Have heavy distortion and weak output on right channel. Have narrowed problem down to the Driver (amp) board. I do not have an oscilloscope, just an hand held audio tester that I use to debug with (along with volt, cap,esr, transistor meters) Schematic and Voltages of the bad channel (right) are shown at the bottom. Right channel parts are represented by everything in the ().
Before some can explain to me what is wrong, I want to understand what is supposed to be right. For example, On the left (good channel) Clear audio comes in Base pin 2 of Q801. I hear good clear audio out the emitter pair, and well as the other base pin 6. In contrast, the left channel has no audio out the emitters pairs and distorted audio out both other base pin as well as the collectors.
So starting with the good left channel, I am confused right off the bat why the audio is coming out the emitters
**My question 1 - I thought the audio path was to go out the collectors? But it seems in this case the audio is coming out the emitters, then onto the base of Q805 & Q807. Then out the collectors? and onto the base of Q809 & Q811? Then out the collectors again and to the speaker? Or do I have that wrong? I want to clearly understand that first and what the expected audio path is from input on that driver board to output
NEXT - For the bad right channel, Voltages are severely messed up. There's clearly not enough voltage Collector Q804/Bases of Q806Q808, and the final stage Q810/Q812 look like the base/emitters might be shorted. Both were easy to disconnect from the board and test (simple pulloff tabs). Q810 tested fine. Q812 was not registering well. Turns out the little fusable link tied to it's emitter is dead. I will have to replace that and I have the part. Doing a diode check on that transistor, it shows a lower voltage .47, whereas all the others are above .5. Further, on a transistor tester, it is shown to be leaky as well. So it's needs to be replaced. It's a custom fisher part TR01058-5 no public datasheet I can find and google say NTE182 is the only substitution. The 5 watt associated R838 .39 ohm resistor is also registering high (1.2 ohms) so I'll replace that too
**My question 2 - Is the NTE182 the best match? Probably hard to answer without an original datasheet...
The identified failures don't seem to be the source cause of the distortion, as with them out of circuit completely, i still hear it, so it must be coming from an earlier stage. I attempted to set the bias but couldn't get anywhere close (on the right channel) with the current components.
** My question 3 - Why is audio coming out of Q802 in different spots then the left channel counterpart?
** My question 4 - Thought what to investigate next? Components to check out?
** My question 5 - Last one in this message - I promise I'll create a new message for others During probing, I inadvertently broke CR803 (on my good channel of course, figures). Channel still seems to be working though. The part # SIT51B096-5 goggle says replace with NTE116 1A 600V rectifier. I don't have any of those but I do have a handful of 1N4003 1amp 200V. Could that be substituted instead?
Before some can explain to me what is wrong, I want to understand what is supposed to be right. For example, On the left (good channel) Clear audio comes in Base pin 2 of Q801. I hear good clear audio out the emitter pair, and well as the other base pin 6. In contrast, the left channel has no audio out the emitters pairs and distorted audio out both other base pin as well as the collectors.
So starting with the good left channel, I am confused right off the bat why the audio is coming out the emitters
**My question 1 - I thought the audio path was to go out the collectors? But it seems in this case the audio is coming out the emitters, then onto the base of Q805 & Q807. Then out the collectors? and onto the base of Q809 & Q811? Then out the collectors again and to the speaker? Or do I have that wrong? I want to clearly understand that first and what the expected audio path is from input on that driver board to output
NEXT - For the bad right channel, Voltages are severely messed up. There's clearly not enough voltage Collector Q804/Bases of Q806Q808, and the final stage Q810/Q812 look like the base/emitters might be shorted. Both were easy to disconnect from the board and test (simple pulloff tabs). Q810 tested fine. Q812 was not registering well. Turns out the little fusable link tied to it's emitter is dead. I will have to replace that and I have the part. Doing a diode check on that transistor, it shows a lower voltage .47, whereas all the others are above .5. Further, on a transistor tester, it is shown to be leaky as well. So it's needs to be replaced. It's a custom fisher part TR01058-5 no public datasheet I can find and google say NTE182 is the only substitution. The 5 watt associated R838 .39 ohm resistor is also registering high (1.2 ohms) so I'll replace that too
**My question 2 - Is the NTE182 the best match? Probably hard to answer without an original datasheet...
The identified failures don't seem to be the source cause of the distortion, as with them out of circuit completely, i still hear it, so it must be coming from an earlier stage. I attempted to set the bias but couldn't get anywhere close (on the right channel) with the current components.
** My question 3 - Why is audio coming out of Q802 in different spots then the left channel counterpart?
** My question 4 - Thought what to investigate next? Components to check out?
** My question 5 - Last one in this message - I promise I'll create a new message for others During probing, I inadvertently broke CR803 (on my good channel of course, figures). Channel still seems to be working though. The part # SIT51B096-5 goggle says replace with NTE116 1A 600V rectifier. I don't have any of those but I do have a handful of 1N4003 1amp 200V. Could that be substituted instead?