Re: [IRCA] Sony SRF-59 Schematic Now Posted Online

["Paul B. Walker, Jr." <walkerbroadcasting@xxxxxxxxx>]

Group:

I will leave the SRF 59 Diagram posted online for an indefinate amount of
time, so feel free to download the jpg image or share the URL with friends.

http://www.walkerbroadcasting.com/srf59.jpg

Paul Walker



On Dec 28, 2007 12:34 AM, Steve Ratzlaff <steveratz@xxxxxxxx> wrote:

> Thanks to Paul for putting my handdrawn diagram on his webpage. I presume
> that the several of you who asked for the diagram in the past several
> hours
> have obtained it from Paul's site.
> I should note that the diagram is probably not 100% accurate. Several
> traces
> I was unable to figure where they went on the IC1. The sections associated
> with the tuning cap are all using the +1.5 volts supply as the common
> reference, not the minus/ground. This is probably to supply voltage to
> some
> of the IC1 pins thru external circuitry. You'll notice that in the FM
> tuning
> section, L1/C1 and the associated tuning cap section don't go anywhere.
> Since I couldn't tell where pin 29 on IC1 went, it probably goes to the
> junction of C2/L1, for the FM input tuning. Since every other pin on IC1
> is
> used, pin 29 is probably also used.
> The ferrite loopstick connections aren't verified either, just guessed at.
> I'd have to remove the loopstick and trace out the two windings to be sure
> where they really go. The AM tuning section doesn't really look functional
> as drawn, and no doubt is not correct.
> I have another SRF-59 on order and will do some component dissassembly
> after
> I receive a backup radio.
> Someone asked how to hook up an external digital dial to the AM section,
> to
> be able to determine what tuned frequency is dialed in. That would have to
> be done as a new experiment; I have no real idea if the dial could be
> added.
> If the radio in fact has an approximate +57kHz offset from the input-tuned
> frequency, then if the digital dial could be offset that small amount, and
> be coupled to the AM local oscillator such that it does not detune the
> oscillator, then perhaps the digital dial might work.
> I found touching the tuning cap section associated with L3/C5 detuned the
> AM
> section, so that would be a good place to start with trying a digital dial
> connection, with some type of low capacitance isolation buffer stage.
> For what I observed using the spectrum analyzer, with the two presumed
> local
> oscillator RF signals in AM mode, with the lowest one about +57 kHz higher
> than the input frequency, it's possible that what I thought was the second
> harmonic is really the signal that IC1 is using as the local oscillator,
> and
> that the lower one is some type of sub harmonic. But all DSP ICs I'm aware
> of require the input signals to be well below 100 kHz, and using the
> second
> harmonic as the actual local oscillator doesn't seem to fit that
> requirement, where possibly the +57 kHz signal just might.
> An experiment could be done to remove the AM oscillator signal and inject
> an
> external one from a signal generator and try to figure out what local
> oscillator frequency is really used by the radio.
> It seems to me since the radio is not shielded, that if the local
> oscillator
> is really just +57 kHz higher than the input, then a strong local BCB
> station would eventually fall on the local oscillator signal's frequency
> and
> mess up the radio reception. So far no one has reported anything like that
> being noticed.
> I hope to do some experiments once I have another backup radio.
> One might think that if Sony can sell a radio for $15 including free
> shipping, and still make a profit, that this particular circuit might be
> used in other Sony miniature radios, to get the costs of integrated
> circuits
> and such way down.
>
> I have been tracing out circuits for fun for many years--I do it for
> enjoyment and to learn how other designers do things. This little circuit
> board actually was not that hard to get the basic circuit figured out,
> with
> the limitations noted above for parts that need to be removed to figure
> out
> some more details. There's got to be some amazing things going on inside
> IC1
> to take a radio signal in and put out demodulated audio for both AM and
> FM,
> with no external parts except the presumed-FM stereo multiplex
> transformer,
> and external components for the local oscillators.
>
> Best regards,
> Steve
>
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