these resistors, not meaning changing both channel
ok, don't change the capacitor or resistor first
since you have a good working channel, you can test and compare them to spot the problem more easy
thanks for sending the clear pic and I'll study it and try to spot something also
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That will be off because the output has high dc. You measured resistance to the heat sink as low from the mosfets. Is the working channel the same?
I haven't checked but I will. Thanks for response. By the way, I really like your ba line stage. Was a little challenging with the small little parts but combined with Nelson's diy aleph j I couldn't be happier.
Ok, I think I am going to install the mosfets from the channel that isn't working on the other side. The components on the boards are all common stock parts but the mosfets are obsolete. What do you think?........my thinking is it's better to blow or burn a cheap BJT and some resistors than some obsolete mosfets.
Ok, reporting back. After taking a leap of faith i got brave and moved the suspected bad mosfets to the working channel side of the driver board. conclusion?...amplifier plays music and dc offset is 0 volts ..good news! I do not have any bad mosfets.........bad news, i still have a problem with the driver board.......where do we go from here?
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