Marantz 2275 - no stereo FM

ssouci

ssouci

Well-Known Member
having a problem with my Marantz 2275 receiver.....

DESCRIPTION
- FM not in stereo: receives stations well enough, but they're playing in mono, and the stereo lamp does not light up
- *however*, in a few tiny spots on the dial, I can sometimes get a shred of stereo, but extremely poor quality (noisy, unstable, weak, hard to tune)... but it's in stereo, and the stereo lamp lights up!

INFO
- the Muting function works properly, and does NOT kill the sound when activated
- the Muting Level level pot (on backside) works as it should to control muting strength... I've set it to minimum
- the stereo lamp itself is OK: it lights up in Aux/Phono/Tape, plus, works fine in the case of "shred of stereo" (described above)... lamp is a low-current LED
- confirmed: Muting button is off, Mono buttons are off
- confirmed: I'm definitely hearing mono, not stereo
- meters: both signal strength & center meters appear to work normally... signal strength approx. 75% on strong stations
- using a dipole T-antenna
- receiver was fully recapped 7 years ago

THINGS I'VE TRIED
- replaced H321 (multiplex decoder chip) with a new HA1156... no difference, put original back in
- replaced all 2SC2828S transistors with new 2SC1815s (includes: H302, H303, H308, H309, H310, H311, H313, H314, H315, H316, H317)... no difference
- Antenna / Muting Level board: removed & checked integrity, cleaned the 2 pots... no difference
- visually inspected all electrolytic caps on P300 board (all caps were replaced 7 years ago with Panasonic FC, plus some films)... all looked OK

ABNORMALITIES?
- adjusting R311 seems to have very little to zero effect... this seems surprising, and might offer a clue?... accordingly, it can't be adjusted to successfully activate stereo
- *however*, when I can get a "shred of stereo", adjusting R311 does seem to do something, and I can make stereo go on/off (within approx. 20 degrees of rotation)... the effect is minor, but it's there
- note: R311 is the MPX-OSC pot that tweaks the 19kHz signal

schematic for the P300 Multiplex board posted below

my voltage readings from the MPX Decoder chip (H321) posted below

looks like the "no stereo FM" problem is not uncommon, however my situation seems different in that the muting function does not kill the sound and seems to work properly

any help GREATLY appreciated!
 
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MY READINGS: MPX DECODER (H321 on P300 board)

* specs in (parentheses) are for stereo operation
* pin 4 spec corrected for schematic typo

PIN # -----> my reading in VDC
01 = [spec 12.7V] -----> 11.8 (OK)
02 = [spec 3.0V] -----> 3.1 (OK)
03 = [spec 5.3V] -----> 5.2 (OK)
04 = [spec 10.4V] -----> 9.0 (OK)
05 = [spec 10.4V] ----> 9.0 (OK)
06 = [spec (1.0V) 14.0V] ----> 12.0 / ~1.0 (BAD / OK) ***
07 = [spec 0.0V] ----> 0.0 (OK)
08 = [spec (2.5V) 0V] ----> 2.4 (OK)
09 = [spec 2.5V] ----> 2.4 (OK)
10 = [spec 1.8V] ----> 1.6 (OK)
11 = [spec (2.5V) 2.3V] ----> 2.4 (OK)
12 = [spec 2.5V] ----> 2.4 (OK)
13 = [spec 2.5V] ----> 2.4 (OK)
14 = [spec 3.4V] ----> 3.2 (OK)

*** pin 6 reading is normally BAD (too high for stereo spec)... however, if I can pull in a "shred of stereo" station, it becomes OK at approx. 1V (unstable), plus the stereo lamp lights up

I'm not sure if this means that H321 itself is fine and functions properly (and will activate the stereo lamp when the conditions are right) or?... TBD
 
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IMPORTANT INFO, as written/posted by Catrafter (Marantz expert on AK)

----------------------
This applies to the 2275, 2325 and probably the 2250B as well although some of the component designators are different.

FM Stereo MPX operation
IF signal strength is monitored by H308. If signal strength is above muting level, H308 is ON, H309 is OFF.
If there is excessive noise, then H311 is ON which is wire-ORed to H309 keeping H301 (FET) OFF.
If the discriminator is outputting DC due to the tuning being off station, either H314 or H315 is ON which are wire-ORed to H309 as well. This also turns H303 ON grounding Pin 8 of the decoder forcing MONO operation.
If the station is properly tuned, not noisey and the signal strength is high enough,
H308 is ON, SS OK
H309 is OFF, SS OK
H311 is OFF, Noise is OK
H314 is OFF Tuning centered
H315 is OFF Tuning centered
H317 is OFF, SS, Noise and center tuning OK then:
H301 is ON allowing audio and MPX signal to pass into the decoder.
H303 is OFF If SS sufficient for Stereo operation and MONO button is not pressed
H302 is OFF VCO runs (AM not selected)

Tom
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jd3rdcoast said:
Did you try cleaning the Tuning capacitor? Link to thread in Tuners Forum
Click to expand...
yes, did that 1-2 years ago... I blew out the fins with compressed air, used no-residue contact cleaner on the rotary contact surfaces, etc. (and finished by lubricating a few tiny spots with Dexoit Faderlube)

to be honest, the whole assembly seemed pretty clean to start with... I don't remember it making much difference in tuner performance back then
 
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I posted in your other thread and didn't see that you reported the requested voltages. Here it is again:

...Check all of the transistor bases for 0.6 or so volts: H309,311,341 and 315.

Any of these at around that voltage will kill the stereo.
 
taking fresh voltage readings for the transistors, will post them soon...
 
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MY READINGS: TRANSISTORS on P300 board

* in VDC (tuned to strong stereo station, Muting & Mono switches off)

Regular Transistors 2SC2828S, (replaced ALL with new 2SC1815)
-------- B / C / E
H302 > 0 / 3.2 / 0 ..... OFF
H303 > .03 / 2.4 / 0 ..... OFF
H308 > .61 / .07 / .01 ..... ON
H309 > .06 / 9.9 / .01 ..... OFF
H310 > 2.3 / 11.5 / 1.6 ..... OFF
H311 > 0 / 9.9 / 0 ..... OFF
H313 > .59 / .04 / 0 ..... ON
H314 > .04 / 9.9 / 0 ..... OFF
H315 > .38 / 9.9 / 0 ..... OFF
H316 > 1.3 / 11.7 / .68 ..... OFF
H317 > .64 / .04 / .01 ..... ON

FET Transistors (not replaced)
-------- D / S / G
H301 > 5.7 / 5.7 / 6.3
H312 > 11.4 / .96 / -.03


I *think* I've marked the ON/OFFs correctly?
 
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I believe that H310 is not in switching mode so won't be OFF or ON, but running. It's input is the IF signal and is a buffer and the filtered output is one of the things controlling the muting. So it looks good.

H316 is similar, running as a buffer for the signal meter level.

The transistor voltages all look good.

The pin 6 on the MPX IC H321 is for the stereo lamp. I wonder if you've gone back and tried adjusting the VCO pot R311 again? If that were off, it would be doing what it is doing as far as stereo operation. Too far off and the IC can't lock, or barely lock as you've observed. Hook on a scope to J310 if you have one and see if it changes in frequency when R311 is adjusted.
 
I just tried tweaking pot R311 again, but the behavior is still the same:

> has basically NO EFFECT for a normal strong station: I cannot get stereo to be triggered, no matter how much I rotate (I can't help but think this is weird, and thus offers a clue)

> in the few cases where I can get a "shred of stereo", yes it does do something... I'm able to barely trigger stereo (along with the stereo lamp) within a roughly 20 degree rotation zone (but those stations are very staticy, unstable, and unlistenable... I can usually locate about 1-3 of these across the tuning scale)

unfortunately, I don't have any bench equipment other than a multimeter :-(
 
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I wish!... however that's not so easy these days, with the number of qualified techs diminishing... plus, location really matters, because it's not cost-effective to ship there & back... plus, I live out on Vancouver Island, so pretty limited anything tech-wise vs. large cities... so................ I'll keep plugging away, and remain optimistic that I WILL figure this out, probably with some help from AK!... I'm sure it's just one part or connection, or one adjustment that's causing this... I refuse to believe that my otherwise super nice, rebuilt 2275 is essentially "garbage"... thanks for your help, it's really appreciated
 
a thought... I have a Marantz 2230 receiver with decently functioning FM... is there a way I could use it to help debug the issue with my 2275?... eg. somehow connect a radio signal from the 2230 and inject it (somewhere) into the 2275?

obviously, without taking apart the 2230!
 
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jd3rdcoast said:
Did you try cleaning the Tuning capacitor? Link to thread in Tuners Forum
Click to expand...
update: I was inspecting the FM front end board, and just now realized that back when I "cleaned the tuner" (1-2 years ago), I was actually cleaning the AM tuner!... easy mistake, considering the AM assembly (with fins etc.) is much bigger and more accessible than the FM... stupid me... no wonder I experienced zero difference in FM tuning performance back then!

anyway, I now have tried cleaning the FM tuner, by spraying zero-residue cleaner into the fins and the rotary contact points as best I could... it's impossible not to spray it all over (including the fins), because the assembly is locked into a metal cage, and everything is very close together

I tuned back & forth 30 times, had it rest overnight, and sadly it DID NOT FIX my problem... (if anything, it *might* have made the tuning a wee bit noisier/weaker)
 
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I'm still wondering why tweaking my R311 has such little impact... I understand that it fine-tunes the 19kHz signal

so maybe my 19kHz signal is simply too far out of whack to be *able* to be fine-tuned?

Q: how do I adjust this 19kHz signal (coarsely), if that's even possible?

I don't have the equipment to measure it, but I'm willing to try an upstream adjustment to perhaps bring into the ballpark... and then use R311 to fine-tune... my apologies if my understanding of this is laughable
 
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I’m pretty sure both AM and FM are on the same Tuning Capacitor. Small fins and large fins. Just can’t remember which at the moment. Important to get a small drop of lube back into the rotating parts and the contacts at each section ends. Can use some Deoxit F5 or other light lube on a rubber tooth pick dipped into a small amount from a bottle cap or shot glass. You should see it wick into the slots as you touch each one. Don’t put too much that will run onto the discs, that will cause problems. This lube is what will help improve the contact area and tuning.

I would not do anything with the other adjustments or you run risk of making things much worse.
 
not sure about that... here are photos that I believe show 2 separate tuning capacitors: the larger outboard one being for AM, and the smaller "caged" one being for FM... can someone confirm this please?
 

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ssouci said:
not sure about that... here are photos that I believe show 2 separate tuning capacitors: the larger outboard one being for AM, and the smaller "caged" one being for FM... can someone confirm this please?
Click to expand...
Correct! Smaller/lesser fins are for the FM.

On the 2230 you could sub the 2230's IF board output into the 2275's P300 input with a long enough piece of coax cable. That would narrow it down to the P300 board. Likewise, further back the tuner front end can be subbed into the 2275 but I believe you had good meter movement indicating the front end is strong. Now someone could have screwed with the IF can in that front end and got it out of whack!

On both I'd recommend disconnecting the 2230 cable end, don't leave it in place and just tack the "jumper" cable on.
 
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