Help needed! Troubleshooting issue on BeePre

[Daggasound]

Hey all, thanks in advance for any guidance you might be able to offer.

I have a BeePre right now that needed some repairs and a friend of mine took care of for me. 

However, when it came back it had a new issue, namely that the left side outputs full volume regardless of the position of the volume pot (it does respond to the balance pot, it is entirely silent if it is all the way to the right and gets louder when moved to the left). The right side works just fine and when the volume on it is full it is balanced with the left side.

So my guess is something is awry on one of the terminals near the volume pot itself but I have no idea where to start and the friend who handled the previous repair (incomplete) is now gone for months so I want to take care of this myself

I still have the schematic and assembly instructions but looking for guidance on where to begin looking for the issue, I can post pictures if you need?

Thanks so much in advance

 

[Deke609]

Clear, detailed pics of the source selector, balance and volume pot wiring might help.

Do you get the same result if you use a different pair of inputs? [Edit: just reread your post and see that the balance pot works. This suggests that the problem is with the volume pot wiring (or, far less likely, with the pot itself).

cheers, Derek

 

[Daggasound]

Thanks

Yes, same for all inputs, I'll get some pictures of that area later but, just looking at it, all looks to be in the right place unless there's a dubious solder connection that I'm not seeing

 

[Deke609]

PB will surely jump in soon and give you expert troubleshooting advice. My only thought is to check that (1) the white wire attaching the volume pot to the 300B socket is soldered to the middle upper lug of the vol pot (and that no other wire is also soldered to the upper middle lug), and (2) that the white wire connecting the balance pot to the volume pot is connected to the upper lug closest to the the back of the chassis. 

The fact that the left channel doesn't respond at all to the volume pot suggests that the left channel signal wiring is bypassing the pot. That could happen if the white wire from the balance pot was connected to the same lug as the white wire going to the 300B socket.

If that's not it, I'd doublecheck that all the wiring set out on page 50 of the manual has been done correctly.

cheers, Derek

 

[Paul Birkeland]

You guys pretty much nailed it.  I would guess that it's either the scenario that Derek mentioned or there's a missing ground wire and half of the volume pot doesn't have the ground reference that it needs to work.

 

[Daggasound]

Fantastic, thank you all for laying this out so clearly, I'll check tonight and reply with pictures if this doesn't solve the issue

 

[Daggasound]

Hey all

So no luck, I can't see anything around the wiring of the volume pot that isn't as it should be, I checked the places you suggested particularly and soldered those points again.

I've attached a few photos but not sure if they're what you need to see, happy to get more at any angle that will help

One other thing that may help diagnose, this unit was, at one point, working absolutely fine but some pins came loose from one of the 300b sockets (left side) and we had to change out the socket and C4S board which it apparently did some damage to (this was the work undertaken by my friend)

The wiring to and from the volume pots etc wasn't touched at all, just the C4S board replaced as I say.  That doesn't mean that in transporting it around something hasn't come loose elsewhere, just that we're both a bit mystified as everything looks right per the manual (as far as I can see) and at one time the volume and balance pots did behave as they should

Thanks again for your help folks

 

[Paul Birkeland]

Can you perform the resistance checks for terminals 1-19?

Can you turn the volume pot all the way up, then check the DC resistance between the chassis plate and every lug on the volume and balance pots with a black wire on it?  (They should all be 0 ohms, perhaps one is not)

 

[Daggasound]

Ooffff...I think I've hit the end of what I can do here!  Gonna hand it over to a pro.

I'm fine with basic soldering points to other's and simple troubleshooting but this is going over my head now

As I say, the assembly was actually done by someone else initially and while he did the C4S replacement he's been too busy and gone since to troubleshoot this new issue, thought I would have a go but I know when I'm out of my depth!  I appreciate you trying to help me, just need someone with more skills to take this over I think

 

[Deke609]

this is going over my head now

If you have a multimeter, what PB is asking is actually very easy to do. Turn the power off and unplug the amp. Set the meter to measure Ohms (the omega symbol) and make sure the leads are plugged into the correct sockets on the meter (black to COM and red to onve with "V" and the omega symbol).  Then take one lead (doesn't matter which) and press it lightly against the metal chassis plate. Then touch the other lead to a solder lug on either the balance pot or the volume to which a black wire attaches. And read and record what the meter says. Note, if it indicates "OL" that is the opposite of zero. Repeat with every other pot lug to which a black wire attaches. Worst case scenario: it takes you 3 minutes.

cheers, Derek