Marantz SR940 no sound.

[ivo]

Hi guys! Is anybody here with experience with Marantz SR940 Stereo Receiver? There is NO service manual or schematic on the internet. Shortly:
*There is no output sound
*The speaker relays click (there are two relays for A and B speakers terminals)
*I plugged it into a Tone generator(1000hz, 0db) . The receiver input is CD input. I measured this signal with an oscilloscope and I got a wave signal out of the speakers. This signal is not changed when the volume control of the receiver is depressed up and down.
*The signal is measured at the same amplitude at the flat cable going to the Transistors Output board and on the speakers terminal and it's independent of the Volume control.
*Also I measured with Ohm meter the C and E of the output transistor(onboard) and there is NO short signal. The Outputs are 2sc3182. Actually, there is no short signal between any legs.
So my suggestion is that the problem is in the Preamp section. But without schematic...
There is a Toshiba TC9151 HIGH-VOLTAGE, AUTO-ZEROED OPERATIONAL AMPLIFIER(24 pin dip) in the Preamp section, that maybe is the problem...
I may go and do a blind replacement with this integrated circuit.
Any help or idea?
Thanks!!!

 

[The Fuxtor]

Check the regulated power supply. Maybe the the transistors need reflowing? Or possibly replacing...

 

[ivo]

There are two output boards with a massive sink, please see the photo. Both boards are fed from the power supply board with 110vdc!! I don't know if this is ok or not. The definition of the 2sc3182 output transistors is "hi current transistor"...
I can easily desolder a few of them and do the diode test on the bench, but(!) as I said the signal measured on the flat cable connection between power output boards and the rest of the receiver(preamp, tone board) is Indepndable from the Volume control. I measured with the oscilloscope and volt meter. Neither the amplitude nor volts are changed when turning up the volume control.

 

[The Fuxtor]

Is the bottom removable?? I would want to look at the bottom side of power supply.

 

[ivo]

yes, it is. Here are the photos. I'm just wondering about these 110vdc feeding outputs boards...

 

[The Fuxtor]

yes, it is. Here are the photos. I'm just wondering about these 110vdc feeding outputs boards...

Is there no schematic available?

 

[ivo]

That's the problem. No Service manual or schematic available online...

 

[dankik]

You can always buy one .

 

[ivo]

Hi, The Fixtor! I just want to tell you that I already bought a Service Manual and the booklet will be here in a week or so. I'll post when I get it.

 

[ivo]

Hi, The Fixtor! Ok, the receiver is fixed! I got the Service manual book and start my project. Because there was not any sound with any input on both channels, I decided to start with the Power supply. Turned on the receiver and start a visual inspection for bad corrosion glue or bad soldering. At this time I discover that IC701 is abnormally hot. Did the voltage measurements and it was with 15volts different. Q702 was also with bad voltage, so I took it out and did diode test. Q702 was good. Closest R712 and D712 were good too. Next on the line was C715(100uf 16v), measured on the bench and it was leaking with 0uf. So installed a new 100uf 35v Nichicon. Turned on the receiver and measured the voltages - all good!! Plugged a turntable and it sounds great! The tuner is working also nice. Tomorrow I'll do the amplifier alignment.
Well, I spend $22 on this Service Manual but it worts every cent!
Cheers!!

 

[ivo]

 

[The Fuxtor]

Congratulations!

 

[ivo]

I have questions regarding this amplifier alignment. Kind of confusing! Please see the photos of the Manual book and real board.
As it's seen R 646 is missing on the real board. Is than mean to use the upper Dotted line of R650 to cross with R648?? Thanks!

 

[The Fuxtor]

Is there R645 on the board? Check the trace from the empty R646 hole. I'm guessing it goes to the white block resistor sitting beside it.

 

[ivo]

R645 is empty too. Both 645,646 are connected with white resistors R650,649. So I'm assuming the measuring need to be done with crossing upper legs of R648 to R650(L ) and R647 to R649(R channel).
I already did this and got 21mv. It is not big deal but the Service says 13mv, so I think they need to be adjusted. Do you think this is correct?

 

[dankik]

From your photo of the board there is a large white component (R650) with 3 leads on next to the space for R646. It must be two resistors combined into one.
If you look at the PCB diagram, the holes for R646 are connected to R650. I think your R650 is a combined two resistors... that's why R464 is missing.
Your photos of the schematic are blurry so I can't read the part nos.
It's probably similar for R648 and R652.

 

[The Fuxtor]

R645 is empty too. Both 645,646 are connected with white resistors R650,649. So I'm assuming the measuring need to be done with crossing upper legs of R648 to R650(L ) and R647 to R649(R channel).
I already did this and got 21mv. It is not big deal but the Service says 13mv, so I think they need to be adjusted. Do you think this is correct?

Sounds about right

 

[ivo]

dankik, your suggestion is correct this is a .22ohm cement resistor with three legs. The parts list says 8 cement resistors for both Amplifier pc boards and there are just 4...
The Fixtor, I'll do the alignment procedure and finish this project. The receiver works just great! Everything ok even the Clock! Was a confusing game to adjust this clock, because there is no Operating instruction, finaly I got it, actually the Clock adjustment has to be done with the FM/AM buttons! Strange idea!
The receiver has a very nice juicy and warm sound, I don't know why it's a kind of underrated. Very powerful and clear sound... I think this model is on the border of old classic Marantz production and the new black plastic era under Philips...
Thanks, guys it was a pleasure to speak with you!!

 

[wesley_meyer]

Hi guys! Is anybody here with experience with Marantz SR940 Stereo Receiver? There is NO service manual or schematic on the internet. Shortly:
*There is no output sound
*The speaker relays click (there are two relays for A and B speakers terminals)
*I plugged it into a Tone generator(1000hz, 0db) . The receiver input is CD input. I measured this signal with an oscilloscope and I got a wave signal out of the speakers. This signal is not changed when the volume control of the receiver is depressed up and down.
*The signal is measured at the same amplitude at the flat cable going to the Transistors Output board and on the speakers terminal and it's independent of the Volume control.
*Also I measured with Ohm meter the C and E of the output transistor(onboard) and there is NO short signal. The Outputs are 2sc3182. Actually, there is no short signal between any legs.
So my suggestion is that the problem is in the Preamp section. But without schematic...
There is a Toshiba TC9151 HIGH-VOLTAGE, AUTO-ZEROED OPERATIONAL AMPLIFIER(24 pin dip) in the Preamp section, that maybe is the problem...
I may go and do a blind replacement with this integrated circuit.
Any help or idea?
Thanks!!!

I am having this same problem with a Marantz SR 940. Does anyone have a service manual? Thanks for any help cuz I don't want to junk it. I also have the same problem with a Marantz SR 440 and a Marantz SR 640. All from eBay. The SR 430 came from eBay it worked maybe 12 times I turned it on it was ok. Turned it off 1 day few days later turned it on no sound. Did hear any sound like buzzing or hissing not pop nothing just has not worked since. Anyone got any ideas? I'd pay some one fix it but I was told some people say they can then they tell the person I'd so much money to fix it then the idea is have the owner give to the repair person then they fix it and sell it online. Kind of like auto mechanics . I found 2 website that say I can download online repair manual but what else will I be downloading? Maybe a doomsday virus thats my worry about these web sites. I just got hacked a week ago on my pc and some how to got into my PS5 and bought some stuff for there PS 5 and changed a lot of stuff in my ps and my PS5. Anyway I don't want to junk them. Any help will be great.