First restore effort... C-70/M-70

dino74

Active Member
I previously posted about getting a B-2x/C-2x and I'm going to restore those eventually but I've never done it before. So, I ran across a M-70/C-70 combo for $150 and figured it be a good place to start. If I totally mess it up, I wouldn't lose too much. Pics below, C-70 has some scratches on top and the M-70 is decent. In pic 1310, is that an example of the infamous glue in the lower left corner?
 

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In the M-70 the 12v power supply board is the one that will have lots of that Sony bond glue that needs to be removed. There were lots of corroded parts there in my M-70.

Also, on the "Control-1" pcb there is a safety cap that must be replaced. C607. In my unit it was a 0.47µF/250v but in the US models I think that it is different. ?0.22µF/250v? In any case it must be replaced, it can explode.
https://www.mouser.de/ProductDetail/Panasonic/ECQ-U3A224MG?qs=sGAEpiMZZMv1cc3ydrPrF%2bfZ13WJ/r1/0vmwaluRlFs=
https://www.mouser.de/ProductDetail/Panasonic-Electronic-Components/ECQ-U3A474MG/?qs=sGAEpiMZZMvQAn3cSZoTr1%2b0Ye1BktuzFq%2bm14xyTdw=

While you are in there it won't hurt to replace the 3x smaller 6800pF/250v safety caps. C608, 609 & 610.
https://www.mouser.de/productdetail/panasonic/ecq-u2a682kl?qs=sGAEpiMZZMv1cc3ydrPrF0%2bjlB8SXIRuFjuQdipUHOg=

You got those 2 units for a good price. They're pretty good equipment.

Cheers,
James

edit: The replacement cap must be a "safety" cap, X1 or X2 rated.
 
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You got those 2 units for a good price. They're pretty good equipment.

Thanks for the info about the safety, I'll have to look at the schematic to see what the general model uses.

He wanted $250 and thought I'd offer $150, a part of me wanted him to say no so I wouldn't have to drive and pick them up.
 
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These "cross the line" safety caps failed pretty dramatic in the 220/240 models. In the 120v they would just smoke and burn..
Yamaha issued a safety bulletin about those models effected.
https://europe.yamaha.com/en/support/safety_information/amplifiers.html
https://www.whathifi.com/news/yamaha-issues-safety-recall-amps-30-years#LPPYFKhpDmMK5Ymt.99

Just smoke and burn? Why heck, that's not so bad...:eek:.

In my M-50 it exploded the first time that I switched it to 240v after I moved over here. Lucky for me it didn't do any extra damage. I believe that @Oldsansui441 had one that burned and took most of the PSU with it.

Cheers,
James
 
So, I ran across a M-70/C-70 combo for $150 and figured it be a good place to start

Those two are a nice score for 150 dino74, plenty of clean power. They are worth putting some time into. Good call by the other guys referring to the X2 safety cap.

I believe that @Oldsansui441 had one that burned and took most of the PSU with it.

Yes correct, this is what happens shown below, very nasty business.

Here is how the 12v psu board looks with all of that glue caused corrosion..

Yeah that glue was extra corrosive on yours Bratwurst7s.
 

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Before I start taking this thing apart, I wanted to see what state it was in. It works but a couple of leds are burnt out. The weird thing my bedroom is wxc-50 -> mx-35 -> elac so I tried wxc50-> m-70 -> elac. I'm not sure how to explain it but I didn't like it as much as the MX-35.
IMG_1326.jpg
 
Not really, work has been busy and I have one other project with higher priority. A pwm controller for my fish tank LED light but that should be done in the next week.

I starting to plan out my work benches and trying to figure out what I need to buy.
Found two glass top desks (56"x30" each) on CL that I'll use for electronics and computer.

I currently have
Variable temp soldering iron
Desolder pump
Rigol DS1052E Oscilloscope
Various Voltmeters, nothing high end.

Looking at
A good meter that can measure capacitance.
Maybe a signal generator.
Maybe a transistor tester.

Edit: I also picked up a M-35 for $15. I'm thinking that would be a better first try than the M-70
 
The M-35 will definitely be an easier first try and good practice before you jump into the M-70.

For testing components a M328 based tester works great. Direct ebay links are frowned upon but if you go to ebay and use
"Newest version of inductor-capacitor ESR meter DIY MG328 M328 multifunction test" for your search string you will find a good tester for the money.

I paid 2x the price for an earlier 9v battery powered version and found it to be extremely useful for the price. The new version is half what I paid and is powered through a micro usb port or LiIon battery. (no affiliation, just like it for the price).

Cheers,
James
 
I’m using lcr-tc1. It works great and it have built-in rechargeable Li-ion Battery
 
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