MF200 bias adjustment info

[pineappledave]

Hello,

I am in the process of restoring my MF200. Does anyone have a copy of the service manual and schematic diagram?

I would also appreciate if any of you can provide me a detailed walk thru procedure to adjust the bias.

Thank You in advance.

[admin]

First, welcome to CJO. Great to have you with us.

All our available schematics can be found in the troubleshooting section of the forum. If it's not listed, we don't have it.

[AnotherJohnson]

FWIW, there really aren’t any service manuals for CJ gear. CJ prefers that you return their gear to them for repairs so that they can control the quality and protect their sonic reputation. They won’t sell you parts, so getting it restored will be a challenge. But you can probably get it working.

Transistors may get biased, but it is not commonly considered an amateur activity. Sometimes there’s a pot. Sometimes not. You will need a bench quality volt meter or scope.

An MF200 is a good project amp. If you ruin it, you haven’t lost a gem. Just sayin’.

It sounds like a fun project. I would look forward to hearing about your progress.

There are a couple of guys who sometimes post here who are doing restorations from that era. They report excellent results, and you may achieve this too.

Best of luck!

[pineappledave]

I do have a scope, variac, ampere meter, dbt, dmm’s, signal generator but no distortion meter yet.

I’ve done a few BK mosfets, Moscode and Counterpoint hybrids before, MOSFET are very tricky to calibrate. I would assume it would be similar procedures for doing the MF-200 since it’s also a mosfet amp. It best to get a copy of the SM. Idk if there any CJ dealers close to me here in Toronto Canada. I have an electrical engineering background so I am bit adept with electronics.

[AnotherJohnson]

Maybe one of the guys who does restorations will help you out.

Maybe the Canadian importer would help.

CJ is not Technics or Sony or Yamaha. They do not offer service manuals. The protection of their IP is a major focus on this era of counterfeiting and Asian knockoffs.

Best of luck.

[AnotherJohnson]

https://www.conradjohnsonowners.com/vie ... php?t=2285
This thread is related to one of the restorers.
Bob Backert is another guy who has a following. Bill Thielman is another. I may have spelling wrong.

[Joe Appierto]

It's Bill Thalmann at Music Technology. He's the one who converted my PV10AL to a PV10A when he added the phonostage. I believe he was CJ's chief designer/#3 guy for about 20 years or so and left CJ around 2000.

https://www.musictechnology.com/about-us.html

[AnotherJohnson]

It's Bill Thalmann at Music Technology. He's the one who converted my PV10AL to a PV10A when he added the phonostage. I believe he was CJ's chief designer/#3 guy for about 20 years or so and left CJ around 2000.

https://www.musictechnology.com/about-us.html

Thanks Joe. I knew I had it spelled wrong.