Mark Levinson No. 335 - Dead output channel

[erikzulu]

Hello,

This ML-335 has been dead (one output channel) for a while and the mountainous task of sending it off to get repaired, left it sitting in a box for may year. But I want my amp back! My brother encouraged me to open it up and see if we can find what's up.
Note: This unit had a channel go out ( don't recall which side ) within the first year I had it ( bought new ) and it was repaired under warranty; early 2000's - let's say 20 years ago.
And, before I go any further: I am not an electronics expert. I have a Fluke multi-meter and a soldering iron and have repaired things over time; nothing this complicated.

Back to this week: 2023-09-20.
When I opened the top up, things looked a little dusty ( 18 years of use ) and something jumped out immediately ( picture ). I have been scouring the internet to find information via google and happen'd upon this forum, you guys seem to know things ;-) .

Question:
Do any of you know what part this is?

There seem to be other one's that look (size, color, labeling) the same but, I cannot assume they are the same. I have been unable to find this component on the schema shared in other posts - i.e. seeking help.

Thoughts, advice?




Additional images: Left channel (on the right viewed from the back)

Other components seem fine, although you can see they have endured some heat over time.

Regards and thank you,
Erik

 

[Pars]

That looks like an axial film capacitor of some sort. Hopefully one of the knowledgeable forum posters regarding Mark Levinson equipment will weigh in.

 

[Marionks]

Yes this is an 10nF capacitor with 160V these capacitors often fails

For test you can cut the defektice capacitor out, an test if the Amp starts again. But it is better to replace all aof the yellow capacitors

 

[stef1777]

Hello,

You could replace it with this:

https://www.mouser.fr/ProductDetail/Vishay-Roederstein/MKP1839310251?qs=ZC%2BWKP10IGe9JTXcU/W9vw==

Regards,

Stef.

 

[erikzulu]

Excellent. Thank you for the advice and guidance.

I have ordered the parts and de-soldering tool ( can use it for other stuff later ). Will report back later.

The XLR connector was a porblem, but there was a post on diyAudio that helped with that too!

Erik

 

[erikzulu]

Hello.

Update: I replaced the cap, put everything back together and --- the test failed, the channel is still dead.



I will have to start testing the bigger parts and then down to components ( learn how to do that ).

Regards,
Erik

 

[stef1777]

The burned 10NF capacitor is only a symptom of the failure. Not the breakdown itself (like the very blackened resistors all around).

Stef.

 

[Pars]

There are some other threads here re: ML335, 336, etc., such as this one. Reading these may provide some ideas or help.
https://www.diyaudio.com/community/...-335-no-bias-in-one-channel-need-help.363628/

 

[erikzulu]

Stef - I was told that this may not be an easy fix. Something else caused this cap to explode - now the hunt is afoot.

Pars -- thanks. I initially found this blog but everything was related to my issue - now it does. Need to spend some intimate time with that blog.

Erik

 

[stef1777]

Generally when it explodes, it's because the power rail has gone where it shouldn't due to a short-circuited transistor (therefore dead).

These are complicated machines and unfortunately not easy to access.

To go further, you need to identify on the diagram the part that exploded to know what it does.

Stef.

 

[Marionks]

Hello,

Have you ever looked at the circuit board with all the transistors screwed to the heat sink?

Maybe you can already see a defect visually.

Maybe put a picture here.

Please always discharge the large capacitors when doing such work!! This is really dangerous!!

 

[erikzulu]

Hello,

If I understood you correctly, here are pictures of the other side where the heat sinks/transistors are. They do not 'look' impaired/damaged, however, I am including pictures as suggested for review:

A closer look at the rest of them at the top side.

Note: I have not looked at the unit parts that this board connects to yet. That will take some time to carefully document while I am taking it apart - making sure to not short out anything or myself.

Regards,
Erik

 

[Marionks]

Hello, I actually meant pictures of the other circuit board. That's probably where the error is.

What you can do is install the circuit board on which you replaced the capacitor in the other channel to see whether it is the circuit board or the power amp.

To do this, the plugs simply have to be soldered to the other “free” place. Or you can make an adapter cable for it.

 

[Marionks]

Have you made any progress in the meantime?

 

[clevice]

Hi
it's been some time
news

Did you manage to repair it?

.

 

[erikzulu]

Hello,

Thanks for following up. After replacing the obvious broken item, it did not solve the problem or fix it.

I pondered over it a lot and;
- I am not qualified ( know electronics ) enough to fix this
- do not have any equipment to measure components

So --- eventually found someone local to repair it. Will see how that turns out ( cost & repair ).

E.

 

[clevice]

Hi,

Mine 335 was checked, it's better than new

A very important part is replacing the 3 resistors, which are underneath the fuses.

replace with two AMETHERM MS32 2R025
They are 25 Amp. - 2 Ohms -Max Rec. Energy Rating: 300 Joules
Actual Failure Instantaneous Energy: 548 Joules

The problem with the 300 and 33H series is resolved

good luck with the device


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