2245 - FM Stereo, but No Stereo Light

[Flip69]

I have found several threads that address stereo light issues. However, I have not found any clear answer to this situation. I am finishing up work on a 2245. The stereo light bulb is good. It comes on as it should in phono, aux, etc. It does not come on in FM. The FM alignment is definitely off a bit, e.g., 101.3 tunes in at closer to 100.3 on the dial. I do get stereo FM. That is clear when turning mono on and off. The meters seem to be working fine. However, the stereo light does not come on, even when tuned to the strongest stations.

I have an oscilloscope. However, I do not have the other gear I would need to attempt an alignment, even if I were inclined to do so (FM signal generator, etc.). I have not checked to see if someone in my area does alignments. Could bad alignment cause this problem? It seems like the issue would be signal strength, not whether the needle lines up to the right number on the dial. Different threads have referenced different adjustment to different trimmers, but nothing definitive. I have seen references to using compressed air to blow dust off the fins. At least one thread suggested that some models have a chip that plays a role in stereo light operation. Not sure if the 2245 is one of them.

How do I troubleshoot this? I don't want to simply start messing randomly with trimmers. It is not a huge deal, since everything else seems to be working as it should, including FM stereo. However, given all the other work I have done, It would be nice to get this working, if possible.

 

[wurlyman]

If it's working on everything else I would bet on a cold solder joint on the selector switch. Any one else agree on that?

 

[Steven Tate]

Here is a recent thread discussing this problem and embedded in the thread is a link to another thread with extensive discussion. These threads will be a good starting point for diagnosis.
Steve

http://audiokarma.org/forums/index....ght-problems-on-my-2245.793311/#post-10964244

 

[zebulon1]

Probe for voltage (mV's) on pin J563 of board P550 while tuning in stations and report what you observe.

 

[rBuckner]

I think it still could be an incorrect bulb even though it lights on the other functions. More likely is a dirty selector rotary switch. Try some DeOxit D5 on that baby first.

 

[Flip69]

Followed up on some of the replies. The bulb is leftover from a 2270 bulb replacement kit I purchased from eBay or another site. I have checked, and the bulbs should be the same for the 2245. I cleaned the rotary selector switch. No light. I had trouble getting a good solder connection when I installed it. However, since it works in the other positions, it does not make sens to me that there could still be a solder issue that only affects the FM indicator setting. Am I wrong?

I checked the voltage at J563. When tuned in to a good strong station, the reading locks in at .61 V DC. Between stations, the reading ranges from 15 to 35 mV DC.

When I run through the dial, I can hear pretty clearly when a station locks into stereo. It is definitely working. Just no light. I can live with that. I am not inclined to start messing with trimmers and risk making things worse unless there is a real clear indication of what might be wrong and how to fix it.

As I have scrutinized the tuning function, I have noticed two other things. If you think I should start another thread, just let me know.

First, the pointer is off by about one inch (about 1 number in FM and 100 in AM). This is equally true in AM and FM. When this has come up in other threads, the suggestion has been to simply re-position the pointer. I am not sure how to do that. The pointer appears to be glued to the string. The string runs through two slots, with a knob in-between, on the pointer assembly. There appears to be a drop of dried brown glue covering the string in each slot. I would have to try to carefully remove the glue in order to re-position the pointer. Is that in fact what I need to do?

Second, there is a spot where the string is frayed. There is only a thin strand still holding things together. This weak spot travels around one of the pulleys as you tune the unit. I dread the thought of a re-string. However, I do not think it would take much at all for the string to break. Does anyone have any thoughts or suggestions about this? I have thought about possible ways to repair or reinforce the string at that spot. However, the fact that this portion of the string travels around a pulley makes it more difficult.

 

[bluehills5]

I'm following this with interest as I have a 2270 on the bench now with identical issue with the stereo light. It uses the same P550 board and I get a very similar reading on J563. I swapped the bulbs to LED but the issue is the same with either lamp type.

 

[Steven Tate]

I have moved the dial on the string several times. A little tedious, but not that hard. Multiple applications of 91% isopropyl alcohol will slowly soften the brown glue. I use a metal scribe to slowly remove the glue from the slot and string in layers. Once the string can be lifted from the slot, I tune to a known good station near the center of the dial and slide the pointer to the proper position. A drop of wood glue on each slot will harden and keep the pointer positioned. I might say, I haven't moved one a full inch -- maybe a half inch. But I don't know why it wouldn't work.

 

[zebulon1]

The stereo indication function is working, well at least it should be working. The tuner is doing it's job, the rest of the circuit is at question.
The receiver doesn't use the PA1001A Stereo Decoder chip like other sets use, so it has a slightly complicated circuit.

 

[Joshstereo]

If your feeling a bit adventurous you could try to align the tuning needle the proper way. Its really very easy. Just tune to the lowest station that comes in with a strong signal. For me its 92.5 and then adjust coil L104. Its good to have another working tuner to help you identify your on the correct station. So if 92.5 comes in at 93.5 put the needle at 93.5 then slowly adjust L104 by 1mm at a time, youll notice the station has either moved left or right and keep adjust the needle then L104 till it sits at 92.5. Once thats lined up correctly check all the stations on the dial to see if they come in where they should. The ones on the higher end around 105 or 106 may still be off in which case youll want to do the same thing on that end but adjust with capacitor C106. Then as per the manual go back and forth till theyre all lined up. If your comfortable doing this then there are a couple of things you can try to adjust to get the stereo light to come on.

 

[bluehills5]

Not trying to hijack this thread but this may help others trying to troubleshoot the stereo light issue on the 2245/2270 tuners. Following the links posted above, Tom (catrafter) says:

If the station is properly tuned, not noisy and the signal strength is high enough,
H306 is ON, SS OK
H307 is OFF, SS OK AND
H552 is OFF, Noise is OK AND
H560 is OFF Tuning centered AND
H561 is OFF Tuning centered
If SS, Noise and center tuning OK then:
H308 is ON allowing audio signal to pass to the center tap of the 38kHz transformer.
H302, 19kHz amplifier is enabled by H303.
If the 19kHz pilot is present from the broadcast station, then it is doubled to 38kHz by H304 and if of sufficient amplitude to decode stereo, H305 turns on causing the stereo lamp to illuminate.

So on mine I checked the base of H305 and when tuned into a clear FM stereo signal it goes from 0 to 2.5v which looks (to me) like the logic I copied above is functioning. H305 collector is pin J307 but it shows 10.5v regardless of station status and across the 2 lamps I always see about 2v. From what I see, J307 goes to the input selector then through the 2 mono switches and then to the lamps. I checked continuity through mono switches when they are latched and it looks good so there. So should J307 drop to 0v when FM signal is stereo which will put 12v across the lamps and light them? Does this mean my H305 is toast? this is p/n 2SC372 transistor

 

[bluehills5]

I replaced H305 with a 2SC1815 and bingo! Stereo light comes on strong and works perfect. Not sure if OP is still after a solution but pin J307 is worth checking to see if it is functioning correctly.

 

[zebulon1]

Awesome!
I don't have the set here in the shop so I couldn't check on my own.
Excellent post!

 

[bluehills5]

Just to clarify some more as I've looked at this circuit a bit closer now it is working. J307 will drop to 0v (or close enough) when in stereo. This is easy to check as you do not need to remove anything except the dial string cover. Mine shows about 10.5v when NOT in stereo. As the stereo lamps have 12v on one side always, dropping to 0 will complete the circuit and light the lamps.
So check pin J307 first. Then if it not working, start with the base of H305 and go backwards using the flow as posted from catcrafter above (see the link for more details) but you will need to remove AM board to get access to P300 FM board below.
If J307 DOES drop to 0v when tuned to stereo, then the issue is between J307 and the lamps. Trace the grey wire (at least grey on mine) from J307 to the selector. From the selector it goes through the 2 mono switches then to the lamps. On mine I have continuity between J307 and the left side of the lamps (see pic). Switching away from FM or the left mono switch will break continuity. Check for bad solder or a dirty selector or dirty or broken mono switches.

 

[Flip69]

Figured mine out. As is so often the case, it was something simple. The brown wire that runs to J307 had a bad connection. Could not see it until I took everything apart again and started working back through the transistors on Tom's chart. Replaced two before I noticed. Reconnected the brown wire and the FM stereo light works. Thanks to everyone for the help. Absent all of the input, I am not sure how long it would have taken me to figure out that J307 even has anything to do with the FM stereo light.

Will move the dial pointer as suggested by Steven. That should be it for this unit. Next project is a Pioneer SX-1250. Never done one before. Have been reading through the relevant AK threads in preparation. Looking forward to it.

 

[pclissold]

This thread proved to be very helpful as I fixed the Stereo OK but no Stereo light issue on my 2230. Many Thanks!