Marantz Model 120 Tuner Craziness I am Stumped!

[petehall347]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

things to try here .. put cover back on if its off .. try a different antenna or move the present one . then there is the pot that was adjusted . if all that fails i seem to remember a pot that can be adjusted without test equipment . i never really got into fm much . all my builds were am along with factory built stuff that i could align no problem without sig gens .

[Mark R]

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).

Gheeeeeeeeeez. Never noticed the other Skid... Mine is Serial # 1077 which means I was on the wrong Skid.

And it is torcher. I have blown up the skids and did a Print screen and taped the two large blow ups together. I'll have to go back and check the bottom skid. .. But your correct... it's hard to do this over the web. And, I think you are correct..it something with P300. It's a weak FM MPX signal.

You have to tune up or down to find the sweet spot to keep the lamp lit. It is hitting all stations. The FM in Mono is clear so it has to be the MPX or the muting screwing up.

And just to add Fuel to the fire.. I picked up a Marantz 150... which works ok ..( Haven't received it yet) but it wont tune MPX stereo stations. That has two IC's in the MPX board. That should be easy to locate I hope.

I bought it because it was Cheap and physically in good shape. I like to be challenged for the next two years ..L.O.L. I guess I'm a in to punishing myself.

Take a look at the skids for it and look in the MPX section Two IC's.

I'll keep you posted. Thanks for catching the two skid thing.

Best Regards: Mark

Skid below in PDF. Also look at page 4 after the MPX skid notice the output for the lamp driver off the IC.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

things to try here .. put cover back on if its off .. try a different antenna or move the present one . then there is the pot that was adjusted . if all that fails i seem to remember a pot that can be adjusted without test equipment . i never really got into fm much . all my builds were am along with factory built stuff that i could align no problem without sig gens .

Thanks Pete. I have two twin lead 300 ohm FM antennas. One is in my garage with the Marantz 4240 and I have the other one on the bench with the Marantz 120 were working on. It is strung out like the Letter "T" Dipole style.

You say..

"then there is the pot that was adjusted"

Which pot are you talking about? And what other pot are you speaking about for adjustment without test equipment?

I haven't tried putting the case back on but at this point I'm ready to try anything.....L.O.L.

As stated ...FM Mono works ok so Me and Rewire thinks it's in the MPX board or something to do with Muting circuit.

In all the year's I have been wrenching on electronics... I never ran up against an FM Stereo Problem.

I get request to work on gear which I do but Tuners are a B_ _ _H.

Thanks for the reply. It's nice to speak with Tech's like you guys and this is a Great forum...

[petehall347]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Thanks Pete. I have two twin lead 300 ohm FM antennas. One is in my garage with the Marantz 4240 and I have the other one on the bench with the Marantz 120 were working on. It is strung out like the Letter "T" Dipole style.

You say.. Which pot are you talking about? And what other pot are you speaking about for adjustment without test equipment?

I haven't tried putting the case back on but at this point I'm ready to try anything.....L.O.L.

As stated ...FM Mono works ok so Me and Rewire thinks it's in the MPX board or something to do with Muting circuit.

In all the year's I have been wrenching on electronics... I never ran up against an FM Stereo Problem.

I get request to work on gear which I do but Tuners are a B_ _ _H.

Thanks for the reply. It's nice to speak with Tech's like you guys and this is a Great forum...

https://www.badcaps.net/forum/showpo...0&postcount=22

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

https://www.badcaps.net/forum/showpo...0&postcount=22

Thanks Pete:
Will check that out. I think I already tweaked that pot but I'll go back and look at it again.

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

The Model 150 similar bits and pieces as the 120 in the basic tuner design. Just the 150 uses IC's a lot. And even worse on the following wires around schematic torture. A coloured highlighter helps or markups in a picture editor.

First step is the power supply voltages.
Second step is to ID the section or signal that is malfunctioning.
An educated guess, i.e. P300 board can help then take voltage measurements on the transistors on/off station, mono, stereo etc. and look for trouble.

I leave alignment/calibration alone unless I'm trying to force something to work by diddling a trimpot. I mark where they were at with felt pen, or a related voltage first, so I can turn them back to where they were.

I have a 2252B to recap as a winter project. I was going to make custom dial lamp LED replacements for the fuse-lamps. I'd bought some off eBay but they were nowhere close in light quality to how she looked brand new.

[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:
Quote:
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.

Here's what I got...J305 is .025 to chassis ground

...........................H306 Collector is .429 To Chassis Ground

...........................H307 Base is .067 to chassis Ground

............................J303 is good @ 12.70 Vo,ts to chassis ground

H552 Base .581 To Chassis Ground

" Collector .069 Volts to chassis ground.

" Emitter O Volts to Chassis Ground.

I can't get to the cap C559 "Disc" o.1uf as I'd have to do major work to remove the board to gain access to the back to unsolder. The leads are flush into the top board and coated. If you think I have to go there let me know.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

The Model 150 similar bits and pieces as the 120 in the basic tuner design. Just the 150 uses IC's a lot. And even worse on the following wires around schematic torture. A coloured highlighter helps or markups in a picture editor.

First step is the power supply voltages.
Second step is to ID the section or signal that is malfunctioning.
An educated guess, i.e. P300 board can help then take voltage measurements on the transistors on/off station, mono, stereo etc. and look for trouble.

I leave alignment/calibration alone unless I'm trying to force something to work by diddling a trim-pot. I mark where they were at with felt pen, or a related voltage first, so I can turn them back to where they were.

I have a 2252B to recap as a winter project. I was going to make custom dial lamp LED replacements for the fuse-lamps. I'd bought some off eBay but they were nowhere close in light quality to how she looked brand new.

Yep First thing is not to mess with alignment. As you say I always head to PS First thing Then it's the P300 Board.

The 2252 is a nice unit. I've recapped many Marantz's. Big improvement. I do use the color tool in the PDF with the help of "Paint ..Microsoft" by blowing up the section and having Paint in printer set up do the whole page. It prints out both Half's and then I trim and put them together with tape. Makes it allot easier.

BTW. That Skid at the bottom for the 120 does not list voltages. Also "J304" Is no longer a Junction metal terminal on P300. They run that line from P550 board "J555" directly to the board and call it "J304" which is a slotted solder land on the underside of the board.

Other then that the skids look the same.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I think I'm ready for one of these..

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

Petthall and Redwire thanks for your help. Gonna side line this 120 unit for a while and move on to other projects. Got a line on a Sencore SG-80. So if the price is right I'll pick it up and fark around some more.

On an another note....I did pick up a Marantz 150 tuner used cheap in great shape. Seems original. It's back in my All Marantz separates system.

Again I'd like to thank Redwire, Petehall and Badcaps web site for your excellent help and time.

I haven't given up yet on the 120

Best Regards: Mark

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

It's not easy troubleshooting a tuner made with discretes (especially the MPX) and without RF test equipment. I'd still give it a try to measure DC voltages on the transistors to narrow down the section misbehaving.
I'm not sure how Marantz (Japanese) transistors do with age. I see recap kits on eBay that include new small transistors. Gees the old Marantz go for a small fortune now, the 2252b recap kit is $170. OUCH.

The next gen tuner 150 changed over to IC's, which is way easier to troubleshoot.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

It's not easy troubleshooting a tuner made with discretes (especially the MPX) and without RF test equipment. I'd still give it a try to measure DC voltages on the transistors to narrow down the section misbehaving.
I'm not sure how Marantz (Japanese) transistors do with age. I see recap kits on eBay that include new small transistors. Gees the old Marantz go for a small fortune now, the 2252b recap kit is $170. OUCH.

The next gen tuner 150 changed over to IC's, which is way easier to troubleshoot.

I did pick up a 150 and also bought the MPX IC's. The original ones form Hitachi
I put them in my stock. I found one guy that wants $300.00 to do an alignment. Not gonna happen. You can't even talk to him on the phone. You send him an email and a week later he answers. That's how busy he is. He only does retro gear.

I found a Local guy that has some one that will do the alignment cheaper and has the proper equipment. He works for a Local repair shop two days a week. Waiting on a call from him this week.

The 120 tunes mono with no problem and flickers the Stereo lamp and one station locks it on but is slightly distorted. So I thing it's just alignment at this point. Before the caps blew out in the PS it always worked ok.

So I'm going with just the alignment. Every Voltage test point on the MPX board has transistors turned on or off per the skid. Also the P550 board is the same.

All the transistors range out ok on my B&K transistor tester in circuit. Where I'm located there are very few FM stereo stations that are strong using a 300 ohm Dipole. I just picked up and outside or attic FM 75 ohm antenna. I'll mess with that later.

https://www.amazon.com/Stellar-Labs-...%2C175&sr=8-14

Also if you look at the last skid on the PDF (That's My Unit) and look at P500 Bard(on Top under shielding) you will see IC H501 IC. That's tied into this mess also.

Anyway ..It's time to move on. If I had the RF equipment I'd give it a shot at alignment.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I found one guy that wants $300.00 to do an alignment. Not gonna happen.

That would be the Marantz 120.

[redwire]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I find alignment does not drift that far out and I leave it as a last check. The distortion reminds me of a bad transistor or JFET, so I would expect no amount of alignment will cover for that...
Because the problem showed up after the cap popped? I'd suspect the problem is maybe related or a consequence of the recapping and more bad board silkscreen markings.
I take a lot of pictures and then felt pen mark as well when changing caps, still screw up if the phone rings and I get distracted.

[Mark R]

Re: Marantz Model 120 Tuner Craziness I am Stumped!

I find alignment does not drift that far out and I leave it as a last check. The distortion reminds me of a bad transistor or JFET, so I would expect no amount of alignment will cover for that...
Because the problem showed up after the cap popped? I'd suspect the problem is maybe related or a consequence of the recapping and more bad board silkscreen markings.
I take a lot of pictures and then felt pen mark as well when changing caps, still screw up if the phone rings and I get distracted.

Well I rang out the only JFET in the MPX circuit with the B&K. It was in circuit and tested good. Also the correct voltages are there at Drain Source and Gate.

As far as the silk screen thang ..only one cap was marked wrong. It blew up the moment installed it according to the silk screen (+) marking.

As I removed each cap one by one I made note of the (+) marking. I also tested each one out of circuit with the LC102. Then Test the new one to be installed.

So one by one tested removed and then test new installed I made my way thru. Yesterday I got my new Amazon Loop FM antenna ...(75 Ohm) feed down to a 75-300 Ohm Balum to the 300 ohm input on the 120.

I managed to get one local station to lock on solid in stereo with the lamp lit. However it was just so slightly distorted.

So..you might be correct...Maybe there is something leaking and farking up the MPX. The PS board however is screened correctly except for that one error for that one cap. And Also The MPX board which had it's caps changed.


Also remember that the unit was dead and only lit up. The PS had gone south that runs the AM/FM section. All I did was recap everything as it needed to be done.

So....My motto is....Just throw money at it till it's fixed. If this tech can do an alignment and get it working.....that'll be good. If it doesn't work then I'll be back at it trying to find the villain...which could be what you said.. A Sleepy JFET.