Subject: Help for Ramsey Packet Modem users

From: [email-masked] (Michael Skowvron)
Date: 23 Oct 92 02:43:46 GMT

I am posting this for a friend who does not have net access,
but can receive e-mail by UUCP.  Feel free to send responses to
me if mail to frank bounces.  His address is 
[email-masked].

---Included text follows---
I am sorry you made the same mistake that I did and bought a packet
modem from Ramsey as I did. BUT, I have a fix for it that made mine
into something that Ramsey never thought of, "A REAL WORKING PACKET
MODEM" Their basic idea is sound, but not their circuit configuration.
Here are the steps I used to cure the "HARD CONNECTS".

1 - Remove C14 and replace with a .1uF monolithic or ceramic. Anything
	over 10 volts will do nicely.

2 - Remove JMP7.  This removes +5v from pin 10 of the TCM3105JL chip.

3 - Short pin 10 to ground.

4 - Remove R12 and R16. These are 10K resistors that are not what
	should have been used in the first place. Replace these resistors with
	a 50K or 100K trimmer pot. One end of the pot goes into the hole that
	R12 ocupied (+5v) and the wiper terminal goes into the other side of
	R12. This leaves 1 open. The lead goes to ground. Center the pot at
	mid point. This is a good place to start.

5 - If you wish you can place back to back 1N914 signal diodes across
	R17. This will prevent the voltage from the speaker (data) to exceed
	.6v so as to protect the TCM3105JL chip.

6 - Tune up is simple! Connect up to computer and activate Baycom. You
	will find that instead of the low LED on, the HIGH LED is on, don't
	worry. Listen for a WEAK digital signal, less than 1 S unit and turn
    the new pot you have installed ever so slightly either way. The data
    will start to flow in and show on your screen.

I have found that excessive audio now is NOT needed. Turn the volume up
just enough to make both the LED's wink and blink. Too much audio and
the data gets distorted. I found that the modification worked GREAT for
me. I am about a half air mile from our club PBBS and no matter where
I had the audio set or the amount of power I used I could not get a
CLEAN connect. Well I do now in one request. The problem I found was
that the +5v regulator was not staying even close to +5v. It had gone
down to less than +1v during some data input. The replacng of R12 and
R16 to a larger value presented less load and the removal of JMP7
lightened the load. R12 and R16 are bias resistors for the modem chip
also. With the value being adjustable now you can FINE tune the chip
for optimum proformance and keep the +5v line above +4.5v...

Frank Holden - KA3UWW
??? "The Radio Doctor" ???
[email-masked]

Look out folks the "GRAY JELLO" is melting!