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McIntosh MC2505 Strange Issue.. What Could it Be?

Selector Z

Selector Z

New Member
Greetings All!

First off, thank you to everyone for all of your contributions, insight, and wisdom shared on this forum! I have been a big fan for many years and have learned so much from this forum over the years. First time posting to ask for help, I am really fretting over this problem and would tremendously appreciate any insight, ideas, or suggestions you all are able to provide.

After moving from California back to New York I hooked up my system to find an issue with the right channel of my MC2505. (Packed the MC2505 in factory double box and made sure it was safe/ secure during move)

When turning the amp on with no audio/ signal being sent to amp everything is fine and crystal clear, whether the left and right channels are turned up or not.

When any sound is played through the right channel the VU meter instantly jumps and get stuck at about -5 on the right VU meter and about -15 on the left VU meter (with VU meter setting knob at -10). This is accompanied by a what sounds to be the right channel ungrounded. It will stay pegged like this if I turn off the audio source to amp. After another minute or so I hear a faint oscillating tone sound amidst the ungrounded hum sound in the right channel for 30 seconds to a minute followed by the amp shutting off from overheating.

This does not happen if I only play music out of the left channel. As soon as I give any volume or power to the right channel the VU meters jump and get stuck at those positions with the hum followed by the oscilating tone and then the amp shutting down.

Experimenting with trying to source the problem, I noticed that after the VU meters get stuck, hum, etc. if I turn the speaker knob (on front of amp) to off, turn the right channel down completely, and turn the speaker on/off knob to the on position again the issue will disappear. Left channel works fine independent but any volume/ power to right speaker will result in same issue happening again.

Troubleshooting I tried new speaker wire, I switched the wires from amp to alternate speakers (problem went from right to left speaker), then from those speakers to different channels on amp (problem was back in right channel). Also tried a different input sources into amp but same issue.

Tried headphones only on the amp with speakers off and both right and left channels work fine with no problems at any volume. Issue only occurs when sending audio out of the right channel of the amp.

I had a similar problem happen a couple of months ago and found a thread suggesting that the speaker wire on the back of the amp could be touching and causing the problem. Back then, that was the case and adjusting the wires fixed the issue. This time around I have checked and checked and checked but there are not any speaker wires touching.

Any suggestions or ideas as to what may be going on here? Any leads on techs I could connect with to help resolve the issue?

Additional info: Unit was serviced by Terry Dewick about 5-7 years ago by previous owner who stated "Outside a basic tune up, he replaced a power resistor and all electrolytic capacitors. Prior to sending it to him, I replaced all the output transitors as there were a couple that were bad on one channel, I had him verify that they were the correct replacement part (which they are) and bench test the amp. All channels produced more than adequate specs."

Thank you for your time, consideration, and help with this issue!
 
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Could be several things. You say there is good, clean output to headphones so maybe wiring inside the amp at the speaker terminal block is shorting? Only way to tell for sure is to have a good tech check it out. I would absolutely NOT use it until its taken care of or you risk even greater damage. Post where in NY you are and maybe someone can recommend a tech nearby.
 
Too many possibles here, so I'd agree that finding a good tech to check it out would be best. If you live towards the southern part of NY, first recc would be Audio Classics, in Vestal.
 
Selector Z said:
. . .Thank you for your time, consideration, and help with this issue!
Click to expand...

OP shows Brooklyn, NY just below his avatar.

I agree with the recommendation to send out to be repaired. I also recommend Audio Classics in Binghamton, NY. Maybe time for a road trip or you do have the proper packing material to ship it (although shipping Mc glass is always risky).

Or maybe someone in NYC can recommend a good Mc tech in the city.
 
Thank you so much for the replies and the suggestions Bill, CJ, and TSmith!!

I live in Brooklyn and called Audio Classics in Binghampton to inquire about the issue and they mentioned that they were unsure of the issue other than potentially the speaker wires touching which is not the case. They quoted $700-800 for the repairs, kind of tough on my budget would be a while before being able to I dont have a car but I do have the original box (and inside box) and could ship it if needed. Saw there are two authorized Mac techs in Manhattan but the reviews online were a bit concerning. Spoke with Analogique they quoted anywhere from $400 way on up but are backlogged about 8 weeks. Would love to get the amp checked out and back up and running sooner than this.

Any suggestions from forum members on local techs in the Brooklyn, Queens, Bronx, or Manhattan area?

Any other ideas or suggestions as to what may be causing this?

Thanks again to all for any feedback, insight, info, or suggestions you may be able to provide!
 
Selector Z said:
Thank you so much for the replies and the suggestions Bill, CJ, and TSmith!!

I live in Brooklyn and called Audio Classics in Binghampton to inquire about the issue and they mentioned that they were unsure of the issue other than potentially the speaker wires touching which is not the case. They quoted $700-800 for the repairs, kind of tough on my budget would be a while before being able to I dont have a car but I do have the original box (and inside box) and could ship it if needed. Saw there are two authorized Mac techs in Manhattan but the reviews online were a bit concerning. Spoke with Analogique they quoted anywhere from $400 way on up but are backlogged about 8 weeks. Would love to get the amp checked out and back up and running sooner than this.

Any suggestions from forum members on local techs in the Brooklyn, Queens, Bronx, or Manhattan area?

Any other ideas or suggestions as to what may be causing this?

Thanks again to all for any feedback, insight, info, or suggestions you may be able to provide!
Click to expand...
$700-$800 seems high for troubleshooting and repair. That gets you a full recap around here. Hopefully other folks chime in here but you could try another post in this Mac section and title it: Mac Tech suggestions near Brooklyn NY. Its a nice amp and it wouldn't seem to need a full recap as you said Terrry D did that 5-7 years ago.
 
You could call Stereo Exchange in Manhattan. They’re an authorized McIntosh dealer from whom I’ve purchased equipment, and they should service Mac or know of a Mac tech in NYC. Last time I had a tech in NYC work on a piece of Mac (a C28, I think, in the late 1980s) it was very expensive—much more per hour than any other brand. Since then, I’ve always gone to Audio Classics. I presume their quote to you is at the extreme high end of what it could cost. AC won’t overcharge you. They’re very fair, conscientious. When I had them completely overhaul my MR78 and Richard Modafferi update it, the quote was $900-$1000. Turns out, once Richard opened it up, he discovered he had already worked on it once before (not a complete overhaul), so I was billed around $300/$400. I would never have known either way.
 
There have been reports of folks having screws that are too long in the speaker connection barrier strips that cause shorts to chassis. A long shot, but since you are not the original owner and it has been serviced previously it may be worth looking into.
 
Good evening all,

Apologies for the delayed reply, work has been thorough the past couple of days.

Thank you Bill for confirming that and for the suggestion!

Thank you Mackie for the link to Bob, I will give him a call and check in with him. Thanks as well for the suggestion to check Q13, Q15, and R61 and the diagram, Much appreciated! Besides checking to see if theres any damage, should I check it with a multimeter? Any specific way I should test w. the multimeter or info on what I am looking for? I am a novice with the multimeter, got one last year to check my other set of speakers and my cables out but haven't had much practice with it outside of that thus far. I am a rookie for sure..

Thank you Bushikan for the suggestions and the lead to call Stereo exchange, I will check in with them after I talk to Bob who Mackie suggested. I appreciate the recommendation for Audio Classics too! I wish I had a car and could just drive on up there.. Would be a lovely drive, might be worth getting a rental car and making the journey if the leads out here in the city dont work out. Hesitant to ship it but will look into that route some more as well.

Thanks as well Longfellow for the suggestion on the screws potentially being too tight. Would it be a bad idea to unscrew the speaker terminals on the back and see if the wires connected to it have any issues?

I really and truly have tremendous gratitude and appreciate for the help, advice, suggestions, and support you guys provided! The Audiokarma community is amazing!
 
Before you bring it in, there are a few things you could visually check if you are comfortable doing so. If you remove the bottom cover you could look for a loose bolt around the speaker outputs or by the speaker on/off switch. I had a tiny bolt that is used to mount the speaker terminal block missing in my amp. I looked all over for it for fear it would short some terminals but never found it. Something could have come loose in the move. If there is nothing obvious then take the amp in. As stated in earlier posts, you do not want to cause any further damage so only turn the amp on if you think you found the problem. It seems to me that if the amp works fine with the speakers off and headphones plugged in then the problem 'must be' between the speaker on/off switch and the speaker terminals. Basically the wiring from switch to autoformer to speaker terminals are the main suspects. Probably worth a try. Good Luck!
PS: as far as speaker wires go, some terminals on the ends of the wire are worth the time. They keep accidental shorting to a minimum. If you are wrapping bare wire around the screws on the terminals it is time for a better solution. It is too easy to have one strand bridge the gap. Hope this helps :)
 
For your Speaker connecting safety....... try these cheap solutions:
upload_2022-4-19_14-55-41.pngThese spade connectors ( can probably find at local hardware)

OR on Amazon


upload_2022-4-19_15-0-1.jpegRight Angle Speaker Fork Spade Y Connectors & Binding Post, 4MM Gold Plated Banana to Spade Adapter Plug, HiFi Speaker Cable Wire Connectors 4PCS
AND

upload_2022-4-19_15-2-8.jpegMonster XP QuickLock Connectors - Best Banana Speaker Wire Plugs for DIY Installations - 2 Pair (4 Total)
 
Selector Z said:
switched the wires from amp to alternate speakers (problem went from right to left speaker), then from those speakers to different channels on amp (problem was back in right channel). Also tried a different input sources into amp but same issue.
Click to expand...
so are you saying the problem followed the speaker?
 
Thanks for the link to the tech sberger! I will check in with him.

Thank you Refugee for the suggestions as well. Some spade connectors are definitely in order.

Jimbo, when I changed the wires I switched the speaker wire from the right channel of the amp that connected to the right speaker (originally heard issue in the right speaker) to the right channel of the amp connected to the left speaker the problem at that point was then noticeable in the left speaker.
 
Selector Z said:
Thanks for the link to the tech sberger! I will check in with him.

Thank you Refugee for the suggestions as well. Some spade connectors are definitely in order.

Jimbo, when I changed the wires I switched the speaker wire from the right channel of the amp that connected to the right speaker (originally heard issue in the right speaker) to the right channel of the amp connected to the left speaker the problem at that point was then noticeable in the left speaker.
Click to expand...
Gotcha,
I have a mc2205. It had a blown output and emitter and power supply issue.
It was an easy rebuild with the help of AK'S guy's and a lot of reading.
 
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