The voltages on channels 2 and 1 are the same as I got before now that I've swapped the resistor networks.
Pair 1: 0V silent, 0.3mV playing
Pair 2: 0.3mV silent, 1.3V playing
Pair 1: 0V silent, 0.3mV playing
Pair 2: 0.3mV silent, 1.3V playing
Lift the transistor that's between the two ch2 outputs (Q436) and heat it (blow dryer, heat gun, not a torch) while monitoring the voltage across the resistor while playing.
Does the voltage across the resistor change significantly while playing?
Does the voltage across the resistor change significantly while playing?
It appeared to jump from a couple mV to 1.3V. I didn't want to run it too long with heat on it so I didn't observe multiple cycles.
That's correct. I held my soldering iron a few millimeters from the ground surface on the back on the transistor.
The metal on the back of the transistor is connected to the center leg so you have prevent making contact with it. Some soldering irons have a grounded tip and some are isolated.
Compare the readings on the lifted transistor with the one in ch1. Check with the probes on 1-2, 1-3 and 2-3 then reverse the probes and re-check. This will likely be best done with the meter on diode-check.
Compare the readings on the lifted transistor with the one in ch1. Check with the probes on 1-2, 1-3 and 2-3 then reverse the probes and re-check. This will likely be best done with the meter on diode-check.
Ch2 B+, E-: 0.625v steady
Ch2 B-, E+: 1.8V dropping toward 1.2V and back to 1.8V
Ch2 C+, E-: 2V dropping toward 1.3V and back to 2V
Ch2 C-, E+: 1.2V dropping to 0V and back to 1.2V
Ch2 B+, C-: 0.6V steady
Ch2 B-, C+: 3V dropping to 2V and back to 3V
Ch1 B+, E-: 0.625V steady
Ch1 B-, E+: 1.8V dropping toward 1.2V and back to 1.8V
Ch1 C+, E-: 2V dropping to 1.3V and back to 2V
Ch1 C-, E+: 1.1V dropping to 0V and back to 1.1V
Ch1 B+, C-: 0.625V steady
Ch1 B-, C+: 3V dropping to 2V and back to 3V
Measuring with COM on the base and + on the collector on Channel 1 made the 20A fuse I had installed blow.
Ch2 B-, E+: 1.8V dropping toward 1.2V and back to 1.8V
Ch2 C+, E-: 2V dropping toward 1.3V and back to 2V
Ch2 C-, E+: 1.2V dropping to 0V and back to 1.2V
Ch2 B+, C-: 0.6V steady
Ch2 B-, C+: 3V dropping to 2V and back to 3V
Ch1 B+, E-: 0.625V steady
Ch1 B-, E+: 1.8V dropping toward 1.2V and back to 1.8V
Ch1 C+, E-: 2V dropping to 1.3V and back to 2V
Ch1 C-, E+: 1.1V dropping to 0V and back to 1.1V
Ch1 B+, C-: 0.625V steady
Ch1 B-, C+: 3V dropping to 2V and back to 3V
Measuring with COM on the base and + on the collector on Channel 1 made the 20A fuse I had installed blow.
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Thanks for being thorough but when using the meter on ohms or diode-check, you do so with no power applied.
Whoops. Hopefully I haven't damaged something. Here are the values with the power off:
Ch2 B+, E-: 0.63v
Ch2 B-, E+: 1.8V
Ch2 C+, E-: 1.3V
Ch2 C-, E+: 1.2V
Ch2 B+, C-: 0.62V steady
Ch2 B-, C+: 2V
Ch1 B+, E-: 0.64V steady
Ch1 B-, E+: 1.8V
Ch1 C+, E-: 1.3V
Ch1 C-, E+: 1.1
Ch1 B+, C-: 0.63V steady
Ch1 B-, C+: 2V
Virtually identical between transistors. As a sanity check I tested the transistor in another channel on the emitter and base legs and got identical values as these two.
Ch2 B+, E-: 0.63v
Ch2 B-, E+: 1.8V
Ch2 C+, E-: 1.3V
Ch2 C-, E+: 1.2V
Ch2 B+, C-: 0.62V steady
Ch2 B-, C+: 2V
Ch1 B+, E-: 0.64V steady
Ch1 B-, E+: 1.8V
Ch1 C+, E-: 1.3V
Ch1 C-, E+: 1.1
Ch1 B+, C-: 0.63V steady
Ch1 B-, C+: 2V
Virtually identical between transistors. As a sanity check I tested the transistor in another channel on the emitter and base legs and got identical values as these two.
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I pulled the output transistors from Ch2 and tested them and got the following values:
Ch2 D718
B+ E-: 0.060V
B+ C-: 0.060V
E+ B-: 0.060V
C+ B-: 0.057V
C+ E-: 0.002V
Ch2 B688
B+ E-: OL
B+ C-: OL
E+ B-: 0.518V
C+ B-: 0.516V
C+ E-: OL
This suggests that the B718 is bad, yeah?
Ch2 D718
B+ E-: 0.060V
B+ C-: 0.060V
E+ B-: 0.060V
C+ B-: 0.057V
C+ E-: 0.002V
Ch2 B688
B+ E-: OL
B+ C-: OL
E+ B-: 0.518V
C+ B-: 0.516V
C+ E-: OL
This suggests that the B718 is bad, yeah?
The D718 is definitely bad. I would have expected the amp to be driving DC to the speaker and not able to produce audio.
You'll have to use the FJA4213 and FJA4313. Replace them both.
Check the base resistors.
You'll have to use the FJA4213 and FJA4313. Replace them both.
Check the base resistors.
I've been calling this Channel 2 because it's the second one I tested when checking the transistors between the output transistors but I don't actually know which channel it is; Channel 4 seemed to be dead in earlier testing, so this may well be that issue.
Is there a reason to use those particular transistors rather than a generic D718/B688 pair?
What should I check in the base resistors? Do I need to remove them from the board?
Would it be reasonable to redo the solder joints on the other output transistors? I've visually inspected them for cracking and I haven't seen anything obvious but based on repair videos and whatnot I've watched cracked solder joints seem pretty hard to see without magnification.
Is there a reason to use those particular transistors rather than a generic D718/B688 pair?
What should I check in the base resistors? Do I need to remove them from the board?
Would it be reasonable to redo the solder joints on the other output transistors? I've visually inspected them for cracking and I haven't seen anything obvious but based on repair videos and whatnot I've watched cracked solder joints seem pretty hard to see without magnification.
Any of the original part that are available are likely counterfeit.
You need to check the resistors for value. They are likely connected to nothing on one end with with the outputs out of the board. If that's true, you can check them in the board. You're checking them to confirm that they're within tolerance.
The only components that I've commonly seen with bad solder connections in this type of amp are the large emitter resistors.
You need to check the resistors for value. They are likely connected to nothing on one end with with the outputs out of the board. If that's true, you can check them in the board. You're checking them to confirm that they're within tolerance.
The only components that I've commonly seen with bad solder connections in this type of amp are the large emitter resistors.
After installing new output transistors on the channel with the bad one I seem to have steady playback! I'm going to do a test install in my truck and see how it does.