Autoformer bypass

Patrice, I think that was a picture of a to220 transistor used as a driver....I experimented with that years ago and found it would want to oscillate......
 
In today's world being a "authorized" McIntosh service center means you have a account with them to buy parts wholesale......being a authorized dealer selling equipment means more but still not like what it meant 20 years ago.....

Since I too have never seen a shorted McIntosh output autoformer in 40 years I am sure the local service tech would remember having to bypass one.....

Authorized means that they have right to do warranty repairs. Anything else does not count. Loosing rights to repair under warranty is a big deal and thus they will not likely do botched repairs.

Craigslist deals are based on "as-is" statement, and thus there is very little chance to unwind the deal and get money back.
 
Authorized means that they have right to do warranty repairs. Anything else does not count. Loosing rights to repair under warranty is a big deal and thus they will not likely do botched repairs.

Craigslist deals are based on "as-is" statement, and thus there is very little chance to unwind the deal and get money back.
Typically I agree with "as is", but this guy lied through his teeth. It's a pretty unit, but everyone can see the damage that's been done.
 
Typically I agree with "as is", but this guy lied through his teeth. It's a pretty unit, but everyone can see the damage that's been done.

Indeed, sometimes its the nature of the game, I got lied to with the packaging on my MC2205, and a Sansui G9000 and a few others.....some people are just like that....
My approach is I rise above it and just repair it....I'm in it and can't be bothered with the stress of a dispute...those people will have theirs coming one day, that much is certain.
 
Not sure this will work but it is worth a try as a test of the autoformers.

As I understand them, they are one coil with multiple taps, input and a few outputs for different impedances.

First, you want the amp unplugged long enough for all caps to discharge.

Take a small, low power amp and hook a sound source to it, MP3 player, phone, cd player, tuner, it doesn't matter. Using a 4 ohm resistor to make sure that there is a load on the amp, hook one channel to first the 4 ohm resistor then to the output of the autoformer. This is a series circuit, that is positive on small anp to one side of resistor, other side of resistor to positive 8 or 16 ohm output of autoformer, common terminal of autoformer back to negative terminal of the small test amp. Play some music and hook a speaker to the common terminal of the autoformer and ANY other terminal of the autoformer as long as it is NOT the one hooked to the resistor. IF the autoformer is good, you will hear music from the speaker.

This is similar to checking output transformers in a tube amp.

Good Luck

Shelly_D
 
Just chiming in here that I've only rarely seen an output transformer fail on a Mac vacuum tube amp, but have never seen a shorted autoformer on a solid state one. And as clinic-audio has already mentioned, if the tech doesn't understand that an autoformer like is used in these amps is a low impedance device as it is, and will measure very low resistances when checked with a DC ohmmeter, he might very well think it's shorted. Possible? Yes. Likely? Not very. If it was on my bench, I'd be looking for almost anything else first.

The mention of the terminal strip screws shorting on the chassis is a good one-- I've seen that quite a number of times over the years on some Mac amps. (Can't say for sure it applies to an MC250 without looking at one.)
 
Hello

The mention of the terminal strip screws shorting on the chassis is a good one-- I've seen that quite a number of times over the years on some Mac amps.

I did too ! and gess which unit was involved ? one MC1000 . Shorted output transformer ....Can you believe this ? :yikes:

After receiving a brand new one everything go back to normal function ...:rflmao: Very , very heavy and not easy to replace (need 3 hands)
 
Well all, I'm not sure I am willing to take this on myself. I paid $470 for this d*mn thing. It is obviously going to need extensive work to get it back to stock. I'm not having good luck with my first 2 pieces of Mac gear. The MA6100 I bought about a month ago is having volume control problems. I'm typically a hardcore Sansui guy, and I'm not sure I'm meant to own McIntosh. The first units I looked at from a collector had immediate problems that sent the amp into clipping. I understand these are old, but I've rarely had any issues with my Sansui stuff. I know Terry Dewick is a respected tech. If it costs more than a couple hundred bucks, considering the autoformer may be bad, I may have bought a $470 boat anchor. I have too many other things going on to mess with it myself.
 
Well all, I'm not sure I am willing to take this on myself. I paid $470 for this d*mn thing. It is obviously going to need extensive work to get it back to stock. I'm not having good luck with my first 2 pieces of Mac gear. The MA6100 I bought about a month ago is having volume control problems. I'm typically a hardcore Sansui guy, and I'm not sure I'm meant to own McIntosh. The first units I looked at from a collector had immediate problems that sent the amp into clipping. I understand these are old, but I've rarely had any issues with my Sansui stuff. I know Terry Dewick is a respected tech. If it costs more than a couple hundred bucks, considering the autoformer may be bad, I may have bought a $470 boat anchor. I have too many other things going on to mess with it myself.

BTW, the terminal screws weren't touching any wires.
 
Most used McIntosh that not come from Terry or Audio Classic will require T&M (time and material) to bring to spec and operation.
 
Mike, you need to be careful with the McIntosh gear around town, and with who you buy it from, There have been a number of estates in the past couple of years with decrepit and unused Mac gear, and I think you have managed to get both pieces from such estates in roundabout fashion. You definitely need to let me know about the 250 seller, I may know him and be able to exert some pressure. Hopefully he is not the guy from Centralia.
 
Never have seen a shorted autoformer, have seen shorts caused by screws that were too long on the speaker terminal blocks, they can short to the chassis causing some odd symptoms...
I thought for sure that I had a bad autoformer on one of my Mc2300's. It turned out to be a hopelessly dirty stereo/mono switch
 
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