| aantunes |
Hi,
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?
Thanks |
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| Netlist |
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.
/Hugo |
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| anatech |
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!
-Chris |
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| aantunes |
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 |
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| anatech |
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.
-Chris |
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| aantunes |
Need help indentify ceramic capacitatores:
50k01
50k047
100v.1
104j50 nis
104j50 nis g
50jkck
maybe its a basic question but I'm just a beginner regarding electronics |
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| anatech |
Location numbers for those?
Parts with a "j" are in pF, but I'm not sure about how you've listed them.
-Chris |
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| aantunes |
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? |
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| anatech |
| quote: | | Location numbers for those? |
C7xx numbers please? |
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| aantunes |
50k01-----c713
50k047-----c710
100v.1------c721
104j50 nis------in paralel with r730
104j50 nis g---in paralel with r731
50jkck---c706
thanks |
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| anatech |
Hi aantunes,
C713 .... 0.01uF not critical at all (protection transistor)
C710 .... 0.047uF use 100 V or higher.
C721 .... 0.1 uF ? couldn't find it. Looks like supply decoupling.
C706 .... 0.1 uF
Your other two across the resistors .... 0.1 uF 100V Not critical, for supply.
My schematic copies for this amp are very hard to make out. Very poor scans.
-Chris |
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| aantunes |
HELP
After replacing all electrlytic caps on board p700 the resistor r759 always burns out!!!!!!
Anyone as any clue |
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| aantunes |
Another strange thing when replacin capsc717 and c718
the manual mentions 10uf but in the 2 channel the old ones that were there were of 22uf
Any clue? |
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| anatech |
Hi aantunes,
I can't read my schematic in that area very well. Is R759 a 3R3 in series with the base of the output transistor?| quote: | | After replacing all electrlytic caps on board p700 the resistor r759 always burns out!!!!!! |
Something else changed. Wire off and shorting? Solder splash shorting traces?
| quote: | | Another strange thing when replacin capsc717 and c718 |
My manual shows those as 22uF. Depends on the market possibly. It's simply part of the filter in the protection network. No biggie, use 22uF.
-Chris |
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| aantunes |
hI ANATECH,
Big problems, after the burn transistor I found that I've placed the power transistor in the wrongh place, this meas instead of replacing in the original position I've switch betwwen 2 of them.
I think I may have ruined my amp :dead: !!!!!!!
Aterf replacing the burn resistence and placing the transistors in the correct place, 3 others resistors burnout!!!!
Te problem is I'm a stupid nubbie! First I don't have an external ac power, so I was just connecting the channel to the ampplifier and power it on to test...what i think is stupid!!!
so now i'm going to study http://www.kpsec.freeuk.com/index.htm
and try to learn something about electronics, try to test all the components and see if I can save this little baby...
Help needed!!!!!!!!!!!! |
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| anatech |
Hi aantunes,
Too bad you're there and I'm here. I could rebuild it properly. Setting the idle current may be troublesome now though.
A new set of outputs for that channel. No ifs, ands or buts. This is a great little amplifier. I'm sorry to hear about the trouble. It's a bad amp to learn on too, because it's a little different to most.
Hugo may be able to help you. You should take stock of your situation and ask him how much. This is a classic little amplifier with the ability to stomp on many others for sound quality. So it's well worth what ever it reasonably costs to repair.
Hugo is "Netlist". He is a very good technician as well.
-Chris |
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| jblmar |
Just came across this thread.
Sounds like thermal runaway issue. Are the heat sinks (either left or right) hotter that the other? If so, the protection circuit will cut off the speaker realy. As the heat sink cools, the thermistor will allow current to flow and the relay will be switched back on.
Ron |
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| anatech |
Hi Ron,
This model does not have thermal cut out. It does have thermistors that people tend to break the leads on. High bias. Boom.
-Chris |
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| jblmar |
Hi Chris,
The thermistors are what I meant. My 300DC developed a thermal runaway condition on one channel about 4 years ago. The channel would cut out when the heat sink reached a certain temperature (resistance). The thermistor would cut the current. Took a few minutes for the HS to cool and restore function until the next cycle.
Ron |
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