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Saturday
Oct202012

A Toasty Marantz 250 is Delivered to the Shop

This week a Marantz Model 250 amplifier was dropped off at the shop. The story behind this amplifier is that it was stored away in someone's attic for the past 6-8 years along with a Marantz 3600 pre-amplifier and a Marantz 112 tuner.

The owner decided to sell off these units and the 3 pieces were sold as a set. In the excitement of such a great find the 3 pieces were reassembled into a system and the power button was pushed.

Immediately following the button push there was smoke from the amplifier.

The decision was made to have the 250 looked at first and find out what the condition of it really is. As you can tell form the pictures, it's pretty toasty inside. I would guess that after all of those years in the attic the heat, cold and humidity has taken its toll on this amplifier.

 The transformer is very rusty, there's a lot of corrosion everywhere and there are signs of previous work that has been done. I expect to find many bad solder joints and all sorts of other problems with this 250.

Of all of the amplifiers the were made by Marantz, the 250 seems to have quite a mystique about it with enthusiasts. The desirability of the 250 might only be surpassed by the model 500. Part of the mystique of the 250 is with it's reputation for power and possibly its unreliability due to its design.

There are rumors that the 250 is an inherently unstable design and perhaps this is true. There are many Factory Service Bulletins which outline modifications a for the 250. There are also no less than 3 versions of the 250 /250M which seems like a high numbers for the 6 years of production for these models.

The closest cousin to the model 250 in the Marantz line up is the 1200 / 1200B. On first glance these models share the same basic design and share many of the same boards and parts. The primary difference is the rated output, the 250 is rated at 125 WPC and the 1200 is rated at 100 WPC.

The difference in output many have been achieved by lowering the operating voltage on the 1200, or was the operating voltage raised on the 250 to increase its output? I don't know.

Since the course of this model 250 project is still undetermined, I plan on using the extra time I have with the 250 to document the difference between this early model 250 with a model 1200 for the same period.

I think that it will be interesting to see exactly what the differences and similarities are between the two models.

See all of the Marantz Model 250 pictures here.    

Marantz Service Manuals and Service Bulletins for the 250 here.

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Reader Comments (11)

Chris ,
first i would like to thank you for your website !!!!!
I have an ealy Marantz 250 like this one wich need repair and my local tech ( i am French ) tried to fix it with no result .He had the amp during two year .
The issue is an idle current on the right channel .
So i will follow this post with much attention .
Greetings
Marc

October 20, 2012 | Unregistered CommenterMarcantz

Hello Chris!

Nice website.

Wow!!! That 250 has certainly seen better days. I will be very interested in following your progress on this project. Still, I can't help but feel a little ill everytime I see such a fine piece of equipment treated with such disregard...sigh. However, after seeing your posts on AK, and browsing your website, I'd say that 250 will be brought back to it's former glory in no time!

Anyway, really glad I found your website through AK. I'm currently studying Electronics/Engineering Technology @ Oklahoma State University IT, and hope to be working on these old vintage Marantz units myself someday soon.

Thanks for sharing your knowledge and love of electronics.

Cheers!
Paul
Echoplex @ Audio Karma

November 26, 2012 | Unregistered CommenterPaul

Hi Chris ,
Just wanted to let you know the 250 is up and running with a pair of Tannoy
DC 3 speakers and sounds marvelous, I've A/Bd it with MaCormack DNA1 and a pair of NAD 2155 bridged and I can definately hear the crystal blue Marantz sound in all it's glory. Brings me back to an era in Ist class style .
Using a separate 6sn7 tube preamp wit CDP drive and DAC with it as the other components aren't quite ready for prime time.
Thank you again for being there, for caring so much about reviving these audio piece correctly, and making the memories they bring back.Best,Terry

January 18, 2014 | Unregistered CommenterTerry Simcik

Dear Chris,

It is really exciting to read through your journey on this Marantz 250. I just got one which is actually working. However, the right channel (B) always starts with noises some times the noise (current) is so large, which would temperatly black out the whole amp. The noise will go away after some time when the amp is heated.

Would you please kindly shed some lights on how to start to look into the problem?

thank you so much!

June 1, 2014 | Unregistered Commenteryunpli

Hi Yunpli,

The problem you describe is very general, so my answer will also be general.

Not knowing the overall condition of the amplifier there could be many causes for a problem that disappears when the amp warms ups. You might have some cold solder joints that reconnect after the warm up or you may have some marginal components that work better after a warm up. It may also be a combination of many issues.

The 250 is not an easy amplifier to work on, you will need some some better than average experience to have a good chance to repair and rebuild it.

Thanks
Chris

June 2, 2014 | Registered CommenterChris

Thank you so much, Chris!

I will check through the cold solder joints first :) Will keep you posted :)

June 3, 2014 | Unregistered Commenteryunpli

And you are right. i am definitely not qualified to repair it by myself. But my dad, who is about to visit me from China, was working on appliance repairs for good 30 years will help me to give some initial check-ups.

Meanwhile, may i ask another specific question? From the "trouble analysis" of 250 service manual, it says
"High hum and noise level" --> Check filter capacitors C1, C2, C501 and C504. Do you think the "high hum/buzz before warm-up" issue could be related to those capacitors?

June 3, 2014 | Unregistered Commenteryunpli

It will be very important that you identify which version of the Model 250 you have and the you will need the correct Service Manual and all of the Service Bulletins.

One of the things you have to factor in when you using the service manual for troubleshooting tips is that it was written when your amplifier was new and the suggestions for the cause of certain problems is based on everything in the amplifier being fairly new.

Since your amplifier is not new at all, you will need to look beyond the manual for tips on what's wrong.

C501 and C504 are small inexpensive caps, so replacing them is a simple and inexpensive guess. C1 and C2 are very expensive parts and guessing about them would be the wrong approach. They should be measured and tested before they are replaced. Since these parts are large and easily accessible there is a tendency to want to replace them.....in the hop they are the problem.....

I would look towards the power supply board as the first cause of a basic problem like a humm

Chris

June 5, 2014 | Registered CommenterChris

Thank you Chris for your help!

The manual is the original with the amplifier (very old and dusty) ^_^

BTW, I opened the amplifier today and noticed that one the solder join is completely broken and the wire is not connected (number 20 in the Amplifier Board Component Assembly Diagram, which i believe is the ground). I am surprised the amplifier was able to play before.

After re-soldering the wire, i thought the issue would went away. ... But, the issue is still there. The right channel has very unpleasant current noise (from the meter of the right channel, the point will shoot up to the rightest and then comes back). Meanwhile, the left channel is perfectly fine.

June 6, 2014 | Unregistered Commenteryunpli

I will try to post some pictures for you :)

June 6, 2014 | Unregistered Commenteryunpli

Hello

Nice job.

I have a 250M with no left channel

So I miss the whole amplifier board, do you think I can easily find one ?

April 26, 2015 | Unregistered Commenterlionel

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