• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MC2100 repairs

c_dk said:
I believe the MC2300 schematic details all the mods needed to use the last updated kit for driver update.

The kit from Mac consisted of drivers, heatsinks, new bias diode, resistor and instructions to remove ceramic caps and add a jumper. IF I REMEMBER CORRECTLY. it was 30 years ago when we expected to do ALL mc2300s. MC2105s were optional.

The AKdatabase might have the MC2300 schematic.

i checked the database....the schematics are incomplete, they do list all updates supplied to warranty service shops.
Click to expand...

You are right Chris !

Here is the document from the MCINTOSH kit 044-980 from many many years ago ....
 

Attachments

more precision ?

Pictures of original capacitor recto verso + picture of the kit :thmbsp:
 

Attachments

  • DSC04434-680pF-recto.jpg
    DSC04434-680pF-recto.jpg
    24.8 KB · Views: 63
  • DSC04435-680pF-verso.jpg
    DSC04435-680pF-verso.jpg
    22.5 KB · Views: 59
  • DSC04433-kit-044980.jpg
    DSC04433-kit-044980.jpg
    51.5 KB · Views: 61
OK parts are in, but now I have a slight issue.

Now when I originally figured it was a particular board. The bulb would be brighter when it was in. Now the bulb is the same rather it's in or out. So that would lead me to believe the board is fixed. However when I plugged it directly into the wall socket the power transformer squealed a little then the fuse pop. So I went and got another fuse , now I thought the first one was a slow blow, but it may have not. Now the new one is a slow blow. So I removed the board I thought was bad and plugged it directly into the wall which I still had the squealing so I instantly unplugged it. Put the other board back in. Plugged the light bulb variac back in, and just let it run for a couple of mins. Then I tried it directly into the wall and this time no squealing and the fuse didn't pop. Now I didn't let it run for to long.

So my question is would it be all right or recommended that I plug in the variac and let it run for a while. Or is it possible there is something wrong and I just didn't let run long enough to find out.
 
Tried to get a handle on all you have done scattered thru many posts....

What new outputs and did you replace any wirewound resistors?

Did you lift a lead and test all the resistors on the driver boards?

Can you get one channel to work with either driver or output combo?

There are more things......
 
c_dk said:
Tried to get a handle on all you have done scattered thru many posts....

What new outputs and did you replace any wirewound resistors?

All the outputs are new, only the wire wound resistor on the driver board on the one channel was replaced.

Did you lift a lead and test all the resistors on the driver boards?

No,

Can you get one channel to work with either driver or output combo?

I never hooked anything up speaker wise, but the fuse would only blow with the one driver board in(which is the one I ended up rebuilding).

There are more things...... I can only imagine, but greatly appreciate your time and help.
Click to expand...

I will say I tried to plug it in last night to see what would happen. The squeal is now gone, however the power transformer hums. But the fuse did not blow either.
 
OK moving in the right direction, I now know how a dim bulb should look just that dim. So here is the new run down, I have narrowed down the hum to the other driver board We'll call it the right side (the opposite to which I originally thought was the problem). But for some reason the bulb was still a little bright with the left side board. So I got to poking around and found out that the wire wound resistors that I replaced had the wrong value. Since I knew the left side board didn't hum I removed the right resistor from the right side board. Installed that resistor into the left side board and whala. Very dim bulb, now what about the right side board, I am not sure yet so I went ahead replaced the transistor and now need to source another good resistor.
 
Check the resistance of all the carbon comp resistors on the driver boards. These tend to drift up in value with age.

Apologies if you've already done this. I read the whole thread and saw no mention of this having been done.
 
Ray Gianelli said:
Check the resistance of all the carbon comp resistors on the driver boards. These tend to drift up in value with age.

Apologies if you've already done this. I read the whole thread and saw no mention of this having been done.
Click to expand...
This is something I think needs to be done. When I got the one board in that wasn't blowing the fuse, there was scratchy sound. Last time I had this on a repair I did it was a bad resistor I believe in the feed back loop. But I'm not a tech so don't know if that was correct. Anyway I don't see how lifting the resistor and check for drifting, would hurt anything.
 
Ok I was able to pull some of the resistors on the troubled board. Yes over half of them where out of spec. One problem is I don't know what the serial number is on this, so I don't know which resistor values to use. I did find a 470 ohm resistor that schematic says it should be a 100 ohm resistor. So I put the 100 ohm in, plugged the board in after replacing the 5-6 resistors on the bottom of the board. No bright light, so I removed my light bulb tester and gave it a trial run. I now have a working amplifier minus a scratchy channel. After I fix the scratchy channel, I will then move on to rebuilding the power supply. I will continue to post my progress here to hopefully help someone along the way, so thank you all for the ideas that lead us to save another vintage McIntosh piece. Cheers.
 
Ok after making progress I hit a wall. So I thought that maybe there were some issues in the input board, so I replaced some of the caps and resistors. Now there are 2 caps that are electrolytic but don't have plus or minuses on them. I will look to verify which ones I am speaking of. Second I replaced the caps and resistors according to the schematic in the database, know when I plugged the amp into the in line light bulb the bulb lite back up and didn't dim out. I guess it could be something I did incorrectly or was could it be the changes in the schematic aren't correct.

Some help would be greatly appreciated.

Thanks
 
Why don' t you post a picture of the good and bad boards......should help in finding the correct values.

Have you compared the "good" board values to the " bad" board?
 
duder1982 said:
This is something I think needs to be done. When I got the one board in that wasn't blowing the fuse, there was scratchy sound. Last time I had this on a repair I did it was a bad resistor I believe in the feed back loop. But I'm not a tech so don't know if that was correct. Anyway I don't see how lifting the resistor and check for drifting, would hurt anything.
Click to expand...
It's advisable to check the resistors on both boards.
 
duder1982 said:
Ok I was able to pull some of the resistors on the troubled board. Yes over half of them where out of spec. One problem is I don't know what the serial number is on this, so I don't know which resistor values to use. I did find a 470 ohm resistor that schematic says it should be a 100 ohm resistor. So I put the 100 ohm in, plugged the board in after replacing the 5-6 resistors on the bottom of the board. No bright light, so I removed my light bulb tester and gave it a trial run. I now have a working amplifier minus a scratchy channel. After I fix the scratchy channel, I will then move on to rebuilding the power supply. I will continue to post my progress here to hopefully help someone along the way, so thank you all for the ideas that lead us to save another vintage McIntosh piece. Cheers.
Click to expand...

I would stick with the values that are currently on the board, unless you are following a service bulletin that advises changing them. Many pieces of electronic equipment undergo revisions as time passes, with some components changing value. So the schematic you're following may not accurately reflect the equipment on your bench.
 
I will go back and make sure all resistor where original to the ones on the board. Hopefully I can figure it out. Most where replaced on both boards. The light bulb didn't stay on until after I recapped the input board, now the Caps I was referring to were 309, and 310. I did replace 303, and 304 with 470uf according to the schematic I have, but where 680 uf I believe. I will double check the old schematic as I just realized I had that and put all components back to what was in except the service update on the output boards. Good points guys. C_dk I will take pics of the 3 boards. 2 outputs, 1 input.
 
First I like to say that you guys are great and I love your enthusiasm and interest in getting the MC2100 up running in its original if not better condition.
MC2100 is one of the best classic/vintage amp I've ever owned and used. If you ask me I think the MC 2100 are way under rated. I have owned mine since the 80s and the sound quality never change. Here's my set up that adds a little encouragement to your project before I switched to MC601. Don't get me wrong, I still have my MC2100
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom