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Hi, Michael, do you know of a reference guide, book or article that someone unfamiliar with FM could read and use to help in repairing FM receivers? I have gotten quite a few of late and all the ones I have worked on so far have issues from dead to poor stereo FM, and being a beginner is that area is not allowing me the skills to get these sets fixes and out the door. Thanks!
Follow Ups:
Randy
The best you can do is start with a heathkit receiver and manual as it's so self explanatory..I learned it that way and thru logic and alignment manuals for Mcintosh MR67 tuners.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Thanks, Michael, I will check that out!
I slipped off a step ladder by missing the last step coming down as I was putting a new bracket on my garage door opener screwdrive rail..Anyway,I landed hard on my tail on the cement floor..I had it X-rayed and there are no fractures so I just have to heal..The kidney stones are no more but now this.It has been 3 days but they want to do an MRI because my lower back hurts but I've been icing it daily.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 11/12/16
I've heard that a bone bruise can take some time to heal.
So a good excuse to just sit back and listen to music for awhile.
Happy healing.
"The piano ain't got no wrong notes." Thelonious Monk
I know and I don't want an MRI and I don't want to sit.I was going to keep icing it and then use heat to expedite healing and take Glucosamine three as I have been.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Mickey, so sorry! Hope you feel better!
I went back inside to poke around and measure the coils to see if there were any broken coils or wire connections that may have opened. Didn't really see anything but did move some wires around a little. When I turned it back on, the FM was working, woo hoo! Now, the question is do I replace the ceracap coupling caps? I did all those in the audio section as these are always trouble, but have not in turner section of which only a few have any significant voltage on them. So, just replace the ones with significant voltage? thanks!
FM work requires a more sophisticated test bench than "mere" audio does.Do you have a 200 MHz. bandwidth o'scope? The function generator has to be top notch too. Sweep alignment of FM tuners takes time to "master". Old hand "Ham", Mike Samra, knows his way around RF equipment.
NEETs has some good introductory info. about FM. The 3 types of FM demodulator found in tube equipment: Foster/Seeley discriminator, ratio detector, and gated beam detector are discussed.
Run a Google search for FM MPX spectrum. What's broadcast is quite sophisticated. For downward compatibility, the primary signal is mono. The information needed to recover stereo amplitude modulates a 38 KHz. sub-carrier that is DSB (double sideband suppressed carrier) processed, which (in turn) is added to the FM mix. Notice the 19 KHz. "pilot", which indicates the presence of stereo and is frequency doubled to regenerate the suppressed 38 KHz. sub-carrier.
Eli D.
Edits: 11/07/16 11/08/16
we're not aligning the transmitter, only the receiver! :-)Heck, the old "TV men" could align NTSC (analog) color TVs with a 5 MHz scope. The color subcarrier signal frequency was 3.579545 MHz.
One does need, at least, a calibrated sweep generator and a marker signal to align the FM, a good, accurate VTVM -- and a frequency counter's nice to have, too, but folks aligned (mono) FM receivers in the 1950s, with 1950s "repair person" grade electronics, to good effect.
caveats:
1) I don't mean to imply that it's easy, especially for a nonspecialist. I "know" how to do it, but I do leave it to the pros.
2) MPX stereo is yet more sophisticated.
all the best,
mrh
Edits: 11/08/16 11/08/16
If you want to "snoop" the TRF front end, mixer, and/or local oscillator, an o'scope whose bandwidth is greater than 100 MHz. is necessary. The local oscillator will go as high as (approx.) 119 MHz.
Eli D.
The only exception to tbis is the Dynaco tuners (FM3 and FM5) which were specifically designed to be aligned without test equipment (FM3) or were pre-aligned (FM5)
The truth is that even the FM3 will most likely need an instrument alignment at its current age. The problem is that the entire home alignment procedure is predicated on the IF transformers being fairly close to 10.7MHz. As supplied they were pretuned to this frequency. Every FM3 I've played with had IFs way off this frequency so while they received stations, sensitivity was below par and dial tracking was way off. VanAlstine describes the situation in more detail at his website.
is breaking the tuning slugs in the transformers
;-)
be VERY careful working on fifty, sixty year old (or older) tuners!
all the best,
mrh
Just wondering: Has anyone tried blasting the IF coils with a hair dryer to loosen up the slug?
Is that a Radio Craftsman mono tuner/preamp?
Dave
nt
all the best,
mrh
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