Wow! Very impressive work!
When dealing with old equipment like this amplifier is there anything you recommend replacing while you are already in there troubleshooting or are you of the mindset if it isn't broke don't replace it? I was just curious, because what you did obviously took a lot of time and labor.
Mark Levinson makes some nice gear and it was cool seeing the inside guts of one of these massive amplifiers. Thanks for sharing!
When dealing with old equipment like this amplifier is there anything you recommend replacing while you are already in there troubleshooting or are you of the mindset if it isn't broke don't replace it? I was just curious, because what you did obviously took a lot of time and labor.
Mark Levinson makes some nice gear and it was cool seeing the inside guts of one of these massive amplifiers. Thanks for sharing!
For class A amplifier like this one, usually the electrolytic capacitors are the first to fail due to the high temperature inside the enclosure.
Some people just replaced all the electrolytic capacitors regardless of condition but just on age.
I like to test them first especially in old high quality amplifiers before I changed them. The capacitors of vintage years, found from experience to be very well manufactured.
One real incident to relate here. I was tasked to replace a bunch of electrolytic capacitors from an old Audio Research Amplifier. The owner had order modern new capacitors for me to replace.
I measured the old ones first and found out that the capacitors were still holding their capacity and the ESR were actually better than the new ones.
I recently repaired a Krell KSA250. The owner also wanted to replace the large computer grade electrolytic capacitors. Those are very well made and very robust. I measured them and they were perfectly fine.
In summary, if the capacitors are easy to replace and you are substituting with audiophile grade capacitors, I would recommend to go ahead and just change out all the old ones.
I will be more prudent when it comes to big electrolytic capacitors. Some new modern capacitors with the same value and voltage are in fact a lot smaller in physical size than the old original ones.
In noticed that all HiEnd amplifiers still use those giant size computer grade type capacitors.
Hope that helps.
Some people just replaced all the electrolytic capacitors regardless of condition but just on age.
I like to test them first especially in old high quality amplifiers before I changed them. The capacitors of vintage years, found from experience to be very well manufactured.
One real incident to relate here. I was tasked to replace a bunch of electrolytic capacitors from an old Audio Research Amplifier. The owner had order modern new capacitors for me to replace.
I measured the old ones first and found out that the capacitors were still holding their capacity and the ESR were actually better than the new ones.
I recently repaired a Krell KSA250. The owner also wanted to replace the large computer grade electrolytic capacitors. Those are very well made and very robust. I measured them and they were perfectly fine.
In summary, if the capacitors are easy to replace and you are substituting with audiophile grade capacitors, I would recommend to go ahead and just change out all the old ones.
I will be more prudent when it comes to big electrolytic capacitors. Some new modern capacitors with the same value and voltage are in fact a lot smaller in physical size than the old original ones.
In noticed that all HiEnd amplifiers still use those giant size computer grade type capacitors.
Hope that helps.
I have examples of caps like those that are in good condition after nearly 50 years.
Nice find on that SCR, KweeSong - there a probably a few in a drawer up in Sherman hahaha! Great writeup and a fantastic repair. I would've needed therapy or a stiff drink after it failed on burn-in!
This is the equivalent of debugging computer based hardware when it crashes on boot up or an interrupt. You just can't use a debugger, you have to go back to the design and do some analysis to figure out how to decompose the HW/SW architecture and figure out, by elimination, the source... Often times you don't even have a core dump to analyze.
It takes time, effort and know how. The hardest thing to debug... when a component has failed spuriously.
Bravo, really nice debugging logic and troubleshooting implementation... and BTW, great write up.
Did you charge the owner for a month's work of debugging? He probably lives around Orchard St. huh? I mean where else can you have a place big enough to house that amp? If so, they should be able to afford your work. ;-)
It takes time, effort and know how. The hardest thing to debug... when a component has failed spuriously.
Bravo, really nice debugging logic and troubleshooting implementation... and BTW, great write up.
Did you charge the owner for a month's work of debugging? He probably lives around Orchard St. huh? I mean where else can you have a place big enough to house that amp? If so, they should be able to afford your work. ;-)
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Haha. Sounded like you have been to or stayed in Singapore before. 😊
Two weeks, training WDC people. I stayed at the Hilton on Orchard St. Beautiful place... but, in June, the humidity was nuts. I guess you need to run that AC hard when you run that amp...
I had three days off and I used them to the maximum... Went all over the place: parks, Chinese Gardens, Japanese Gardens, National museum, Chinatown, downtown, East, West, North... Took the metro/train, did the loop around the island. Talked to a lot of people, drank cold beer... Takashimaya, underground shopping centers, high rise shopping centers.. Absolutely the polar opposite of SoCal. It was fun. The Gardens By The Bay, Flower Dome, the Cloud Forest... National Orchid Garden... the trees all over the city.. simply amazing... bought souvenirs there... Didn't to go to the top of the Marina Sands... it started rain hard... mid afternoon.
But we shut down the office two years after that... so I never went back.
My last memory was from Changi. They had a duty free scotch whiskey store, across from Starbucks. At 8AM the lady at the whiskey store gave me four shots of really fine single malt whiskeys, "just to taste". Somehow I made it to the Starbucks and got a triple shot of espresso, then went to the gate and flew back... Slept half the way to Haneda. It's an 18 hour flight from Changi to LAX ( split into two 9 hour legs.... ). The whiskey helped. ;-)
Beautiful place... now, likely a better sounding place too.
I had three days off and I used them to the maximum... Went all over the place: parks, Chinese Gardens, Japanese Gardens, National museum, Chinatown, downtown, East, West, North... Took the metro/train, did the loop around the island. Talked to a lot of people, drank cold beer... Takashimaya, underground shopping centers, high rise shopping centers.. Absolutely the polar opposite of SoCal. It was fun. The Gardens By The Bay, Flower Dome, the Cloud Forest... National Orchid Garden... the trees all over the city.. simply amazing... bought souvenirs there... Didn't to go to the top of the Marina Sands... it started rain hard... mid afternoon.
But we shut down the office two years after that... so I never went back.
My last memory was from Changi. They had a duty free scotch whiskey store, across from Starbucks. At 8AM the lady at the whiskey store gave me four shots of really fine single malt whiskeys, "just to taste". Somehow I made it to the Starbucks and got a triple shot of espresso, then went to the gate and flew back... Slept half the way to Haneda. It's an 18 hour flight from Changi to LAX ( split into two 9 hour legs.... ). The whiskey helped. ;-)
Beautiful place... now, likely a better sounding place too.
Fantastic job KweeSong!
(I used to go to Sing on business twice a month between 2006 and 2009 - fantastic place - I loved it!)
(I used to go to Sing on business twice a month between 2006 and 2009 - fantastic place - I loved it!)
Thank you Mr. Lim!
This is an article from God and I believe this is the only article so far on internet about repair of ML 20.6 power amp in such details.
Definitely your article will help a lot in my repair of my ML20.6.
I got a chance to buy the ML 20.6 about three years back. There're some issues so I only switch them on occasionally for listening music.
When I switch them on, it will be either on or almost immediately shut down (trigger protection?) If one unit of ML20.6 can be switched on, the other one (totally two because they are monoblocks) can be switched on. Whenever one unit cannot be switched on, the other unit cannot be switched on. How can both units have the same problem at the same time? When they can be switched on, they can work hours until I switch them off.
Please could you give me some idea?
Thank you Mr. Lim!
This is an article from God and I believe this is the only article so far on internet about repair of ML 20.6 power amp in such great details.
Definitely your article will help a lot in my repair of my ML20.6.
I got a chance to buy the ML 20.6 about three years back. There're some issues so I only switch them on occasionally for listening music.
When I switched them on, it would be either on or immediately shut down (trigger protection?) If one unit of ML20.6 could be switched on, the other one (totally two because they are monoblocks) could be switched on. Whenever one unit could not be switched on, the other unit could not be switched on. Strange. How can both units have the same problem at the same time? When they could be switched on, they could work hours normally until I switched them off. When they couldn't be switched on, I'll try again one or two hours later and usually they could be switched on with two or three attempts.
Please could you give me some ideas?
Dear H,
Glad you found my post useful. I learned a lot over the years through forums like this. So I wanted to share my experience so others can learn from it too.
The protection circuit monitors the following :
1. excessive DC offset at the amp output
2. Over temperature.
3. Over current / short circuit
4. Unregulated power rail over voltage
5. Regulated power rail over voltage
My guess is that it could be fault no 4. 1,2 and 3 are unlikely as both amps always behave likewise at the same time. As for no 5, once voltage regulator fails it will always fail and not recover on both channels at the same time.
You are from UK? Mains is 240V ? The unregulated voltage rails will fluctuate with the mains. Check your voltage selector setting. Could it be set like 220 or 230V instead of 240v?
I was thinking there may be a component failure on the protection board just like the SCR in my case but your amp failure symptom of both working and failing at the same time suggest same fault at the same instant which may point to environment like temp and line voltage. Unlikely to be temperature as it is also unlikely that two thermal switches fail at the same time.
I call this kind of fault finding as looking for gremlins. Makes very little sense.
Of course there is always the brute force approach. Eliminate one fault at a time even though it may feel unlikely to be the cause like I did on the protection board.
Take a look at me post with the highly marked out protection board circuit and go from there.
Good luck 😊
Glad you found my post useful. I learned a lot over the years through forums like this. So I wanted to share my experience so others can learn from it too.
The protection circuit monitors the following :
1. excessive DC offset at the amp output
2. Over temperature.
3. Over current / short circuit
4. Unregulated power rail over voltage
5. Regulated power rail over voltage
My guess is that it could be fault no 4. 1,2 and 3 are unlikely as both amps always behave likewise at the same time. As for no 5, once voltage regulator fails it will always fail and not recover on both channels at the same time.
You are from UK? Mains is 240V ? The unregulated voltage rails will fluctuate with the mains. Check your voltage selector setting. Could it be set like 220 or 230V instead of 240v?
I was thinking there may be a component failure on the protection board just like the SCR in my case but your amp failure symptom of both working and failing at the same time suggest same fault at the same instant which may point to environment like temp and line voltage. Unlikely to be temperature as it is also unlikely that two thermal switches fail at the same time.
I call this kind of fault finding as looking for gremlins. Makes very little sense.
Of course there is always the brute force approach. Eliminate one fault at a time even though it may feel unlikely to be the cause like I did on the protection board.
Take a look at me post with the highly marked out protection board circuit and go from there.
Good luck 😊
It does seem to be a common external input that is affecting both amplifiers, huh?
Do the amps behave the same way when plugged into a different circuit?
How about (1) get a simple AC voltage meter? IF the power is no good, then (2) some kind of an AC regenerator.
Although if the AC line coming out of the socket is that bad, it could be a much bigger issue.
We had an AC line in the house that over time dropped from 120 to 100 somewhere in a 15 foot run in the wall. Needless to say, we ripped the walls out and installed all new wiring in that part of the house. The last thing we wanted was a fire.