Schematics needed for a Marantz 1020

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Giaime

Giaime

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Joined 2004
giaimeugliano.tk/
#1
I have an old Marantz 1020 solid-state integrate amplifier. It sounds good, however someone during a party short-circuited the left channels outputs, and now the left channel only hisses a little, but no sound. I think I must replace the output transistors. Can someone help or send me the schematics? I found these only for the 1030 which has a different type of output transistors (I think).
 
#4
Hello sllydderrr! Thank you for posting the schematics. If you have fixed many, maybe you can help me: before my friend sent me this amp, it was working, only one channel, I suppose I had to change the output transistors (hard to find, btw). Now when I plug to the mains outlet and I press the power on, the lamp doesn't glow! I have cheked all the fuses and the wiring, and that's perfect, no signs of corrosion, overheat, broken wires, bad solder joints. I measure 0 volts between the fuses and the cabinet, but the 230V does reach the two outlets in the back. What's that? How can I do? I'm a little unexperienced in solid-state pc-board stuff....

Please help me!
 
#5
Hello Giaime,

I can't take credit for the schematics, they are not mine. I just knew where to find them.😉

With regard to your problem... did you check for continuity on both sides of the power switch? On both sides of the fuse holder? The switches have a tendency to die unexpectedly.

I'm assuming that the lamp didn't burn out in the meantime?

I honestly don't know what else could cause your new problem. Usually it is something almost TOO simple 😀

sllydderrr
 
#6
In fact, it was too simple. The smallest fuse holder wasn't making good contact with the fuse. Now the amp works for the right channel, but the left one simply hums. I believe that the right channel transistors are the two right ones (seeing them under the cover, from upside), and the left channels transistors are the left ones. Well, I read the voltages on them and on the right side I see many 30VDC and a 0,6VDC, on the left ones I see only 70VDC! That's strange, something is happened down there. If the voltages are high, there's usually an open device, but I'm not much experienced. Someone's able to help?
 
#8
Hello! I submit an update: I desoldered the output transistors' leads from the PCB, and checked the transistors with the directions of this site:

http://www.elexp.com/t_test.htm

I know that the Marantz' are NPN BJT, and I measured them with a DMM that has the diode check. I put the negative lead of the DMM in the base (at least what I suppose to be), the positive at the collector and measured 2 ohm. I started trying every connection possible, B-C, B-E, C-E, I swapped the leads of the DMM and all the readings are the same: 2ohm. I suppose this is a short, and it's the leftmost transistor.

The other left channel transistor, the middle-left one is inexplainable. All the four transistors are marked the same number, 2sc897 Hitachi. But this one wants the base with the positive DMM lead to read a value of 200mV! So it should be PNP. But they are all marked the same!
The other strangeness is that either polarity I put between C and E, I read 0 ohm. Should it be another short?

I searched the web to find a 2SC897 substitute, and I find the MJ15001. Are there others? I need a modern, ready-to-buy one, because strange and old transistors are very HARD to find here in Italy!

Please Help Me!!!!!!!!!!!!!!!!!!!!
:bawling: :bawling: :bawling: :bawling: :bawling:
 
#11
I forgot to add, do not just replace the faulty devices with substitutes - if you are doing this, replace ALL of the output stage transistors, otherwise they will not be matched and the circuit will probably be unstable. That means, replace all NPN outputs with MJ15024 and all PNP outputs with MJ15025.
 
#12
Thank you for the reply! Yes, I have looked at the various subs for the 2sc897, and I found the 2N5631, 2N3773, 2N6609, SM3159, MJ15001.

The problem is: the original transistors are all marked the same!
I may be wrong, but I don't know how the Marantz works. If they are all the same number, I suppose they're part of a parallel single ended class A stage... But my knowledge of the output stages is taken from the tubes, so I don't know if I'm right with these solid-states...

Maybe the middle ones are PNP, but they are still marked 2SC897 like the others!

Someone knows something about the Marantz 1060 output stage topology? Is it the obvious Class B push pull or a more complicated design? 😕
 
#13
Maybe TIP35/36 can be easy in Italy, and those units can work too...no problem ...

To assemble in the other type"s place...not pretty, but works too.

Sometimes turns better, i did it in many Marantz that used crazy numbered transistors.

If i can remember, the result was better than the factory unit, as the modern transistors can reproduce better treble because it's speed.

Have to respect only if PNP and NPN, and reading the numbers, and the leads point down...from the left to the rigth you will have base, colector and emitter...the isolation can be cutted with a scissor to fit in those more modern transistor capsules.

regards...va benne

arrivederci

Carlo
 
#14
There are no PNP devices in the output stage...this is a quasi-complementary single-ended cap-coupled output. When the the output is functioning properly, half of the supply voltage should appear at the output side of the emitter resistors.

MJ21194 will work fine...as a matter of fact it's quite serious overkill.
 
#16
Dear EchoWars: I love you! Thank you very much!
😀

I was very unsure at the beginning, 😕

When I pulled away the transistors I noticed that the still-living ones are all NPN! 😱

If it was a push pull, with one channel broken, I should had a PNP and a NPN, and two bad ones. Right? 🙄

WRONG! :xeye:

Tomorrow I'm gonna look for a replacement.... 😎

Thank You All!
 
#19
Exactly that: I didn't get the basic answers I need. Someone suggested me to buy a matched pair PNP-NPN. If I followed him, probably I would have burnt the Marantz. He's old, but it's still working! If my friend stops to use it for parties, I will make a complete restoration of it, caps, resistors, a complete rebuilt...

Thanks again!
 
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