Marantz 1200

[MarantzRefrb]

I had forgotten what the sockets looked like, but there does appear to be a yellow component melted on yours, between the sockets. This is the best pic I could find of mine (not great):

Is that the thermal diode that melted?

 

[ocdecio]

From what I could measure it is a 85nF capacitor.

 

[Steven Tate]

What serial# do you have Steve?

Just got around to looking at the back of the unit. It looks like 5541. Must be a late unit. AMK production numbers guess that 2273 units were manufactured, but only 50% certainty. I wonder if they started with unit 1001 like so many others.

 

[MarantzRefrb]

I would love to know exact production numbers, and all the details about the various versions.

Do you guys have this same chassis ground?

 

[Steven Tate]

Here is mine. It has a plastic knob on the chassis ground.

 

[MarantzRefrb]

You still have your stock jumpers, and even the Aux 2 and Phono 2 termination plugs (or are they just caps?), yours was very well kept. Interesting to see you have the later style chassis ground, and the gain switch was changed to black.

Would be curious to know what serial number the 1200B model was introduced with.

 

[tonebells]

The first manual update was at 3500. The B update was at 5900.

Tony

 

[Steven Tate]

The first manual update was at around 3000. The copy I have has 2795 written on it. The B update was at 5900.

Tony


View attachment 2186836

Interesting. So, mine might have some features of the B model while still cosmetically being a non-B.

 

[ocdecio]

Mine has the metal chassis ground, no plastic.

I am scratching my head as to what might have caused the left channel to blow up so spetacularly. All outputs are fried, and the heatsink is discolored.

 

[ocdecio]

Does your good channel make any noise?

Just put it on a gen and scope and got a beautiful waveform, 400Hz square wave without any bends. That channel is promising and will be my reference on this rebuild.

 

[ocdecio]

Pre-driver blown:

 

[tonebells]

Interesting. So, mine might have some features of the B model while still cosmetically being a non-B.

The big change was the balance and volume pots and amp circuit. The 1200 had 100k and 250k pots. The 3500 and up had 25K and 50K. There are other small changes in power supply and other places.

Tony

 

[N8Nagel]

If you find a good set, post a link, I think I'd rather get a new set than try to find my old ones.

The best IMHO is one made by Lee Valley that is sadly discontinued.

 

[ocdecio]

I had forgotten what the sockets looked like, but there does appear to be a yellow component melted on yours, between the sockets. This is the best pic I could find of mine (not great):
Is that the thermal diode that melted?

I confirmed in the schematics - this is C801, never knew it existed. 0.1uF and it measures exactly that so one thing less to worry about.

 

[ocdecio]

Circuit modification as per Addendum - add 5.6ohm 1W resistor in series with Q510's emitter. Installed new 2SC2344 Sanyo Audio Power Transistor NPN hFE=144.

Added jumper for Q510's collector.



As per new schematic:

 

[tonebells]

Circuit modification as per Addendum - add 5.6ohm 1W resistor in series with Q510's emitter. Installed new 2SC2344 Sanyo Audio Power Transistor NPN hFE=144.

Added jumper for Q510's collector.

View attachment 2190329

As per new schematic:

View attachment 2190332

I am not seeing this mod this in the addendums that I have. I can see R552 added on the V2 and B schematic. Can you share where you are seeing it.

Tony

 

[ocdecio]

I am not seeing this mod this in the addendums that I have. I can see R552 added on the V2 and B schematic. Can you share where you are seeing it.

Tony

Sure, there is always a chance I am modifying the wrong version.

 

[ocdecio]

Germanium diode is busted. New one looks better.

 

[tonebells]

Sure, there is always a chance I am modifying the wrong version.View attachment 2190546 View attachment 2190543 View attachment 2190544

Are you modifying your 3058 to update to the 3500 changes?

Tony

 

[ocdecio]

Are you modifying your 3058 to update to the 3500 changes?

Tony

Correct. My theory is that this board got into a thermal runaway situation, and from the little I can understand of the changes they seem to help with that even though that is not explicitly stated in the manual.

My last resort will be to convert this into almost a B by replacing the diode/transistor with the transistor/transistor solution.