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

Geoffrey Dick wa4ikq at nevets.oau.org
Sun Jan 20 10:29:55 EST 2008

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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