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
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
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
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
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
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
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?
-Chris
I can't read my schematic in that area very well. Is R759 a 3R3 in series with the base of the output transistor?
Something else changed. Wire off and shorting? Solder splash shorting traces?
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
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
!!!!!!!
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!!!!!!!!!!!!
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
!!!!!!!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!!!!!!!!!!!!
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
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
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
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
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
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
After replacing a total of 11 transistors,
a number of resistors, a couple of diodes and
whatnot (there was a hole burnt in the pcb,
major disaster) in a Marantz 170DC, I need to adjust
bias as the heatsink becomes too hot (+54 Celsius).
How do I do this? (no pot present).
Very grateful for some hints...
a number of resistors, a couple of diodes and
whatnot (there was a hole burnt in the pcb,
major disaster) in a Marantz 170DC, I need to adjust
bias as the heatsink becomes too hot (+54 Celsius).
How do I do this? (no pot present).
Very grateful for some hints...
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