Little to no sound from Pioneer 2 channel integrated amp

[Tronik24]

Hello everyone, my first post and I am somewhat new to troubleshooting, but have a small background with DC and AC theory.

My question is I have a Pioneer A-676 2 channel Reference Amp that a person sent to me stating there is little to no sound.

The amp:

> turns on and I see the red lights on both channels
> I hear the relay kick in
> When I turn the speaker selector from Off to A to B to A/B I hear a click when each is selected
> I do not notice any bulging caps or smell smoke nor do I see any burnt areas from higher heat component areas

I sold this amp in excellent working order and it got damaged in transit where the MC selection knob (far right) was pushed into the amp. The buyer turned it on and reported this problem.

I got it back and lucked out that there was no other physical damage to the amp itself.

I am teaching myself electronics and learned so far that a person needs to 'isolate' the product (no Earth Main) just in case one hooks up their probe from a scope the wrong way. The only thing is the video does not say you plug the 'amp' into the isolation transformer or you plug the scope into the isolation transformer when testing.

There is a video I watched on testing the 'rail'?! Where there are two 5W (white) resistors I believe and the SRC transistors (I think they call them that).

I will plug in a set of headphones to report if there is volume or not, as I wanted to ask if there is something I need to make sure of before I begin to search for this problem (afraid to hook speakers up or basically take that first step).

This is a journey I would like to learn from and gain skills and confidence with each repair/fail!

I thank everyone in advance for advice/help with what to look for if this 'low to no sound' issue is the case.

[KhronX]

I slightly "got bitten" by a similar symptom a few weeks ago, with an old Yamaha stereo amp. On that one, it had a "preamp out" and "power amp in" pair of RCA jacks, and those needed an external jumper - in hindsight, that was sort of obvious 

This Pioneer doesn't seem to have that sort of arrangement, though.

Does this happen regardless of the selected signal source? Assuming that, of course, you have some signal source plugged into at least one of the input pairs

<later edit>

Found the service manual over here: https://www.eserviceinfo.com/download.php?fileid=55608
Download all three parts before decompressing it, though

As expected, that switch that got bumped belongs strictly to the phono preamp section, so that shouldn't affect anything else in the preamp or power amp sections.

Given that it's an aging unit, it might be worth giving all the switches a bit of a workout, ideally with a little squirt of contact-cleaner into them. Also, 1-2 removals of whatever connectors you can reach would help ensure those haven't developed wonky contacts.

[Tronik24]

Hi KhronX.

I just found the issue. It is the selector switch for A, B, A/B at the front of the panel.

A works fine.

B does not - unless - you slightly turn it toward the A+B selection. I did not have two sets of speakers so I tested them one side at a time. Whew, so I think I will go into the manual and find the part# for this - (is this a 3 position switch?).

I am not sure if anyone knows if a person can just replace with a quality selector switch?

I am not sure on the specs of this yet, but I am hoping this poor thing now gets the respect it deserves!

The selector switch clicks for the MC and such on the far right it just does not stay put as it was pushed in during shipping and I need to see or figure out how to fix...I really do not want to gob glue on but I do not own phono stuff anymore.

I hope this post may helps out...not much but I fluked out by turning the switch slowly and then fast and noticed the B channel cutting in and out...could try deOxit on it but I think I will try to fix, what a sound though!!

Thanks everyone!

[Tronik24]

Hi KhronX,

I saved that schematic site, I am not sure how to open a .rar file. I found the manual on Hi-fi ... I think the speaker channel selector switch is wonky for sure but will try to give it some deoxit.

That phono switch I am not sure but there were some loose material inside and must be the part that held the switch in place, right now not worth the worry, this will be my backup and Frankenstein amp, but the sound it so nice! I truly wish I did not do the eBay thing but trying to pay my buddy for the Wharfedale Valdus 500's (I think they are called) I got from him.

Lesson learned, I did not use enough bubble wrap, but the catch 22 is, if you pack it right the size of the box goes up and so does the price...so no more eBay for me at least for selling!!!

[KhronX]

https://www.7-zip.org/ 

[cheeseit]

Or just use hifiengine, much better IMHO. It is free and I use it all the time but registration is required.