McIntosh restoration/repair: Caps and grounding

[c_dk]

McIntosh 70s&80s restoration/repair: Caps, grounding and semiconductors

I have noticed a number of trends in many posts. It seems that many are looking for quick and easy solutions and then are disappointed when the problems are not solved.

Many seem to have performed global cap replacements with marginal or regressive results. Is any one willing to share their systematic replacement results. I have read and reread RonC's tutorial on the C-29 and while much more detailed than the 34, still doesnt hightlight potential problems and specific restoration/improvements.

There seems to be a huge hesitancy to value the basics, the time consuming drudgery of repairing the numerous grounding issues these 20-40 year old devices have developed. Are others willing to share their collective notes on these common issues.

The time it takes to do this circuit work is not respected by the general public
and therfore it is up to us the vintage community to raise up the value of this technical work.

 

[c_dk]

I"ll start:

Relevant to all McIntosh integrated and receivers:

Mac1900 would out of the blue drop volume by 1/2 and would do this at will any time totally intermittant. Was positive it was a volume control or trans but it was so flakey I could not confirm. Mike Spencer, Macs service manager, gave me a hint to roll the balance control next time the volume dropped while the unit played background music for days.

The volume went up as the balance was changed confirming the speaker common ground was acting like a semi conductor as the humidity, temp, whatever changed.
It then became a part of the regular switch cleaning etc. to confirm these grounds on all non autoformer amps.

 

[Westy56]

I remember when my c-28 had similar symptoms, but only with the left channel.
I brought in to a Mcintosh clinic and they (oscar) just replaced the volume control with a new one. Now that was an easy fix.:yes:
The volume control has worked flawlessly for 28 years.

I like the fact that Oscar was going to take the broken one back to Mcintosh and examine why it failed.

I do have the grounding issues that most C-28's have, but it has nothing to do with the volume control.

Steve

 

[c_dk]

I remember when my c-28 had similar symptoms, but only with the left channel.
I brought in to a Mcintosh clinic and they (oscar) just replaced the volume control with a new one. Now that was an easy fix.:yes:
The volume control has worked flawlessly for 18 years.

I like the fact that Oscar was going to take the broken one back to Mcintosh and examine why it failed.

I do have the grounding issues that most C-28's have, but it has nothing to do with the volume control.

Steve

There are at least 5 grounding issues with a 28 (rca jacks, star grounding input boards, drain ferrules, power supply diodes, chassis rivits) as recently highlighted in MrFisheys post.

I'm sure his cap upgrade improved things but with all the issues we'll probally never know unless someone else chimes in.

Is there not a tech in your area that armed with a schematic and 2 or 3 autographed pictures of Mr Franklin couldn't restore this for you.

 

[dewickt]

Cap replacement and resistor checking is a good start, some values can be tweaked for better sound but the most important thing to remember is the quality of the parts used does have a big effect. I have seen several rebuilds that used kit type parts that yielded disappointing results, these kits used reliable but not audio grade components. Have also seen the opposite effect from the use of boutique parts costing $10 to $50 each, they also sounded bad.

 

[Westy56]

There are at least 5 grounding issues with a 28 (rca jacks, star grounding input boards, drain ferrules, power supply diodes, chassis rivits) as recently highlighted in MrFisheys post.

I'm sure his cap upgrade improved things but with all the issues we'll probally never know unless someone else chimes in.

Is there not a tech in your area that armed with a schematic and 2 or 3 autographed pictures of Mr Franklin couldn't restore this for you.

I tried the only Mcintosh dealer in New Mexico numerous times. I never got an answer. Not good advertisement for Mcintosh dealers.
I know most are not this elusive.

Did you work at one of the audio stores in the Grand Rapids area?


Steve

 

[CountD]

"The time it takes to do this circuit work is not respected by the general public
and therefore it is up to us the vintage community to raise up the value of this technical work."

Hear, hear to that.

I have been thinking seriously about the value of circuit work and trouble shooting and how the general public really is outside the realm on this as with most other things, ie. car/motorcycle repair, food growing/cooking, and this list goes on...distanced from the machine itself so to speak.

Not to get too philosophical on the subject but I think I should go to Tennessee and write a book on Terry DeWick who always has a concrete knowledgeable solution to most problems and has a handle on something that is becoming, in short, a lost art. And with vintage gear getting older by the day we have just begun to see the problems inherent in old stuff.

 

[c_dk]

25 years

The new hierachy is much more directed to the big city dealers selling the ever more "biggest" ticket items in the line, rather than the smaller market dealers that supported the entire line: and small town service.

There are patriarchs rolling in their graves.

 

[ron-c]

C DK, the two pieces on C29 and C34 were not repair guides but simply an explanation on care and updates. Neither piece had serious problems but they both had power supply issues. I am happy to report that the buyer of the C29 loved it and the C34v is still functioning perfectly. Since I sold the C34v to the original owner back in the 80s it was fun to bring it back to new.

The issue of capacitors is one of age. As they age they will change value and stop doing their job. New ones are not expensive but it is time consuming to track them down and install the new ones.
As far as grounding issues yes that can be a problem on many preamps and even more so if they have been in a humid or close to the ocean environment.
Dirty oxidized switches are also high on the problem list of older units.
I do appreciate the classic gear as well as the new but I will not listen to it if it is not up to spec and performing as designed.
AK is all about sharing experience so others may enjoy the music.
Thanks,
Ron-C

 

[c_dk]

C DK, the two pieces on C29 and C34 were not repair guides but simply an explanation on care and updates. Neither piece had serious problems but they both had power supply issues. I am happy to report that the buyer of the C29 loved it and the C34v is still functioning perfectly. Since I sold the C34v to the original owner back in the 80s it was fun to bring it back to new.

The issue of capacitors is one of age. As they age they will change value and stop doing their job. New ones are not expensive but it is time consuming to track them down and install the new ones.
As far as grounding issues yes that can be a problem on many preamps and even more so if they have been in a humid or close to the ocean environment.
Dirty oxidized switches are also high on the problem list of older units.
I do appreciate the classic gear as well as the new but I will not listen to it if it is not up to spec and performing as designed.
AK is all about sharing experience so others may enjoy the music.
Thanks,
Ron-C

So to sumarize:
clean switches and controls
confirm and repair grounding issues
replace power supply caps and individual stage filters

Terry seems to suggest replacing the ROE NP coupling caps used thoughout many unts but Keevan disagrees. What is the general consensus?

I had a number of issues with LDRs causing strange intermitant problems, does anyone know if they have been causing sound issues?

 

[ron-c]

If I am going to listen to it all of the audio caps go on anything more than two or three decades old. I am in agreement with Terry on recommending Nichcons. Audio grade Rubycon is fine.
For through hole caps we use Nichicon and some United Chemcon on current production models.
New caps will usually be a bit smaller and have better specs than what we used decades before.
Something we did not touch on that crops up from time to time is deteriorated solder joints. If you find one there will be more so be prepared to touch up a bunch.
Symmetry on channel to channel voltage readings and matching all voltages in the power supply section to the repair manual schematic is important.
Yes LDRs can fail but many are working fine after 30 years or more.

Thanks,
Ron-C

 

[c_dk]

RonC since you are on line:

McIntosh was always at the fore front of supporting techs to insure the continuing value of McIntosh products. As the experience of our friend from New Mexico seems to be more and more the norm what do you see McIntosh doing to turn the tide? What can the owners of Mac equipment do to help grow the restoration business?

 

[ron-c]

Talented techs are a true value. Unfortunately in today's world there are not a lot of young folks going into the repair business. This is an issue of the lack of trade schools in the US and competition for talent from other industries.
As far as the factory we support techs all over the world and have many repair stations that are very capable.
If you are talking about restoration that takes more time than most customers are willing to pay for. It is very easy to spend a lot of hours going through a unit. A C28 rebuild could easily take a whole day which would be 500 to 800 in labor.
The factory does not repair anything older than the 70s but we do supply information, service manuals some faceplate glass and answer questions on much older models. This is not the norm in the audio industry.
As far as your friends I am not sure what their issue is so I can't comment.

Thanks,
Ron-C

 

[Westy56]

Talented techs are a true value. Unfortunately in today's world there are not a lot of young folks going into the repair business. This is an issue of the lack of trade schools in the US and competition for talent from other industries.
As far as the factory we support techs all over the world and have many repair stations that are very capable.
If you are talking about restoration that takes more time than most customers are willing to pay for. It is very easy to spend a lot of hours going through a unit. A C28 rebuild could easily take a whole day which would be 500 to 800 in labor.
The factory does not repair anything older than the 70s but we do supply information, service manuals some faceplate glass and answer questions on much older models. This is not the norm in the audio industry.
As far as your friends I am not sure what their issue is so I can't comment.

Thanks,
Ron-C

Hi Ron, Why does McIntosh let dealers like the one in New Mexico represent the company name?:thumbsdn: He won't even return emails.:thumbsdn:

I stuck with McIntosh because of the service and quality of product. :thmbsp:

Steve

 

[Gregory]

So to sumarize:
clean switches and controls
confirm and repair grounding issues
replace power supply caps and individual stage filters

Terry seems to suggest replacing the ROE NP coupling caps used thoughout many units but Keevan disagrees. What is the general consensus?

I had a number of issues with LDRs causing strange intermittent problems, does anyone know if they have been causing sound issues?

We're going to need an acronym table with that.. c-dk. :yes:

-Gregory

 

[c_dk]

ROE is the brand of non polarized caps that you replaced in your 2205 rebuild.

Light Dependent Resistor was used in the Powerguard circuit in the 2205 as a way to lower the input when the PG circuit detected excesive distortion.

In the next generation of products they were also used in muting circuits and a batch of the cylindrical ones started causing issues. Mac changed to the Vactrols (blocky look) and if you have a weird intermitant and cylindrical LDRs, would look at them as causing the issue.

 

[Gregory]

ROE is the brand of non polarized caps that you replaced in your 2205 rebuild. Light Dependent Resistor was used in the Powerguard circuit in the 2205 as a way to lower the input when the PG circuit detected excessive distortion.

Thanks.. those would be the small brown cylindrical NP caps. ROE from what I've found means Roederstein in Germany. Ron told me to throw all those old caps in the trash can, but they're stored in a zip-lock bag JIC (just in case.)

Now I just have to get that pesky LEFT power meter in the 2205 to stop cutting out.


-Gregory

 

[dewickt]

10 to 20% of the ROE brown caps are defective !! they crack open and leak electrolyte, evident by tan deposits at the cracks. Have opened up a C32 and found 9 out of 10 bad.

 

[c_dk]

Thanks.. those would be the small brown cylindrical NP caps. ROE from what I've found means Roederstein in Germany. Ron told me to throw all those old caps in the trash can, but they're stored in a zip-lock bag JIC (just in case.)

Now I just have to get that pesky LEFT power meter in the 2205 to stop cutting out.


-Gregory

I thought your meter tear down solved the problem.

 

[c_dk]

Terry,
I know the ROEs are in MAC1900, MC2125, MC2205, and C-32; I assume they are in the C-28, C26, and MA6100. How about the MAC4100 and MA6200?