-18.01v on one side of R151 and 16.53 on other side of R151.
On Base Emitter and Collector of Q106 18v....
On Base Emitter and Collector of Q106 18v....
Agree with Mooly's suggestion:
1) Take resistor R300 out and see if the output (node M) goes to fully negative. If that works, then the problem seems to be prior to R300.
2) If not, you can also take out Q106 and check node M again. If M goes fully negative now, then Q106 seems to be the problem.
1) Take resistor R300 out and see if the output (node M) goes to fully negative. If that works, then the problem seems to be prior to R300.
2) If not, you can also take out Q106 and check node M again. If M goes fully negative now, then Q106 seems to be the problem.
You need to measure the resistance to be sure, it could be open circuit.
The B-E voltage has to be done as a single measurement across the junction. Nothing else will do 🙂 The emitter should be the more positive point.
Hi ...
I dessoldered R151,R154,R300 and Q106.
Now left channel works fine,but the level is
50% low more right.
I will replaced all resistors and q106.
Thank you.
I dessoldered R151,R154,R300 and Q106.
Now left channel works fine,but the level is
50% low more right.
I will replaced all resistors and q106.
Thank you.
OK, you're essentially bypassing the entire amplifier stage of this sub-board now, which explains the lower level. I would not recommend to use it for a long time like this until the problem is fixed.
Did you test by taking out the components one by one, or you removed all at once? Because now we don't know for sure which of the components caused the problem, in fact the problem could even be caused by some components that are still on the PCB.
What you can do: measure with a multimeter if R151 has the correct value (should be 4.7k ohm). If so, solder it back on the PCB. If all is well, the DC voltages at nodes K and L should be pretty negative then (like -15V to -18V) instead of being positive as before (16.5V and 18.2V). If that is indeed the case, likely you will fix the problem by replacing R300 and Q106, and re-installing R154. If, on the other hand, the voltage at K and L remains highly positive, the problem lies somewhere else.
Did you test by taking out the components one by one, or you removed all at once? Because now we don't know for sure which of the components caused the problem, in fact the problem could even be caused by some components that are still on the PCB.
What you can do: measure with a multimeter if R151 has the correct value (should be 4.7k ohm). If so, solder it back on the PCB. If all is well, the DC voltages at nodes K and L should be pretty negative then (like -15V to -18V) instead of being positive as before (16.5V and 18.2V). If that is indeed the case, likely you will fix the problem by replacing R300 and Q106, and re-installing R154. If, on the other hand, the voltage at K and L remains highly positive, the problem lies somewhere else.
Can your multimeter measure resistance? Often shown with an Omega symbol. If so, just hold the multimeter probes against the resistor pins. The resistor should not be on the board, just separate. If it is not clear, I can show you a picture to explain.
The value sets the maximum range of the meter, so it should be set to the nearest value larger than the resistor. For example, try 20K.
To be complete:
R151: expected value is 4700ohm or 4.7Kohm, so set the meter to 20K.
R154: expected value is 10ohm, so set the meter to 200.
R300: expected value is 68ohm, so set the meter to 200.
Nothing can break if you use the wrong setting here, so just try.
R151: expected value is 4700ohm or 4.7Kohm, so set the meter to 20K.
R154: expected value is 10ohm, so set the meter to 200.
R300: expected value is 68ohm, so set the meter to 200.
Nothing can break if you use the wrong setting here, so just try.
Ok,the parts are very small and I all balanced in garbage.
I ordered all resistors and q106.
If 4K7 and 4.7K is the same value for resistor for order
I ordered all resistors and q106.
If 4K7 and 4.7K is the same value for resistor for order
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I can't help but think we should be diagnosing this by careful measurements and not just replacing parts in hope 🙂
Instead of replacing the 4k7 for example, you could just tag another across it and see if the fault changes. Always try and do as little actual desoldering of parts as possible when looking for faults.
Instead of replacing the 4k7 for example, you could just tag another across it and see if the fault changes. Always try and do as little actual desoldering of parts as possible when looking for faults.
With the removed components, you could measure voltages at nodes A, B, C, D, E, and Q again. They should now be much closer to the values of the right channel (but still different because not all components are in place). Can you measure these?
Once you have the new components, you can add them one by one:
1) First add R151. Measure voltages at K and L. They should be negative, like -15V to -18V. If not, we need to debug. If yes, go to step 2).
2) Add Q106. Measure K and L again. They should still be negative as in step 1). If not, we need to debug. If yes, go to step 3).
3) Add R154 and R300. Measure M. If M is around 0V now, it looks good. If not, we need to debug.
Once you have the new components, you can add them one by one:
1) First add R151. Measure voltages at K and L. They should be negative, like -15V to -18V. If not, we need to debug. If yes, go to step 2).
2) Add Q106. Measure K and L again. They should still be negative as in step 1). If not, we need to debug. If yes, go to step 3).
3) Add R154 and R300. Measure M. If M is around 0V now, it looks good. If not, we need to debug.