|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
24.164.157.56
In Reply to: Help with dysfunctional MC 240 posted by Will shade on March 27, 2007 at 10:04:13:
Are you dealing with a stock unit??? If you are you are chasing your tail around with the approach you are currently taking.The selenium bias rectifier must go, and at the very least I would replace the coupling caps, and test the filter caps- even though a full replacement is a better option.
A full restoration will not only improve the sound tenfold on your MC240...it will make chasing down weird problems in vintage units much easier since you eliminated many variables. Sometimes it can take days to sort problems on units that have had standard restorations carried out...I would not want the headache of trying to chase down problems on a vintage unit that is 100% original.
Follow Ups:
My 240 was re-furbished by Audio Classics when I first got it, and it's worked flawlessly for five or six years. I noticed a tube glowing cherry red on the plates a few months ago, switched tubes and found the same thing, so I unplugged it and sent it to Terry DeWick. Dewick checked the whole thing over and found nothing wrong with it. Once I had it back from DeWick I played it in a second system for a couple dozen hours, when the offending tube flashed blue and I posted here. I can't really blame DeWick, because it played fine for a while before this problem started happening.I know a bit of electronics, but I've always paid other people to work on my Mac. However, I REALLY, REALLY don't want to pay $70 to ship this thing to another tech - I just got it back from Dewick a few weeks ago. That's why I took the voltage readings and posted here.
Anyway, to answer to your point, the selenium rectifier has been replaced and this 240 has been gone over by two guys who are generally considered the best Mac techs in the business.
I am sorry if my post seemed a little "lecture" like...I have just seen so many people on AA try to troubleshoot stuff when there are about 77 other things wrong with the unit to begin with....although I admit you see much more of that type of behavior on the vintage board.Have the electrolytic cans been changed??? Many techs leave them alone...because they do last a long time...but they are also capable of causing many problems even when they bench test fine. A lot of techs also leave the original silicon diodes in place...which also can cause problems.
When doing the basic stuff (ie-swapping channels with the outputs) does the problem follow???
There are still cans there, but honestly I'm not sure if they're the originals or not. I'm not sure about the diodes - I think they might be original, and I was thinking of changing them myself. Damn digital camera broke (too) so I can't post a pic. Nearly all the resistors and caps are original, however.Not sure what you mean by 'swapping channels with the outputs'...
Yeah, ultimately, you guys might be right... when I posted before, a few weeks ago, the posts lead me to believe I could track down the problem myself with a little help... but I'm not an expert by any means. It just PO's me that I just dropped $200 ($70 shipping and $130 for the bench check) for repair and poor baby's not up and running yet... I love the amp, but I hate to pump more money into it right now.
This post is made possible by the generous support of people like you and our sponsors: