Sorry I couldn't understand. How do I use "2 inputs at the same time"? There is only one 3.5mm stereo receptacle on the Speaker unit. I have multiple stereo cables though and multiple devices that can produce audio (mp3 player, mobile phone, laptop, etc.). I have tried using different cable and devices in a number of combinations with the same result.Yes, if possible with the same source(switch the input from the first jack to the second one, then try to use 2 inputs at the same time even if they are not the same and switch them again).
The TDA7377 has 4 inputs If I short the 2 inputs for the L R speakers I get audio in both speakers (L & R) i.e. I get Left channel audio in both speakers. So the problem seems to be before this amplification stage? Correct?The TDA7377 is the output amplifier with L R and subwoofer,. The lm324 is probably the tone control preamp. You could swap or short the inputs to the tda7377 to prove it.
In my post under "Troubleshooting and things tried so far:" please see point 1:Are you sure that the problem is not in your "Audio source" or settings. If you supply the audio source from a computer, try changing it with a different cable and your phone instead.
Basically each OpAmp handles 2 channels of sound. At each stage I am shorting the channels to see if the Right channel (the channel which I am having problems with) reaches the left speaker. This happens in all cases except at OpAmp U10.1. If only the right channel of audio is allowed to enter the Stereo input jack (J1) by changing the Left-Right balance on input source (mp3 player / computer) and the output pins (pins 1 and 7) are shorted on the 4558C OpAmps (U1 / U5 / U10) or the Volume control IC (pins 2 and 15 on PT2256) it can be seen that right channel audio reaches the left speaker correctly in all cases except when output pins are shorted on OpAmp U10. It would seem that the problem seems to be around the OpAmp U10.
Thats what I thought and tried to swap the chips but alas. Infact I put DIP8 sockets in the place of the opamps so I can try different chips. Didn't fix the problem. In my post under "Troubleshooting and things tried so far:" please see point 3:Looking like the preamp stage then U10, no right chan.
Can you swap chips?
3. Removed OpAmps U1, U5 & U10 and replaced with a DIP8 socket. After replacing all 3 OpAmps with NE5532 (compatible replacement) right speaker still doesn't sound.
Indeed! Strange mix and this is not the only place it has been done on the PCB.Very odd mix of SM the TH parts!
Nice catch!!! I tested (in-circuit) between loudness tap (LT1 & LT2) and AGND. On the TH side it was 3.18 K ohms on the SM side it was open circuit!!! The SM resister doesn't seem to be damaged visually and seems to be soldered correctly but clearly it seems to have a problem. Unless the two sides are not symmetrical. Marking on SMD resister is 392 (3.9 K ohms I think) and TH side is 4 band orange,white,red,gold (3.9 K ohms). Your recommendation? Replace SMD? I might have a close TH resistor. How important is the value?Any chance that resistor might have been damaged or desoldered at one end in changing the IC? It looks like R10 does the same for pin 11, but it's through-hole.
You mean pins 4 and 13? I really don't understand this loudness tap. What exactly is it for?The only thing I can see that might have something to do with it are the "loudness tap" pins, 4 and 11.
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by Luke James
by Luke James