yes you are seeing double i have two sony srf-a100 fm am stereo radios the one on the left
is mine i've had it since the year 2000 it was a gift to me from the
late chris cuff and the one on the right was sent to me by ben from oddity archive
you may have seen it in his recent video where he went on a road trip
to find a couple of radio stations which are still broadcasting in am stereo and unfortunately he
was not able to hear stereo audio from either of them because this sony is not working correctly
so i got in touch with ben and i offered to fix his junk because
i have a known working unit to compare it to i have my own am stereo transmitter
"the place for the most music variety the most music variety in stereo in stereo"
and i have the service manual for it and i hesitate to call this junk because it's in much
better physical condition than mine it has much fewer dents in the speaker grilles as you can see
and it also has the battery door where mine does not and mine also has
a little bit of a hole in the back and to help identify it mine has a
glow-in-the-dark sticker on the top where ben's is in pristine condition on top
the srf-a100 was officially announced by sony on april 13th 1983. it had a
suggested retail price of $89.95 u.s but it was not readily available in stores
until january 1984 when it was joined by its walkman counterpart
the srf-a1 which basically has all the same features just in a smaller package
so first an example of the known working unit this is a multi-system am stereo receiver
because when this was introduced in the early 1980s there were four different am stereo
systems in use you can see here the a position was for the harris magnavox and motorola systems
and the b position was for the kahn hazeltine system and of those four
systems the motorola c-quam system eventually did become the standard
so here's the known working unit i have it tuned to my own am stereo radio station
playing some music from the backtraxx audio library and it is set to am stereo mode and
the tuning indicator is lit and you probably won't be able to hear much difference through
the tiny built-in speakers which are like six inches apart i don't really understand why they
made such a big deal about am stereo and then put the speaker so close together
you can't even hear it in stereo so let me give you a direct connection
it
also has wide and narrow bandwidth
and this is what is known as a forced stereo receiver because of all those
different am stereo systems that were on the air when this was introduced
it would be too expensive for it to try to detect each of them so instead it just tries to receive
everything as am stereo regardless if the station is actually broadcasting in stereo or not so that
is not actually a stereo indicator that's just a tuning indicator because it doesn't actually
detect whether the station is broadcasting in stereo or not it just decodes everything in stereo
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now here's ben's radio and i have it set to am stereo but you notice there's no
tuning indicator except if i switch to mono then the tuning indicator appears
so that's mono i don't hear any difference in stereo except the tuning indicator disappears
and that indicates there's something wrong with the am stereo decoder chip in this
if we look at the block diagram of the srf-a100 receiver it has a combined am/fm receiver chip
just like any other am/fm radio and if you have it set to mono mode in am that chip is what drives
the tuning indicator so that's working but if you switch it to am stereo it's actually the am stereo
decoder chip which drives the tuning indicator so we're not getting any tuning indicator when
we switch it to am stereo that means the problem is with the am stereo decoder chip
here's the basic circuit diagram of how that chip works is the sony cx-857
the tuning indicator led is driven by pin 4 and that is connected to a lock detector which
detects when the voltage controlled oscillator is able to lock onto the station you're tuned to
and that has a 3.6 megahertz oscillator coil and that is adjustable
so i think that is what i'm going to try first adjusting this coil
to see if it can get to lock onto the station
and illuminate that tuning led and that's when it will be able to decode it in am stereo hopefully
the first step in taking apart is to remove the knobs which hopefully won't require
too much effort
you
also have to take out the power switch a little yank with a pliers got that out
now we can unscrew the back cover
okay now the back cover should pop off
and it comes off completely which is good and unfortunately the adjustment we need to
get to is on the opposite side of this board there's one more screw to remove right here
i guess it's just gonna stay there
and now
okay i may have to take out the batteries
and now this whole
circuit board should carefully come out
and i think right there is that adjustment we need to make yep it's L5 which is right there
next to the tuning cord which we thankfully do not need to unstring the service manual
has a procedure of connecting a signal generator and adjusting that coil for a specific voltage
but i'm going to try the simpler approach of just tuning in my own am stereo station and
tweaking that coil until hopefully it pops into stereo mode like it should
if we're not able to get it to do that
by tweaking this coil then we have bigger problems to deal with but here we go
that's my own signal if i put it in mono mode you can see the tuning indicator light up but
in stereo mode it goes out now i'm going to try adjusting this coil until it goes into stereo mode
that is a very stiff coil
it
doesn't even feel like i'm adjusting at all
well i tried several different implements to adjust that coil and i could not get it to budge
i don't know if they put glue in it when they put it in at the factory but i didn't want to force
it and possibly break it and there's this other adjustment in the same metal box here and this
turns freely even with my plastic adjustment tool but for some reason this one doesn't want to budge
and speaking of which this stereo distortion adjustment should be set fully counterclockwise
to give you the cleanest sound with the c-quam system which is what became the standard and
is the only system still in use today and that's the way this one came but my other srf-a100 must
be an older one because it came set to the center position which is a compromise between the c-quam
system and the other systems but i guess on later units like this when it became clear that c-quam
was by far the market leader they changed it to adjust these for optimum results with the c-quam
system so if you have one of these just check that this one over here is set fully counterclockwise
but i think i may have been barking up the wrong tree anyway because the manual says
to connect the signal generator and adjust it until you get a reading of 1.7 volts between
pins 5 and 8 here and if i do that i get 1.7 volts pretty much
1.69 so that is correctly adjusted so that's not even our problem something else is wrong
default is more than likely due to you guessed it say it with me bad capacitors
but you can see this thing is chock full of highly miniaturized surface mount components because sony
was at the forefront of that kind of thing in the 1980s and i know that's not an insurmountable
challenge with magnified vision a lot of patience and a very fine tip on your soldering
iron that would be doable but the problem is gaining access to that am stereo decoder chip
it's on its own little separate circuit board which is inside this metal shielding can
so in order to get to it we would need to remove this can and in order to remove the
can we would need to remove this plastic frame and in order to remove this plastic frame we
would need to remove the tuning dial cord so you need to basically unbake the layer cake
to get to it i don't know if even 12 volt vids would be willing to do a job like this
this is a case where the effort to repair exceeds the value of the radio so what i've told ben is
that if he really wants to get this working in am stereo again what he should try to do
is find one of these that's in rough cosmetic condition but is fully functional and since
this one is in such good cosmetic condition he could swap the internals with the working one
that's easy all you need to do is just unsolder and then reattach the speaker wires and the wires
going to the battery contacts that's easy and then that would get him one of these that's fully
functional and in this really nice looking case i mean it has one little dent there but that's minor
or he could just leave it as is because as you saw it's still perfectly functional as
a high fidelity very sensitive and good quality mono am tuner
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and fm stereo of course so realistically speaking there's not that many am stereo stations left so
most of the time you'll be listening to mono am stations on this anyway so it's no big loss
but i didn't want ben to come home with no ability to receive am stereo so i found this
in my own junk drawer it's an ando ss-100 am stereo little walkman type radio it's only am
and it is am stereo and it was sold in the japanese market as you can tell
this is from around 1992 when they were first introducing am stereo in japan
using the c-quam system the original price was 8,500 yen and i like that am stereo new
and the box is kind of falling apart i also no longer have the little earbuds
it came with but they sounded terrible here's the warranty card maybe someone
can put this through google translate here's the manual stereo am specifications 530 to 1600
kilohertz 28 milliwatts output was on two aaa batteries as you can see there
and there's there is some english here the switch on the right side
switches between off am mono and am stereo and the switch on the left side switched between the
headphone output and the built-in speaker but i didn't see the point of having a tiny mono
terrible sounding pipsqueak little speaker in an am stereo receiver so i removed it so
now it's strictly the headphone output in stereo you get your volume control and tuning dial it's
manual tuning it's a little bit fiddly but it's not too bad and like i said the first
position is mono second position is stereo it doesn't sound quite as good as the sony
it's not as wideband but it's still very sensitive it even says on there super sensitive tuner
and the big advantage of this one is that it is not a forced stereo receiver it uses the motorola
mc13024 am stereo c-quam decoder chip which was their attempt to get c-quam am stereo into
low-cost radios like this and the big advantage of that is that it has a pilot tone detector which
only switches into stereo mode when it detects the station broadcasting in am stereo and the way
you can tell that is when the tuning indicator gets brighter i'll switch it into stereo mode
and there you can see it just got brighter because it's now receiving my transmitter in am stereo so
that little indicator is a big advantage when you're hunting for am stereo stations out in
the wild with the sony you would just need to sit and listen and wait for them to actually
broadcast something in stereo and if it's a talk station that could take quite a while whereas with
this you can see right away when that led gets brighter you know you found a station broadcasting
in stereo even if they're not actually transmitting anything in stereo at the moment
but that mc13024 c-quam decoder chip has one fatal flaw and that is it's sensitive to movement
and it drops to mono when you pick it up and move it around which is what you would
naturally do with a portable radio like this people carry it around they go jogging with it
and this would be constantly dropping to mono if you actually did that you see it's in stereo
every time i give it a little tap it drops out to mono
it's fine if you just sit and leave it alone it works fine but if you're moving this thing around
it's gonna be dropping out to mono so this is my gift to ben to give him some
ability to receive am stereo in case he ever decides to go on another road trip
and now finally the moment you've been waiting for i'll present to you
a direct hookup sample of the oddity archive channel's theme song pavanned
featured in motorola c-quam am stereo as received by the ando ss-100 radio
stay tuned to this channel and others for more exciting am stereo related content
in the near future but for now i'll leave you with a clip of when cfrb the radio station in toronto
ontario canada officially started broadcasting full-time in am stereo on july 30th 1984. i'll
have the full recording available on my other channel i'll include a link to it unfortunately
i only have a mono recording of their first stereo broadcast but they specifically mentioned
this sony srf-a100 as well as its walkman counterpart and also the sansui cx-990 which
was the first car radio to have am stereo cfrb had three of the first prototypes of it
"tell us what stereo is all about and you know how many sets we have in this area i can't tell
you how many were sold sony i can tell you are the one manufacturer with home model sets they're the
only ones on the market now they have two sets one is a table model with headphones it's portable the
other one is the walkman that's almost becoming a generic term but it is a walkman type with am
stereo there is one car radio on the market now we have the first three the prototypes sansui
kromer radio on bathurst to put ours in anybody who sells sansui can tell you about that one"