PIONEER SX-440 FM Reception - Magic Loop?

[JB8]

I'll keep this short!

Picked up my first 440, cleaning it up, 90% of the lights were burnt out, etc. After replacing the lights I found the signal meter and stereo light to be responsive, but, even with an FM antenna attached I wasn't getting much action for either. Then when I touched the small vertical loop shown in the picture, wowza, the signal meter came to life, stereo light burned steady and bright! What gives? I'm assuming I'm essentially becoming a giant antenna, but why is it so dramatic, and why wouldn't the actual FM antenna work as well? The screw mounts for the antenna are showing some wear and should be further cleaned, but even if I bypass them and touch the antenna legs on the interior of the unit I don't get the same reaction, not even close.

Fun little unit, stoked to get it ship shape, really appreciate any insights you can offer!

 

[Punker X]

More than likely needs an alignment. The trim cap that is attached to the loop, tunes the variable cap. Touching it you're changing the capacitance. I'd hook an external antenna. Tune to station around 106Mhz and you can tweak the center and far right trim caps for a peak on the meter. Before you do this you may want to look at the sticky at the top of the forum about cleaning the front-end.

 

[JB8]

Thanks for jumping in, @Punker X I appreciate the advice and explanation. I checked out the sticky around cleaning the front end and used some of the non-residue cleaner (not on the fins, only dusted with compressed air) but don't have any appropriate lube and even if I'm super careful I imagine using any kind of actual oil, like a sewing machine oil, is likely not advised. I did hook the antenna up and it seems to have almost zero effect on the reception, and when I tweaked the center and far right trim caps I didn't get much of a response from the meter, very little change. On other units I've gone rogue with some VR's with decent success - getting the stereo light to kick in, meter strength adjust - but for this I'm still super perplexed that touching that loop takes the reception to such a strong place. I understand the capacitance change, but still eager to figure out how the adjustment points work together to create a better reception.

Another thing to note, and I should have mentioned this initially, when I first started addressing the FM reception I noticed a significant misalignment of the dial need and the actual station. I'd been made aware that there was a small trimmer that could be used (shown in picture circled in blue) to adjust this, so I successfully aligned it to two different stations/dial locations, and not they seem to line up fine, but still sounds super weak when not touching that loop.

I have no FM generator so doing a proper alignment is likely out of the question, but I'm game for any other tips you might have specific to essentially, hacking this thing into shape if at all possible!

 

[Catmanboo]

That middle fm gang you indicate has been tampered with as shown by cracked-off sealing paint. I'd try running the screw all in until it stops, then slowly backing out (with antenna connected) & see if it at some point wakes up. However, count your turns in so in the event nothing changes, you can return to original adjustment, then look elsewhere. Fwiw, I'm looking at my sx440 as I type this, these flea-watt (12wpc) things cost around $300 in 1969 dollars, then dropped to around $220.

 

[JB8]

Hey, @Catmanboo, thanks for chiming in, much appreciated.

I believe I am said tamperer of the FM gang... Earlier in the post it was mentioned that tweaking both the middle and far right trim caps may help, and I was definitely able to hear the difference in certain positions, but overall the reception is still poop. Since the unit isn't super valuable I've been contemplating something unconventional, but have a couple questions first. When I touch that middle ring with my finger and get amazing reception, is anything bad happening as a result of the change in capacitance? I also have some alligator clips and if I pin one to the loop, bingo, great reception. I also tried attaching a bit of wire to the loop and then running it straight to the antenna post on the interior of the board, and again, great reception. Would rigging some sort of jumper be a bad thing? I realize the voodoo I'm trying to do is not common, but since I don't have all the gear to jump head-long into FM alignment I'm eager to see if anything can still be done. This is the worst drift I've ever experienced so I of course would love to tackle the issue even if it's not a via a typical method.

Ultimately, and I'm finding this out with some other Pioneers I'm tinkering with, the loudness function sounds excellent, to me. Others can sound terribly muddy so I don't even use them, but even with this little guy, wow, the sound really shocked me so I'd love to preserve it if I can

Thanks again for hopping in, any words of wisdom would be awesome, or even just words, I'm not picky.

 

[Catmanboo]

Whatever works, do it! Unconventional, yes, but good temporary fix. There's no real voltages in that ckt (RF in/ antenna connx) to damage anything, so no worry there.

 

[Catmanboo]

The 2 pegs are the underside of antenna connections connected to them, pencil point resting between. Check continuity of every trace in this area, any faults there will kill incoming signal from antenna posts. This one I have picks up a lot of sigs even without antenna of any sort connected. Touching any of these traces with a piece of wire should produce reception increase. If not, suspect fault right in that area. Also check solder anchor lugs of tuning gang for breaks in solder flow. As good a place as any to start snoopin' around.

 

[JB8]

Hey there, thanks for your encouragement, I'm game to keep poking around, carefully of course!

You mentioned the traces you're pointing to, was there a picture you were attaching? In the meantime I'll check out the areas, traces and lugs you mentioned for bad solders - it's a pretty small area so even without a picture I'm pretty sure I can figure out what you were talking about.

Really appreciate the extra direction here, makes tons of sense. I'll keep this thread updated with my progress, cheers!

 

[Catmanboo]

Hey there, thanks for your encouragement, I'm game to keep poking around, carefully of course!

You mentioned the traces you're pointing to, was there a picture you were attaching? In the meantime I'll check out the areas, traces and lugs you mentioned for bad solders - it's a pretty small area so even without a picture I'm pretty sure I can figure out what you were talking about.

Really appreciate the extra direction here, makes tons of sense. I'll keep this thread updated with my progress, cheers!

Yeah. I just corrected my AFU incomplete post.

 

[Catmanboo]

Neat thing about this one- dual-voltage power tranny, 100-120 v primary. The **** part is the typical pioneer speaker connections from that Era. Damn plug-in sockets, akai also guilty of same sin back then.

 

[JB8]

I'm with you! Those kookie plugs are a pain. I wish I wasn't so taken by the look of a 1970's black face receivers, but, I'm hooked, crap speaker plugs and all!

 

[Catmanboo]

I'm with you! Those kookie plugs are a pain. I wish I wasn't so taken by the look of a 1970's black face receivers, but, I'm hooked, crap speaker plugs and all!

I've had mine for God knows how long, paid $5 at Sally ann or goodwill I think, long ago.. Did occasional duty in my "office" for a few years, then brought home & parked for a while. Dragged out & ops checked periodically. Huge cool factor, these predate silver-face gear, the blackout face a cool move for pioneer in '68-'69. This thing works phenomenal for its age, no recap necessary, it has nippon chemicon lytics & the single power supply filter, an elna lytic is fine. Dont know if oem or not, but mine has u.s.production RCA output transistors. This model is an excellent headphone receiver due to its low power, excellent sound & basic controls. One could throw this, a pair of rat shack minimus-7 speakers, a portable cd player, couple cables & interconnects in a medium-size suitcase & have a take-anywhere system for a vacation home, camp or hotel room. It shall remain in my inventory indefinitely.

 

[JB8]

Update: I'm not sure why I've invested more time and money in this unit considering it's faulty FM reception, but, I did. I rebuilt the PS and Main Amp, found tons of caps that tested out at double the capacitance, transistors that were wonky, and ultimately a very charming unit. So much so, that I'm not even concerned that the FM isn't great, because the sound of streaming a radio station through the AUX inputs provides nearly the same satisfaction as the real thing, or at least that's what I'm telling myself...

Still has a bit of a ground hum (hey, it's a Pioneer) but its considerably cleaner, stronger, and punchier, then before I dove in. Still love touching the magic loop to remind me of what I'm missing out on, but, whatever.

Next step, resto-mod case project, I'll post some pics when I'm done.

If someone has a magic procedure I can perform to bring the FM back to life that doesn't involve an FM generator or the voodoo of the secretive alignment process, fire it at me, and if not I'm still happy with where this project is heading.

More later, have a great morning or night out there, hope the tunes are hummin.