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mcintosh mc2125 relay issue

entreat11

entreat11

Member
Hello - I have a mcintosh mc2125, it was working then the next day it stopped. meters still get input and headphones work but no output from the main speakers. toggling the off/on switch does not do it. I believe it is a bad relay on the unit, seems common and many threads about it.

I opened the unit and got to the relay, i did not want to poke around to much yet until I am sure about what to do. The relay has 6 connectors from what I can see, my questions are are all of them soldered on the relay or are they all able to be pulled off the relay? Also its it easy to open the relay and try to spray with DeoxIT? Do i risk any other issues if i try this? To open the relay i assume its the two tabs on the side right?

I do not usually diagnose things myself but from what i have read this seems like a majority of the fix, if not then the relay will have to replaced.

Looking forward to hearing back.

Thank you
Michael
 
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I've never worked on an MC2125, but none of the Mac amps I've worked on had solder on relays. They all used slide on connectors. Just make sure to keep track of which connector goes to which terminal on the relay. Before removing the relay, you should be able to tap on it with a pencil to see if it engages the speakers. I just had this same issue with an MC2205. I ended up replacing the relay.

To clean, spray some deoxit on a clean piece of paper, carefully close the contacts together, and slide the paper between the contacts. If there's actual corrosion, you'll have to replace the contacts.
 
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Here ya go:

bendoggie

Thread 'Help with MC 2125'

First hello to all in Mcintosh land. About a year ago I finally got the chance to purchase a mint condition set. A C32 pre and A MC 2125. They look brand new. The man I purchased them from had them gone over by a fella named Tom Manley then they sat unused for five years. He had lots of Mc gear. Now however I am having a problem with the amp. I am driving a pair of Reference 3a serie master speakers and I loose the left channel or it just goes low in volume with static. If I shut it off and turn it on or cycle the speaker mute switch the channel comes back. If I raise the volume high...
 
Update on this...
Relay case did not open as expected. It was sealed around the edges, used a blade to cut around it top and bottom i got it open.

Unfortunately there was a small resistor soldered to the bottom right connector that went to the relay. i did not see this initially, after i opened the relay i looked when i moved and noticed the resistor. The leg that was soldered to the bottom right connector came off. I unfortunately do not solder much in years actually so this will remain like that for now.

I checked with the schematic and a tech who it will go to, he said that should not be there and it might have been a bad job from when it was previously in service.

Not sure how accurate, AI mentioned from looking at description and service manual, that that resistor is not natively there, this is to reduce the incoming 42V that comes from the power supply to turn on the relay. Maybe someone replaced the relay originally and then put this to reduce the voltage to the relay. Now that this is broken the relay will maybe not function now without it.

This amp was so clean i find it hard to believe it was ever opened, i had a hard time getting it out of the wood case!

Only other thing I can think of is this was done at the Mac Clinic maybe it has a couple of stickers on it.

Anyways here are pictures of the said resistor
 

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also side note i hope the relays are still available for this, not sure if it can be replaced with exact one Mcintosh used or it will a different value one.
 
By the time the MC2125 was introduced in 1976, repairs were no longer performed at the clinics which were limited to testing only.
 
The Mcintosh service manual identifies the relay as K301. It's an Omron relay, LAB2 or LAB2L, 24v. Mouser lists it as obsolete although I did find some used ones on Ebay.

Here's some more info on this relay:

The Omron LAB2L 12V relay associated with designation K301 (often found on Play/Rec or safety/mute PCBs in vintage TEAC/Tascam reel-to-reel tape decks like the Teac X-series) is a compact DPST (Double Pole Single Throw) or specialized reed/power relay used for signal switching, muting, or power-up routing.

And, I found this on the Tascam forum:

The power mutes K1-4 (OMRON LAB2L 12v) were all working before I pulled it apart, but I want to do this job once and do it properly, and not have to pull the MB out for another 10 years at least. So I want to replace them. I read in another thread that the member Skywave suggested COTO part 8L02-24-00 (although that was for a 40 series machine I think). It's an awkward form factor, but I suppose with some extra wiring I could make it work. I can't find any information about the Omron original part, but I believe it is a DPST, Normally Open, 12v coil.

* Should I be buying the COTO 8L02-12-00 for the 58 instead? (12v coil)
* There's stacks of n.o.s. OMRON LAB2 24v on feebay, which just seems to be a 24 v version. Could I use that? Maybe I'd need to remove R-R4 (1k2) to get the coil voltage up.
* On feebay I've also found a FUJITSU FRL764D12/2AS-02 12Vdc which is DPST and appears to have the right form factor (6 pins, 3 at each end). But I can't find a datasheet. Worth a punt? Don't know if it's NO or NC.

Please post a pic of your relay.

Murray
 
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