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Pioneer sx-1980 FM dial calibration. I'm thinking about doing something that is considered taboo by the best Pioneer Tech I know. Edit: I gave up

Your HP instruments certainly are nice but you need a signal generator that will output level adjustable signals on 90 and 106 MHz. This is essential. Without one fuhgeddaboudid. I have several, my fave is my Marconi 2023. I also have a 2024 which is identical but goes higher in frequency. There are many available intended for AM/FM stereo adjustment from the likes of Kenwood, Leader, Sencore and many more. Shop around a bit.

Having said that, still cannot find L(o). There is a line/wire that could be a resonator on the side of the tuning cap:
IMG_9242_anno.jpg

Touch it and see if your receive frequency runs away. Bend it down to see if your receive frequency goes down as well. Then readjust the trimmer. You should end up higher.

As for the other coils, I marked them for you:
IMG_9245_anno.jpg

L(A) can't be adjusted but that is not such a big deal as it peaks very wide. L(R2), -3 and -5 can easily be adjusted by compressing/expanding the turns with a plastic tool (spudger). Remains L(o). You can unsolder it and lift it to increase its value but it's finicky. First confirm that white plastic holder with its wire is that inductor. Never seen it done like that. Not for FM in any case. You can even crack a ferrite core and glue that into its vicinity and hope for a good result. If all else fails bend the vanes away from the stator. It looks like the vanes are in the zero position and haven't been touched.
 
I can't see the bottom of the board where white plastic holder with its wire is that inductor resides. There's a metal shield mounted and soldered to the board. Not easily access at this point.

I took the bottom off and discovered someone has been tinkering about. There's a bodge wire across a broken trace on the FE underside (For the AM) and a few solder connections are fresh. The shield top cover was desoldered (Not by me).
I did restore this particular 1980 five years back and worked on the tuner board/MPX by replacing only the Tantalums. I didn't remember an issue with the dial calibration but that is something I pretend not to see if there's no complaints.
I don't know :dunno:
 
Okay.
A ton of reading the 1980 SM and I have an idea of the tuner operation. It's a piece of ingenious but complicated work. A little beyond my complete understanding, but I'm getting closer.
Suffice to say that this project is coming to an end. I'm going to leave it.
As I read the FM tuner operation in the SM which is several pages of text and explanation I remember markthefixer's discussions about the symbiotic relationship between the APC and LO in the FE. ConradH noticed the varicap diode which peaked my curiosity. Coincidentally, Mr. Carlson's most recent video explained the operation of one (varicap diode) in his recent Fluke SG repair. The 1980 SM confirmed my thoughts on any further attempt to calibrate this dial.
I might look at APC voltages as they relate to the adjustment procedure, only as a reference. Like I said the tuner is working well, it's just not calibrated to the dial.
I'll set the tuner pully so most of Marc's favorite stations are dialed in (Which are conveniently located in the center dial area) and let the ends be off by the .75 MHz or so.
Thanks for the discussion.
 
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Pity you gave up. I offered instructions (PM) on how to go about adjusting the vanes of the LO section to calibrate it to the dial. It should not be difficult, just finicky. You have the right kit. The APC is easily disabled.
 
The SX-780 and SX-880 tuner section is set up the same way - a variable cap for the high end and manual tweaking of the tuning cap fins for the low end. I've recalibrated many of them. It's not difficult at all - just takes a little time and patience as the high- and low-end adjustments affect each other, so the tuner needs to be repeatedly dialed to both ends to check for changes and make adjustments. The intermediate coils almost never need adjusting (on all tuners I've worked on), but the variable caps almost always need fine-tuning.
 
There is no LO inductor in these. You have to tweak the vanes on the cap (at the end furthest from the antenna) in order to "stretch" the tuning to match the dial. PITA with the potential for a hell of a lot of trial and error.
 
It's not off enough to take the chance of messing it up. I centered the dial around the stations Marc favors. If it was mine I would of dove in head first but without experience, I wasn't going to experiment on his tuner. It just wasn't over that "I have nothing to lose" temptation. Which, by the way, got me where I am now.
PE9ZZ was very helpful and we found the capacitance device that Alps used to set the dial calibration for the different models the FE was used in. I half wonder if the tuner was from a different model? How much bending would get you to the 1.6mHz needed to spread it out?
 
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