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4230 - Another: No FM Stereo or Signal Strength Meter movement

jd3rdcoast

jd3rdcoast

Super Member
Been fighting with this 4230 trying to get the FM to output Stereo mode. Pretty typical symptoms, FM output is only in mono; Stereo beacon is good. Signal Strength Meter (SSM) stays to left. Very little Tuning meter movement. Mute button cuts the output. Seems my primary issue is no DC voltage change at the bases of H110/H111 or H112 for muting or auto-stereo operation. And very little voltage at J109 (490mV) to operate the SSM. No voltage at junction of rectifier diodes H121/H122 (check good) coming off of L108. H109-C == 14v.
I tested H103-H109 found H106 bad (see below).
Touched up a couple solder joints that were suspect. Checked the caps in circuit with an Atlas ESR70 but I may need to pull a couple that couldn't be read properly.
I cleaned the all the switch contacts with tiny cleaning swabs and Deoxit D5.
Rebuilt both amps and re-capped P800. Only found one bad 3300uf coupling cap. Several caps looked like had outgassed some but still measured good.

H114:
Pin-1 = 2.8v
Pin-2 = 0.0v w/no change w/tuning vs 0v (1.7)
Pin-3 = 0v
Pin-4 = 8.7v w/no change w/tuning vs 9.1 (10.8)
Pin-5 = 1.7v
Pin-6 = 7.2v vs (4.2v)
Pin-7 = 1.7v
Pin-8 = 7.1v vs (4.4v)
Pin-9 = 12.9v vs (9.6v)
Pin-10 = 10.1v vs (6.8v)
Pin-11 = 10.1v vs (6.8v)
Pin-12 = 3.9v
Pin-13 = 3.9v
Pin-14 = 12.6v vs (9.5v)
Pin-15 = 1.8v w/no change w/tuning vs 1.7 (1.4)

I did find one bad transistor H106 B-E is open. I moved a 2SC930C from H105 location to the H106 location and put a KSC1845 in the H105 location. My thinking was H106 seems to feed base of H109 which in turn provides DC from rectified Sub IF signal to base of H110 thru R153 for muting and Auto-Stereo and Signal Strength Meter operation. But that setup did not yield and change in operation of either of those functions.

Couple other Transistors that don't match the spec'd H103-H109 2SC930C called for in SM are:
H104 = 2SC380; TO92 pkg. Viable sub, ft 125 MHz
H107 = 2SC772B; R145 pkg. Viable sub per specs. ft 150-300 MHz in different datasheets.
H108 = 2SC829C; TO92 pkg. Viable sub. but ft only 75 MHz
H105 - KSC1845; TO92 pkg. My sub but only 50 MHz ft so may be a bad choice.

So, it seems this tuner was worked on at some point with the TO92 subs installed.

I have 10 Sanyo 2SC930's on order from BDent. Should be here in a few days. I figured I'd use them to replace the odd transistors one at a time to see if can get my DC voltage out of H109 to trigger H110 and so on. I do have a scope if need to measure any signals anyone might suggest. Any other suggestions or comments would be much appreciated. These FM Muting and Auto-Stereo circuits are the bane of my existence!!! But I am determined to not let this one beat me, hopefully with some input from some of you.


Attached is copy of circuit with values I measured:
edit - this is the schematic from 105 Tuner which is identical board part number and circuit as 4230 P100 board. This has voltages on it where the one in 4230 manual does not. So they should be close but possibly not exactly the same.
 

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Don't forget, it could just be an alignment problem. Looking for bad components won't fix it if it's out of alignment. And it sounds like it has been worked on, so who knows what the alignment situation is?
 
Steven Tate said:
Don't forget, it could just be an alignment problem. Looking for bad components won't fix it if it's out of alignment. And it sounds like it has been worked on, so who knows what the alignment situation is?
Click to expand...
Thanks Steven. I was wondering about that as another possibility. I did step through the basic adjustments without making any tweaks to make it worse. One thing I noticed when tuning to a station there is a sweet spot where the signal seems clear but then as you move to the left of that point the signal gets louder but with distortion before it drops out. As if there is a wider bandwidth then there should be. Not sure what part of allignment that would fall under, but I was wondering if that was a symptom of poor alignment or perhaps issues that were component related. (caps, resistors etc.) Since the whole board is enclosed, the tuning cap is dust free and there was no typical noise from dirty contacts when tuning, so I didn't spray it down with contact cleaner. I just added a drop of fader lube to the contact points.

Would you recommend taking the time to try and replace some of the odd transistors with the new 2SC930's I have coming?
 
One value that stands out is at H106 emitter is showing 0 vdc instead of 2.9. So not showing diode drop from the base voltage. I would expect it to be apx 3.4 vdc if base is measuring 4.1. I may look closer at C129 (10uf/16v) and the cap/resistor combo G103. Not sure what the function of those components are or what effect they have if go wonky.

upload_2022-3-7_23-5-29.png
 
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jd3rdcoast said:
Thanks Steven. I was wondering about that as another possibility. I did step through the basic adjustments without making any tweaks to make it worse. One thing I noticed when tuning to a station there is a sweet spot where the signal seems clear but then as you move to the left of that point the signal gets louder but with distortion before it drops out. As if there is a wider bandwidth then there should be. Not sure what part of alignment that would fall under, but I was wondering if that was a symptom of poor alignment or perhaps issues that were component related. (caps, resistors etc.) Since the whole board is enclosed, the tuning cap is dust free and there was no typical noise from dirty contacts when tuning, so I didn't spray it down with contact cleaner. I just added a drop of fader lube to the contact points.

Would you recommend taking the time to try and replace some of the odd transistors with the new 2SC930's I have coming?
Click to expand...
Sure. If you can't find any other problems. My own warped way of dealing with changing transistors as a shot in the dark on tuners is to change one, try it, and if it doesn't help, put the old one back (unless it is an exact replacement). I don't know if that's the best policy, but if I keep changing transistors, the gremlin in the back of my head wonders if I am piling up spec differences that make a difference on their own and make it more difficult to diagnose.

jd3rdcoast said:
One value that stands out is at H106 emitter is showing 0 vdc instead of 2.9. So not showing diode drop from the base voltage. I would expect it to be apx 3.4 vdc if base is measuring 4.1. I may look closer at C129 (10uf/16v) and the cap/resistor combo G103. Not sure what the function of those components are or if would what effect they have if go wonky.

View attachment 2506297
Click to expand...
I would absolutely pull, test and try replacement of H106. Also, I can't help but wonder about that G103 - cap and resistor in parallel - and wonder if that could prevent current flow through H106 if bad. I'm not exactly sure how to test it though, since I think its main effect would be on AC. I would at least check it for continuity and make sure it is not open. AC and DC should pass through the resistor, but only AC should pass through the capacitor.

FWIW, I am dealing with the same symptom on this 2245 I am working on. Good strong FM, but no stereo. Haven't had a chance to dig in yet, so just hoping I can figure it out. I'm going to start by tweaking alignment, and if that doesn't work, I'll be on the same chase you are on.
 
Before grabbing a soldering iron... did you measure the ohms from H106 emitter to ground? It may be shorted which may be the cap in the combo or someone's handiwork [sarcasm!].

EDIT: If so, it may have blown the H106 transistor.
 
rBuckner said:
Before grabbing a soldering iron... did you measure the ohms from H106 emitter to ground? It may be shorted which may be the cap in the combo or someone's handiwork [sarcasm!].

EDIT: If so, it may have blown the H106 transistor.
Click to expand...
Good point because H106 was the original bad tranny with B-E Open. I moved H105 to this H106 location. Replaced H105 with KSC1845 temporarily till I get 2sc930’s shippped. will check to see if H106 is blown again.

Edit: Measuring 705 ohms H106-E to Gnd. Spec in SM on G103 says .022uf cap and 680 ohms resistor. So, the resistor seems intact.
 
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Probably not applicable in your case, but that 2245 with no stereo turned out to be simple. Before even hooking up an rf generator, I decided to tune to no station and center the tuning meter - which was way off center with no station - and adjust the black slug on the discriminator transformer. It took 3/4 of a turn, but with the tuning meter centered on no station, when I tuned to a strong station, the stereo light came on and I definitely had stereo. I wish they were all that easy. I'll wait until I recap the tuner boards before touching up the overall alignment. Anyway, it might be worth a look at the equivalent step on your 4230 to see if this adjustment could be out of whack. I've seen this secondary discriminator core be the cause of no stereo a few times. The equivalent adjustment looks like the upper core of L107 as outlined in step 8 of the FM alignment procedure. In that case, you are adjusting a test point to 0V.
 
H114 pin 6 and 8 voltage overage will be cured by replacing the bad transistor.
Pin 10, 11, 14 I think are ok, either schematic is wrong or could be the todays higher mains?

(I hate this P100 board!)

:mad:
 
A funny thing happened on the way to start swapping in some new 2SC930 transistors...I found that when I moved H105 over to the H106 spot (edit I installed it backwards. Not a 180-degree rotation as mentioned pre edit). Pulled it and confirmed it was still good, reinstalled in correct orientation, tested and the stereo beacon came on. For what it's worth the R145 package is a little hard to see which side has the little flat edge, but I try extra hard to get these right and still manage to flub it. Errrg!
So, the original problem was the open H106 B-E upsetting the signal voltage from H109 getting thru L108 to be rectified and going to 110 to turn on the IF amplifier final stage, the Stereo Beacon and driving the Signal Strength Meter. The center meter was now off, but that was easily adjusted. Went back through the basic tweaks and all operating as it should.

upload_2022-3-9_23-8-14.png
 
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jd3rdcoast said:
A funny thing happened on the way to start swapping in some new 2SC930 transistors...I found that when I moved H105 over to the H106 spot, I didn't rotate the transistor 180 for the new location. Pulled it and confirmed it was still good, reinstalled in correct orientation, tested and the stereo beacon came on. For what it's worth the R145 package is a little hard to see which side has the little flat edge, but I try extra hard to get these right and still manage to flub it. Errrg!
So, the original problem was the open H106 B-E upsetting the signal voltage from H109 getting thru L108 to be rectified and going to 110 to turn on the IF amplifier final stage, the Stereo Beacon and driving the Signal Strength Meter. The center meter was now off, but that was easily adjusted. Went back through the basic tweaks and all operating as it should.

View attachment 2507899
Click to expand...


Just for clarity and if someone looks at this in the future.
Transistors H105 and H106 are facing the same direction, so no 180 degree needed?
Maybe I am wrong.
Which were the 2 you swapped?

Thanks!
 
patfont said:
Just for clarity and if someone looks at this in the future.
Transistors H105 and H106 are facing the same direction, so no 180 degree needed?
Maybe I am wrong.
Which were the 2 you swapped?

Thanks!
Click to expand...
(Edit-rewrite of original reply to clarify.)
After careful review of my notes I believe when I moved H105 to H106 I installed it backward. So you are correct, not a 180 degree rotation needed. I simply installed it backward.
 
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Just looking at the P100 board layout in the service manual, H105 and H106 are basically facing the same way. 106 is canted slightly counter clockwise. You obviously have it right because it is working. Is your board different from the service manual? I notice H107 is 180 degrees from H105. Just trying to clarify why your description sounds different from the service manual board layout.
 
jd3rdcoast said:
A funny thing happened on the way to start swapping in some new 2SC930 transistors...I found that when I moved H105 over to the H106 spot, I didn't rotate the transistor 180 for the new location. Pulled it and confirmed it was still good, reinstalled in correct orientation, tested and the stereo beacon came on. For what it's worth the R145 package is a little hard to see which side has the little flat edge, but I try extra hard to get these right and still manage to flub it. Errrg!
So, the original problem was the open H106 B-E upsetting the signal voltage from H109 getting thru L108 to be rectified and going to 110 to turn on the IF amplifier final stage, the Stereo Beacon and driving the Signal Strength Meter. The center meter was now off, but that was easily adjusted. Went back through the basic tweaks and all operating as it should.

View attachment 2507899
Click to expand...

Hopefully, when my parts board to replace L110 on my unit gets here I will be able to experience some of the same success.
 
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