been a while since ive asked for any help and i try not to these day as i want to be able to work it out for myself-but!
i have one here i just cant work out, both speaker outputs are -26v
when i got the amp both output transistors were blown on the right channel and fuses along with them as you woudl expect, so they were replaced.
I have since checked and tested all other transistors in the output Q401 through to Q418, both channels and all are ok.
the power sections on both rails have the correct outputs.
i have -26v on all 4 output transistor bases and emitters
i also have -26v on the feedback resistors R429 and R430, in fact pretty much -26v all over the place so i dont have a good starting place.
ive been trying to work out what what genericaly could affect both channels the same 😕
any ideas?
i have one here i just cant work out, both speaker outputs are -26v
when i got the amp both output transistors were blown on the right channel and fuses along with them as you woudl expect, so they were replaced.
I have since checked and tested all other transistors in the output Q401 through to Q418, both channels and all are ok.
the power sections on both rails have the correct outputs.
i have -26v on all 4 output transistor bases and emitters
i also have -26v on the feedback resistors R429 and R430, in fact pretty much -26v all over the place so i dont have a good starting place.
ive been trying to work out what what genericaly could affect both channels the same 😕
any ideas?
Maybe huggy means have you checked all the rails. Are all four supplies correct, in particular the two positive rails of +43 and the +32/28 volt rail.
You need to check that those voltages are reaching the output stage at their destinations. Measure at these exact locations. It is possible a resistor is open.
Be sure to use the bulb while working on this.
And if they are present and correct then it gets more interesting 😉
Be sure to use the bulb while working on this.
And if they are present and correct then it gets more interesting 😉
Attachments
already checked at these points
Q407
E -26V
C -23V
B -26V
Q405
E -26V
C -24V
B -23V
R544 is shorted
Q415 collector is -26v
always have the lamp plugged in, and the light isnt on at all.
Q407
E -26V
C -23V
B -26V
Q405
E -26V
C -24V
B -23V
R544 is shorted
Q415 collector is -26v
always have the lamp plugged in, and the light isnt on at all.
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Well there is your fault 😉
If they are at -26v and yet you measure the correct positive values (as per your diagram in post #5) at the power supply then there has to be an open circuit.
They are the same point... yes 🙂 Take a step back and recheck on the power supply and then on those points again.
If they are at -26v and yet you measure the correct positive values (as per your diagram in post #5) at the power supply then there has to be an open circuit.
They are the same point... yes 🙂 Take a step back and recheck on the power supply and then on those points again.
OK 🙂 have a remeasure at the PSU to check it really was OK and then work from the power supply toward the output stage.
Hope you are feeling better soon.
Hope you are feeling better soon.
so both R 437 and R 436 were open circuit
i noticed that both resistors were negative one side and positive the other, so it had to be around that location
all voltages now normal.
whats the odds agaisnt both going at the same time.ive put 1/2 w ones back instead of 1/4w
i noticed that both resistors were negative one side and positive the other, so it had to be around that location
all voltages now normal.
whats the odds agaisnt both going at the same time.ive put 1/2 w ones back instead of 1/4w
excellent.Unless you know the amps history its probably fair to say that anything might have happened to it. Maybe someone tried measuring voltages there and had a meter on a current range instead of voltage and zapped both in the same way. You'll probably never know.
very true.but ive started logging all the faults i find and resolve, that way next time it will give me a stear, and belive me if you had my brain you would need it 😀
Lol, it all comes with experience and practice. Making notes is good but eventually you will get beyond that and just work from gained knowledge. But it takes time.