I was trying to load one transistor at the time when I was working on the repair. I haven't tried loading these new parts on the good working channel (with the exception of Q51). I did have BF422 loaded in place of BF423 (Q807/Q63) by mistake and then realized it was incorrect transistor but had the amped powered on. So I ordered BF 423 replacement... I think I have spent less time repairing SVS Bash amplifier than this guy (had to figure out the schematic, sad parts covered in epoxy...). I thought I could repair Xtant in my sleep since I have done it many times before...
Today I have swapped back Q37 and Q40 (original transistors). Previously I reported that I have installed original Q40, but I meant to say Q39.
I am not getting the same Ohm readings on output transistors as well as Q38 and Q40.
I have tried shorting the output pins on Mosfets just in case. Here is what I am seeing:
On Q2/Q3/Q4
Good channel:
1+ 2- 11.26 MOhm
2+ 3- -1.6 MOhm
1+ 3- 6.03 MOhm
2+ 1- 2.04 MOhm
3+ 2- 1.6 MOhm
3+ 1- 6.48 MOhm
Bad channel:
1+ 2- 1.8 MOhm
2+ 3- -1.58 MOhm
1+ 3- 200 kOhm and going up
2+ 1- 2.4 MOhm
3+ 2- 1.6 MOhm
3+ 1- 200 kOhm and going up
ON Q5/Q6/Q7
Good channel:
1+ 2- 11.24 MOhm
2+ 3- -1.6 MOhm
1+ 3- 6 MOhm
2+ 1- 2.4 MOhm
3+ 2- 1.6 MOhm
3+ 1- 6.43 MOhm
Bad channel:
1+ 2- 1.8 MOhm
2+ 3- -1.58 MOhm
1+ 3- 200k Ohm and going up
2+ 1- -1.1M going down MOhm
3+ 2- 1.59 MOhm
3+ 1- 200k Ohm and going up
Q38:
Good channel:
c+ e- 6.23 MOhm
e+ c- 6.42 MOhm
Bad channel:
c+ e- 200 kOhm and going up
e+ c- 200 kOhm and going up
Q39:
Good channel:
b+ e- 6.32 MOhm
c+ e- 6.29 MOhm
e+ b- 6.11MOhm
e+ c- 6.1 MOhm
Bad channel:
b+ e- 290 kOhm and going up/sometimes 0.6 MOhm
c+ e- 0.6 MOhm (possible didn't catch when it is in kOhm range)
e+ b- 200 kOhm and going up
e+ c- 200 kOhm and going up
I am not getting the same Ohm readings on output transistors as well as Q38 and Q40.
I have tried shorting the output pins on Mosfets just in case. Here is what I am seeing:
On Q2/Q3/Q4
Good channel:
1+ 2- 11.26 MOhm
2+ 3- -1.6 MOhm
1+ 3- 6.03 MOhm
2+ 1- 2.04 MOhm
3+ 2- 1.6 MOhm
3+ 1- 6.48 MOhm
Bad channel:
1+ 2- 1.8 MOhm
2+ 3- -1.58 MOhm
1+ 3- 200 kOhm and going up
2+ 1- 2.4 MOhm
3+ 2- 1.6 MOhm
3+ 1- 200 kOhm and going up
ON Q5/Q6/Q7
Good channel:
1+ 2- 11.24 MOhm
2+ 3- -1.6 MOhm
1+ 3- 6 MOhm
2+ 1- 2.4 MOhm
3+ 2- 1.6 MOhm
3+ 1- 6.43 MOhm
Bad channel:
1+ 2- 1.8 MOhm
2+ 3- -1.58 MOhm
1+ 3- 200k Ohm and going up
2+ 1- -1.1M going down MOhm
3+ 2- 1.59 MOhm
3+ 1- 200k Ohm and going up
Q38:
Good channel:
c+ e- 6.23 MOhm
e+ c- 6.42 MOhm
Bad channel:
c+ e- 200 kOhm and going up
e+ c- 200 kOhm and going up
Q39:
Good channel:
b+ e- 6.32 MOhm
c+ e- 6.29 MOhm
e+ b- 6.11MOhm
e+ c- 6.1 MOhm
Bad channel:
b+ e- 290 kOhm and going up/sometimes 0.6 MOhm
c+ e- 0.6 MOhm (possible didn't catch when it is in kOhm range)
e+ b- 200 kOhm and going up
e+ c- 200 kOhm and going up
Latest discoveries and things I have tried:
Removed gate resistors R2, R30 and R32: Q2, Q3 and Q4 output transistors appear to be normal.
Removed gate resistors R38, R41 and R43: Q5, Q6 Q7 output transistors appear to be normal.
D55 shows 0.69V drop whereas on good channels it is 0.73V.
When connected to power supply via resistor I am seeing 8.79V regulation on good channel and on the bad channel 7.43V. Removing R26 and D1 - made no difference.
Removed gate resistors R2, R30 and R32: Q2, Q3 and Q4 output transistors appear to be normal.
Removed gate resistors R38, R41 and R43: Q5, Q6 Q7 output transistors appear to be normal.
D55 shows 0.69V drop whereas on good channels it is 0.73V.
When connected to power supply via resistor I am seeing 8.79V regulation on good channel and on the bad channel 7.43V. Removing R26 and D1 - made no difference.
Did you ever try the replacements that you had in a good channel to confirm that they were all suitable replacements?
Did all of the components you pulled match their counterparts from the other channel's components?
Did all of the components you pulled match their counterparts from the other channel's components?
Did you ever try the replacements that you had in a good channel to confirm that they were all suitable replacements?
Not yet. I was thinking of replacing BF423 in Q63 spot and BF422 in Q52 spot.
Did all of the components you pulled match their counterparts from the other channel's components?
Not sure what you are asking here. I assume you mean if I had loaded correct BF422, BF423 and 3B transistors in the right ref designators, then the answer is yes. As mentioned previously I have loaded BF 422 (npn) in Q63 spot once and powered the amp on shortly before realizing the issue. It has been replaced with BF423 (pnp).
Not yet. I was thinking of replacing BF423 in Q63 spot and BF422 in Q52 spot.
Did all of the components you pulled match their counterparts from the other channel's components?
Not sure what you are asking here. I assume you mean if I had loaded correct BF422, BF423 and 3B transistors in the right ref designators, then the answer is yes. As mentioned previously I have loaded BF 422 (npn) in Q63 spot once and powered the amp on shortly before realizing the issue. It has been replaced with BF423 (pnp).
After something has been worked on for so long and so many parts replaced, it's easy for a component to be misread or misplaced. Confirming that there are no such errors can save a lot of time by catching mistakes.
I fully agree with your statement.
I have tried new BF422 in Q52 location and BF423 in Q63 location. Had to adjust the DC offset but didn't encounter any problems in a working channel with these new components. 3B Q51 I am using has already been replaced in that channel.
Going back to the bad channel, I removed Q51 on the bad channel to prevent component damage and probe a few spots:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.9V
a 34.78V
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c 35.31V
a 34.78V
D55 zener does behave differently on the bad channel as confirmed with DMM diode test and bench power supply/resistor voltage check.
I am tempted to start swapping output transistors but I doubt they are the culprit. Will swap D63 (TL431) next.
With Q51 removed on the bad channel I have noticed that the DC offset was in 2.8V range. Adjusting the offset CCW or CW all the way brought it down to 0V. Adjusting the gain made no difference. Once the amp warmed up the DC offset went to 2.8V and stayed there. That is the DC rpot had no effect on it any longer.
PS: this thread turned into my personal blog. 🙂 Hopefully I can use it in the future or someone else find my measurements helpful to troubleshoot this amp in the future.
I have tried new BF422 in Q52 location and BF423 in Q63 location. Had to adjust the DC offset but didn't encounter any problems in a working channel with these new components. 3B Q51 I am using has already been replaced in that channel.
Going back to the bad channel, I removed Q51 on the bad channel to prevent component damage and probe a few spots:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.9V
a 34.78V
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c 35.31V
a 34.78V
D55 zener does behave differently on the bad channel as confirmed with DMM diode test and bench power supply/resistor voltage check.
I am tempted to start swapping output transistors but I doubt they are the culprit. Will swap D63 (TL431) next.
With Q51 removed on the bad channel I have noticed that the DC offset was in 2.8V range. Adjusting the offset CCW or CW all the way brought it down to 0V. Adjusting the gain made no difference. Once the amp warmed up the DC offset went to 2.8V and stayed there. That is the DC rpot had no effect on it any longer.
PS: this thread turned into my personal blog. 🙂 Hopefully I can use it in the future or someone else find my measurements helpful to troubleshoot this amp in the future.
Last edited:
Recheck:
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c 35.31V
a 34.78V
Are you sue you have anode and cathode right?
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c 35.31V
a 34.78V
Are you sue you have anode and cathode right?
typo:
Going back to the bad channel, I removed Q51 on the bad channel to prevent component damage and probe a few spots:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.9V
a 34.78V
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c -0.9V
a 35.31V
Swapping D63 from bad to good channel made no difference.
On the bad channel I haven't loaded Q51 yet though. This time DC offset measured fully clockwise -0.915V and fully counter clock wise 1.8 to 2.2V. I let the amp run for a bit and I was still able to adjust the offset this time. Also at one point in time I have measured 3.4V in ccw position.
There are plenty of SSD transistors that I haven't tried swapping.
Q61, Q60, Q64, Q66, Q67. Also I don't recall if I have swapped Q62 yet.
Going back to the bad channel, I removed Q51 on the bad channel to prevent component damage and probe a few spots:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.9V
a 34.78V
D2 good channel:
c 1.83V
a 36.63V
D1 bad channel:
c -0.9V
a 35.31V
Swapping D63 from bad to good channel made no difference.
On the bad channel I haven't loaded Q51 yet though. This time DC offset measured fully clockwise -0.915V and fully counter clock wise 1.8 to 2.2V. I let the amp run for a bit and I was still able to adjust the offset this time. Also at one point in time I have measured 3.4V in ccw position.
There are plenty of SSD transistors that I haven't tried swapping.
Q61, Q60, Q64, Q66, Q67. Also I don't recall if I have swapped Q62 yet.
Last edited:
Fixed:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.915V (with 500 Ohm Rpot set fully CW) 1.8-2.2V (with 500 Rpot set fully CCW)
a 34.78V
D2 good channel:
c 36.63V
a 35.96V
D2 bad channel:
c 35.31V
a 34.78V
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel:
c 34.78V
a 27.17V
D1 good channel:
c 1.83V
a 35.96V
D1 bad channel:
c -0.915V (with 500 Ohm Rpot set fully CW) 1.8-2.2V (with 500 Rpot set fully CCW)
a 34.78V
D2 good channel:
c 36.63V
a 35.96V
D2 bad channel:
c 35.31V
a 34.78V
c = cathode (stripped)
a = anode
D1, D2 and D55 zener have their cathodes connected to each other.
a = anode
D1, D2 and D55 zener have their cathodes connected to each other.
Look at your numbers. If those cathodes were directly connected (as in the diagram), the voltages would match and they do not.
Sorry for confusion Perry. So many mistakes. I shouldn't have typed anything today.
c = cathode (stripped)
a = anode
Fixed:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel (Q51 removed):
c 34.78V
a 27.17V
D1 good channel:
c 35.96V
a 1.83V
D1 bad channel (Q51 removed):
c 34.78V
a -0.915V (with 500 Ohm Rpot set fully CW) 1.8-2.2V (with 500 Rpot set fully CCW)
D2 good channel:
c 35.96V
a 36.63V
D2 bad channel (Q51 removed):
c 34.78V
a 35.31V
c = cathode (stripped)
a = anode
Fixed:
D55 zener good channel:
c 35.96V
a 27.17V
D55 zener bad channel (Q51 removed):
c 34.78V
a 27.17V
D1 good channel:
c 35.96V
a 1.83V
D1 bad channel (Q51 removed):
c 34.78V
a -0.915V (with 500 Ohm Rpot set fully CW) 1.8-2.2V (with 500 Rpot set fully CCW)
D2 good channel:
c 35.96V
a 36.63V
D2 bad channel (Q51 removed):
c 34.78V
a 35.31V
Last edited:
I didn't make any changes to the bad channel and the testing was done with Q51 removed.
When the amp was powered on initially I had 3.4V on D1 anode with Rpot set fully CCW I didn't keep it in that position for long but it wasn't jumping up and down. Then a few minutes later I have noticed that with Rpot set to CCW D1 anode voltage was jumping up and down in 1.8-2.2V range. Maybe there is some kind of oscillation...
When the amp was powered on initially I had 3.4V on D1 anode with Rpot set fully CCW I didn't keep it in that position for long but it wasn't jumping up and down. Then a few minutes later I have noticed that with Rpot set to CCW D1 anode voltage was jumping up and down in 1.8-2.2V range. Maybe there is some kind of oscillation...
I haven't tested audio to the excessive negative offset on the output with Q51 loaded. Today I have replaced Q62 on the bad channel and swapped 1L Q64 with a good channel. I decided to test D55 out of circuit but unfortunately it broke when I was trying to remove it. I don't have 9.1V zener at home, so I have installed 6.75V zener instead.
Good channel:
is still good meaning Q64 wasn't a problem.
Bad channel:
without Q51 nothing changed. I have adjusted the offset so that the voltage on D1 anode is at 1.8V. The output offset is at 0.67V at that point.
Loaded Q51 back. The output voltage offset is lower than what I had initially. I no longer see -28.8V. It is between -5.7V and -7.6V depending on what the offset is set to.
At D1 anode I see -6V with offset turned cw and -9V with offset turned ccw (could be flipped, didn't right it down).
Tempted to swap the output transistors but now need to source 9.1V zener. Not sure how critical it is in this circuit.
Good channel:
is still good meaning Q64 wasn't a problem.
Bad channel:
without Q51 nothing changed. I have adjusted the offset so that the voltage on D1 anode is at 1.8V. The output offset is at 0.67V at that point.
Loaded Q51 back. The output voltage offset is lower than what I had initially. I no longer see -28.8V. It is between -5.7V and -7.6V depending on what the offset is set to.
At D1 anode I see -6V with offset turned cw and -9V with offset turned ccw (could be flipped, didn't right it down).
Tempted to swap the output transistors but now need to source 9.1V zener. Not sure how critical it is in this circuit.
I wouldn't expect the circuit to work normally without it.
Have you confirmed that the TL431 regulator is working properly?
Have you confirmed that the TL431 regulator is working properly?