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Repair and disassembly information for amplifiers in home audio systems.

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I need help trouble shooting a circuit, schematic attached.

I attached a schematic of a circuit I am troubleshooting. In red, I have marked where I should be seeing 1.6V on the negative side of two capacitors, but I am getting 0V. What would cause this to happen? The capacitors themselves are good, the + side is getting the appropriate voltage, but I am not getting the 1.6V on the - side.

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thank you in advance for your help!

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Just querying if you're measuring for AC voltage with a signal injected into the amplifier?

They’re both coupling capacitors which allow the AC component of the signal (-ve and +ve going transients) to pass through but not the straight DC. They are directly connected to the R & L, V inputs of U16.

Did you measure at pins 3 & 6 on the IC?

Are the U16 voltages i.e. VCC1A, VCC1B, VCC2 & VDD, all OK.

Here’s the datasheet for the IC.

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I did check 3 & 6 there is no voltage there, that is really the issue I am troubleshooting. There should be 1.6VDC, obviously nothing on the output side either. I am measuring for DC voltage. On a known good board it measures 1.6 on the - side of the caps I mentioned and obviously the VIN pins.

The voltage on the + side of C35 is around 0.6 (which is okay) and the + side of C41 is 2.5V (also okay). I know U22 (TLC2274C) is good but pins 1, 2, 3, should also be getting 1.6V and is not. I also know U16 is good, all other pins are getting the appropriate V, including 11 & 10 (or 9 & 10) which are getting 1.6V. an interesting note, I applied 1.6 V to pin 3 of U16 and no voltage present on the output side.



Looking at the schematic U16 pin 1 & 2 should have +3.3 Clean (which I assume is a voltage) unless C31 or C37 is dragging it down or maybe U16 pins 1 or 2 or 24.

The datasheet for a TLC2274C (see p.2) looks different to what your circuit shows, although admittedly the "C" version is not mentioned as such. Is it either a CD, CN or a CPW version perhaps? But they only have 14 pins and not 24 as shown in your schematic.


TLC2274C is U22, I believe is just a quad op-amp. Sorry for the confusion on that.

All other pins on U16 other than VINR, VINL, VOUTR, VOUTL are getting the appropriate voltages, including 1,2,24 at 3.3V.



Sorry. It was my confusion, not yours

I confabulated your reply and was thinking that U22 was U16, I'm getting old ;-(

Did you use an oscilloscope to check the U16 clock input? Looking at its datasheet pin 9 gets the clock pulses and these can be used reset it once VDD on pin 14 is >2.2V (see p.23)


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Aaron zal eeuwig dankbaar zijn.

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