Marantz Model 120 Tuner Craziness I am Stumped!

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Ok Here are some of the results... Not necessarily in order.

Could not find 19Khz at H302 or 38Kkz at H304 so the MPX is not enabled.

The FM stereo lamp is not lit. and at J307 there is 12.75 Volts?? And at Collector H305 same voltage .

At H559 Collector is a steady .024 Volts while tuning on or off station.

J307 has 12.75 Volts on the collector while tunning

J305 is .037 Volts all the time.

H306 collector .852 Volts

H307 Base is .639 Volts

Something is open some where...I'll finish ringing out the other transistors on the MPX board with my B&K transistor In Circuit/out of Circuit tester. All the other components on that board seem good.

So get another cup of coffee ...maybe with a few drops of JD. Let me know when you want to say Uncle.....L.O.L.

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

A trick that might save time is moving the Muting Level potentiometer R005 (it's on the rear panel) and force it to think there is lots of signal, it might then kick in to Stereo Mode. See what it does.
We want H306 ON, J305 +ve a few volts at least.

JD with boards that have -550VDC for the CRT, well that doesn't always go well lol.
This looks like peak point-point wiring, lots to work around.

Adding:

J305 is .037 Volts all the time.
H306 collector .852 Volts
H307 Base is .639 Volts

Power comes in on J303. I would see if C559 is shorted or H552-C is on? at P550.
It lools like signal coming in on H551 will turn on H552, so J555 goes low which shuts off power to H307. It doesn't make total sense to me - you want the opposite - strong signal H552 OFF to enable the MPX section but turning H306 ON.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

A trick that might save time is moving the Muting Level potentiometer R005 (it's on the rear panel) and force it to think there is lots of signal, it might then kick in to Stereo Mode. See what it does.
We want H306 ON, J305 +ve a few volts at least.

JD with boards that have -550VDC for the CRT, well that doesn't always go well lol.
This looks like peak point-point wiring, lots to work around.

Adding:


Power comes in on J303. I would see if C559 is shorted or H552-C is on? at P550.
It lools like signal coming in on H551 will turn on H552, so J555 goes low which shuts off power to H307. It doesn't make total sense to me - you want the opposite - strong signal H552 OFF to enable the MPX section but turning H306 ON.

A trick that might save time is moving the

Do you mean "REMOVING "the pot?... I'll get back on this tomorrow and try to trouble shoot what you said. Right now I need some diner,

And yes the -550 Volts from the scope already got me once when I first opened the unit and didn't watch where I put my hands....LMAO.

Thanks for hanging in there with me Redwire.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Didn't get a chance to wrench on the 120... had some other issues come up. I'll attack it tomorrow. I'll disconnect the leads from the muting threshold pot and see what happens...

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Move as in 'rotate', see what it does, while observing voltage at J305. Leave the pot wiring alone lol.
We need to get J305 up, and am working backwards to find out why it's acting like the FM signal strength is too low- when it isn't.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Move as in 'rotate', see what it does, while observing voltage at J305. Leave the pot wiring alone lol.
We need to get J305 up, and am working backwards to find out why it's acting like the FM signal strength is too low- when it isn't.

Ok Got It Rewire.... It's 10:35 AM Sunday EST in the USA... Gonna have some breakfast and then dive into the 120. I'll report back and let you know what's up.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Move as in 'rotate', see what it does, while observing voltage at J305. Leave the pot wiring alone lol.
We need to get J305 up, and am working backwards to find out why it's acting like the FM signal strength is too low- when it isn't.

Ok RedWire..Here the results.. ....

Powe on Station Tuned

Positive lead on J305..(Terminal On the board)

Negative to chassis ground...

Muting Level Control turned off =.026 Volts DC @ J305

Control Rotated Fully on = .045 Volts DC @ J305

From Fully Rotated off ...rotating the control slowly to fully on you can see the voltage track up..to ...045 Volts DC.

Hope this helps.

Thanks:

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Ok RedWire..Here the results.. ....

Powe on Station Tuned

Positive lead on J305..(Terminal On the board)

Negative to chassis ground...

Muting Level Control turned off =.026 Volts DC @ J305

Control Rotated Fully on = .045 Volts DC @ J305

From Fully Rotated off ...rotating the control slowly to fully on you can see the voltage track up..to ...045 Volts DC.

Hope this helps.

Thanks:

One other note redwire... When I turn the rear muting level control to min ....
No station can be tunned!!! Something is going on there....

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

The FM tuner has three levels of signal strength assessment "muting", some have priority over the other (when it works). So it's hard to narrow down which of the three is sick and I'd have to write a long book how this works lol.

1st is RF signal strength (voltage) comes off the IF amp at J207, then to the Muting Level potentiometer. *Can you measure the voltage at J207, on and off a station. It's at the Muting Level potentiometer or the P200 board.
Then that feeds J305. If J305 is stuck low (which it is), then *is H560 or H561 ON? Measure their base voltages.

So... the P550 board amplifies the signal strength voltages coming out of the detector board P500. It also determines thresholds to mute FM and FM Stereo.
Jumping to the middle, it looks like FM Stereo 19kHz carrier AC comes out at J506 and then onto P550, H551 and H552 determine FM stereo signal strength. *H552-B voltage should show that, if H552 is ON then good FM stereo carrier seen.

P.S. What is "Quadradial" J008 ? It looks like a FM Stereo carrier take off, I don't think quadraphonic ever made it to FM?

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

The FM tuner has three levels of signal strength assessment "muting", some have priority over the other (when it works). So it's hard to narrow down which of the three is sick and I'd have to write a long book how this works lol.

1st is RF signal strength (voltage) comes off the IF amp at J207, then to the Muting Level potentiometer. *Can you measure the voltage at J207, on and off a station. It's at the Muting Level potentiometer or the P200 board.
Then that feeds J305. If J305 is stuck low (which it is), then *is H560 or H561 ON? Measure their base voltages.

So... the P550 board amplifies the signal strength voltages coming out of the detector board P500. It also determines thresholds to mute FM and FM Stereo.
Jumping to the middle, it looks like FM Stereo 19kHz carrier AC comes out at J506 and then onto P550, H551 and H552 determine FM stereo signal strength. *H552-B voltage should show that, if H552 is ON then good FM stereo carrier seen.

P.S. What is "Quadradial" J008 ? It looks like a FM Stereo carrier take off, I don't think quadraphonic ever made it to FM?

In reverse,,,,,,,, No I don't think the Quad thing made it to FM.. Same as discreet 4Ch sound from records,,, Only Panasonic figured that one out with theit CD-4 system and the use of there demodulator and the Audio Technica
Cartridge and Sahbata Styles.

Sanusi Faked it with There "SQ" sound that really wasn't discreet 4 channel.

Any way ..Back to reality.. Ok I'll have to attack this tomorrow and do the measurements. What a Complicated system...Gheeeeeeeeez.

So I'll print your instructions out and try and run this down tomorrow.
Whish you were closer....I'd take a Road trip to your house or shop. I could use a vacation. I have a friend who lives in Canada I havent spoke to in a Very long time. I met him on the Corvette Forum and we travelled a few places together down her in the lower 48. Great Guy. Alos met his buddy who was with The RCMP.

Anyway..I'll Be Back....

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

In reverse,,,,,,,, No I don't think the Quad thing made it to FM.. Same as discreet 4Ch sound from records,,, Only Panasonic figured that one out with theit CD-4 system and the use of there demodulator and the Audio Technica
Cartridge and Sahbata Styles.

Sanusi Faked it with There "SQ" sound that really wasn't discreet 4 channel.

Any way ..Back to reality.. Ok I'll have to attack this tomorrow and do the measurements. What a Complicated system...Gheeeeeeeeez.

So I'll print your instructions out and try and run this down tomorrow.
Whish you were closer....I'd take a Road trip to your house or shop. I could use a vacation. I have a friend who lives in Canada I havent spoke to in a Very long time. I met him on the Corvette Forum and we travelled a few places together down her in the lower 48. Great Guy. Alos met his buddy who was with The RCMP.

Anyway..I'll Be Back....

OK Redwire... This ones for the Books.... I was checking point to point wiring from the P550 board to the MPX board P300.

When I got to J555 on P550 and followed it back to P300 the skid shows a connection at J504....

Well Dam..?? There is no stand off terminal J504 on P300 on the top side?? So I look on the board and there is a Marking for J504 which is a small thru slot cut into the board . No Terminal.

So I flip the board over and there is a white wire which looks like it is soldered to a round solder land on the solder side. When I touched it ..it popped off. Cold solder joint!

So I soldered it back on to the land and Bingo.. the stereo lamp flickers on. Next I try tunning thru the scale and all I get is a flicker when I hit the station in stereo. One or two lock on but the signal is weal and audio Distorted ( Not totally Clear) Stereo lamp still flickering ..Signal Strength?

I had made a 300 Ohm Dipole out of Zip cord which I have hung up. And the muting level is turned all the way to Min. Next I go out to the garage and lug in my Marantz 4240 Quad-radial receiver and lug it back in the shop and hook up my antenna. It captures about 4 stations with solid Stereo Lamp indication Signal strength meter varies from station to station.

So at this point I'm not sure if It just needs an FM Alignment or there might be something I missed. If you look on Page #7 and #8 of the manual it shows how to align the FM and also adjust Stereo Separation.

Now ..I don't have an FM Freq Generator. Do I buy one ? Or is there a way Of tweaking the unit with a Scope and VOM?
I don't think so..... FM alignment is not for the fait of heart. I think unless I can find some one with the proper equipment for FM alignment I should keep my hands out.

What would you suggest? Did I also miss something else at this point I can check in the way of the circuit operation .... Voltage Etc?

Where almost there...Don't leave me Now...LMAO

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

So far, it was an open connection to shielded cable for J504?

When you say "all I get is flicker", is that the Stereo lamp or white noise or signal cutting in and out? What's the signal strength meter doing?

I would first see how it does in FM Mono. That will tell you if the RF amp, IF amp etc. is reasonable or there is already weak signal right off the bat and we need to go there.
If any transistors were changed in that then the FM alignment could be a bit off.
I leave alignment as the last possible fault because it's difficult without the right tools and test equipment.

What is potentiometer R018 about? It connects to J504 and shunts signal there.

I'm not sure if it's weak signal for FM (mono) or only in stereo it's flickering.
J204 gives front-end FM signal strength as a voltage back for AGC. The DC voltage there should come up with stronger signal, look for it if it levels off on strong stations or not.

So, at this point just seeing if FM Mono is working OK or not.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

So far, it was an open connection to shielded cable for J504?

When you say "all I get is flicker", is that the Stereo lamp or white noise or signal cutting in and out? What's the signal strength meter doing?

I would first see how it does in FM Mono. That will tell you if the RF amp, IF amp etc. is reasonable or there is already weak signal right off the bat and we need to go there.
If any transistors were changed in that then the FM alignment could be a bit off.
I leave alignment as the last possible fault because it's difficult without the right tools and test equipment.

What is potentiometer R018 about? It connects to J504 and shunts signal there.

I'm not sure if it's weak signal for FM (mono) or only in stereo it's flickering.
J204 gives front-end FM signal strength as a voltage back for AGC. The DC voltage there should come up with stronger signal, look for it if it levels off on strong stations or not.

So, at this point just seeing if FM Mono is working OK or not.

Ok..First of there is no Signal strength meter..just the scope which shows (In Audio Mode) the signal with mono display in audio.

As I tune I can hit a station which will cause the stereo Lamp to flicker on and off but not solid on that station (The Lamp Lights the Name "STEREO" on the front panel.

When it flickers the scope will show a Stereo Display intermittently. Very few Stereo stations will trigger the lamp maybe 1 or two. The actual audio is not clear but fuzzy. Some stations will be strong as they are local but will not trigger the stereo. indicator.

So far, it was an open connection to shielded cable for J504?

This is not a shield cable but a single conductor white wire. And yes it was attached to J504 but not conducting due to a cold solder joint.

No transistors were changed at all on any board. The only thing change were all the caps in the power supply and the Caps On The MPX board.

What is potentiometer R018 about? It connects to J504 and shunts signal there.

I followed J504 and I can't find "R018"..?? I did see it connect to the switch array and down to the panel lamps. Are you sure R018 is not a Typo on your end. Or if not what board is it on? Give me a Transistor H call out. I don't see it?

I

'm not sure if it's weak signal for FM (mono) or only in stereo it's flickering.
J204 gives front-end FM signal strength as a voltage back for AGC. The DC voltage there should come up with stronger signal, look for it if it levels off on strong stations or not.

OK I'll check that out.

I've printed this out and will check some more. I think it just needs a Complete Alignment due to all those caps being changed. Maybe I'm wrong.

I test What we talked about here and get back to you..

Thanks: Regards:

Mark R

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I need to know if it can receive FM MONO okay.
Then it is either the FM Stereo enable that is screwing up now, or it just can't have enough signal for stereo. The distortion is the thing to figure out, unless it's just weak signal - which would also show up for mono.

What screwed me up is the service manual has 2 schematics:
pdf pg. 20/35 is S/N range X ?
pdf pg. 32/35 is S/N 1001-1510. (this has potentiometer R018 at J032 next to H004).
What schematic matches yours?

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I need to know if it can receive FM MONO okay.
Then it is either the FM Stereo enable that is screwing up now, or it just can't have enough signal for stereo. The distortion is the thing to figure out, unless it's just weak signal - which would also show up for mono.

What screwed me up is the service manual has 2 schematics:
pdf pg. 20/35 is S/N range X ?
pdf pg. 32/35 is S/N 1001-1510. (this has potentiometer R018 at J032 next to H004).
What schematic matches yours?

Ok I'll check the above out.. Here's my PDF version which looks about right,

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Here's a Video of the 120 not doing it's thing. When it tunes the stereo light goes out you off tune a hair it'll flicker. Allot of stations not pulling in stereo at all.

https://youtube.com/shorts/u_nkyBjIIS0?feature=share

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Here's a Video of the 120 not doing it's thing. When it tunes the stereo light goes out you off tune a hair it'll flicker. Allot of stations not pulling in stereo at all.

https://youtube.com/shorts/u_nkyBjIIS0?feature=share

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Originally Posted by redwire View Post
I need to know if it can receive FM MONO okay.
Then it is either the FM Stereo enable that is screwing up now, or it just can't have enough signal for stereo. The distortion is the thing to figure out, unless it's just weak signal - which would also show up for mono.

I have a Mono station tuned in now. Good strength. Mono display on the scope(Diagnoal Line) strong. But when I switch to stereo ...it doesn't show it. Not sure if this is a stereo station as it is Talk Radio.

On station shown in the YT video above off tunned will flicker the stereo lamp as shown.
Download the 120 PDF I posted. Can't see to get enough signal to light stereo. I have 300 Ohm FM T shaped antenna on there now. The 4240 Marantz from my garage had no problem pulling in about 4 FM stereo stations with a solid Stereo Lamp lit.

So you tell me...what do you think?

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Originally Posted by redwire View Post
I need to know if it can receive FM MONO okay.
Then it is either the FM Stereo enable that is screwing up now, or it just can't have enough signal for stereo. The distortion is the thing to figure out, unless it's just weak signal - which would also show up for mono.

I have a Mono station tuned in now. Good strength. Mono display on the scope(Diagnoal Line) strong. But when I switch to stereo ...it doesn't show it. Not sure if this is a stereo station as it is Talk Radio.

On station shown in the YT video above off tunned will flicker the stereo lamp as shown.
Download the 120 PDF I posted. Can't see to get enough signal to light stereo. I have 300 Ohm FM T shaped antenna on there now. The 4240 Marantz from my garage had no problem pulling in about 4 FM stereo stations with a solid Stereo Lamp lit.

So you tell me...what do you think?

Update Sunday the 5th. It now seems to be hitting all FM stations with Stereo ..But the signal doesn't seems to be strong enough to keep the STEREO Lamp lit. If I rock the fly wheel tuning knob I can get it to modulate with the voice or music. But it won't stay solidly locked.

Your ball.... if you haven't left the building ...

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

From the video I could not tell where you were tuning a station (below, on it, above it etc.)
I was wondering if that raspy distortion showed up in Mono mode. It is usually an old weak transistor that makes that.

So it is working OK in Mono? That means the RF front end and some of the IF stages are working OK.

Still there yes but following the wires on the schematic is pretty much torture. Then there's the switches. Did you figure which schematic in the service manual (there are two) applies to your tuner?

It's hard to diagnose over text in forums sometimes.

It is either the FM Stereo decode is making distortion, or the muting for FM Stereo is screwing up.

I would look at voltages on transistors again, to see what might be far off.
Wild guess P300 board, it amplifies the FM Stereo signal and Read 3.2 it gives some ideas on the 2nd level muting (it's got three levels of muting).