Marantz 2215B: FM mono only issue...

[kasbah512]

Im working on this unit and have followed the service manual to undo whatever i did on the tuner and i get a clean signal, however it stays mono. I made the stereo adjustments as stated with the equipment i have on hand, but i can not get stereo no mater what i do. the switches and pots are cleaned and tested for functionality, but i cant seem to fix the issue. The stereo bulb worked before i messed with it (I thought another issue was with the tuner, but it was not so i have to undo the mess). On the oscilloscope im only getting a diagonal line when set to x-y mode as proof. I set the clock to 19khz within 1 decimal place (i dont have a dedicated frequency counter so i used my scope) My signal generator doesn't specify how many volts are being output so im not sure if this is the issue. I have slowly adjusted R301 to see if there was a sweet spot, but it doesnt appear to change anything on the scope.

 

[DeadRock]

Ok...I'll ask The Dumb Questions....are you close to strong FM signals? ...are you using an antenna? I know with my 2265B...some FM signals are just not strong enough for stereo...Cheers!

 

[kasbah512]

Ok...I'll ask The Dumb Questions....are you close to strong FM signals? ...are you using an antenna? I know with my 2265B...some FM signals are just not strong enough for stereo...Cheers!

I am near some strong signals and I have an antenna. I also have a cheap signal generator that triggers stereo on other units i have on hand. Before i started making adjustments, it worked. I have a new HA1156 showing up in the mail tomorrow on the off chance that's the cause. I would want to know how to read the rotary switch schematic to see if maybe now I'm not getting continuity. The rotary switch triggers mono mode. If it was a button for mono, it would be easy, but alas it is not and has 30+ wires plugged up to it.

While the signal generator i have is mono only, i know that the radio stations near me use stereo and when i look at it on the oscilloscope i just get a diagonal line, indicating the same signal is being output from both channels

 

[DeadRock]

Hmmmmmm...???

 

[kasbah512]

I checked all the voltages on H301 (HA1156) and they are all in spec. i am getting 10v at pin 6. On the schematic it shows 10 in parentheses. Im guessing this for if the stereo lamp is engaged or not.

 

[kasbah512]

I purchased a home fm "signal generator" to play a left-right sweep off my computer, to hopefully debug this issue. Just waiting on it in the mail.

 

[kasbah512]

I realize after the IC arrived that I ordered the similar but not identical HA1156W. While in most cases im sure they are compatible, I couldn't get it to work in circuit for the 19khz pilot signal. The highest i could get it was 18.9khz. For this to work it would require modifying the circuit to adjust the timing.

 

[rBuckner]

To really adjust the 19kHz correctly you need to be applying an FM signal with no 19kHz stereo pilot tone on it which a signal generator made for servicing FM will do. If your generator that is on the way only produces the composite audio signal vs. 88-108MHz, you'll have to inject that into the stereo decoding circuitry after the IF processing stuff. With no pilot tone on of course.

That point would be at the negative end of cap C301, after it is unsoldered on that pin only and the leg pulled up.

 

[patfont]

Is the tuning dial as indicated?
If you tune in at 93.3 is that the correct station playing.

I had 2 2215B's here and they were both problematic with your same FM stereo problem.
For both of mine it was not the IC.
I will check my notes.

 

[kasbah512]

Is the tuning dial as indicated?
If you tune in at 93.3 is that the correct station playing.

I had 2 2215B's here and they were both problematic with your same FM stereo problem.
For both of mine it was not the IC.
I will check my notes.

I figured it out. It was the 19khz clock that wasn't quite aligned and my scope wasn't quite high enough resolution to align it. The rest of the alignment was pretty easy IMO, but the stereo separation was near impossible due to the accuracy needed (or a strong enough signal to slowly adjust). The little radio transmitter I bought has done wonders so far. The only down side is that i cant manually lower the FM signal output, only modulation levels.

I'm debating on modifying an antenna with a potentiometer to lower the signal voltage and connect that straight to the antenna terminals on the receiver. I can play any test-tone or sweep needed.

The reception is finicky on this receiver for me at least, even with an antenna hooked up to the wall, where as other devices pull a stereo signal without any antennas attached so this further complicated the alignment process. I ended up returning the $75 FM "signal generator" I initially purchased for the task due to its limited functionality.

To really adjust the 19kHz correctly you need to be applying an FM signal with no 19kHz stereo pilot tone on it which a signal generator made for servicing FM will do. If your generator that is on the way only produces the composite audio signal vs. 88-108MHz, you'll have to inject that into the stereo decoding circuitry after the IF processing stuff. With no pilot tone on of course.

That point would be at the negative end of cap C301, after it is unsoldered on that pin only and the leg pulled up.

With the device i purchased, im able to set the FM output to mono, thereby removing the pilot signal. I cant recall if that's exactly what i ended up doing, but its aligned. Basically i slowly turned the clock adjustment and I heard a "click" whenever it was perfectly lined up through my headphones. I believe the pocket radio transmitter was set to mono, but i was trying every combination i could think of until it worked.

 

[patfont]

Nice work, thanks for the detailed update!