2245 restore / no FM stereo

Thumper

Thumper

Well-Known Member
Hey guys,

Finally getting around to doing a full recap on my 2245. Also swapped out all of the lamps for LED's courtesy of Don Haywood. All boards have been fully redone with Panasonic FC's (and films where appropriate) except for the power amps, I'm saving them for last.

I've got a couple of issues, one being that it occasionally blows the 2.5A fuse on power up. There's a slight hum/buzz in the right channel and I noticed that something on the right power amp board is running a bit toasty. Hopefully I can get all of that sorted when I go through the amp boards.

After recapping the FM detector and MPX boards this thing pulls in stations like a boss now! But, alas, there is no stereo. I know the lamp works and I know the mono/stereo switch is clean. I found some posts from rbuckner and bktheking talking about adjusting the black pot (or coil) L501 on the P500 FM detector board. I tweaked it and managed to get the tuning indicator dead center when the signal strength meter is maxed. And I mean maxed as in the signal strength meter is pegged! Still no FM stereo, though.

I know the real answer is to take it somewhere to have it aligned, but in the meantime, is there anything I can try without messing anything up royally? I read about the VOC pot L301 on the MPX board, can I try tweaking that?

Rob
 
It looks like the pot to tweak on P300 is R365. Just remember where it was before you try adjusting it. If that does it find the place where it just works and adjust it through the range where it works and until it just doesn't work again and put the adjustment in the middle. Hope that gits it!
 
Nope, I've tried tweaking r365, l301, and both the black and pink coils on the p500 fm detector board. At least i haven't made things any worse... I can now get stereo and the lamp to light, but only when the signal strength is weak and the tuning meter is waaay off to the left when tuned in to a strong signal.

I suspect I just need a proper alignment. No?
 
Yes you do it seems to me. It could be a bad component still though. That board could use a recap which should be done before the alignment. It's a bear to get to and I usually undo some of the wires on the AM board above it so at least it can "flop" completely out of the way.
 
As I mentioned in my first post, the whole shebang has been recapped with Panasonic FC's except for the power amps. I hear what you are saying about the AM board, I had to desolder two leads to it and one to the MPX board to get to the back of it. Not fun. Not a very clear pic, but you get the idea...



BTW I realized I had one cap on the MPX board in backward, as the silkscreen is wrong. I put a new cap in the correct way, and it still doesn't work.

But I was thinking, even if the alignment was waaaay off, shouldn't this thing still put out a stereo signal when tuned to a strong station? I'm starting to think a transistor or resistor on the MPX board is hosed...
 
??? God no, if the alignment is way off it won't pull in stereo-I've aligned enough receivers and tuners to state this fact. 2245 has a switch in the back IIRC, is it set to in or out?
 
Hey bk, you're the pro here, not me! I was just asking a question...

Switch is set to "out". And I have the muting off. Some stations are strong enough to completely peg the signal strength meter, still no stereo...
 
Sorry , I wasn't trying to be rude. I can stick an alignment tool in a core in the front end of that 2245 and turn it 1/4 of an inch and you 'll never get stereo. Think of fm stereo as a set of lock tumblers- if one number is off=no stereo, no unlock. You tried adjusting the black core to no avail correct? There are so many factors regarding "fm stereo" not coming in it can get complicated. Since you have no light, issue may be in the front end or the MPX section. If you have a signal gen for FM you could disconnect the IF and inject a MPX signal into the MPX board to see if the light illuminates.
 
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No worries, man! That lock tumbler analogy is a good one. Makes total sense.

I've tried turning the black core, the pink core, the MPX core and the MPX separation pot. At this point I'm starting to think it really is just an alignment issue. The other night I had it dialed such that it WOULD sort of pull in some weak noisy stereo, but only when the indicator was to the left of the station. And now it's off to right.

I've a scope, signal generator, a bunch of meters and soldering irons. I've even got a 1,200 watt dummy load. But no distortion analyzer or FM signal gen which I understand you need to do an alignment.

I wonder if there's anybody in Maryland who would do it for me AND let me watch? I'd love to see how it's done...
 
It does, but I'm not sure I'd want to trust it. It's an ancient all tube Heathkit deal from the 60's. I basically just use it for looking at the distorted waveforms of guitar and bass amps after work and checking for full output power.

 
On second thought, it doesn't. Since the horizontal gain is adjustable I'd have to inject a known frequency first to calibrate the fool thing...
 
No sir... I really need a new scope. I've been casually looking for the last few years but haven't come up with anything.
 
Some digital meters have a frequency measuring function, maybe you have that?

This could also be an issue in the IF strip and even the tuner front end. These kinds of issues can take hours to chase down even for experienced techs. I'm not trying to be a downer but trying to give an accurate depiction from what I've read so far. But hey, if you want to take a trip to Arizona we could play with it. :D
 
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