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Marantz 1200 blows speaker relay board caps and diodes

macman007

macman007

Mcintosh..Made In USA
A stated above I have a model 1200 integrated amp that blows the 2 blue small capacitors and 2 diodes on the speaker relay board (the board in the middle of the case) next to the 2 big caps. I have replaced both diodes and both small caps 3 times to just in case polarity was wrong on any of them. Also, before the of this start the dc offset was checked and found to be in spec.I had no other problems at all. The unit powers up and the protection relay clicks, even with the caps and diodes blown but no sound. If I replace the diodes(I think correctly) the unit will power up and play from 20 to 30 minuts at any level then the replaced caps and diodes blow and I get confettti and smoke, but no blown fuse. The unit still operates perfectly as a preamp. I am sitting here scratching my head wondering what to do (I hate repair shops) too much shoddy work done in the past. Where do I go from here? Also, when the blow up happens I loose both speaker outputs but again the unit works fine as a preamp.

I want my Marantz sound back HELP!!!:tears:
 
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Values and reference designators for the failing components would be useful, oh and...
:worthless

Tom
 
I'll get back to you with some high quality photos and we'll go from there. At this point all the physical /visible damage seems to be in the center board containing the speaker relay: again 2 identical diodes and 2 identical capacitors. More to follow.
 
Do you need a schematic. You are going to have to pull the board and replace all the caps, diodes as well as check out the other components.

It should be the same relay board as the 250 amp

charles
 
Yes, I have no schematic. What wattage solder iron do I need to remove the big wires from the board? What grade rosin core solder do I use when re-soldering and installing the new components, once the old bad ones have been identified?





Thanks! 007

BTW, I may need help identifying the proper direction for the caps and diodes for proper polarity. The old diodes are melted and the caps are confetti and oil!
 
I sent you the service manual and also sent a copy to the database.
Does the board look like this? If so, which components are blowing?

Tom
 

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macman007 said:
Yes, I have no schematic. What wattage solder iron do I need to remove the big wires from the board? What grade rosin core solder do I use when re-soldering and installing the new components, once the old bad ones have been identified?
Click to expand...

I use a 50 watt Weller WES51 iron. It's really nice, analog temp control from 350-850F. That should do just fine for most audio projects. For solder, I use Kester "44" eutectic solder. It's a 63/37 solder, no plastic state. Good luck on the 1200!
 
Looks like the 6v 200uf caps, and there are an identical pair, both blown, and 2 diodes, also blown and identical values. I don't see the diodes in you picture, but the diodes were the same value as well 4404 was the number on them, I think.Again, a pair of them .. BTW your soldering job on the big wires on the board in question is much better than my unit has... assuming mine are unmolested. The parts I replaced them with (twice) were available at the local rat shack. Also, my original caps were coated in a blue paper , not the poly coated ones you have. I believe they were called sprague (sp)? Note: the unit would power up and play fine before the caps exploded after 1/2 hour or so of playing (both times) and took out both caps and diodes both times. Lots oil, confetti and a bit of smoke but no blown fuse. The unit still powers up fine and the relay clicks after a few seconds of turn on time but no sound from the speaker taps. As a preamp it works absolutely perfect. Headphone output is ok as well as all othere functions. Hopefully the problem isn't too serious. Hope this helps


007
 
I don't have a 1200 here right now to look at, but from my service notes:
CR705 and CR706 should be 1N4004 diodes, 1A 400 PIV.

C701 should be a 22 uF/25V electrolytic capacitor.
C702 should be a 220 uF/6.3V electrolytic capacitor.
C705 should be a 22 uF/63V electrolytic capacitor!

I think you are putting a 6.3 volt cap in place of a 63 volt one for C705. When it shorts (and it's sure to with 10 times over voltage) CR705 and CR706 blow from excessive current. :yikes:

Hope this helps!

Tom
 

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Awesome, thanks for the pix! I will check it out this weekend and see whats what. What is the value of the other diode you didn't list( cr 707) 1n4004 1a 400 piv, same as others? Can't screw up installing the caps as they plainly point to the ground plane on the board, esp. in your schematic. Same with the diodes , since they are marked as well..at least the new ones.



Thanks 007
 
Typically, what would cause these components to blow and why?. I would hate to put new correct components in and have the board blow again.:thumbsdn:


007
 
Phil,
6 volt caps where 25 and 63 volt caps are required usually causes bad things to happen.
The only other thing I can think of is if you have it strapped for 120 volts and have it connected to 220 volt mains, but I think more than a few parts on the relay board would smoke in that case.

If you want, I can send you the diodes and caps you need to replace your blown ones, my treat. I already have your address, just let me know if you want them.

Tom
 
Tom, you are the definition of "Audiokarma". Thank you for your generous offer. I would like that very much. It would save me a trip of 50 miles or so since the closest rat shack is only selling cell phones and such nowadays. And as you know, mail order usually requires a minimum order on small parts.

If there is ever anything you need to know automotive related (or anyone else who reads this) feel free to pm me. I am a Master Automobile Tech with over 25 yrs. exp. and have experience with almost anything car or truck related. Business is a little slow with holidays coming up and having a family to take care of, cash flow is a bit thin. Your generous gift is greatly appreciated.

If there's ever anything I can do, don't hesitate to ask. I will do my best to spread your good Karma in any way I can.


God Bless,

Phil-

aka 007
 
@ Catrafter (Tom)..

I was looking thru the threads and realized I never replied back to this thread. I think I posted or emailed you that I had gotten the parts, and installed them. The 1200 has been singing sweetly now for nearly 6 YEARS! I had repaired it and stored it for about 2 years in 14/15, then brought it back out and it still sounds great. I can not thank you enough, I listen to this unit every day near about.

I would like to go thru the unit now and replace the caps and anything else such as transistors and diodes that you think need attention. I know you are booked solid and would like to do the unit myself anyway since I do my own work now. However, I would like to replace the parts needed or recommended with suggested upgrades to get the most out of it possible where sound quality is concerned. The unit has no issues, so I guess I'm asking what would you replace beyond the obligatory 'lytics, and (not the main big filter caps, they are OK) whatever you would recommend at this point.

I'd like to pay special attention to the Phono stage as I spin mostly LP's these days, and I know these can sound very good with the Phono stage done correctly.

What brand caps (s) do you suggest? How about the transistors and diodes (zenier and so on), I thought maybe you would have a list of favorite things you suggest for these)

By the way, fantastic job on the 4400 Quadradial , if it sounds half as good as it looks then it must be something special indeed!

I'm assembling my 1200 with a 115 tuner and other silver vintage gear for a killer 2 channel analog system, thus my desire to do this thing up. Everyone refers to you as 'THE Marantz Guy' and I I concur..!!

Philip.
 
Hi Philip,
What a blast from the past! I'm glad you got it going again and that it's been working OK.

I don't have a list of electrolytic caps that should be replaced for the 1200, perhaps someone else can chime in with a list.
There are a lot of axial electrolytics in there, AML138 types are what I like for those, but they are getting harder to find.
If you can, it's usually a good idea to replace any electrolytic types in the signal path with film types.

Tom
 
Thanks Tom. And thanks for the heads-up on Vishay axial's. I think I will start a separate thread on the subject and see what the consensus is. If nothing else it may help others as well. These Marantz units are very well built and a joy to service since they seemed to have been designed with serviceability in mind. I have heard besides the power supply that the Phono, Tone and power supply boards net the most significant improvements in sound when replacing with modern caps ans semi's. It will be interesting to see what the old girl is capable of once the 45 year old components are replaced with quality modern parts!
 
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