need tech help with my new garage sale find

[rhinofly]

Today I found a Mcintosh MC 2505 amp and a MX 113 preamp/tuner at a garage sale. They are in outstanding condition and have the walnut cabinets to boot. Here they are


mc2505 and mx113 (http://f1.pg.photos.yahoo.com/ph/noble.miller@sbcglobal.net/vwp?.dir=/Vintage+Audio&.dnm=mac.jpg&.view=t)

The preamp works perfectly but the amp needs repair. In digging into it I found the following on left channel power board

burnt components (http://f1.pg.photos.yahoo.com/ph/noble.miller@sbcglobal.net/vwp?.dir=/Vintage+Audio&.dnm=burnt.jpg&.view=t)

Here is what the right channel...not burnt looks like

not burnt (http://f1.pg.photos.yahoo.com/ph/noble.miller@sbcglobal.net/vwp?.dir=/Vintage+Audio&.dnm=burnt+(2).jpg&.view=t)

The burnt channel looks like it has two resistors, a ceramic cap, maybe two, and a diode or something like it that are fried.

Do you guys think I should run down to the rat shack, buy some new components and solder them in and try it? Or is this a job for a pro? I dont yet have a distortion meter, function generator and scope...but this may be a good reason to get em.

Also does anyone have any idea what causes this kind of damage? Shorting the speaker leads under power maybe?

I think its probably worth fixing the amp, but I am not sure if its worth paying a Mac expert to do it.


What do you think?

The preamp sounds great BTW.

[B3Nut]

Just hazarding a guess here...it looks like at least one or more of the output transistors on the burnt channel shorted and took those resistors along with them. I'd take out all the power transistors and check them for shorts before proceeding further.

And yes, you're darn tootin' it's worth fixing. :)

Awesome score, BTW

Keep us all posted, and check those output trannies. I bet a dollar to a donut that's what happened.

TP

[rhinofly]

B3Nut: I had thought about that but dont know enought about that mode of failure to test it. Is it common for output transistors fail catastrophicaly like that? Does something cause it?

How does one test a transistor for a short? Can I do it with just a multimeter?


I suppose if I found a shorted output transistor that would be a good indicator of what happened.

[Wardsweb]

Yep output transistors usually fail dead short and take part of the bias circuit with them. The Allen-Bradly carbon comp resistors are really generic, but not worth replacing until you find what shorted and pulled enough current to fry those components. Looks like a job for a professional. You could always ship it off to one of our newest McIntosh gurus like Dewickt.

[rhinofly]

I dont know who Dewickt is. Does he have a mac repair service?

edit:

Is he Dewick repairs in Knoxville, TN?


Ok now that I have discovered this Mac forum I have a better idea who Dewickt is:)

This was moved from the Vintage Audio forum. Thanks.

[Number 9]

Terry DeWick

www.mcintoshaudio.com

Knoxville, Tennessee

Very knowledgeable.

[Johnny]

That is some super handsome gear you've got there rhino' I'm really starting to dig the look of the Mac gear. Hope you get yours up and running soon :cool:

J

[rhinofly]

Yes I always thought the Mac stuff was a bit weird looking. But after playing with this stuff a bit I am finding that I like it quite alot. The sense of quality just permeates this gear and has a real presense in person that I did not get from pictures. After getting it fixed I may leave it as a second bedroom system since I REALLY like my Kenwood 600 alot and it likely wont be going anywhere anytime soon.


edit:

I spoke with Terry. Seems like a good and reasonable way to get it fixed. Thanks folks.

[dewickt]

Easy fix if you have done a few -- he he, OK it has a shorted output, open .33 ohm emitter resistor, shorted sense transistor and it's 2 resistors are burned.
The fun part is, parts will not be found at Rat Shack, output has a more modern sub and sense transistor will have to be crossed to a totally different part because it is an obsolete transistor - none at McIntosh.
This part of the diagnosis is easy, now if all the rest of the parts are good, will need trusty Simpson to give the board a 100% check. This is an easy one to troubleshoot, only 9 transistors in the output section.
Have talked to RHINOFLY (need to check profile for name before I answer), will be seeing amp in the next week or so. He has a very good idea on shipping, pull the glass panel and keep it at home, quik way to save $134 for new glass and a hassle with UPS.
The MX113 and MC2505 are a perfect match, they were made for each other, now all they need are some nice speakers....

[rhinofly]

Heh. I build my own speakers. When I am not painting the house, mowing the lawn, changing the oil in the cars, playing with the kid....or hunting up vintage audio gear:rolleyes:

[Brian]

I have owned the nonmetered version for over 30 years and really enjoyed it. Yes I have found more revealing amps blah blah , etc. but, for just sitting back, listening to and enjoying the music the amp really stands out (or dosn't which is a a complement). Get it fixed and with the 113 you'll have one of the nicer music systems you can buy. If you really want to go all the way, find a set of ML1s to go with it.

[rhinofly]

Terry check your PM's.

[rhinofly]

The amp is fixed and on the way back from Terry. I have been listening to the preamp using the kenwood 600 as a power amp and it sounds outstanding. Cant wait to hook the MX113 up with the mc2505 and see how they sound together. Should find out in a few days.

[GordonW]

Lucky you! I thought I was doing good when I traded a next-to-free Yamaha integrated amp and a pair of small speakers, for a Marantz 3200 preamp and 140 power amp a while back! :p:

Oh well, there's always the Better Deal Out There Somewhere... time to go shopping again! :zoom:

Regards,
Gordon.

[GordonW]

Originally posted by Brian
I have owned the nonmetered version for over 30 years and really enjoyed it. Yes I have found more revealing amps blah blah , etc. but, for just sitting back, listening to and enjoying the music the amp really stands out (or dosn't which is a a complement). Get it fixed and with the 113 you'll have one of the nicer music systems you can buy. If you really want to go all the way, find a set of ML1s to go with it.

This man has the right idea, but I'd go straight for the gusto, and get a pair of ML-2Cs. :guitar:

I restored a pair for a customer where I work a year ago, and man, that speaker has some of the BEST BOTTOM END OF ALL TIME. Genuine PITCH DEFINITION down to BELOW 20 HZ! The rest of the spectrum ain't no slouch either! Ah, nothing like beefy, long-throw dual 12" woofers not having to work hard, in a solid sealed box!

BTW: if you do that, also look for the 101 or 107 Environmental EQ. Makes the package that much sweeter. Tuning the bottom end for the room... ah, bliss...:bigok:

Regards,
Gordon.

[Brian]

All the ML series requires the Mc equalizer (and you thought Bose had a corner on the market). I agree the ML-2 is the better but then again my favorite is the ML4. Sadly anything less than a 2100 won't get these babes to strut their stuff. Biggest problem with them is renting a crane everytime you need to move them.

[GordonW]

The nice thing, is that the ML2 is "portable"... BARELY. You can actually fit them into an SUV or minivan, and two people can lift one. :D

Also, I can tell you, an ML2 is capable of running from surprisingly small amps. During testing, I ran the restored pair on a dinky little NAD 350 integrated amp (60w/ch) and it got loud enough to FEEL the bass! Nice thing about BIG boxes, it's almost impossible for them to NOT be relatively efficient! :rockon:

Dunno what the heck I'd do if I found a pair of ML4s. I so have nowhere for something like that to go, but I'd almost HAVE to buy them, if they were cheap. Could get ugly... :eek:


Regards,
Gordon.

[dewickt]

Have to agree that the ML2s are good sounding, got mine in a trade, basically free, had all 4 bass driver refoamed. Took about an hour to break them in, I call them my impact system with a MC2300 driving them I can clean the dust from the cieling !!
At about 128 pounds each they match the MC2300, that is the way a system should be with the amp weighing as much as a speaker......
Have used my MC250 on them and found it could drive them reasonably well but they really like 100+ watts to sound as full as possible, they will take all that the 2300 can give, watching the meters bounce past 300W is amazing.

[Brian]

Time to buy shares in the hearing aid company :).

[GordonW]

EH? WHAT? DID SOMEBODY SAY SOMETHING??? :p: :p: :p:

Regards,
Gordon.