Autoformer bypass

[backinthelou]

i just picked up an MC250 on CL a couple days ago, but didn't have time to hook it up before today. Someone else posted an ad on CL wanting to "contact the person that bought the McIntosh MC250 because he had information he thought the new owner should know". I opened it about an hour ago to retrieve 2 nuts from the connector strip that had fallen inside. Written inside was "Right channel autoformer shorted" "Autoformers bypassed". The guy I bought it from claimed to have recently serviced at the Sound Room, which is a local high end store. He claims he lost the paperwork they gave him. It's in very nice condition, so I trusted what he was saying. The power transformer also has a loud hum that I didn't notice while we were talking in his basement during the sale. Anyway, I am sure that if he had it serviced he would KNOW that the autoformers were bypassed. I paid too much money for this thing to let this be a live and learn moment. Any advice?

 

[backinthelou]

i just picked up an MC250 on CL a couple days ago, but didn't have time to hook it up before today. Someone else posted an ad on CL wanting to "contact the person that bought the McIntosh MC250 because he had information he thought the new owner should know". I opened it about an hour ago to retrieve 2 nuts from the connector strip that had fallen inside. Written inside was "Right channel autoformer shorted" "Autoformers bypassed". The guy I bought it from claimed to have recently serviced at the Sound Room, which is a local high end store. He claims he lost the paperwork they gave him. It's in very nice condition, so I trusted what he was saying. The power transformer also has a loud hum that I didn't notice while we were talking in his basement during the sale. Anyway, I am sure that if he had it serviced he would KNOW that the autoformers were bypassed. I paid too much money for this thing to let this be a live and learn moment. Any advice?

Btw, I still haven't heard back from the guy that posted the ad wanting to talk to the buyer, so I don't know what he has to say yet.

 

[clinic-audio]

Call A.C. they probably have one output transformer in stock

 

[dewickt]

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...

 

[clinic-audio]

Yes , Terry , I saw that too, more than once

 

[backinthelou]

Gentlemen, do McIntosh repair centers track pieces by serial numbers?
Also, I would assume that an authorized Mac service center would never bypass the autoformers? I called and left a message where this guy said he had the work done.
He is refusing to refund my money.

 

[MACKIE1975]

Craigslist save money but require you to take extra strength Tylenol.
He is not honest from the beginning so don't expect a refund.

 

[c_dk]

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.....

 

[backinthelou]

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.....

That's my guess. Considering the guy obviously lied, I'm not even sure he took it to the Sound Room-may have been name dropping. He only said that it "blew a channel and had to have it repaired" and that was after the sale was complete.
The Sound Room does sell McIntosh gear.

 

[backinthelou]

I just talked to The Sound Room and they have no record of this amp being in their service department.

 

[c_dk]

Some tech somewhere put the note in.....pull the bottom cover a post a picture or two. Could be the owner refused the service and the tech had to set it aside........maybe for decades.

 

[backinthelou]

Some tech somewhere put the note in.....pull the bottom cover a post a picture or two. Could be the owner refused the service and the tech had to set it aside........maybe for decades.

 

[backinthelou]

 

[clinic-audio]

Gentlemen, do McIntosh repair centers track pieces by serial numbers?
Also, I would assume that an authorized Mac service center would never bypass the autoformers? I called and left a message where this guy said he had the work done.
He is refusing to refund my money.

OK
Let's do something :
Can you post closer pictures of above view (inside view) when unit is upside down ?
His the guy really a good tech or official service center ? Autoformer can be measured shorted to ground if you don't know how it is working . This transformer will connect any DC Offset directly to ground and this can be one explanation why this guy think that this transformer is shorted .

I asked you the numbers on the board because if you have one specific version of 250 , I can find the right schematic because of these numbers and them immediately find the dedicated schematic

 

[clinic-audio]

pictures arrived during time of tipping my message so ...

I can see the wire for the input of the audio transformer insulated with a black sleeve .

This mean (as it is wroten on inside of the chassis that the output of your amplifier is directly connected to the speaker terminal !
This way your amplifier is unsecure regarding the speaker because there is no more the protection with the output transformer . This mean that if any DC voltage come out the amplifier (one channel dead) everything connected to this channel (all speakers , woofer, tweeter, medium) will be destruct for ever
If you don't know anything about electronic , I will suggest you to bring it to a real professionnal tech

 

[backinthelou]

Some tech somewhere put the note in.....pull the bottom cover a post a picture or two. Could be the owner refused the service and the tech had to set it aside........maybe for decades.

Looks like I goofed on the pictures. Let me know if there is anything else I can post.

 

[backinthelou]

Looks like I goofed on the pictures. Let me know if there is anything else I can post.

 

[backinthelou]

pictures arrived during time of tipping my message so ...

I can see the wire for the input of the audio transformer insulated with a black sleeve .

This mean (as it is wroten on inside of the chassis that the output of your amplifier is directly connected to the speaker terminal !
This way your amplifier is unsecure regarding the speaker because there is no more the protection with the output transformer . This mean that if any DC voltage come out the amplifier (one channel dead) everything connected to this channel (all speakers , woofer, tweeter, medium) will be destruct for ever
If you don't know anything about electronic , I will suggest you to bring it to a real professionnal tech

I suspect I know who did this, because he mentioned another "tech" that did work on his preamp. Considering the fact that every single piece of gear I've seen with that techs shop sticker has been a complete mess. My 11 year old son could solder better. People around here mention his name all the time, but literally every single piece I have seen from him looks like terrible plastic surgery. The guy is pretty creative at screwing up vintage gear.

 

[clinic-audio]

yes
I can't read the numbers on your board (picture not enough closer

 

[c_dk]

Well if he is that incompetent maybe the autoformers are actually good......