MC 2100 trouble

I just picked up my first Mcintosh pre amp and amp. The pre amp is a C28, which is in good working condition. The power amp however, is a MC 2100 that isn't showing any signs of life. Correct me if I'm wrong, but this amp doesn't have an indicator light or on/off switch so once its plugged in-its on and when its unplugged its off? When it is plugged in I can hear a very faint buzz from the transformer (I think it's from the transformer...) but that's all. Am I missing something?:scratch2:

If your MC2100 is like my MC250, there is no indicator light and no I/O switch. Just a 2-prong power plug. You can plug it into the "Power Amp" outlet of your C28 The top panel of the C28 has an I/O switch for a power amp. I usually use this outlet on the back of the C28 to plug the MC250 in. I think it is "switched" - meaning that the amp will power on or off along with the power switch on the C28. It might not be though and it would not be the end of the world. An MC250/2100 can be left on full time with little to worry about. That's how they were designed. I believe that switch on the top panel of the C28 is to power off an amp when "headphones only" are in use. Your C28 has a dandy headphone amp built-in.

There are other power outlets on the back of the C28 that are un-switched - meaning always on when the C28 is off. I plug an iPod dock in there. It keeps the iPod always charged. This is necessary as it's an old iPod with a weak battery. My tuner too, (an MR77), as I like it to switch on when I power up my system.

If you can be sure that the MC2100 is plugged into a live plug, you might try resetting the circuit breaker. You might have a dirty rocker switch - the one that goes between Mono/Stereo, or you might have dirty volume pots or shorts at the RCA input jacks, although the latter two would be less likely to cause more than one channel to not function. Odds are at least one side would work.

Over and above all that, you might have something funky inside the unit. I'm not one of those guys that ever pokes around inside. But older, wiser heads than mine do and they will likely chime in.

You can search here at AK or on the wider web and find owner manuals galore. You might find something as you read them that will identify a simple connection issue you may have missed. I was lucky. I plugged my stuff in and it worked although I sometimes get a hum from the C28 Phono 1 section. I can usually move the input lines just a bit and it goes away. I do have a dirty rocker switch on my MC250. A little shot of cleaner helps and some manipulation to find the spot where it works. Keep cleaner and other liquids away from the glass faceplate of your C28! You don't want to bubble the paint on the backside of the glass.

You came to the right place bmc1987. Lots of great folks here to talk to as you continue the McIntosh journey. Again, others will touch base here and give you input I may miss. Finally, bear in mind that this equipment is old. Things get dirty and loose. Electronic parts wear out. Your new toys might very likely benefit from being gone over by a good technician. Terry is the one we always turn to, but there are other McIntosh factory authorized services around the country. If you did not pay too much for your units, adding some money to bring them up to factory specifications will be a great investment. Full-on good working order could help these units outlast you. Again, they were designed to last practically forever. A little money spent now will be cheap in the long run. Have fun!

Thanks bpeder. I just tried cleaning the mono/stereo switch with deoxit and working the switch but its still doing the same thing. I did notice a faint hiss in the speakers though. I mean very faint, with my ear against the speaker and I could also hear a very faint "pop" sound when I was switching back and forth from stereo to mono.

If you hear a faint hiss, it sounds like you have signal reaching your speakers. With no input signal and both volumes on the MC100 full out, you ought to hear a slight hiss. McIntosh amps are quiet, but not perfectly so. Try turning the volumes down one at a time and see if the faint sound drops out of the corresponding speaker.

If you are hearing hiss, it may be that you are not getting a signal to the amp from the C28. I assume you are patching a CD player, a tuner, a turntable or maybe a tape deck into the C28? The Aux input channel works well for an iPod. Check those connections. I have heard that some guys use "Brasso" to polish the RCA jacks on the back side and that they can really shine although I never tried that trick. But wiggle them a bit anyway. Same goes for the outputs on the C28. Those are the RCA from the L/R out to the input jacks in the MC250. Don't use the center channel. It does have a use, but if you are running just a simple 2-speaker stereo set-up you won't need it for now.

Once you get one set of speakers running, you may wish to spring for a speaker relay. The McIntosh SCR2A will wire in between the C28 and the MC100 and allow you to run 2 sets of speakers. The speaker selector push buttons on the front panel of the C28 are not much use without the relay, but they are easy to find and not too expensive.

May I ask, how did you come into this system? Some guys are lucky and inherit McIntosh goodies from a father-in-law or some such. If you can chat with whoever you got the system from, maybe they can tell you how to set it up.

Plug your cd player or tuner directly into your 2100 and use the gain controls as volume controls and you will know if your amp needs repair.

bpeder said:

If you hear a faint hiss, it sounds like you have signal reaching your speakers. With no input signal and both volumes on the MC100 full out, you ought to hear a slight hiss. McIntosh amps are quiet, but not perfectly so. Try turning the volumes down one at a time and see if the faint sound drops out of the corresponding speaker.

If you are hearing hiss, it may be that you are not getting a signal to the amp from the C28. I assume you are patching a CD player, a tuner, a turntable or maybe a tape deck into the C28? The Aux input channel works well for an iPod. Check those connections. I have heard that some guys use "Brasso" to polish the RCA jacks on the back side and that they can really shine although I never tried that trick. But wiggle them a bit anyway. Same goes for the outputs on the C28. Those are the RCA from the L/R out to the input jacks in the MC250. Don't use the center channel. It does have a use, but if you are running just a simple 2-speaker stereo set-up you won't need it for now.

Once you get one set of speakers running, you may wish to spring for a speaker relay. The McIntosh SCR2A will wire in between the C28 and the MC100 and allow you to run 2 sets of speakers. The speaker selector push buttons on the front panel of the C28 are not much use without the relay, but they are easy to find and not too expensive.

May I ask, how did you come into this system? Some guys are lucky and inherit McIntosh goodies from a father-in-law or some such. If you can chat with whoever you got the system from, maybe they can tell you how to set it up.

Click to expand...

This is no inheritance, just cash... I bough these from the seller knowing something was wrong. I assumed it was the power amp because I hooked up my ipod directly into it when I was buying it and I couldn't get any sound. Saved a few bucks but here we are...

strat10 said:

Plug your cd player or tuner directly into your 2100 and use the gain controls as volume controls and you will know if your amp needs repair.

Click to expand...

I just tried that again after cleaning the controls. No luck. No static or scratchy noises from the speakers. Nothing but the faint hiss. The C28 is working fine hooked up to another unit btw.

Time for someone to get inside and check the power supply voltages. If you pull the cage remember the heat sinks are hot.....have seen the mounting clips crack allowing the heatsink to short out the negative supply to chassis ground.

c_dk said:

Time for someone to get inside and check the power supply voltages. If you pull the cage remember the heat sinks are hot.....have seen the mounting clips crack allowing the heatsink to short out the negative supply to chassis ground.

Click to expand...

Ok c dk, can you tell me where to check specifically? I have the schematic and its all opened up at this point. I've worked on mainly Marantz receivers up to this point. Where should I test? Thanks.

How about the B-and+ at the main filter caps. Then at the secondary supply.

c_dk said:

How about the B-and+ at the main filter caps. Then at the secondary supply.

Click to expand...

Thanks c dk. The main caps are giving me 75v on one set, and 0v on the other (that's +ve from one to -ve on the other). How can I check the secondary supply?

Hmmm ... Set your meter to measure DC Voltage with a range of at least 50 Volts. Connect the black probe of your meter to the chassis. Measure from the chassis of the amp to the positive terminal of the capacitor which has its negative terminal tied to the chassis as well as from the chassis to the negative terminal of the capacitor which has its positive terminal tied to the chassis. You will have a positive number and a negative number. Report those here.

75v? I think you measured the two capacitors at once. If yes, is okay.
The voltaje must be + 35v in c201 + terminal and -35v in C202 - terminal, reference to ground.

Secondary suply:
According to the schematics check C203 multicap can.

C203c (▲) 90v
C203 (without or ▬ ) 80v

Caution, the picture is from my MC2105, I think must be the same but I'm not sure.

damacman said:

Hmmm ... Set your meter to measure DC Voltage with a range of at least 50 Volts. Connect the black probe of your meter to the chassis. Measure from the chassis of the amp to the positive terminal of the capacitor which has its negative terminal tied to the chassis as well as from the chassis to the negative terminal of the capacitor which has its positive terminal tied to the chassis. You will have a positive number and a negative number. Report those here.

Click to expand...

Ok, I have a reading of +36.8v and -36.9v

acmmty said:

75v? I think you measured the two capacitors at once. If yes, is okay.
The voltaje must be + 35v in c201 + terminal and -35v in C202 - terminal, reference to ground.

Secondary suply:
According to the schematics check C203 multicap can.

C203c (▲) 90v
C203 (without or ▬ ) 80v

Caution, the picture is from my MC2105, I think must be the same but I'm not sure.

Click to expand...

I'm uncertain which caps are the c203s?

It´s the metal can. Check the symbols near to the terminals in the bottom

On the input board there are 2 470 mfd caps that are of a type that are failing in all electronics of this age.

acmmty said:

75v? I think you measured the two capacitors at once. If yes, is okay.
The voltaje must be + 35v in c201 + terminal and -35v in C202 - terminal, reference to ground.

Secondary suply:
According to the schematics check C203 multicap can.

C203c (▲) 90v
C203 (without or ▬ ) 80v

Caution, the picture is from my MC2105, I think must be the same but I'm not sure.

Click to expand...

Thanks for clearing that up. Here's what I got:

(▲) 102.9v
(without or ▬ )89.7v
(Square) 108.6v
(D)114.4v

Should I swap out the 2 470's? Can I use radial caps instead of axial?

You can use axial or radial. Replace all electrolytics.

Are they the problem?

You need to solve the issue first. Both channels dead would seem to point to a power supply issue.

All these amps are at least 40 years old and so there are any number of parts to replace prudently.