Looking for someone to do an alignment on a Marantz 2240

[GreggT]

Looking for someone to do an alignment on a Marantz 2240, paid fee.
I do not have access to the necessary equipment. (SG & Freq. counter)
The radio has been re-capped with the voltage settings, set. Works fine, except,
no stereo light when tuned to a strong FM station. (Stereo bi-pin lamp is good)
AM & FM dial setting are off a bit. (971. is at roughly at 96.7, etc.)
AM, FM, and MPX alignment needed.
Prefer someone with equipment that has done this a few times.

 

[Steven Tate]

Alignment is only one of the possible reasons for no stereo light. Inadequate antenna or connections, dirty tuning cap, input select, mono or muting push switches, power to any of the tuner boards, a broken wire between boards, or a failed component on any of the tuner boards can cause a no stereo condition. It just needs a good diagnosis. When you run the dial pointer across the dial, does the signal strength meter move significantly or barely move at all?

 

[GreggT]

Thanks for the reply!
I have read the posts on this subject. I have checked R322 and the trace to pin 6 of the HA1156W chip. All good.
I did not want to adjust any trimmers or coils without a signal generator.
So, after reading your post, I thought to myself, this thing is off and a very tiny adjustment cannot make it any worse.
Well, I did do a very small adjustment of the FM Oscillator trimmer on the main tuning capacitor.
I knew one of the FM related trimmers would be responsible for adjusting the position of the dial pointer
with respect to the tuned in FM radio station. Well, this one did just that. So, the dial pointer now aligns pretty close to the frequency of
the FM radio station on the dial. I tried the small adjustment of L201 as one post suggested, no effect. Then, I thought I would try the R311 pot on
the MPX board again, which had no effect with respect to the stereo light with my initial adjustment.
I moved it slightly either way and I thought I heard a small crackle. I moved it back the other direction
and I saw the stereo light flicker. I tried again very, very slowly and the stereo light lit and you could hear it was in stereo.
The only issue is it is so hypersensitive to adjust. I listened for a while and it lost the stereo signal again. I barely touched
R311 and stereo lamp came back on. Then, after a while, it dropped out again. I am wondering if there is a resistor associated
with R311 that may have changed value over time making this adjustment hyper sensitive. I checked the schematic and R312 a 16K resistor in series with R311. I checked it and that resistor is well within tolerance. So, I wonder if the actual R311 pot is bad/intermittent?
Maybe I should re-solder that pot and see if that helps. R311 is a 5K trim pot. I could put a 5K 10 turn Bourns trim pot in its place and see if that helps.
I am not sure if R311 is supposed to be so sensitive of an adjustment. I guess I will see what your opinion is and what other posts come in after this post.

 

[Steven Tate]

It certainly could be a problem with R311. If it were mine, and I had a 5k trim pot, I would change it to rule it out. H303 is an important component in the unit turning on the stereo light. It is a switch that is on or off depending on base voltage, which is dependent on signal strength. If the signal is too weak for stereo operation, the base of H303 will be around 0.6V and be turned on, grounding pin 8 of the IC and preventing stereo condition, including the light. If the signal is strong enough for stereo, the base of H303 should be close to 0V, turning it off, removing the ground from pin 8 on the IC, and allowing stereo operation, including the light. First, it is important to know if the signal strength meter moves quite a bit while tuning stations or if it nearly stationary. If it is mostly stationary, you have a problem in the front end or IF amp (or antenna problem). If it moves quite a bit, then measure base voltage of H303 on a strong station and between stations. It should be 0.6V between stations, and near 0 on strong stations. I'm betting the voltage is staying near 0.6V regardless of station strength. If so, have to find out why.

 

[GreggT]

Yes, the radio station is the local Public Radio Classical station.
The signal strength meter is almost at the top of the scale, very strong.

I am going to change R311, the pot. I have a Digi-Key order coming that coincidentally has a couple
of Bourns 5K 10-turn trim pots. I think it is the pot. The station is in stereo and then after a while it flutters and loses stereo.
The minute I barely touch my finger to the top of the trim pot, R311, the stereo light comes back on strong.
My speculation....the small horseshoe shaped piece of resistive material inside the R311 trim pot that the wiper travels on may have a small crack
right at the spot where the wiper needs to be to produce the stereo signal. I also thought about R312, the 16K resistor in series with the trim pot.
These two series resistors (R311 & R312) are shunted by a 470pf a capacitor. I wondered if that capacitor might be leaky.
It is a "film" cap and they usually are not an issue. I guess I will replace the trim pot first. I have already reheated the trim pot's three
solder connections on the PCB to make sure they were not "cold". It made a little bit of improvement as it holds stereo longer, now.
Not sure how the current trim pot is internally constructed with respect to the connections at either end of the small horseshoe shaped piece of resistive
material. I am not sure if these connections are soldered or pressed in place on each end that resistive material.
After heating the three connections on the trim pot, it does seem to be a bit more stable, holding stereo, until I physically move the radio around.

It still may need to be aligned. When I have the station tuned in (discriminator meter centered ) and then turn the radio off to attend to
something else and come back later, the discriminator meter is off to the right a bit, not perfectly tuned in (centered), when powered back ON.
However, if I leave it there without adjusting the tuning knob, after a few minutes the discriminator meter will almost center itself, like a warm-up period. I have other Marantz receivers and they do not do this, Once the discriminator meter is centered, it is still centered even after being off overnight. So, not sure on that issue.

Another thing, if I hold the right and left corners of the radio and lift it up just a little and gently flex (twist) the receiver front panel it pops in and out of stereo.
I first thought...gee, a partially broken PCB trace??? Again, I guess I will replace the trim pot and go from there with more physical tests to verify reliability
after re-capping.

 

[GreggT]

I just received my order from Digi-Key. I got a number of items including some Bourns 5K and 10K 10-turn trim pots.
I just replaced the original R311, a 5K single turn trim pot, on the Marantz 2240 MPX P300 board with one of the new Bourns 10-turn pots.
Gee, now on even a low level signal strength station, I have FULL, strong stereo. No more flutter or dropping out.
I adjusted the 10 turn pot and found the high-low window of operation for stereo. I set the pot for the center spot of that window.

There is a series resistor, R312 (16K), and a 470pF film capacitor that shuts both R311 & R312. As soon as the other items arrive, I will replace
the 16K with a 1% metal film resistor and the film cap with a new WIMA 470pF. That should take care of the no stereo/no stereo light well into the
future. I will probably still get the radio re-aligned for maximum sensitivity and correct dial accuracy.

 

[ssouci]

I am going to change R311, the pot. I have a Digi-Key order coming that coincidentally has a couple
of Bourns 5K 10-turn trim pots. I think it is the pot.

hi GreggT, I have the exact same problem as you!

Q1: was it ONLY the R311 pot that fixed the problem, or also the connected resistors and capacitor?

Q2: do you have a Digikey P/N for the best pot to use here?

thanks