[aprssig] APRS - discriminator direct on FT-2800M ?
ron.tonneson at gmail.com
Sun Jan 20 10:17:26 CST 2008
I think you want the modulator, not the discriminator. The
discriminator is what extracts the audio from the received signal.
In looking at the schematic for the FT-2800 I see that there is an
inductor in series with each of the mic connector lines. If you do not
have it here is the pinout:
3 +8 VOLT OUTPUT
5 MIC INPUT
I would guess that it may be the coil in series with the +8 volt output
that is damaged. If so you could just try putting a jumper across it.
Ron - K0QVF
Geoffrey Dick wrote:
> Subject: discriminator direct / or repairing FT-2800M for APRS Wx
> This is a question of how to find the input to the discriminator
> circuit, so I can wire a WxTrak directly into it on a Yaesu FT-2800M.
> I took a chance and purchased a damaged radio at a tailgate. The
> radio seems to receive okay, but there is no audio when it keys up.
> The circuit board in the radio head has a burned component on it from
> a short in the microphone cable. I believe worn, twisted wires in
> the cable shorted to 5 volt power in the cable near the connector.
> My options are:
> 1) Replace the burned component on the radio head circuit board.
> It looks like a diode, or could be a surface mount capacitor,
> but is too damaged to read the markings on it. I can take a
> photo of it and send it to someone who would know how to
> identify it.
> 2) Send it into a Yaesu repair center. With shipping, it would
> almost cost as much as a new 2M radio with a warranty.
> 3) Find someone who has a FT-2800M with a different problem, i.e.
> damaged final, etc. and salvage the radiohead circuit board.
> 4) Use the radio as-is by simply wiring audio directly into the
> discriminator circuit, and somehow keying up transmit by
> another hookup that bypasses this section of the radio head.
> I have a schematic, but no component layout or parts list
> to guide me.
> Anybody on the SIG have any suggestions that might play into
> these 4 options, so I can use the radio for a weather station.
> Geoff, WA4IKQ
> Winter Park, FL
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