Hi Everybody,
Just got a McIntosh MC2205, it has some issues and was hoping to get everyone's ideas. The previous owner said that they noticed some blackish liquid under it one day and so they stopped using it. Prior to that he hadn't noticed anything wrong with it and even when he did notice the liquid it was working. So it sat, until I bought it, unused. I know that the black liquid was most likely the potting tar around the power transformer. My question is could the transformer be over heating due to something that's worn out like a bad diode or cap straining it and if so where do I start to find the problem? Here's some pics of the bottom of the transformer. I only noticed very slight traces of grease/black stuff on it.
Just got a McIntosh MC2205, it has some issues and was hoping to get everyone's ideas. The previous owner said that they noticed some blackish liquid under it one day and so they stopped using it. Prior to that he hadn't noticed anything wrong with it and even when he did notice the liquid it was working. So it sat, until I bought it, unused. I know that the black liquid was most likely the potting tar around the power transformer. My question is could the transformer be over heating due to something that's worn out like a bad diode or cap straining it and if so where do I start to find the problem? Here's some pics of the bottom of the transformer. I only noticed very slight traces of grease/black stuff on it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'd be interested in seeing some pics a little bit farther away.
Not close ups.
Take some before, during, and after pictures.
So that you remember how it was,
what you've done or will do and how
the wiring was, as you go through it.
First thing is get some compressed air
and gently blow all the crap out of it.
That might have started the problem
then not being able to derate led to others.
You're right up there in MC Country,
with parts aplenty and cheap.
Not close ups.
Take some before, during, and after pictures.
So that you remember how it was,
what you've done or will do and how
the wiring was, as you go through it.
First thing is get some compressed air
and gently blow all the crap out of it.
That might have started the problem
then not being able to derate led to others.
You're right up there in MC Country,
with parts aplenty and cheap.
Those are inside pics and two pics of the inside of the bottom cover, it's the middle transformer, the power transformer. It powers up.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I was thinking of going through and changing out all the electrolytic caps with Nichicons and I was wondering about changing out the trim pots, I saw one person change them out with higher precision trim pots
Change all the electrolytic capacitors, and possibly all cappacitors, the trim pots look relatively new, I suspect they have already been changed out once, on a previous repair.
Posted by djk (M) on March 4, 2012 at 17:02:45
In Reply to: input tweaks - McIntosh MC2120 posted by raq on March 4, 2012 at 11:48:03:
This is what I do:
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
************************************************************
You should just be able to jump across the input caps and sensitivity switch with no problems there.
If you're trying to use better input jacks the grounding and the 0.01µF caps to ground become important. If you try and eliminate the input attenuator you will probably need a cap to ground from the node of R201 and C203 on the driver card, somewhere between 10pF~100pF.
Good luck.
In Reply to: input tweaks - McIntosh MC2120 posted by raq on March 4, 2012 at 11:48:03:
This is what I do:
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
************************************************************
You should just be able to jump across the input caps and sensitivity switch with no problems there.
If you're trying to use better input jacks the grounding and the 0.01µF caps to ground become important. If you try and eliminate the input attenuator you will probably need a cap to ground from the node of R201 and C203 on the driver card, somewhere between 10pF~100pF.
Good luck.
Thinker,
There you go. The good thing is you got it all blown out and cleaned
up so far. That's always a good place to start.
Have you Identified the problems source yet?
or is it still working okay just running hot?
There you go. The good thing is you got it all blown out and cleaned
up so far. That's always a good place to start.
Have you Identified the problems source yet?
or is it still working okay just running hot?
Brought it to Audio Classics for a quick look over, not a true bench test. Was told to look into the output section resistors and transistors. The output relay wasn't turning on, and the meters weren't doing anything. Got it home and thought I would first do a thorough cleaning. Took the whole thing apart, deoxit the controls and connections, rust removal and waxed the chrome, checked the resistors and transistors that control the relay didn't find anything, and put it back together. Now the output relay is working. I'm guessing something was dirty? and the meter responded but, the right side power guard light came one and the meter was showing full power. I felt the stacks and the one was very warm, the rest cold. I switched the power boards and it stayed on the same side. I then removed the stack and started testing the transistors with my multimeter, the first three are the same type. The first two tested at .45 - .48 the third read .25 and the third one conducted both ways so I'm thinking it's broken. Thoughts?
damn collectible
get it to someone both trusty and versatile in amp repairs
that's no thingy for first steps in amp repair
get it to someone both trusty and versatile in amp repairs
that's no thingy for first steps in amp repair
Transistor #1
Positive Probe Base, Negative Probe Collector .476
Positive Probe Emitter, Negative Probe Collector Open
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .48
Negative Probe Base, Positive Probe Emitter Open
Transistor #2
Positive Probe Base, Negative Probe Collector .416
Positive Probe Emitter, Negative Probe Collector Open
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .449
Negative Probe Base, Positive Probe Emitter Open
Transistor #3
Positive Probe Base, Negative Probe Collector .426
Positive Probe Emitter, Negative Probe Collector .647
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .257
Negative Probe Base, Positive Probe Emitter Open
Positive Probe Base, Negative Probe Collector .476
Positive Probe Emitter, Negative Probe Collector Open
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .48
Negative Probe Base, Positive Probe Emitter Open
Transistor #2
Positive Probe Base, Negative Probe Collector .416
Positive Probe Emitter, Negative Probe Collector Open
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .449
Negative Probe Base, Positive Probe Emitter Open
Transistor #3
Positive Probe Base, Negative Probe Collector .426
Positive Probe Emitter, Negative Probe Collector .647
Negative Probe Base, Positive Probe Collector Open
Negative Probe Emitter, Positive Probe Collector Open
Positive Probe Base, Negative Probe Emitter .257
Negative Probe Base, Positive Probe Emitter Open
Use the diode test range and check all base-emitter junctions, and all collector-emitter junctions.
I've been told that all the output transistors should be changed when one goes bad, in my amp the McIntosh part numbers are 132-188 and 132-189 but, the manual refers to them as 132-164 and 132-165, which can be replaced with MJ15003G and MJ15004G but, the drivers McIntosh Part # 132-151 and 132-152 are nearly impossible to find outside of replacements from McIntosh which cost about twice as much as going to a parts supplier. There is one transistor that is close the MJ15024G but the gain is 15 to 60 where the original was 20 - 100. So I'm not sure if that's a suitable replacement.
Another thing I learned was that the early production MC2205's used Inductive resistors that could cause oscillation that were replaced later with non inductive resistors, you can tell the difference by look at the them, the inductive type will have 5WL where the non inductive will have 5WW. I've been looking for replacements and was wondering if this would work http://www.mouser.com/ds/2/427/lvr-239788.pdf it says Low inductance and "• Ideal for all types of current sensing
applications including switching and linear
power supplies, instruments and power
amplifiers" if not the only resistors that I can find are $1 more a piece that are rated non inductive. which might sound silly but I'm finding repair costs are adding up fast 😛
Last thing, I know that I'm going to need thermal compound when I replace the transistors and I was wondering if anyone could recommend some, non conductive of course.
Thanks 🙂
Another thing I learned was that the early production MC2205's used Inductive resistors that could cause oscillation that were replaced later with non inductive resistors, you can tell the difference by look at the them, the inductive type will have 5WL where the non inductive will have 5WW. I've been looking for replacements and was wondering if this would work http://www.mouser.com/ds/2/427/lvr-239788.pdf it says Low inductance and "• Ideal for all types of current sensing
applications including switching and linear
power supplies, instruments and power
amplifiers" if not the only resistors that I can find are $1 more a piece that are rated non inductive. which might sound silly but I'm finding repair costs are adding up fast 😛
Last thing, I know that I'm going to need thermal compound when I replace the transistors and I was wondering if anyone could recommend some, non conductive of course.
Thanks 🙂
I second Zen Mod's sage advice. Find a McIntosh specialist, there's lots of them out there, and let them do what needs to be done. I sold these back in the day, and it's a very nice amp, equally at home with the big JBL's and Klipschorns of that era, as well as Magnepans and other power-hungry beasts. Not as fast or transparent as some solid state amps, but very mellow, very pleasant to listen to for hours on end.
Thinker - considering that many could tell you that you're stroked with golden lightning ......... either sell it for good money to some collector or - if you want to keep it - be patient rather than ruin it working without proper skill and knowledge ;
with some luck , I'm sure you'll find that someone skillful from Diyaudio is near you , so proper repair will cost you some gas and some beer
and you may find new friend .......
I would gladly fix it for ya free of charge , probably even parts for free , but we have significant amount of water between us
your honest and simple sentence I don't have the money to pay someone to repair it ...... worth half of gold bar itself
with some luck , I'm sure you'll find that someone skillful from Diyaudio is near you , so proper repair will cost you some gas and some beer
and you may find new friend .......
I would gladly fix it for ya free of charge , probably even parts for free , but we have significant amount of water between us
your honest and simple sentence I don't have the money to pay someone to repair it ...... worth half of gold bar itself
That's wrong I misread a post, the original design needed the slight inductance to prevent oscillation.
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