Need help with MX-2000

Errr, I'm not sure if my last post was clear... what I'm wondering is, when a signal is fed into the amp (as opposed to it sitting 'idle'), would the voltage measurements at those same test points spike upwards? If so, what is the range generally, from idle to full signal?
 
I can screw in a lightbulb; I can turn on a switch...that's about the extent of my electrical prowess; nonetheless, this has been a fascinating thread to read. I can't wait to see pictures of the finished product. Congratulations!
 
Errr, I'm not sure if my last post was clear... what I'm wondering is, when a signal is fed into the amp (as opposed to it sitting 'idle'), would the voltage measurements at those same test points spike upwards? If so, what is the range generally, from idle to full signal?

It will vary up and down as well as the DC offset will swing. But of course it will no longer be at "idle " will it?
 
It will vary up and down as well as the DC offset will swing. But of course it will no longer be at "idle " will it?

Ha, true. I'm just wondering how much it would swing... just a few mV from idle to peak signal, or perhaps something more drastic?? Of course, the gain setting of the potentiometers would be a big factor as well... but, just for general education, we can use rough figures... For example, let's say I fed a 1khz test tone through at about half volume, pushing about 10 watts... would the test points read something like 65mA, or more like 250mA?

Also, speaking of DC offset... I'm curious -- what are the DC offset measurements on the MX-2000s you have?? I'm interested how they compare...
 
Alright everyone -- I finally had a little time today to finish taking the pictures and to upload them... everything below is in the finished, post-restoration stage... here we go:

Crude capacitor schematics:



Input board:





Input board mounted and new power caps:



Meter board:



Power board:



Right amp board:



Left amp board:



New Lexan meter covering:



New glass, mounted:





Naked assembly:



Finished:





 
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Maybe someone has the answer to this riddle... I never figured out what these pieces pictured below were for... they are the consistency of a thick matte board and were mounted on the inside of both of the original wood panels, right next to both amplifier boards. All I can think is that it has something to do with moisture... I don't know. Any ideas?

 
hello !

They call it "barrier" in service manual part number VF476800 ....

Barrier against what ? ......

Nice job for your front panel restauration :thmbsp:
 
Maybe someone has the answer to this riddle... I never figured out what these pieces pictured below were for... they are the consistency of a thick matte board and were mounted on the inside of both of the original wood panels, right next to both amplifier boards. All I can think is that it has something to do with moisture... I don't know. Any ideas?

Maybe they're asbestos barriers/insulators that keep the wood panels from catching fire when you're really pushing the amp? :scratch2: :no: :D
 
It turned out pretty nice. How doe she sound ? Those don't look like the OEM side panels. Did you refinish them. They look fabulous. Lexan front panel as well .:thmbsp:
 
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They call it "barrier" in service manual part number VF476800 ....

Barrier against what ? ......

Nice job for your front panel restauration :thmbsp:

I thought about replacing the two 'barriers' because the original ones had warped and bubbled out over time (which you can't really see in the picture I took). Since I didn't know what benefit they had, I decided to just have the inside of the new wood panels uncovered where they rest next to the amp boards...

Thanks for the kind accolades.

Maybe they're asbestos barriers/insulators that keep the wood panels from catching fire when you're really pushing the amp? :scratch2: :no: :D

I'm glad you guys are as stumped as I am... Actually, maybe you are on to something here -- maybe whatever stain / coating they had soaked into the original panels dried slowly, and was highly flammable. Luckily I used a linseed oil based formula on the new ones, and only on the visible faces.

It turned out pretty nice. How doe she sound ? Those don't look like the OEM side panels. Did you refinish them. They look fabulous. Lexan front panel as well .:thmbsp:

Thanks! It means a lot to hear you say that. It sounds superb... better than it did before, by memory... more spacial separation, a little less 'bite' on the highs while retaining an incredible amount of detail retrieval... I've owned and listened to a healthy number of 'audiophile' level amps in the past, and this is the best I've ever heard.

I did replace the panels as they were heavily chipped away on the corners. I bought some curly Cherry and slung some sawdust... it was tricky to get them where they are, because the original screw holes had to match up exactly to the new ones, with the same offset distances from the edges in order for the wood to be even close to lining up correctly. It still isn't 'perfect', partly from the nature of hand made woodwork, and partly because the original steel face and top panels aren't completely flat / straight... probably from being dropped... so I did my best with it, and at some point with these projects we have to decide that it's quite 'good enough'.

The glass is another thing -- you can see that the top edge was cut just *slightly* out of 90 degrees, so the clear silicone shows behind it... but it was so tough to find someone to even make this cut, let alone get as close as he did on the dimensions, that again I had to decide it was 'good enough'.

Lexan! I was trying to remember the name of it yesterday, but just typed 'Plexiglas' instead... I did use Lexan -- much less prone to scratches. You were able to tell it was Lexan just by appearance??
 
Na, I e-mailed those guys and explained what needed to be done in order to duplicate the original piece, and they never wrote back... that was the beginning of the 'glass' saga. It turns out that, in order to make a piece with a lip on the backside (as the original piece was), two separate pieces need to be adhered together with a special glue that is completely clear. Not only that, but it needs to be done in a vacuum chamber which drops the pressure to about negative 5 atmospheres... apparently this is the only way to get all the air bubbles out when it is curing.

At that point, I decided to just buy a thick piece of glass from a local guy without the lip and silicone it in place -- luckily he was able to make a cut on a 1/2" thick piece, so I had enough bite on the backside to get a good hold, while still having enough glass to protrude from the front of the face.

Ya, it's one of those things that looks simple, but turns out to be crazy. Getting it mounted in place properly was an adventure too...
 
Fantastic job! I think your side panels are much better looking than the original side panels.
 
Thanks for the compliments everyone! Sometimes your not sure how some of your aesthetic choices are going to turn out, so I'm glad you like what I did with it.
 
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