A little problem with my MA6200 amp - help requested

[FauxHall]

Picked up a clean-looking MA6200 integrated in Seoul and lugged it back to Abu Dhabi. The previous owner had already modified it for 240v operation.

When I get it set up at home it started to have intermittent right channel dropout after it warms up.

Then the right channel goes out within a minute or two.

I suspect a cold solder joint somewhere. I found a tech in Dubai to work on it but he is by no means a McIntosh expert. Such expertise is hard to find in this part of the world - everything is so new!

Perhaps this is a generic problem or someone may have some experience to guide my tech in getting a fix.

 

[c_dk]

Basics first:

Has it been cleaned? The variable loudness control can cause a channel drop out if it oxidized. Same with the mode and input selectors. They are mechanical in the MA6200.

Pull the preamp to amp jumpers and use a patch cord to see if the issue swaps channels. If it changes it is the preamp, stays the same the amp.

The ROE bipolar electrolytics are a always replace item if I have a board out and a hot iron.

The unit is 15 years past due for a major recap but that will not normally solve a dropped channel issue unless one of the ROE caps is acting up.

 

[FauxHall]

None of the preamp controls affect the dead channel. I just got the schematic so that may help isolate the problem.

I asked the tech about recapping and he got a puzzled look on his face. I explained in more depth but we left it at just checking the caps. I doubt that will happen.

At this point I'd just be happy for both channels to work. I'll keep looking for a more experienced local tech for a future overhaul.

 

[clinic-audio]

Speaker relay is the gulty one !

 

[c_dk]

Of coarse he had a puzzled look, replacing caps will seldom fix a channel dropping out. You replace the caps to give it a chance to sound as good as it did 38 years ago when it was new!

Sticking to the basics you have now determined that the amp section is at fault. Patrice's suggestion is dead on, a dirty, arced, relay will cause all sorts of dropped channel issues. It can be temporarily cleaned but your best solution would be to replace with a like kind from a vendor like Mouser, Digikey, or a European distributor.

If cleaning does not solve the issue then your tech will need to dive into the driver boards etc. to do the basic circuit board testing.

 

[FauxHall]

My block schematic shows one common relay with two contacts for the two channels. So one could be dirty and the other clean. Quick fix is clean both.

I'll pass that on. I want the guy to do the minimum until he proves himself.

Note that the recap was always an optional task. Recapping was not considered the probable remedy by me.

 

[kevzep]

I would replace the relay, in my experience, when the contacts are corroded/worn/arced to the point where the audio is dropping out, its needing to be replaced. Cleaning is a waste of time because it won't last very long.

 

[c_dk]

Yea, but now he is going to ask for the generic part number and I don't remember it let alone what he can get in Abu Dhabi.

 

[kevzep]

Yea, but now he is going to ask for the generic part number and I don't remember it let alone what he can get in Abu Dhabi.

Yes, indeed. I am pretty sure I got the information off the cover of the relay in my MC2205 to obtain a part number.

Mouser ships world wide, I use them here in NZ for my caps, especially Nichicon fine gold etc .....
If your order is over $100US its free shipping..

 

[FauxHall]

My tech said he found the problem and it was the relay. His fix was to short it out.

Isn't its function to prevent turn on bump? He claimed that wouldn't be a problem.

I pick it up Sunday.

 

[kevzep]

Seriously? Short it out? That is no solution at all, why not just replace it?

That is very bad tech work I have to say.....relays are cheap and available worldwide, no excuse to do that...

And yes, not exactly good for your speakers, the relay disconnects the speakers whilst the power supplies stabilize...so yes momentarily there is DC on the output of the amp during that period...

Buffoonery!!

 

[c_dk]

We would call that a roadie repair, sure when the show has to go on OK, but for a amp of the high caliber, disgraceful.

It unplugs if memory serves me right. Have him at least lightly burnish the contacts so you can use it and post a picture of it so we can help you get a generic replacement.

 

[kevzep]

We would call that a roadie repair, sure when the show has to go on OK, but for a amp of the high caliber, disgraceful.

It unplugs if memory serves me right. Have him at least lightly burnish the contacts so you can use it and post a picture of it so we can help you get a generic replacement.

We don't even do barbaric repairs like that on the road Chris!!

Indeed, a picture and lets take it from there...

 

[c_dk]

O come on, I've seen plenty of roadie repairs over the last 40 years......

 

[kevzep]

O come on, I've seen plenty of roadie repairs over the last 40 years......

Not from me my good man. But I do know what you mean......I have seen that sort of thing before from desperate situations....
I'm always prepared however...

 

[FauxHall]

I got the bill already via email. 200 dirhim or about $54 USD.

At least I have an expectation that I'll hear the thing.

For my initial power up I select no speakers then select my Sony SS-HA1s as they were much cheaper than the Spendors.

If that goes ok I'll try the Spendors.

I'll also open it up and get the relay part number and consider a Mouser order.

 

[c_dk]

I do not want to even think of how sloppily he could have bypassed it. Sometimes not rushing in is the best path......patience pays off in the long run when doing vintage restoration.

 

[Bob]

bypassing means he soldered a wire/short across the relay contacts, and you
will have to reverse engineering or Sherlock Holmes it back. then go forward.

I'd suggest you keep the Spendors off it until fixed - it might still pass a high DC
offset to the speakers, or a really good transient.

 

[c_dk]

I will admit I have been having to much fun fixing up the plethora of turntables since I have been doing the turntable clinics at the local record store and posting over in the Turntable forum how we McIntosh dealers used to set up tables back in the 70's and '80s. I did have a few moments this morning to pull out the MC2125, MAC4100,4200, and MA6200 schematics and can report they all use the same DP DT 24 volt relay for the speakers. Mac's part # is 087-019; no generic number yet but maybe a search thru this forum for a 087-019 might turn one up.

I am still looking for the MAC4300 schematic to see if Joe when he wrote it, put in the generic number.

 

[FauxHall]

Here's the MA6200 back from the tech. Looks like there are two relays inside. The one still installed is the one that had the problem. I don't see the jumpering - probably had to take the bottom cover off too. I don't know the purpose of the one in hand. Probably involved in the power supply - I don't see it on my sketchy schematics. Sorry for the mediocre cell phone photos!

I have it playing my Sony SS-HA1 stand-mounts and it sounds wonderful! Much crisper and authoritative than than the Sony TA-A1 where the focus is on smoothness.

I was planning on flipping it but now I'm rethinking that that idea.