SX-1250 AWH-048 won't pass dim bulb.
- Thread starter drmazzei
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- pioneer sx-1250
drmazzei
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VR2 is still 0volts.
Hmm I feel like we are on the right path here, what did you use for replacements, if I may ask? And did you verify that you are still getting the correct voltages at pins 2 and 3? It's tricky, but those base measurements of Q7 and Q8 might help us. I recommend connecting your probe to the leg with the board loose, carefully reconnect the molexes, then power on the unit, see what the meter says for voltage. I am curious if you are getting the proper voltage step down or not, cause too high or low can really mess up the trimmer's ability to bias.
Edit: just noticed you're missing about 30V on Q4B, but Q3B looks okay, they both come off the -65V rail, then go through the 16Ks at R11, and 12 for the -62V. R11 may be failing and increasing value if that rail is being squeezed down that much. Wonder if that alone wouldn't cause all the issues?
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Those readings are nice.
How did you reach them?
The amp is missing the + side in the prestage. There's the +65 coming in on pin 3 but you're reading negative at Q5 and 6.
All legs on Q5 and 6 should be positive.
Either the transistors (5&6) are backwards or NPN's, or not connected.
Readings at the emitters could help but maybe a good look at the install and parts used?
How did you reach them?
The amp is missing the + side in the prestage. There's the +65 coming in on pin 3 but you're reading negative at Q5 and 6.
All legs on Q5 and 6 should be positive.
Either the transistors (5&6) are backwards or NPN's, or not connected.
Readings at the emitters could help but maybe a good look at the install and parts used?
drmazzei
Member
For dc voltage readings, I'm using a DMM w/ negative using chassis as ground and positive probe is micro grabber. R15,16 were BBQ'd and C8 tested bad on Purple Atlas tester. All three were replaced. R21,22,27 tested ok out of circuit. R11, 12 tested ok out of circuit.
Current readings:
Q8 E -0.15 C -0.17 B -0.756
Q7 E 0.14 C 0.15 B 0.71
Q6 E 64.5 C 0.895 B 0.003
Q5 64.3 C 63.8 B 63.9
Q1, Q2 are Hfe matched KSA992.
Q3, Q4, Q7, are TTC004.
Q5, Q6, Q8 are TTA004.
Orientation of transistors was verified to be correct.
Current readings:
Q8 E -0.15 C -0.17 B -0.756
Q7 E 0.14 C 0.15 B 0.71
Q6 E 64.5 C 0.895 B 0.003
Q5 64.3 C 63.8 B 63.9
Q1, Q2 are Hfe matched KSA992.
Q3, Q4, Q7, are TTC004.
Q5, Q6, Q8 are TTA004.
Orientation of transistors was verified to be correct.
drmazzei
Member
I'm trying to figure out why Q7 voltages are so off.
Checked R17, 18, 19, 20 and all test ok.
Burnt trace pin #15 to D11; replaced D11.
Replaced D6, D10.
Q9c is 0.159v.
Pin #15 is 71.7 vdc. Pin #14 is 0vdc.
C13, C14 test ok out of board, but not getting 0vdc on either side of C13 in circuit.
Checked R17, 18, 19, 20 and all test ok.
Burnt trace pin #15 to D11; replaced D11.
Replaced D6, D10.
Q9c is 0.159v.
Pin #15 is 71.7 vdc. Pin #14 is 0vdc.
C13, C14 test ok out of board, but not getting 0vdc on either side of C13 in circuit.
C13 would have +70v on one side and 0v on the other. Pin 14 is chassis ground.
C14 would have -70v on one side and 0v on the other.
Q9 collector should read +70v strait up. Maybe D6 and 10 are installed backwards or another trace is broken?
Burned up traces in that area is a sign something unusual happened. What I mean is, it wasn't a natural failure. Something got hooked up incorrectly or installed backwards.
In this case, the best course is to go through the entire board. All the components, all the traces. or you will be chasing your tail. You probably already spent as much time than what it would take to know for sure the condition of the board. It might take less than an afternoon if your organized.
You could use the other good board to compare resistor values. That would speed up the audit. Consider replacing all the silicon as well. I know, but taking chances they are still good after all the mucking about might add to the woes.
C14 would have -70v on one side and 0v on the other.
Q9 collector should read +70v strait up. Maybe D6 and 10 are installed backwards or another trace is broken?
Burned up traces in that area is a sign something unusual happened. What I mean is, it wasn't a natural failure. Something got hooked up incorrectly or installed backwards.
In this case, the best course is to go through the entire board. All the components, all the traces. or you will be chasing your tail. You probably already spent as much time than what it would take to know for sure the condition of the board. It might take less than an afternoon if your organized.
You could use the other good board to compare resistor values. That would speed up the audit. Consider replacing all the silicon as well. I know, but taking chances they are still good after all the mucking about might add to the woes.
drmazzei
Member
Parts installed from Mouser. Replaced R15, R16, R17, R18, R19, R20 that were BBQ'd when I accidentally shorted Q3 during testing. Also, replaced Q3, Q4. Checked orientation D6, D10. Verified D6, D10 were good w/DCA55. Checked (w/one leg removed) R14, R23, R24, R25, R26 and found all ok. Checked and verified continuity of colored wires to both NPN power transistors. Both MJ21196 transistors tested good w/Peak DCA55. Voltages as follows:
C13 -73.3 0.0
C14 +71.5 .001
D10 -73.7 -0.5
D6 1.86 -0.5
Q9C 1.86
Q7C 0.977
C13 -73.3 0.0
C14 +71.5 .001
D10 -73.7 -0.5
D6 1.86 -0.5
Q9C 1.86
Q7C 0.977
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Your still missing the 68v collector voltage on Q7 and Q9.
Your transistors are in backwards or the diodes D6 and 10 are damaged. Or a break in the trace between them.
It would be nice to see Q8 and 10 voltages.
I'm not familiar with the transistors you are using. You do have one board working so I'm going with that thought.
Your transistors are in backwards or the diodes D6 and 10 are damaged. Or a break in the trace between them.
It would be nice to see Q8 and 10 voltages.
I'm not familiar with the transistors you are using. You do have one board working so I'm going with that thought.