Marantz Model 120 Tuner Craziness I am Stumped!

[Mark R]

My Marantz 120 Tuner stopped receiving Stereo signals. It works fine other then Stereo. I have a fully loaded shop here with all test equipment except and RF signal Generator.

I get great reception on FM so I have used that signal troubleshoot. I have been all over the MPX board and replaced all caps. Also the entire power supply caps were replaced.

All Voltages on the MPX board are good... all Transistors Good...All Diodes Good and other components.

The stereo lamp is good as I powered it up and it lights. The signal flow to that lamp is unbelievably complicated.

I am at a loss to try and figure out what has happened? Last time I powered it up in my system with a Model 500 and 250 and 3300 all was good. I haven't powered up the tuner in about a year.

Been all over YT and nothing. There was one guy working on a 120B which had the same problem but that circuit is different. And he only fixed it by removing one transistor and replacing it with a resistor. This left the unit without a muting control.

Anyway If you want I can upload a PDF of the Service manual. I'm missing something. Any help greatly appreciated.
Thanks: Mark R

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

My Marantz 120 Tuner stopped receiving Stereo signals. It works fine other then Stereo. I have a fully loaded shop here with all test equipment except and RF signal Generator.

I get great reception on FM so I have used that signal troubleshoot. I have been all over the MPX board and replaced all caps. Also the entire power supply caps were replaced.

All Voltages on the MPX board are good... all Transistors Good...All Diodes Good and other components.

The stereo lamp is good as I powered it up and it lights. The signal flow to that lamp is unbelievably complicated.

I am at a loss to try and figure out what has happened? Last time I powered it up in my system with a Model 500 and 250 and 3300 all was good. I haven't powered up the tuner in about a year.

Been all over YT and nothing. There was one guy working on a 120B which had the same problem but that circuit is different. And he only fixed it by removing one transistor and replacing it with a resistor. This left the unit without a muting control.

Anyway If you want I can upload a PDF of the Service manual. I'm missing something. Any help greatly appreciated.
Thanks: Mark R

Also forgot to add that when I first powered it up in the rack ...the face plate lit up and the scope was dim and there was no audio. This was because a 47@ 50V cap blew up and killed the power supply. Back in the day electrolytic caps had the blow out protection on the bottom using a soft potting compound. Todays use the section cut top where they vent.

The one on my board was cocked over to one side as the bottom had blown out. I just rechecked the PS and all seems ok.

Also : it would be nice if the Edit Button stayed on all the time. But I guess the Mod's have good reason to turn it off after a while. Had to google that one ...L.O.L.

[stj]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

do you see the differrential signal on the mpx line?

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

[...]Back in the day electrolytic caps had the blow out protection on the bottom using a soft potting compound. [...]

Uh back in the day NO small electrolytics had safety vents, they blow up really good used to do it for fun, as a kid.

If you had power supply problems with the cap blowing up, make sure the related rail and 13.5VDC voltage regulator H001 survived as well and is bang on pun intended.

I would check DC voltages in the MPX section- assuming it thinks it has enough signal strength to go to stereo mode and muting switch H303 is on.
I think voltages in (brackets) are stereo. It doesn't play FM mono, I can only find muting but no stereo/mono switch.
If it's in stereo mode H303 on, then look for 19kHz pilot signal at H302, H303 see if it is there.

I find it's usually the tuner thinks signal strength is too low which is why no stereo. But this tuner has a built in scope, that's so coooool

[R_J]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Which cap blew? this might help with the diagnosis, Have you cleaned the mono, AM and FM switches? do you have 13.5v on H001/H003
What voltage do you have on transistor H305, Base and Collector and does it change when the FM signal is tuned

Voltage in ( ) are with signal

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

do you see the differrential signal on the mpx line?

Thanks for the reply..... I got to be honest here... I have no clue where the differential line is? The skid does not indicate that.. Since I am not well versed in MPX and trouble shooting FM MPX ..the Marantz skids are not helpful in indicating what is what and where.

I have scoped around and found audio on the board but since there is no indication of what that signal is ....it is confusing.

I know some of these transistors have to turn off and on to operate the MPX and stereo lamp.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Uh back in the day NO small electrolytics had safety vents, they blow up really good used to do it for fun, as a kid.

If you had power supply problems with the cap blowing up, make sure the related rail and 13.5VDC voltage regulator H001 survived as well and is bang on pun intended.

I would check DC voltages in the MPX section- assuming it thinks it has enough signal strength to go to stereo mode and muting switch H303 is on.
I think voltages in (brackets) are stereo. It doesn't play FM mono, I can only find muting but no stereo/mono switch.
If it's in stereo mode H303 on, then look for 19kHz pilot signal at H302, H303 see if it is there.

I find it's usually the tuner thinks signal strength is too low which is why no stereo. But this tuner has a built in scope, that's so coooool

L.O.L. yeah they do blow up good. Back in Electronic school we use to do the same thing... This one in the Marantz blew out the bottom and was kind of rubbery.

It does paly Mono . There is a Mono switch on the front panel. When you select FM.. it should tune stereo ...you can also then press the mono switch to go mono at that point.

H001 is mounted on the chassis as a Heat sink and is BANG ON....!!! L.O.L.

Yep the scope is cool... It has an external input....(RCA JACKS) and that does indicate Stereo. When the FM goes stereo you get the X/Y display as the same as external.

But in FM... No psychedelic Jimi Hendrix display.

Thanks for the info ..I'll trouble shoot your above items while I burn some funny stuff....LMAO

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Which cap blew? this might help with the diagnosis, Have you cleaned the mono, AM and FM switches? do you have 13.5v on H001/H003
What voltage do you have on transistor H305, Base and Collector and does it change when the FM signal is tuned

Voltage in ( ) are with signal

Hey RJ..Thanks For the reply...The Cap that blew was a 47MFD@50Volts (C407)
First thing I did was to repair and replace all the caps. I have a Sencore LC102 and most all were way out of spec @ 80% + -20% not to mention that were shorted or the ESR was very Super high along with Dielectric Absorption.

Then I cleaned and checked all function switches. I use Caig DeOxit D5 which I have used for years on contacts on the large format Yamaha Audio live sound Mixers.

I am Printing all your replies and will go back and check what you have suggested.

This is a Fantastic site!!!!! With Experts like you here I hope I can find this problem. I want to let you all know that have replied to my thread that Ireally apricate it. I'll keep you posted on my hunt.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

OK let me run this buy you gentleman... Look at C405 in the power supply 330 UF @ 50V.
The top side of the circuit board is marked C405 with a Plus and - symbol on the board indicating how to replace the cap for correct polarity Even the Pictorial View shows the same.

Here's the rub.... When I replaced that cap with the correct polarity placement.... It exploded!!!.. This is when I first was replacing all the caps. Ok??? I reversed the placement polarity and it worked fine with a New cap. Then I checked again and thought maybe they marked the cap wrong with the covering...But the long lead was the pos and it was correct.

That + rail has a Aproxx -30 Volts on it. Did Marantz Mark the board wrong and the Skids.
Or did I make some kind of stupid mistake and or analyze it wrong?

[petehall347]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

look on audiokarma there is a list of schematic and silkscreen mistakes for marantz

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

look on audiokarma there is a list of schematic and silkscreen mistakes for marantz

Good call ..Thanks.... I'll shoot over later Thank You.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Which cap blew? this might help with the diagnosis, Have you cleaned the mono, AM and FM switches? do you have 13.5v on H001/H003
What voltage do you have on transistor H305, Base and Collector and does it change when the FM signal is tuned

Voltage in ( ) are with signal

Ok RJ...Here's the skinny.

H001 is right on +- a few 10ths.... My unit has the 2SD315 which is called H001....... H003 Is a BZ140 which is not there or on the unit

Now Transistor H305 Base and collector are as follows..

Collector is 12.5 Volts DC ..... Base is "0" Volts. those are not the ( ) Volts..Stereo..?? The ( ) Volts Are (Collector 0.16 v) Base (0.8V)

Now Redwire said to Check H303...

Collector read is 3.40 () shows (0.13 V)

Base is Read .051 () Shows (0.7)

So something has turned off the stereo No ?/Yes?

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

look on audiokarma there is a list of schematic and silkscreen mistakes for marantz

Hey Pete jumped over to Audiokarma. Man!!! you are right ..a bunch of listings for mistakes on ever thing. I'll disregard that silk screen "+" mark. When you blow up two caps it's gotta to be wrong. Thanks Again for the heads up.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Just received some new transistors for this 120... Maybe I'll just start swapping them out

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Ok RJ...Here's the skinny.

H001 is right on +- a few 10ths.... My unit has the 2SD315 which is called H001....... H003 Is a BZ140 which is not there or on the unit

Now Transistor H305 Base and collector are as follows..

Collector is 12.5 Volts DC ..... Base is "0" Volts. those are not the ( ) Volts..Stereo..?? The ( ) Volts Are (Collector 0.16 v) Base (0.8V)

Now Redwire said to Check H303...

Collector read is 3.40 () shows (0.13 V)

Base is Read .051 () Shows (0.7)

So something has turned off the stereo No ?/Yes?

That measurement was on a station or not? H303 is OFF which means it's in mono (muting) - power is shut off to the MPX section at H302.

If it was on a station at that time, then work backwards at J305/H306-base which needs to be on at 0.7V (I think) and if not then it's a problem with the muting thresholds which is a bit complicated on the P550 board.

Don't just blindly swap out transistors because they affect the alignment and calibration, and nobody wants to redo that, it can make it worse. I prefer to track it down to the problem even though that takes more time and patience.

Exploding C405 is the -45V rail, check H003/C001 100uF 25V are OK. I don't know what that little section does. Check H406 36V regulator output is OK as well.
Just looking for after-effects due to C405 poppen corken.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

That measurement was on a station or not? H303 is OFF which means it's in mono (muting) - power is shut off to the MPX section at H302.

If it was on a station at that time, then work backwards at J305/H306-base which needs to be on at 0.7V (I think) and if not then it's a problem with the muting thresholds which is a bit complicated on the P550 board.

Don't just blindly swap out transistors because they affect the alignment and calibration, and nobody wants to redo that, it can make it worse. I prefer to track it down to the problem even though that takes more time and patience.

Exploding C405 is the -45V rail, check H003/C001 100uF 25V are OK. I don't know what that little section does. Check H406 36V regulator output is OK as well.
Just looking for after-effects due to C405 poppen corken.

Thanks Redwire....

I'll go back and check all. I'm like you I want to know what failed.. It's like solving a murder mystery. "Who Done it"

I never checked H003 the (BZ140) Diode....or the C001 (100UF @25 Volts.) I might of had tunnel vision and looked passed them. Thanks.

The exploding cap thing is due to a silk screen mess up by Marantz. Found that out from Petehall 347. Checked Audiokarma and there is a list of FU's by Marantz on there. The board is marked wrong. Polarity marking is reversed on the board.

I think I checked H406 and it was Ok but I'll go back and check it or 36 Volts.
It's kind of cool the way the transistors turn each other off and on for FM stereo. The trick is understanding MPX Circuits.

Thanks Again For your help. I'll keep all posted on your target area's.

Regards: Mark R

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Ok RedWire...update. Finally found H003 and C001 100@25 Volts. They were hidden on a terminal strip nowhere near the PS Board. The H003 is good .. both the 1.5K Ohm resistors are good and the 150 Ohm is good. The Cap showed Leak on the Sencore LC 102.

So I replaced the cap with 35 Volt in stead of 25 Volt. Still had the -45 skid reading which is actully -43 Volts taking into the age and spec given at the time. Who knows how accurate it was.

Taking a break for a cigar and will Trouble Shoot the rest per your last post. Thanks again for the help.

Regards: Mark R

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

That measurement was on a station or not? H303 is OFF which means it's in mono (muting) - power is shut off to the MPX section at H302.

If it was on a station at that time, then work backwards at J305/H306-base which needs to be on at 0.7V (I think) and if not then it's a problem with the muting thresholds which is a bit complicated on the P550 board.

Don't just blindly swap out transistors because they affect the alignment and calibration, and nobody wants to redo that, it can make it worse. I prefer to track it down to the problem even though that takes more time and patience.

Exploding C405 is the -45V rail, check H003/C001 100uF 25V are OK. I don't know what that little section does. Check H406 36V regulator output is OK as well.
Just looking for after-effects due to C405 poppen corken.

That measurement was on a station or not? H303 is OFF which means it's in mono (muting) - power is shut off to the MPX section at H302.

Hey Redwire,
Here's an up date.. H303 Base. .026 V Emitter..011V Collector... .853 V

J305 Which feeds the base of H306 is .026 Volts. Which lead me back to P550. I checked all components on that board and they all checked ok. Replaced the two Caps 10UF @16 with 25 Volt-ers. There should be .............. 0.1 Volts No stereo and (0.6)Volts stereo @ H306

I have an audio signal on the scope at certain points and places on the transistors.
Also... Where is a good place on this circuit to pick up 19 Kkz and 38 Khz?

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I need a coffee before diving into this lol.
Your H303 is off (no base drive=mono), although the collector voltage should be higher than 0.853V, schematic says 3.9V when H303 is off. C324 might be leaky or H302 open E-B.

How it works.. H306 ON (+ve voltage at J305, signal strength is good), turns OFF H307, which turns ON H303 to enable the MPX amp H302 = FM Stereo decode.
Reversed: H306 OFF (no voltage at J305), turns ON H307, which turns OFF H303 to disable the MPX amp H302 = FM mono.

So I'm not seeing the FM Stereo enable to the MPX. Then we'd go back to the P550 board.
I would try tuning off and on a station, while looking at signal strength voltage at H559-C, I think that is what is going on there.

Does H305/J307 turn on the FM Stereo lamps (two are in series)?
You would look for 19kHz at H302-C, 38kHz at H304-C but only if the MPX is enabled in the first place. If will be dead with no Stereo mode on at J305.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I need a coffee before diving into this lol.
Your H303 is off (no base drive=mono), although the collector voltage should be higher than 0.853V, schematic says 3.9V when H303 is off. C324 might be leaky or H302 open E-B.

How it works.. H306 ON (+ve voltage at J305, signal strength is good), turns OFF H307, which turns ON H303 to enable the MPX amp H302 = FM Stereo decode.
Reversed: H306 OFF (no voltage at J305), turns ON H307, which turns OFF H303 to disable the MPX amp H302 = FM mono.

So I'm not seeing the FM Stereo enable to the MPX. Then we'd go back to the P550 board.
I would try tuning off and on a station, while looking at signal strength voltage at H559-C, I think that is what is going on there.

Does H305/J307 turn on the FM Stereo lamps (two are in series)?
You would look for 19kHz at H302-C, 38kHz at H304-C but only if the MPX is enabled in the first place. If will be dead with no Stereo mode on at J305.

You need a cup of Coffee????? !!! ..L.O.L.
I need some JD!!!!!!! This is like "Who's On First"

Getting ready to check out your above task's... The tools are closing in on me...I'm running out of room on the bench..LMAO. It's a good thing that the MPX board is like the trunk of your car and works in reverse. I must have folded it up and down a 100 times.

In fact ... I boke some of the lower underboard wiring lose from there terminals an lost FM. But I'm back in the game again, ready for another round. I swear ..I'll never work on another Tuner again...L.O.L.

Now if you'll excuse me...I have to make some room on the bench...The tools are getting ticked off at me and closing in.

I'll let you know what I find.