[aprssig] APRS - discriminator direct on FT-2800M ?

Dave Baxter dave at emv.co.uk
Mon Jan 21 04:38:25 EST 2008

Search the web for a manual for the radio, with schematic (try mods.dk
for example, there are other sites too that don't need you to register)
then you'll be able to identify and replace the part restoring the radio
to full capability.  I'd be surprised if someone hasn't put a book for
that "on-line" yet.

I'd also say dont short out the part as K0QVF suggests, if it was a
coil, I'd expect the 8V to collapse way before any damage was done.
Caps' don't (usualy) get hot, so it was probably a resistor or diode, so
shorting it, could do other more expensive and fatal damage to the

You could bypass the mic amp altogether, but you should not perhaps go
straight to the modulator, unless you are going to run 9600bd packet, as
you still need to keep the audio filtering and pre-emphasis in line
(idealy) for 1200bd use.


Dave G0WBX.

> -----Original Message-----
> From: Geoffrey Dick [mailto:wa4ikq at nevets.oau.org] 
> Sent: Sunday, January 20, 2008 3:30 PM
> To: aprssig at lists.tapr.org
> Subject: [aprssig] APRS - discriminator direct on FT-2800M ?
> 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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