Manley Vari-Mu noise issue

[Ike Zimbel]

Manley has been wonderful. They've given me a lot of tips, sent me a new set of caps, and checked in to see how I'm doing. Way more than I would expect, and more trouble for them than simply tell me to just send it to them for repair.

I've finally found something repeatable:

• If I press down firmly on the input transformer, the noise goes away, until I remove the pressure.
• pressing down with a pencil on the main pcb around the transformer does not have the same effect.
• I removed the transformer (tricky job), since there are some solder pads under it I could not reach to re-flow. I cleaned up the header, re-installed it, and installed a couple jumper wires to be sure I could get a good connection to those pins that I couldn't reach easily to solder well.
• I re-flowed the points on the input transformer pcb itself

After all that, it makes the noise when it is idling by itself. If I press down firmly on the transformer, the noise disappears. My hunch is that the issue is in the input transformer pcb itself, meaning it's not the pressure that creates on the main pcb that is restoring the proper connection. I've passed this on to Manley to see if it sounds familiar to them.

This still sounds like a cracked trace to me. I can't remember if Manley boards have solder mask on them or not but in any case a lot of the cracked traces that I have found have been right at the transition point between the pad and the trace (which is also where you go from tin to solder mask, hence the question). If there's solder mask, I would scrape off about 1/8" or so where it meets the pad and then bridge with solder from the pad out along the bared trace. If there's no solder mask, I would clean the trace with some isopropyl and then do the solder bridge as mentioned above. OR, just try metering from somewhere on the trace to the pad, as per my earlier post.

 

[skidmorebay]

After lots of time into this today, it's looking more and more like it's the input transformer. The channel works correctly if I press on the input transformer in just the right way. I've checked and checked all the connections in that area, re-flowed everything, on top of the other steps I took previously (re-cap, tube sockets, tubes, etc.)
Manley is thinking that it's likely there is a partially broken winding in there that I am effecting when I press on it. I'll talk to them about a replacement on Monday.

thanks for the tips here.

 

[skidmorebay]

I've got a new input transformer on the way from Manley. They agreed this is the best next step. I was surprised to find that you can order them right from the website (tubesrule.com) for $85.
They claim their won't be any sonic difference between the new one and the 1997 transformer in my VariMu. If I notice one, I can always order a second for the other side. I went with just one for now, since I'm not 100% certain it will fix the problem.

 

[skidmorebay]

Hi folks. Long time.

My Vari Mu is working very well now. It took a while to find the time to dig into this. Long story short, I replaced the input transformer with a new one from Manley. This did not do the trick at first. I later found a solder bridge I had created when transferring the transformer's mounting PCB to the new transformer. That resolved the last issues I was having. I'm happy to say that it is once again sounding wonderful.

Manley was really helpful in this. Many thanks to Len Knitter and his crew for the technical advice and support.

 

[lassoharp]

https://groupdiy.com/threads/anyone...n-matching-b-supply-power-transformers.88565/