MA5100 grounding issues???

[sensa]

I have an MA5100 that is very dear to me. 20 years ago I stumbled on a yard sale. They were using it to play music...... for the yard sale. I asked if they were selling it. They said yes. I asked how much. They said $15. And here we are. I adore it.

After two recent back-to-back negative repair experiences (with two different McIntosh authorized shops) trying to get it in tip-top shape, it began acting up again.

I was ready to through in the towel when by chance my troubleshooting took an interesting turn.

I hope some kind soul can help me weed through my findings. All things now point to grounding -- at a minimum -- either outside the unit or inside the unit, or some combination of both.


===== INITIAL SYMPTOMS ====

It began as a hiss, not quite broadband, in the right speaker only.

Over days the hiss got louder, and eventually it would produce these bursts/pops like static discharge.

Over more days, the level and bandwidth of the hiss grew more, and it just became unusable at any volume.


===== TROUBLESHOOTING =====

* Speakers/drivers: OK
* Input source, eq pots, filter switches, etc.: NO CHANGE/NO EFFECT
* Signal paths before the amplifier stage: OK (RCA ins and outs clean);
* Pots, rotary switches, rocker switches (recently serviced): OK
* Unplugged all signal inputs and outputs (only speakers and power connected): NO CHANGE
* Unplugged all other AC devices that share the residential electrical circuit: NO CHANGE
* Unplugged wireless devices in the home (router, chromecasts, etc.): NO CHANGE
* Changed to a different AC circuit: NO CHANGE


===== LUCKY STRIKE??? ======

Today things got interesting.

It occurred to me than some kind of RF interference from a device outside the home could be at play.

Why not: I grabbed a sheet of common kitchen aluminum foil and laid it on top of the unit.

This produced light crackles and pops as I ran my hand over the foil. All of a sudden:

**** THE RIGHT CHANNEL ISSUE WENT AWAY COMPLETELY.****

I couldn't believe it. Even idling hiss from both speakers seemed better than I could remember.


===== THE PLOT THICKENS =====

A few hours of listening enjoyment later, I revisited the foil, wanting to recreate the problem and solution.

Turns out the light crackles and pops were not from the interaction of the Mac and the foil, or from shielding it in some way: I hadn't noticed that the foil had draped over the side and would occasionally lightly graze the chassis of a Furman power conditioner that sits next to it. This interaction is what made the right speaker issue go away.


====== OUTLET CHECKS =======

Out came the circuit checker and multimeter.

Outlets on the Fuman:
OPEN GROUND (Neutral to hot: 118; hot to ground: over 60; neutral to ground: under 60).

Wall outlet:
OPEN GROUND

Next wall outlet (same circuit):
OPEN GROUND

3rd wall outlet (same circuit):
CORRECT (neutral to hot: 118; hot to ground: 118; neutral to ground: 0)


====== MOVE TO THE GROUNDED OUTLET ======

I moved the Furman and Mac to the good circuit and powered up. So far so good.

I fiddled with the foil again, and on first contact grazing the chassis of each: the circuit tripped.


===== WHERE TO GO FROM HERE ??? =====

Obviously the outlet grounding needs to be corrected (I'll speak to the landlord).

The big question: what might be wrong on the Mac side?

A loose connection somewhere leftover from the recent repairs?

A failing component?

I'd love to have a look, but it's not my strong suit and don't know where to start. In my current situation, a third visit to a repair shop won't be in the cards for some time.

Thanks for reading. Will appreciate anything you can impart.

 

[c_dk]

A authorised McIntosh repair shop is authorised to lose money on every McZintosh warranty repair they do........I do not have the exact reimberment sheet in front of me but ost companies pay a fixed amount for warranty repair on a unit independent upon what the local cost of living is........that amount is typically 60 to 40% of what regular rates are.

Most such shops are now dealing with computer control and IC issues not 50 year old semiconductors.

An anology might be dropping off a old Carter quadrajet to your local GM dealer asking them to rebuild it.....they probably would look to see were it would plug into their diagnosis computer, but for the old guy off in the corner who would see it and remember........back in the day.

There are no authorised McIntosh restoration services, I believe there should be, but right now most are independent in the sunset period of their lives.

All that being said you need to expect a restoration service to invest at least 6-7 hours into your now 50+ year old unit.

A guess is that your unit has cracked solder joints and/or intermittant semiconductors, cracked/cold solder joints are notoriously intermittant, the same with flaky transistors.

Five, six, seven hours on a techs bench will not be cheap but so goes the world of restoration, again not repair.

 

[ajward549]

Listen to c_dk, my 5100 was brought up to spec by Tom and Terry when I purchased it and I think it sounds fantastic. 100% reliable and no issues. Invest in restoration and you will be happy you did!

 

[sensa]

Guys, first of all nice to meet you. Thanks for taking the time to reply.

C_dk: I'll start by having a close look at cold solder joints. As far as transistors, given the nature of the issue and also how it manifested on the right channel only, could you recommend a place to start, the most likely culprit perhaps? I have a PDF of the service manual, but not much sense of where to begin.

I'm hoping to understand is where some answers may lie, starting with the low-hanging fruit and working my way deeper. But also to understand more about the mechanics/physics at play. I'm in over my head with what may be at play, but I am fascinated by it, and also where my troubleshooting has taken me: to a sort of semi-fix and new problems to pursue.

Also safety. In terms of grounding behavior outside the unit -- chassis to another device's chassis, or unit to wall power, is the shorting behavior something that can be expected for an ungrounded outlet and/or a 2-prong device like the Mac.

Unfortunately for me, I've spent all I can for now on my Mac. Between two shops, about $900 and several months. Water under the bridge. I continue to deliberately omit details because the point of my post was not to rant about them.

A further complication: I work(ed) in live sound. The long-term view is about as bad as it can be. I need to try and make due with what I have: a beautiful Mac that's been a big part of my life, some decent skills, a lot of time, and the desire to understand.

==========================

Re: market factors at play and the overall state of things for a unit of this age, your points are well taken, c_dk, as well as your advice, AJ. McIntosh, however, was not involved here, no petty reimbursements were at issue. What you say is true, but it's similarly incumbent on a service business, of any kind, to do the work they bill for, or to not take work they are not qualified to do. Communication and honesty. I won't go further than that; this is not a bash a shop thread. Some may even say it's all on me, but that won't help me either. Been down the shoulda-coulda-woulda road too much as it is. Moving forward.

 

[sensa]

Update:

I haven't had a chance to open things up yet to follow c_dk's tips. I have been focusing on the electrical issues inside the home first.

All tests confirm an open ground on some receptacles. Sample metering at the ungrounded ones:

H-N = 119
H-G = 63
N-G = 57

Then, metering at a properly grounded receptacle, or a bad outlet metered to a good ground outlet via the ground socket on an extension cord:

H-N = 119
H-G = 119
N-G = < 0.5

Next, metered Mac chassis to Furman chassis while on ungrounded outlet:

61v
(roughly The same as H-N on the revaptacle, which makes sense)

Then, metered Mac chassis to Furman chassis on properly grounded chassis:

<0.2v

Here's the interesting thing (well, at least to me):

1) If I use aluminum foil to short the Mac and Furman chassises (?) while on the ungrounded receptacle (see first post) it temporarily solves the crescendoing hiss/static/zaps/pops in the right speaker.

2) If I try the same thing while on a properly grounded receptacle, shorting has no effect. The issue in the right speaker persists.

Similarly, if I corrected the issue during (1) above, then power down and move to the grounded receptacle, the right speaker issue will still come back, and then there is no remedy.

As you can see, I know just enough to be dangerous. Could any of this help hone in a most likely culprit inside the Mac? Or might it point to many? I would really appreciate anyone's thoughts, ideas, or explanation of factors at play. Thank you.

 

[TSmith8605]

If you want to fashion an RF shield with foil, you have to connect the foil to the chassis of the Mc or it won't make a good shield. You may have accidentally made that connection when the foil touched the Furman chassis.

The whole Idea of plastering foil on top of electrical things makes me nervous - seems like lots of opportunities to short stuff out.

I would think that AC grounding issues would result in consistent hum in both channels, not hiss and pops in only one channel. RF interference would also likely affect both channels more or less the same. If a shield does fix the issue in one channel, that may mean that something is wrong inside the Mac making the one channel susceptible to RFI given that other channel does not need a shield.

I think your Mc needs repair and apparently some of your outlets need to be fixed.

Have you tried the Mc directly into one of your good outlets with the Furman thing turned off and out of the circuit?

Have you cleaned all the controls with FaderLube?

 

[c_dk]

I do not know the proper name for them but you can purchase from your local big box building supply a device just Iike your electrical inspector uses to onfirm that a outlet is wired correctly by just plugging it in.

Most likely a lifted neutral because electrician used the stab connections instead of the screw terminals.

Trying to remotely diagnosis a intermittent noisy component or bad solder joint is impossible.......a probe to trace though the circuit while observing a good signal from the good channel and comparing it to the bad channel is the traditional way to use a osciscope and probe to find where a problem first crops up.

Shortcuts are just luck....which sometimes does work.

 

[sensa]

Hi Terry, thanks so much for weighing in.

If you want to fashion an RF shield with foil, you have to connect the foil to the chassis of the Mc or it won't make a good shield. You may have accidentally made that connection when the foil touched the Furman chassis.

This makes sense. The thing that stumps me: it only works if the receptacle is ungrounded (and significant voltage across the Mac and Furman chassis). Where there is a proper ground, the foil and it's making contact seems to do nothing.

The whole Idea of plastering foil on top of electrical things makes me nervous - seems like lots of opportunities to short stuff out.

I'd have to agree with you lol I'm glad it seems to have pointed me to something, but I'm not proud of it, and don't see it as something viable I should keep doing.

I would think that AC grounding issues would result in consistent hum in both channels, not hiss and pops in only one channel. RF interference would also likely affect both channels more or less the same.

Somehow, the system is entirely free of hum (funny: just yesterday, in a radio station's tribute to Bill Withers, they played some live recordings full of 60Hz hum while I was in an unusual spot in my room that doesn't have a modal null there, and I had to mute the speakers to make sure it wasn't the Mac). Likewise, the left channel is always flawless, no matter what. And when the right channel acts up, and is 'remedied' by the foil short, it matches the left channel perfectly -- no artifacts left over.

Have you tried the Mc directly into one of your good outlets with the Furman thing turned off and out of the circuit?

Yes, in my early testing, but I will retest given what I've learned about different receptacles since. One of the first things I tried was nothing plugged into the Mc -- neither signal RCAs nor courtesy AC -- on the Furman first, and then the Mc directly to a different receptacle in the house. I will to do this again.

[A side note: the Mc issues predate this, but a couple of weeks ago I had the power utility come out when the Furman was flashing and tipped me off to outlets all over the property metering 137v (I rent a back house; landlord was away and also checked outdoor outlets around the main house). This lasted around 3 hours and was back to 122v by the time the tech came out. He checked the main panel and found no problems. He explained it could have been caused by a period of "bank switching" or "local control," and to call the trouble dispatcher if it happens again (and they could then confirm if they were bank switching or if something in the neighborhood needed fixing). Anyway, I mention this because the coincident timing has clouded my troubleshooting a bit if that makes any sense.... ]

Have you cleaned all the controls with FaderLube?

Yes, after the first round of shop service all controls came back flawless and have stayed that way. Super clean/smooth toggling both physically and audibly on rockers and rotaries. All pots noise free. All knobs continue to be as consistently and reassuringly firm in rotation as they always have.

Thanks again for all the insights. I'll get to retesting now.

 

[sensa]

Update: re-tested the Mc on a good outlet.

• With the right speaker issue still audible at power down, I moved the Mc to a good outlet, but initially left the Furman plugged into the wall (it powers other gear feeding the inputs of the Mc);
• Powered on the Mc: issue still present;
• Went about incrementally severing all ties between the Mc and the Furman (interconnnects with other gear one by one);
• No audible effect along the way

Eventually arrived at the present scenario:

• Mc plugged into good outlet
• No connections to any other gear of any kind, just L and R speakers
• Furman completely unplugged the wall outlet -- zero physical connection to Mc or power; by extension, all disconnected audio gear also completely powered off and no longer linked to the Mc
• Finally, I disconnected everything else in the home (not much) that occupied the same good circuit, making the Mc it's sole occupant (well, at least as far as what I can see and control inside the home)

Result: the right speaker issue persisted.

Since the Mc was now on a proper grounded outlet (chassis to ground metering 1.8v), I couldn't resist brushing the foil between the Mc chassis and the completely unplugged Furman chassis.

I was surprised that It fixed the issue again. After a few minutes of clean operation, the issue returned.

One observation, for whatever it's worth (probably not much), is that the right speaker issue seems to both arise and then partially subside faster than before. That is, instead of a hiss that can go on for some time before turning into zaps and pops, and then tending to stick around, it goes from good, to bad, to not as bad, faster (man is that ever a funny statement).

Next up: getting inside the Mc for a visual inspection to see if anything glaringly obvious is amiss. Thanks again for all tips so far. All thoughts welcome.

 

[sensa]

I do not know the proper name for them but you can purchase from your local big box building supply a device just Iike your electrical inspector uses to onfirm that a outlet is wired correctly by just plugging it in.
Most likely a lifted neutral because electrician used the stab connections instead of the screw terminals.

Thanks c_dk. I have and usually start with one of those outlet testers, but have read about some scenarios where they do not report correctly (and in some cases, by design, simply can not). One example: they won't necessarily detect a bootlegged ground (wall neutral wire connected to the ground screw of receptacle, then jumped to the receptacle neutral). As a result of my experiments, I decided to go through the entire house. When I opened one of the outlets reporting only a bad ground through the 3-prong plugin tester (different circuit than the ones I've used here), I found such a bootlegged ground instead. Insane that people do that sort of thing.

So, I start with that simple tester, then meter, then physically open and inspect each outlet, make notes of whether they are midstream or end of stream in the circuit, and follow the clues from there.

Luckily, it seems there are no open neutrals or swaps anywhere (if I am interpreting the metering results and line traces correctly), just some open grounds. And thankfully, physical inspection of each ungrounded outlet (except the one above) confirms correctly wired/pigtailed grounds with bare copper connected to the receptacle screw terminal. So, all signs now point to a junction box outside the home, and a lifted ground there or between there and the first outlet on the circuit.

Trying to remotely diagnosis a intermittent noisy component or bad solder joint is impossible.......a probe to trace though the circuit while observing a good signal from the good channel and comparing it to the bad channel is the traditional way to use a osciscope and probe to find where a problem first crops up.

You mean there's no smartphone app for a 50 year old beauty like this? I do appreciate the guidance. I don't have access to a scope and haven't used one but would be up for trying if I did. All phone jokes aside, for rudimentary testing, are any of the iphone/ipad peripherals I'm seeing online viable (hardware measurement interface paired with an app)? I ask because in my live sound work, I was inherently (if not completely justifiably) skeptical of phone-based RTA/FFT measurement. But of course the same principals applied: if the mic was a good mic, properly calibrated, properly powered, properly interfaced with the number-crunching software, why not? It took me seeing teams from Dolby Atmos using them for system calibration at a very high profile event to have that finally sink in.