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aantunes 2nd July 2007 03:43 PM

marantz 170dc

I just bought a Marantz 170 dc in Belgium, it works fine until like 40 min running then the relay starts to switch off and after a few seconds on again. Does anyone have an idea what is wrong with it, maybe a new relay?


Netlist 2nd July 2007 03:54 PM

This amp could need some new capacitors. First, check for DC on the output, before the relay. If all is fine, start replacing the caps on the relay board.
It might also suffer from bad solder joints and loose power transistors.


anatech 2nd July 2007 05:35 PM

Hi aantunes,
What you have there is an outstanding amplifier! This most certainly is a keeper (I've rebuilt a few). The sound quality will be very difficult to top if you handle this rebuild properly.

The first step would be to take it apart, remove the amplifier assemblies (they unplug) and give the chassis a good cleaning. Clean off the amp assemblies at this point.

Set up on your work bench and take the first one apart, take digital pictures showing where the transistors and wire go. Take some more of the board from each angle. Remove the power output transistors (you will have bought some heatsink grease and TO-3 mica insulators already). Now inspect the solder side of the PCB. If you see bad solder connections, remove the solder. Don't bother resoldering yet.

You may as well replace all the electrolytics. Also, replace all the ceramic caps with mica, polypropylene or polystyrene capacitors. 160V minimum ratings on these small caps. Refresh the solder connections at this point (I would normally test all the transistors and match some of them now). Clean the board off and look for shorts. I tend to use a little electronic solder flux to resolder the board. Clean and regrease the output transistors, test them first if you can. Clean and dry the heatsinks (you can do this earlier), remount the power transistors using new insulators and grease. When you tighten the mounting screws, try not to over tighten them.

If you can, replace the old speaker relay now, also check that the main filter caps do not have any punctures. You could replace then as well, not a bad idea and this amp is well worth it. Also, replace the electrolytic caps on the relay board.

Install your rebuilt channel (just the one) and slowly power it up using a variac or lamps in series with your AC power. You could use and external DC supply if you have one. Check to make sure it's working properly. If it isn't, you still have an original to check it against - you should have already done that actually.

Once you have your redone channel working, it's safe to do the other channel. Same thing as before. Power up slowly again.

Now, assuming it's working, check your meter lamps. Make sure they are the 200mA 8V type. Change them if they aren't. Now you are ready to listen to it. You are going to love this thing!


aantunes 2nd July 2007 10:25 PM

Thank you very much to both of you guys.

It seems that I will have a few weekends to spend on this, but it will sing like a bird in the end.

By the way do you advise me to replace also the big capcitator?

All the best

anatech 2nd July 2007 11:11 PM

Hi aantunes,
Only if you see the seals damaged. This can be done later once you have it running. If you really like it (and I'll bet you do), replace the main filter caps when you have the money.

The amp you have sounds almost as good as it's big brother, the 300DC. That's what I normally use, and I love it. If I didn't have the 300DC, the 170DC is a natural.

Take your time and do a good job. Take lots of pictures (memory) and ask if you get stuck. Keep us posted on your progress.


aantunes 3rd July 2007 10:14 PM

Need help indentify ceramic capacitatores:




104j50 nis

104j50 nis g


maybe its a basic question but I'm just a beginner regarding electronics

anatech 4th July 2007 01:26 AM

Location numbers for those?

Parts with a "j" are in pF, but I'm not sure about how you've listed them.


aantunes 4th July 2007 07:24 AM

These are the writtings I find on the ceramic capacitators. Each line I wrote is one type of capacitator.

ex/ 50k01 those this mean 50000nF and 01 the tolerance? and isn't the j also the tolerance?

anatech 4th July 2007 05:21 PM


Location numbers for those?
C7xx numbers please?

aantunes 4th July 2007 06:03 PM




104j50 nis------in paralel with r730

104j50 nis g---in paralel with r731



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