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MC2105 restore from a shipping disaster

Left a message with Gary over at Mcintosh. Hopefully I hear from him in the next few days.

In the meantime to keep doing the recap I am going to reinstall the old transistors/revert the service bulletin.
 
If you want I can mail you the full compliment of components I removed from my boards when I did the service bulletin. Let me know.
 
Talked to Mcintosh and while they didn't have a fix for me they did send me an updated service manual (with the service bulletin applied!).

So going to go over my circuit vs their circuit and update any other values I see as off, really think it is a resistor value or two. I have attached all the manuals they sent to me and will update the AK database later. Newest one being 038922
 

Attachments

How is the fitment between your boards and the edge connectors on the amplifier chassis? I had all sorts of strange issues with my amp until I cleaned and tightened the edge connector terminals in order to pinch the board tighter. The boards should take a little effort to push into the edge connector, and they should be able to stand up straight once inserted.
 
Motnick said:
How is the fitment between your boards and the edge connectors on the amplifier chassis? I had all sorts of strange issues with my amp until I cleaned and tightened the edge connector terminals in order to pinch the board tighter. The boards should take a little effort to push into the edge connector, and they should be able to stand up straight once inserted.
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It seems to be fine. I don't see the issue when I swap the driver boards.

I am going to go with a full recap and ignore the service bulletin today. But I am going to design a replacement driver board based on the schematics above and then do a drop in replacement. I don't mind sharing my gerber files with whomever but going to take me a bit of time to design and test it to make sure it works.

I think this is going to be the right solution as I don't want to go crazy replacing half the original resistors and adding more in.
 
@Johnny_Law
If you have closer shot at your new boards from mcintosh/back of the boards that would be awesome :P If not that is fine just wanted to see what the resistors they are using.
 
First, what are you using for D103/D104? This is not supposed to be a common 1N4001 etc. diode, it is 070-046 a specially screened Motorola stabistor (currently available from McIntosh Parts) that needs contact with the transistor for thermal reference. A single diode will not work, two 1N4001 in series will make the board work but will not protect as designed.

Next is the board. I am not familiar with the 043-805 board, must be an early amp? Hopefully a compatible board with the update, but note that the service update is for the 043-899 (2100/2105) and 044-243 (MC2300) boards. @Johnny_Law has posted an 043-899 and the new 044-243 boards, not the same.

I guess last would be that the board has suffered a bit and has some repairs, be sure that they are all good repairs. The two missing resistors on your board are consistant with the original 043-805 configuration in the MC2105 but I do not know about C117 without looking through all versions of the S/M.
 

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SaturationPt said:
First, what are you using for D103/D104? This is not supposed to be a common 1N4001 etc. diode, it is 070-046 a specially screened Motorola stabistor (currently available from McIntosh Parts) that needs contact with the transistor for thermal reference. A single diode will not work, two 1N4001 in series will make the board work but will not protect as designed.

Next is the board. I am not familiar with the 043-805 board, must be an early amp? Hopefully a compatible board with the update, but note that the service update is for the 043-899 (2100/2105) and 044-243 (MC2300) boards. @Johnny_Law has posted an 043-899 and the new 044-243 boards, not the same.

I guess last would be that the board has suffered a bit and has some repairs, be sure that they are all good repairs. The two missing resistors on your board are consistant with the original 043-805 configuration in the MC2105 but I do not know about C117 without looking through all versions of the S/M.
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Yeah I saw that I was watching a video
and he talks about replacing the diode w/ 2 separate diodes for my eventual rebuild.

But my current circuit I placed the diode under the transistor but didn't help any. It is interesting that the service update only applies to 043-899 so maybe my 043-805 is not effected then :idea:

And the missing C117 is a valid config according to the manual for my serial number. So going to just go with my recap (avoiding the service update) and enjoy my amp while I work on just reworking the entire board outside of the amp. I might just bite the bullet and buy it straight from McIntosh if they have any left as I already need to buy a new volume pot.
 
People who replace D103/D104 with two diodes don't understand the design/function of the circuit, one of the hazards of trusting youtube technicians and ebay engineers. It needs to be the proper stabistor and AFAIK McIntosh Parts is the only source. Not an expensive part, but an expensive failure if the unit goes into thermal runaway.

These amplifiers were designed, tested, and perfected by Engineers, not recappers.
 
SaturationPt said:
People who replace D103/D104 with two diodes don't understand the design/function of the circuit, one of the hazards of trusting youtube technicians and ebay engineers. It needs to be the proper stabistor and AFAIK McIntosh Parts is the only source. Not an expensive part, but an expensive failure if the unit goes into thermal runaway.

These amplifiers were designed, tested, and perfected by Engineers, not recappers.
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Really appreciate the insight. Yeah I will figure out where I want to go next. I might call the parts department to see if they have new driver boards and go from there.
 
wizage said:
Talked to Mcintosh and while they didn't have a fix for me they did send me an updated service manual (with the service bulletin applied!).

So going to go over my circuit vs their circuit and update any other values I see as off, really think it is a resistor value or two. I have attached all the manuals they sent to me and will update the AK database later. Newest one being 038922
Click to expand...
Thanks for posting these! I'm hopefully going to be working on a broken MC2105 starting with AH8XXX and hadn't come across a version of the SM that covered anything that late.
 
Last time I contacted the factory they did not have any new boards but they did have D103/D104.

I have seen some boards on ebay that are new - made by an AK member I think.
 
Refugee said:
Last time I contacted the factory they did not have any new boards but they did have D103/D104.

I have seen some boards on ebay that are new - made by an AK member I think.
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Call me a skeptic but I ain't purchasing anything on ebay. Most of the time it is over marked up and not worth the price. Rather buy from AK directly or partners of AK or just buy the parts. Last one I saw was something near $400 for a pair of driver boards with little info about what was on the board or what parts they used.
 
wizage said:
Call me a skeptic but I ain't purchasing anything on ebay. Most of the time it is over marked up and not worth the price. Rather buy from AK directly or partners of AK or just buy the parts. Last one I saw was something near $400 for a pair of driver boards with little info about what was on the board or what parts they used.
Click to expand...
Can't agree more that you have to be careful on ebay. It may be worth contacting the seller if it is the only option but I would ask a lot of questions for sure. Let me know if I am wrong but I don't think the board is available from the factory or from audio classics. It has been a few years since I inquired. If the factory had some I would probably buy as a back up - along with the gain pots. I would rather populate the board myself if that was an option.
All that to say, "I agree". LOL
 
Check the thickness of the left board compared to the right. There was a thread about some boards being thinner.
 
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