[RTTY] OMNI VIB+ ( if you don't have one, delete )

[K4SB]

Think I mentioned when I posted my score that my Omni gave up the
ghost about 4 hours before the end of the contest. Problem was when
the unit was switched to transmit, it
popped the power supply circuit breaker, and although it would accept
a reset, same thing would happen again.

Talk about something which will drive you crazy! I finally succeeded
in getting the thing to transmit by disconnecting the receiver RF
input line. That allowed the unit to go to transmit, but then found a
little more than 10 volts of RF on the B+ line. Finals were
oscillating like crazy, and of course popping the cb in the PS.

Finally called Ten Tec and asked them if I was going crazy, and they
confirmed that the OMNI does indeed have this problem. It seems that
the design of the unit is such that when you go to transmit, the
receiver is NOT disabled, but is biased very heavily toward cut off by
3 diodes on the low pass filter board. ( page 4.7 in my manual, cable
17 marked TO RX INPUT. Well, I checked the diodes, and all were good,
but replaced them anyway. Problem still existed. So at this point, I
installed a very small 12 v relay, and physically cut the RX input
line and ran it through the relay. B+ to the relay
was obtained from TXd of 4 pin connector 9.

So, in effect, the unit now breaks the RX input line on transmit.

Ten-Tec advised they often see this condition and have a new board
which corrects it.
So, if you have to send yours back to mother for repairs, you might
ask them to replace this board. Strangely enough, I also found D2 and
D3 ( SWR circuit ) were blown. 

Or, just do as I did. Unit now on line and operating perfectly. I do
not know if all versions of the OMNI series do it this way, but you
might check your schematic.

And sorry for the band width for those of you not affected.

73
Ed