#! rnews 5369
Path: news.demon.co.uk!dispatch.news.demon.net!demon!cisas91.demon.co.uk
From: D.Gray@AutoComm.cityscape.co.uk (Donald Gray)
Newsgroups: alt.radio.scanner.uk
Subject: DISCRIMINATOR output mod for FRG9600
Date: Fri, 11 Oct 1996 21:42:38 GMT
Lines: 121
Message-ID: <845070124.12712.5@cisas91.demon.co.uk>
NNTP-Posting-Host: cisas91.demon.co.uk
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I'm a G3, so here is a mod for the Yaesu FRG9600:-

To gain access to the NFM discriminator on this radio is easy BUT only
do it if you feel capable of doing one very fine solder connection....

Basically what you have to do is connect a short length of audio coax
via a smalll capacitor, to pin 14 of the mixer/nfm discriminator chip
(MC3357P). This coax can be bought out to one of the spare phono or
jack plugs on the back of the radio. There are several sockets on the
back and I have used the "MPX" socket on my radio because I will never
want to put a multiplexer on it!  Here is how to:-

Components required:-
	About 12 inches of thin audio cable
	one 0.1 uF capacitor
	one small cable tie (not essential but recommended)
	one cup of coffee (to steady the nerves!) - essential

Disclaimer: The following is given in good faith. I cannot be held
responsible for any omissions or errors, or to any damage caused to
any radio howsoever caused....All care but no responsibiity!!!!

1) disconnect power and other cables at the back.

2) remove top and bottom covers.

3) from the top, locate the N.F.M. board (4.25 inches [115mm] from the
back panel)

4)  very carefully solder one leg of the 0.1 copacitor to the solder
side of the pcb where pin 14 pokes out. Be careful to correctly
identify this pin AND be careful with the soldering, it is a fine bit
of soldering and is easy to short out this to the ajacent pads.

CHECK and double check that you have done a good "clean" solder job
here - It's vital to be very careful - I cannot stress this enough!

Leave the capacitor hanging in the air for the moment...

5) Use a small needle file to drill a small hole in the top portion of
the nfm pcb wher there are no tracks. through this hole, thread a
small cable tie and leave in situ for the time being.

6) with a sharp knife, scrape a section of the solder resist from the
top, right hand "Earth" track (as seen from the solder side of the
pcb) and tin it with solder (To confirm that you have the correct
track, it is the one connected to the can of the xtal on that board!)

7) prepare the coax by:-
	(a) stripping back the outer insulation by about one inch. (25mm),
twist the shielding together and tin it for about .25 inch [6mm] and
then trim it down to this length. 
	(b) stripping back the inner by about 1/16 inch (2mm) and tin the
inner conductor.

8) solder the screen of the coax to the earth track so that it will
present the inner conductor very close to or touching the free leg of
the capacitor.

9) now clamp this coax cable into position using the cable tie to
secure it into position.

10) Solder the inner conductor to the free in of the capacitor

11) orientate the radio so that the front pannel is facing you and
looking into the radio from the top, thread the free end of the coax
to the bollom by way of gap between the main pcb and tha case at the
back, right hand side (near the two white connector plugs)
tuck the coax under the big choke (the thing that  looks like a
transformer). BE CAREFUL not to put any strain on the coax. Leave a
little slack ...

12) now turn the radio upside down and orientate it so that the dial
is facing your right. The coax should be poking up at the left hand
side nearest you!

To use the "MPX" jack socket as the access point:-

13) Identify the 3 mountin pins of the MPX jack. They are 2 5/8 inch
[65mm] from the edge facing you,  of the main pcb .

The pin on the left is the earth (ground) pin. The center if the
"live" pin and the right pin is not used electronically (only as a
mechanical mounting point and is ignored in this mod)

14) carefully cut the track leading to the centre "live" pin about
half way along it's length (This removes the unused "MPX" signal to
the jack socket.

15) prepare the audio coax appropriately and solder the screen to the
earth pin and th inner core to the middle pin.

Replace the top and bottom covers, making sure that there is no strain
on the coax and that it is not being "pinched" by the covers.

IMPORTANT - Add a "MOD NOTE to the inside of the radio and also in the
instruction book:-

 	a) a small self adhesive lable stuck to the metal screen on the
underside of the pcb with words to the effect :" 10/10/96 - track cut
to remove mpx and coax added to give access to the NFM discriminator
output"
	b) similar lable on the back denoting the MPX now toi be "MFM
Discriminator"
	c) if you have a circuit diagramme, note the change also thereon!!!

The discriminator output is at a fixed level (about .7 volt) and
totaly isolated from the volume control - the setting of the volume
control will not effect the discriminator level. The squelch control
WILL cut in and out on the discriminator line in the same fashion as
oon the normal audio.

Happy hunting...


Donald Gray
Free Agent V1.0 - 
Eudora Lite V1.5.4
Please do not short the output or severe damage will be caused to the fuse.
         (On a Sony power supply leaflet!)

