Rotel RTC-850 Preamp left channel is silent. After some interconnect swapping, I determined I have a problem with my Rotel preamp. When I play my CD input into the LEFT channel i get the following: Silence when the CD (L or R) is plugged into LEFT CD input. Low volume when CD (L or R) is plugged into LEFT AUX input. Any ideas? Is this worth repairing, or is it time to get a new preamp? Any help would be great.

NEW CHANNELS? find channel Press Memory button then #button to associate. (see link to manual pg 5) NO global reset.
https://www.manualslib.com/manual/142512/Rotel-Rtc-950ax.html

Without knowing more details, I would be enclined to suspect the power supply has a bad capacitor, which is a sign of bad filtering. Bad ground or bad capacitor!!! My guess. Hope it helps.

Yes amps buzz when something gets near them - say a pen or probe and if you know what it is safe to touch a finger! Fortunatly for you the left channel is the same as the right. So if you believe it's the pre-amp work backwards from the where the power amp connects to the pre-amp, going through the pre-amp stage by stage - prodding the parts. Remember a buzz in the right a buzz in the left! No buzz in the left but one in the right fault found!
Ignore the power supply it's nothing to do with that as it's common to both channels.

First, lets's determine if it's the amp or the preamp...

Swap the Left and Right channel cables between preamp and the amp with each other.

Did it stay on the right? = amp problem.

Now on the left? Preamp or source.

Plug any Line Level device (CD?) directly into the amp inputs. Work now? Preamp problem.

ALL sources? Preamp - toggle all controls, especially a Tape Monitor to possibly wipe of any built-up oxides in them.

If I understand you, the 'sound' of the AR preamp is what you're trying to preserve. Presumably you're just running a phono through it as nothing else needs a preamp these days.

The multichannel inputs bypass all of the Rotel's processing except the volume. Use the Front L and R.

Yes, sounds like your DSP chip has an issue. Not an inexpensive repair if that's the culpret. Around 400-500 to replace the chip. It's an awesome receiver and worth 300-400 in repair, however, a 3800 or 1800 can be had for 600-800 depending where you look. If you need more help, post a comment and I can help you some more.

Connect a set of stereo RCA cables from the 'Output 2' on the Hafler to the line imputs on the Sub.Turn on the '1+2' output switch on the Hafler and rock out!

It sounds like the preamp wire that carries the left channel signal between the HU and the 2ch amp has an issue. Here's two quick things to check.

1. Check that both ends of the left preamp cable between the deck and 2ch amp is not loose or disconnected.
   
2. Swap the left and right preamp connections at the amp. If the issue stays with the left channel, the issue is with the amp. If the issue moves to the right channel, the issue is with the preamp cable or the HU's preamp output.

Let me know what you find out!

I'd suspect that one of the two output transistors on that channel has gone bad. If you are unsure how to test or troubleshoot this, then you might try replace both the NPN and PNP outputs and catch the bad one that way. If your amp uses an output module then you would of course have to replace the module which would replace all the output transistors on both channels. Good luck. Another thing to look out for, is the emitter bias resistors. They are the large white ceramic ones near the outputs. Sometimes one of those will open up too. They will be of a very small resistance value like .5 ohms (point five ohms) or something in that general ballpark, and have a wattage value of typicaly 5 watts. So they are pretty big resistors. Be sure to check them all even if you do find a bad output transistor. They will often go out with the transistor. Good luck.

Hi i don´t speak a good Englis but i think what you have a problem whit a filter in the preamplifier, just in the final amplification block, open it end check for any spill o exploded filter