Manley Vari-Mu noise issue

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Ike Zimbel

Well-known member
Joined
Apr 17, 2011
Messages
109
Location
Toronto, Canada
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

Well-known member
Joined
Aug 1, 2011
Messages
121
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

Well-known member
Joined
Aug 1, 2011
Messages
121
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.
 
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