Updated with results - Need help with MC2300 - dead channel

tom1066

tom1066

AK Subscriber
Subscriber
Never posted in the McIntosh forum before but been a long time lurker. I have been running a 2300 into a stack of JBLs (my own Wall of Sound) for a while now and this AM had my first problem ever with it. I lost the right channel and smelled the dreaded electronic burning smell. I shut it down (luckily my speakers lived thru the ordeal) and took the top off. Immediately on the board behind the left autoformer I saw a burnt resistor so I pulled it out - see the pics below.

I am going to pull the obviously charred ones and replace them but need to know if something else either upstream or downstream should be checked and/or pulled.

I have never worked on a Mcintosh before but have recapped and serviced some Marantz 22xx receivers with luck.

Thanks so much for the input and help!
2300 board.jpg 2300 board corner.jpg
 
The driver transitors should have been upgraded decades ago, Mac provided us a kit to do it and would have been done at N/C if brought into a amp clinic.

The best thing to do now is to see if Mac parts still has replacement updated boards. If not maybe AC does or you can look in past posts for many discussions about this.

Hopefully the outputs are OK but it would not surprise me if a few were taken out which with today's parts replacing them all.
 
Thanks -

I will just get two new boards and replace them both. And pull the outputs to check them- hadn't done that in a while.
 
tom1066 said:
Thanks -

I will just get two new boards and replace them both. And pull the outputs to check them- hadn't done that in a while.
Click to expand...

Check the emitter resistors as well, they do like to go open in cases like this.
 
Hello tom1066
I will suspect some output shorted with such dammage on the driver board .As Kevin said check emitter resistors and of course take care about the "beryllium" insulators because there is some TO3 with, and some other without ! don't mix them because place (where they are) are drastickly important . Take pictures to be sure to not make anything wrong !
 
Thank you guys for the responses. I will get with audio classics and get new boards ordered hopefully tomorrow, thanks for the link damacman.

I will be away from the amp this week but when I get back i will get to looking at the outputs and emitter resistors as well. A fellow AKer sent me the link to the service manual so I will start studying it and trying to come up with a plan. Thanks for the tip about taking pics, I always forget that step.

I'm sure I will be back.
 
tom1066 said:
Thank you guys for the responses. I will get with audio classics and get new boards ordered hopefully tomorrow, thanks for the link damacman.

I will be away from the amp this week but when I get back i will get to looking at the outputs and emitter resistors as well. A fellow AKer sent me the link to the service manual so I will start studying it and trying to come up with a plan. Thanks for the tip about taking pics, I always forget that step.

I'm sure I will be back.
Click to expand...
Share a pic of your JBL Wall of Sound!
 
damacman said:
Share a pic of your JBL Wall of Sound!
Click to expand...

I looked for one today and couldn't find one but as soon as I get this amp back up and working I will definitely post one.:thumbsup:

I got my boards from AC today. I finally was able to pull some of the outputs. I have checked 6 so far and one is definitely bad. I found that the replacement is MJ15003. Do I just replace the one or all of them? I found some threads where it was suggested you should replace all of them for some smaller receivers and amps but was wondering about this one since there are so many. But that way I wouldn't have to test the rest so it wouldn't hurt my feelings.

Thanks for the help
 
They're MJ15003G now, "lead free" and yeah, I would replace them all, check all the emitter resistors as well.
 
Just remember there is only one insulator used in channels transistor banks and if you see some hints of oscillation there is a simple cure.

The MJ15003s have a bit more gain and "speed" than the original 132-070s so oscillation can always rear it's ugly head.
 
c_dk said:
Just remember there is only one insulator used in channels transistor banks and if you see some hints of oscillation there is a simple cure.

The MJ15003s have a bit more gain and "speed" than the original 132-070s so oscillation can always rear it's ugly head.
Click to expand...

I'm going to be honest with you, most of that is over my head but I'm definitely willing to try and understand/learn.

I'm not sure I understand what you mean by the "one insulator used in channels transistor banks". Also how would I detect the oscillation? Would I be able to hear it or is this something a scope would detect? And what is the simple cure?

Thanks for the help and knowledge.
 
The originals are available
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wizcr5tBEmMy0eavstlb0w2M=
Mac didn't match them . I used the newer ones without issue (oscillation).
On each power assembly there are 3 transistors mounted to heatsink. 2 are mounted directly (nothing between sink and device except maybe some thermal compound). The third has an oddball insulator. If you pull devices to test make sure the one that had an insulator ends up as the one with the insulator. I'd clean everything with denatured alcohol and apply a very thin layer of thermal compound during reassembly. I've been told if the emitter resistor failed, source them from Mac. There's something special (inductance maybe?) that is necessary.
If i may, unless you have some electronic repair experience, perhaps you should hand it off to someone more experienced. While these aren't super difficult, they're not for the beginner to learn on.
 
Also how would I detect the oscillation ? if your output stage is overheating , there is a chance yes

Would I be able to hear it depending what is oscillate . If it is in output stage you can "hear" it in output transformer yealing like an alarm or in the speakers sometime you can't hear anything (high frequency)

or is this something a scope would detect ? whatever the level is , frequency is , oscilloscope will show it yes !

I will suggest you to check emitter resistors first with a precise tool (not ordinary multimeter) . The value is so low that ordinary meter will show a wrong value .
0,56 ohm is 0,56 not 0,80
same for 0,33 ohm and 0,15 ohm.
If you have a doubt buy new resistors from factory . You will be sure to use the right type (inductive or no inductive) and the price is very low
 
I've been told if the emitter resistor failed, source them from Mac. There's something special (inductance maybe?) that is necessary.

yes , this is because in some amp , these resistors should be inductive or no inductive . There is a code on the resistor

L is the code letter for non inductive resistors
ex: 5W L0,15 ohm is non inductive
5W 0,15 ohm is inductive
 
Last edited:
Oh for point of reference, c_dk and clinic audio are authorized mac service techs, Kev is a professional tech with Mac experience, I'm an amateur tech so pay much closer attention to them than me.:thumbsup:
 
Last edited:
nj pheonix said:
The originals are available
http://www.mouser.com/ProductDetail/Central-Semiconductor/2N5303/?qs=sGAEpiMZZMshyDBzk1/Wizcr5tBEmMy0eavstlb0w2M=
Click to expand...
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/Wizcr5tBEmMy0eavstlb0w2M=

I have been wondering about this for quite some time. I do not understand why individuals are always advocating the use of the MJ15003 type when the type originally specified (according to McIntosh service information), the 2N5303, is still readily available at a comparable price from reputable suppliers.

The MJ15003 is an excellent device,but sometimes prone to oscillation in this application. And you need a savvy tech to guard against this,as it doesn't always occur under similar operating conditions: Frequency,power level or short duration tone bursts can all trigger the oscillation. You need to be very comprehensive in your testing to be absolutely certain of stability.
 
Patrice has corrected me.
He only was Mac service for 20 years through 2000
Still in high end service.
It wasn't my intention to mislead. More to give credit where it was due:dunno:
 
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