MC2205 Watt meters issue

ManyMoonsAudio

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Hello,
I have a 2205 here. Everything works fine, but the meters will not settle to zero on the watts setting. They work. I don't see any real excessive DC or noise anywhere testing the pins of the meter board, so I am a bit puzzled. Problem is the same on both meters. +/-15V looks nice and clean.

Anyone been here before?
 
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Hello,
I have a 2205 here. Everything works fine, but the meters will not settle to zero on the watts setting. They work. I don't see any real excessive DC anywhere testing the pins of the meter board, so I am a bit puzzled. Problem is the same on both meters. +/-15V looks nice and clean.

Anyone been here before?
PM sent..
 
I skimmed, but did not find a symptom listed that matched mine. Would you mind telling me which post has this info?
I am aware of the bad internal connection of the meter posts, the ribbon cable, the shorted 2200uf caps, and the diodes that blow when this all goes wrong. This is all taken care of. My symptom is they do not zero when set to watts. They work fine. Just jump up about 1/4 scale at power up.
 
Hello ManyMoonsAudi

They work fine. Just jump up about 1/4 scale at power up this is normal
I am aware of the bad internal connection of the meter posts, the ribbon cable, the shorted 2200uf caps, and the diodes that blow when this all goes wrong good ! this problem is caused by the 2200µF capacitors who goes shorted with the time but once you have replaced the both capacitors + the both diodes and restore the fuse on the board , everything go back to normal function . There is no relation between this power supply and the both meters . The meters can't damage anything in the unit .
I don't understand : they do not zero when set to watts
what do you mean exactly ?
Have you adjusted mechanical zero ?
Are they moving when no level at all (gain pots at zero ) ?
What is the relation between WATT and zero ??
Waiting to know a little bit more about it ....


42 years working on Mc Intosh products
 
Unlike most metered consumer amp designs, which sample the output to directly drive the meter coil thru a resistor, McIntosh metered amps have a dedicated amplifer constructed to accurately drive the meter mechanism making calibrated corrections for meter mass and the human eye's perception issues. It also drives the meter coil differently for watts vs. log readings.

Your issue will need to be troubleshot the same way a tech would toubleshoot any amplifer problem, there is no "silver" bullet.
 
I don't understand : they do not zero when set to watts
what do you mean exactly ? They deflect 1/4 scale and stay there. They go to zero with any other setting, or power down. This is with no signal.
Have you adjusted mechanical zero ? It is fine.
Are they moving when no level at all (gain pots at zero ) ? Yes, if I set the meter selector to watts

c_dk, yes, I understand. Thanks
 
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Not much in common between the meter L and R meter drive and also between the watts and log amp circuits.....

The power supply of coarse is common to both but not acting up on even the -20dB log setting but acting up on the watts setting makes this a "interesting" repair. Does it hold at that setting when you engage the hold function?

There has to be a sustained voltage even when in the hold setting, supplied by a discharging cap, the number is not at hand.
 
It does hold there with hold selection. Both meters raise slightly at the -20dB, although much less than if Watts is selected, of course. 0dB and -10dB are good.

Supply was my suspect from the beginning, because of the commonality, but this issue is eluding me.
 
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I found noise, both channels about the same on the scope. Traced the ground to a riveted ground terminal on the chassis. Soldered rivet to the chassis, happy meters.

I didn't find the noise before, because when I flipped the amp over to test, it acted fine with different stress on the chassis. However, because my dumb ass didn't bother looking at the meters when it was flipped, I didn't notice all was fine when upside down... :crazy:
 
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Chasing down faulty paths either signal or to chassis ground, whether rivet issues, corroded ferrules, or cracked or cold solder joints is just a on going part of the mundane restoration process that is not near as fun or sexy as finding sonic nirvana by swapping in the latest boutique audiophile capacitor.....but though time consuming must be done.
 
Chasing down faulty paths either signal or to chassis ground, whether rivet issues, corroded ferrules, or cracked or cold solder joints is just a on going part of the mundane restoration process that is not near as fun or sexy as finding sonic nirvana by swapping in the latest boutique audiophile capacitor.....but though time consuming must be done.
Whatever you're into man, some guys like changing and assessing caps, some guys like repairing and restoring, each to their own, everyone is entitled to their own road they take...

Manymoons is a fine repairer and restorer of classic/vintage audio for all makes, not just McIntosh, same with me, at the moment I seem to be a Sansui quadraphonic expert with three on the bench right now, next week it might be a MC2205 and C33 who knows, all in a days/weeks work.....

@ManyMoonsAudio , I actually have a very similar issue with my personal MC2205, thanks for sharing your repair, I suddenly feel motivated to get it on the bench, once I can get these Sansui's out of the way...
 
Thanks Kev, and no problem.
Post here when you do, if you wouldn't mind. I am curious about your findings.
 
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