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Marantz 1200B-No Sound

nickdawes

nickdawes

New Member
I recently picked up a Marantz 1200B in excellent cosmetic condition with original box, Manual, Warranty and Plastic face cover.
I'd been wanting a Marantz of this vintage for some time and It looked like a good bet.
After replacing the 4A mains fuse with a 3.75A I had available (the original was still intact but the glass had broken in a re-boxing accident), the blue light came on but no sound via phones or speakers.
I noticed the protection circuit wasnt clicking in and read a couple of posts on here regarding testing.

The problem I have is that I cant relate the schematic to whats' in front of me very well and I've caused a few sparks trying to test with a multimeter. Any advice on this would be so gratefuly appreciated as i would love to get it going so badly.

Just a note... I was trying to test with the components still in the circuit as I've been reluctant to remove anything so far for fear of going in over my head.

Thanks you in advance for any help..
 
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Rebuilding the rectifier/relay board will probably solve your initial problem. Replace all of the capacitors, test any replace any resistors that are out of specification. I usually replace all of the diodes and the relay while I'm there.

Your may also want to replace the bridge rectifier, for some reason they seem to have a tendency to fail after rebuilding the board.
 
Thanks Chris, it does sound like quite a big job for me so may have to get an expert on the case.

This is probably a stupid question but are there any potentialy simple problems that might be causing this, the guy who I bought it off assured me that it worked when he last used it so I wondered if anything had occured in transit?

Also, is it a possibility that the protection circuit may actualy be working and just preventing a dodgy amp stage?
 
Hi and welcome to AK. Yes it could be that the protection is doing what it's supposed to. If you could post what state or country you live in perhaps a local tech would PM you with an offer to service your new baby. Best wishes on getting it running again.
 
Thanks for the welcome! I've admired this forum for a while and the great knowledgeable folk that are on here so I'm honoured to receive advice.

I was hoping of a farely simple project to cut my teeth with but it seems this isnt it, I'm also fearing a large repair bill though so that spurs me on to have a go!

I'm in Nice, South of France France at the moment so If there's anybody out there...
 
I was just having a look at some of the components on the Rectifier/Relay board and tried to google modern equivalents. Namely 2 of the 3 transistrs are SPS439 but I can't find these or what they are in 2011. Is there a resource for this sort of thing or is it a case of sourcing original parts?
 
Your problem is too much bias current, or 1 or more output transistors are shorted, or bad, or both!
 
Thanks cademan, Is the excess bias current a result of the shorted transistors? Is this something I can check before pulling it apart?
 
What's your level of expertise? Are you willing to dig in, or are you wanting to have someone else do it for you?

Usually, the reason a relay won't click in is because there is DC at the output and that usually means 1 or mor output transistors is bad.

Sometimes an amplifier will blow fuses if an output is shorted, and sometimes the relay (protection circuit) will not engage to prevent DC from getting to your speakers.

First, set you bias voltage (according to a schematic), and if the relay doesn't engage, check you output transitors for shorts.
 
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This would be my first although I have a basic knowledge of components, I would really like to dig in if possible so I really appreciate the advice!
 
nickdawes said:
Thanks cademan, Is the excess bias current a result of the shorted transistors? Is this something I can check before pulling it apart?
Click to expand...

Models 30, 32, 1200 and 1200B use a similar rectifier/relay board design. I have repaired 3 model 32's 1 model 30 and 1 model 1200 in the past year which all showed up in the same condition as Nick's 1200B.

All of these units were initially made functional by rebuilding the rectifier/relay board. These are fairly easy models to troubleshoot and isolate which board is causing the problem. I wouldn't jump to bad outputs or bias problems first.
 
I usually buy components from Mouser. Since I don't have a service manual for your 1200B I don't have a list of the exact parts your will need. If it is similar to a 1200 there are five capacitors that will need to be replaced.

Your initial goal should be to get the unit working so you can perform further testing and decide what may need to be done next. If this is your first repair project, proceed slowly and make small changes one at a time.
 
ChrisMarantz said:
Models 30, 32, 1200 and 1200B use a similar rectifier/relay board design. I have repaired 3 model 32's 1 model 30 and 1 model 1200 in the past year which all showed up in the same condition as Nick's 1200B.

All of these units were initially made functional by rebuilding the rectifier/relay board. These are fairly easy models to troubleshoot and isolate which board is causing the problem. I wouldn't jump to bad outputs or bias problems first.
Click to expand...

+1 on a Marantz 250 power amp I repaired a few months ago. Very common failure, and an excellent idea to focus on before you do anything else.
 
Thanks guys, I'll start here. Does anybody know a reputable source for PDF Serivice manuals, I only have a schematic at the moment.
 
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