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An audio/video receiver (AVR or home audio receiver) is a consumer electronics component used in home theaters that convert signals into sound.

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Issues with right channel phono pre-amp being too low/non existent

I am dealing with a Technics SA-EX100 stereo receiver. My issue is that the right input for phono is super low. This is what I've tested so far using my headphones:

-Swapped left and right phono in, made the left side quiet and the right side normal volume

-Plugged the phono into CD and tape inputs. They were very quiet since it lacks the pre-amp, but they were at an equal volume for both left and right

-Playing something else like the radio give equal volume in both left and right

I have been able to hear the phono right side at a low level by turning the balance almost all the way to the right and then turning the volume up to max.

What I'm looking for is where I should be focusing on when I open this up. Does it seem like a dry solder joint situation or bad caps? Are there electronic components I'm not thinking about like resisters that would cause this? Is this a rabbit hole that I don't want to go down?

I have this specifically for playing records, and this is really bumming me out ATM.

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@sparkelpimp this"Swapped left and right phono in, made the left side quiet and the right side normal volume" is the oddest thing. It would mean that your right side is actually ok. Can you explain how you switched it. Has this amp ever worked for you before? Anything happen to it? Do all the other inputs (CD/TV/VCR all work? What else do you have connected to the Amp?

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@oldturkey03 Sorry about that. I should've said that I pulled the RCA cables that were going into the phono in and swapped them. It was to rule out that the right channel wasn't bad on the record player itself.

All other inputs work as far as I know. I don't have components to test them with other than the record player itself. But without the pre-amp of the phono input, the music is very quiet.

I had purchased this from Goodwill and was taking a chance on it. So I don't mind getting in there if it can be a cheap fix. I'm OK with a soldering iron and wouldn't mind if I had to get a few electronic parts. I just don't know where to start or what I should be testing (with multimeter or other methods).

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@sparklepimp when you switched the wire it should not change anything on the receiver. So, my concern is that it is either the record player or the cables you are using that are causing this. If you have another set of wires give it a try. Otherwise just use one side. Try the red first. Use it in R phono and then L phono. Then do the same with the white end. Let us know what you get. Oh yes, make sure balance is somewhere in the center.

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@oldturkey03 The RCAs are wired into the record player and I can't use different ones.

Using only one RCA at a time and balance is centered:

- Red going into right phono input. Music is so low that you can still barely hear it at max volume

- White going into right phono input by itself. Same result with low music

- Red going into left phono input by itself. Left side sounds perfectly normal at a normal volume setting.

- White going into left phono input by itself. Left side sounds perfectly normal at normal volume setting.

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@sparklepimp okay going over the schematic right now and let me see what I can find out.

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Hi @sparklepimp ,

Here's the phono section of the service manual for the receiver, showing the input circuit.

I'm at a bit of a loss to understand why the volume would change when swapping the L & R inputs because if the right phono input in the receiver was faulty then it would always be faulty whether the left output or right output from the turntable was connected to it and not change to the left input.

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Thank you for the link. I may have mis-wrote my question. The right channel phono input on the stereo receiver is faulty regardless of what I plug into it. The left channel sounds perfect.

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@sparklepimp

Both L & R phono inputs are wired pretty much the same so I would check capacitor C452 (supplier example only) is OK and not high resistance to AC current flow

Bit hard with a DMM as you really need an esr meter. (supplier example only) to measure the capacitor's equivalent series resistance and also its capacitance, but they're not cheap for only a one off use. They're really good if you're doing a lot of electronic board level repairs. Gets rid of the uncertainty whether a capacitor is good or bad.

One way I suppose would be to unsolder both C451 and C452 and swap them over and check if the problem moves to the left channel. If still no good measure resistors R470 and R454 and check that they are as specified - perhaps compare them to R469 and R453 (resistors used in path for L channel input) - and not that one has gone high resistance

If you try this, remember that they're electrolytic capacitors so polarity is important. Check where the negative stripe is on the capacitor body. Also usually the board marks the positive leg of the capacitor. Apologies if you already know this ;-)

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Hey Michael,

Its been a while since i worked on audio amps but you could be looking at anyting from poor connections to faulty components. getting your hands on a circuit diagram for the model and tracing the line back from the output would be a good place to start, check the components for discolouration and if you have a multimeter on hand and know how to use it, check for open circuits where they shouldnt be.

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Thank you for that. I do have a multimeter, but I have not found diagrams for my stereo yet. I usually come to ifixit for my repairs (hence the post), but they don't have this particular model.

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