(another)Yamaha C-70 Project

[HerrMeier]

It has been a year now since I updated my own Yamaha C-70 with a nice replacement relay switch part for SW503 (Parametric Tone Control on/off) from Kurt Jacobs. The C-70 is still working great and I use it everyday in my office.

A fellow C-70 owner who lives fairly close to me contacted me, also about a year ago, to see if I could fix the SW503 switch in his unit. Along with that Parametric Tone Control switch replacement he would like me to look over the C-70 to see if there are any other updates he would like to make.

This C-70 has already been recapped so tomorrow I will open it up and look at the condition inside.

To start off this post here are some photos of the outside.

Hi,
The Magnetic Switch, SW 503 ist not wonking any longer. I wanted to by a replacement from the US, but the guy toll me that all the custems regulations sending to Germany are to complicatet.
I bridged the pins of SW 503 so that the C-70 is working with Equalizer on.
Do you know an othere replacement or solution available?
Thank's for your help.

 

[Yamaha5000]

Hi,
The Magnetic Switch, SW 503 ist not wonking any longer. I wanted to by a replacement from the US, but the guy toll me that all the custems regulations sending to Germany are to complicatet.
I bridged the pins of SW 503 so that the C-70 is working with Equalizer on.
Do you know an othere replacement or solution available?
Thank's for your help.

Why don't you just have Kurt send you the Gerber files?

 

[avionic]

i,
The Magnetic Switch, SW 503 ist not wonking any longer. I wanted to by a replacement

Probably just needs to be disassembled and cleaned. It is a real PITA to re-assemble and I know what I'm doing! The KURTS switch is the easiest, almost, drop-in replacement.

 

[avionic]

Probably just needs to be disassembled and cleaned.

I have been fabricating a precision tool from aluminum stock just for this app. I'm a daytime machinist.

 

[sonavor]

I have been fabricating a precision tool from aluminum stock just for this app. I'm a daytime machinist.

I would be interested in that tool when you finish it.

 

[Dr. Ear]

Nice job! BTW, TR536, TR542 and TR547, would it make sense to replace them with new ones? They get very hot.

 

[Sparkplug]

Nice job! BTW, TR536, TR542 and TR547, would it make sense to replace them with new ones? They get very hot.

Not if they’re not damaged, they’re pass transistors and any replacements will get equally hot as well. I place a low RPM (600 rpm) PC fan on top of the C-70 vent which really helps lowering the temperature due to those transistors. Make sure they’re heat sunk properly, fresh thermal compound, tight mount, etc..

 

[avionic]

Why don't you just have Kurt send you the Gerber files?

 

[avionic]

Unfortunately, I disassembled and cleaned the SW-104 switch assembly years ago, before I did the full restoration of my C-70.
I didn't take any photos at the time but it wasn't too difficult of a task. Just take your time and go slow during the disassembly.
If you do the disassembly, take plenty of pictures every step of the way and post them on a new C-70 thread here. That would be helpful.

However...before going through all of that I would double check that SW-104 is a problem.

-sonavor

@sonavor I remember years ago. Somebody did an excellent documentation (thread or post) of the disassembly and cleaning of SW104 here on AK. -- Nudies included

I'm still searching for it.