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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!

Diese Frage beantworten Ich habe das gleiche Problem

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Hi,

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.

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@Aaron

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.

von

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.

von

@Aaron

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 wird auf ewig dankbar sein.
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