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TFM-45 Whistling

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gunner64

Newbie

Posts: 44

Joined: Sun Mar 14, 2010 11:57 am

Location: Dubuque,Iowa

Post Thu Apr 08, 2010 12:51 pm

Re: TFM-45 Whistling

Hi Gary,If What Billd suggested doesn't give you a reading Try some deoxit or other quality contact cleaner on the Pots.Mine were very dirty,and wouldn't allow any voltage at r94 or 95.Also make sure your testing across 1 resistor or the other.-Take r94,put 1 lead of your meter on the top lead of r94,the other lead on the bottom lead of r94.you should get a reading.reversing the leads,as Billd said will reverse polarity.it may be helpful to have multimeter leads with mini clips or small alligators.then you can clip the leads on and see the reaction of the meter when you manipulate the bias pot.also pushing slightly on the amp boards above the bias pots(at the edge,with a non conductive tool,NOT your finger)Will expose a bad solder joint.(it did on mine)Also If you can find a decent digital multimeter it would be in your best interest to do so.your meter will work,but digital is so much easier,and accurate.I'm just a layman also,and repair my own stuff as a hobby,there's people on here a lot smarter than me,That may be able to help you better.I can only tell you from my experience with my own amplifier.And if you can't get a Bias reading,sounds like you have the same prob. I had with mine.(dirty pots,Dirty pots,dirty pots,)Did I say dirty pots?If you go to spray contact cleaner on the pots, take small pieces of tissue and wad them around the pot,to avoid hosing down the intire inside of the amplifier.Just be careful not to disturb anything else inside when doing so.and remember to remove the tissue before powering up.If you can't get a Bias reading after all that then I'd say your amplifier needs more service than you or I can give it.(don't forget the damping adjustment either)Good luck!
Robert
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gary_wong5

Newbie 50+

Posts: 70

Joined: Fri May 16, 2008 8:17 pm

Post Fri Apr 09, 2010 8:57 am

Re: TFM-45 Whistling

I sprayed and cleaned the pot with contact cleaner but still gained dead reading. So I cross-checked and compared both left and right AMP boards. I discover that the Q4 (transistor MPSU60) is dead. Is this the culprit (and also turn on/off thump?)?
This was long discontinued transistor and not available here. Is MPSW92 equivalent to MPSU60 without giving problem sonically?
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gunner64

Newbie

Posts: 44

Joined: Sun Mar 14, 2010 11:57 am

Location: Dubuque,Iowa

Post Fri Apr 09, 2010 4:06 pm

Re: TFM-45 Whistling

I don't have a clue about transistors..Like I said I'm just your average guy who likes to work on my own gear.Maybe someone else has an answer for you.From what I've read in your old posts your amplifier has given you nothing but trouble since you've had it.Maybe its time to buy another.Especially if someone who wasn't intirely sure what they were doing changed or "upgraded" the amp. not knowing what they did to it leaves you at a huge disadvantage trying to troubleshoot it.Trust me,I've worked on some "upgraded" tube amps that had to be rebuilt from the ground up because of someones mess.sometimes that's easier than figuring out were the person messed up.I still would search out bad solder joints before I went tearing any transistors out.I've had quite a few Vintage Carver components and about 90% of them had bad solder joints.They all sounded fantastic when working properly,but for some reason I've personally found a higher number of bad joints in Vintage Carver stuff than any other Vintage brand I've owned,I love my Carver stuff and they'll have to pry it out of my cold dead hands before I'd give it up,but that has been my experience.I mean no disrespect to the brand or the man,who is obviously a genius.As far as the thump I'd get the bias reading problem figured out first,then set the damping adjustment.the damping adjustment makes the amp do some wierd stuff when out of whack,and before I went on a hunt for the source of the thump I'd make sure thats set proper.small movements of the pots make gigantic differences.Thats about all My experience can tell you.Good luck and find a digital M.M.,its so much easier.
Robert
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BillD

User avatar

(pair of) SILVER-7 TUBE AMPs

Posts: 7295

Joined: Wed Jun 06, 2007 8:29 pm

Location: The west's most mid-western town, Scottsdale, Arizona

Post Fri Apr 09, 2010 4:34 pm

Re: TFM-45 Whistling

You really need to find a device that has mostly similar values AND the same pinout. IIRC, the MPSU60 had center pin base, and most replacements would be center pin collector. You might try THIS pair
It should sound like it isn't there!
There is a difference between hearing and listening...
Making life enjoyable through expensive electronics.
_________________
Carver: C-4000 & C-1 preamps, PSC-60 preamp/tuner, TX-11a tuner, M-400 (2), C-500, M-500, M-500t, M-500t Mk.II, A-500x, AL-III loudspeakers (2 pr.)
Sunfire:Theater Grand III processor, Ultimate Receiver, Cinema Grand Signature 400 ~ seven, True Subwoofer Mk. II, D-10 Subwoofer
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gary_wong5

Newbie 50+

Posts: 70

Joined: Fri May 16, 2008 8:17 pm

Post Mon Apr 19, 2010 9:41 am

Re: TFM-45 Whistling

As NTE240 too is not available here, I bought a piece of Motorola MPSU60 from eBay. Replaced Q4 on the right amplifier board. No more switching on/off thump! =D>
My next to do is adjust damping by following gunner64's procedure. But before that, I have to buy and learn signal generator... ](*,)
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