This is kind of long but I got the impression that this is a common mode of
failure if you take a lightning strike and maybe some others might profit
from my experience and symptoms. I could have sent the rig back to Ten Tec
(which was their suggestion) but one of the main reasons I got the Omni was
that I want to be able to take care of the rig myself. I have repaired some
of the Japanese rigs and it is a nightmare compared to Ten Tec rigs. I have
owned 3 Ten Tec rigs and I could repair all of them.
Recently my Omni VI took a lightning hit. At first the only problem seen was
that the power output was not shown on the Omni meter even though my
external watt meter showed expected power.. I traced it to op-amp U1 on the
9MHZ filter boad called Ten Tec and received the op-amp at no charge. I
changed the part (if you look at the 9MHZ filter board and compare it to the
schematic you might wonder where all the parts are. Well they are surface
mounted on the solder side of the board), started to tune the antenna and
'poof' smoke from the band pass front end filter board and the Omni's fuse
blew. Never being one to reflect when action could be taken I put in a new
fuse. I noticed that all was well until I hit about 50 watts then another
fuse, and another, and another etc. until if fixed it so well that I had no
output power. At this point all I had to do was hit the tune button with the
RF drive at minimum and the fuse blew. I found that if I disconnected the
drive to the finals or the cable from the low pass filter board to the band
pass filter board(this is the receive input) I could press the tune button
without the fuse blowing.
Of course I think the finals are shot so I better call Ten Tec. With their
usual accuracy they said it was probably a lightning strike and the finals
were OK but that all the diodes on the low pass filter board were probably
damaged as well as 4 on the band pass filter board (also two resistors in my
case).
Another shipment of free parts was on the way including a small 5.6 micro
henry inductor on the BPF board (that's where the smoke came from). This
inductor looked just like a resistor but Ten Tec explained what it was.
While I was waiting for the parts I figured I would check out the rest of
the rig and found that the serial port was not working with my logging
program. I traced that to the MAX232 IC on the logic board, got one locally,
replaced it and the serial port was working again.
The parts from Ten Tec arrived and I replaced the diodes and resistors on
the low pass filter board and started on the BPF board when I noticed
another inductor and a resistor were burned so another call to Ten Tec and
another shipment of free parts.
I got the new parts and repaced all the obviously damaged ones and the ones
Ten Tec Service said I would need to, put the Omni back together and had
95-100 watts on all band with normal current. Hooray! right? no not with my
luck the Omni was deaf as a post on any band above 30 meters so another call
to Ten Tec (thinking all the time that I am going to have to send it back
just as they suggested from the beginning). But again Ten Tec service came
through. They said that one or more of the filter switching diodes on the
BPF board were probably damaged. These diodes are just switching diodes so
they didn't have to send any since I had some(I got so many free parts from
them they probably will have to add my name to the stockholders report). I
checked all the diodes on the board and sure enough the one that switched in
the 80 meter filter was shorted. I replaced it and now the Omni is 100%
again.
I also discovered that the schematics in the manual may not match the actual
hardware so check with Ten Tec if you discover that your board does not
match the schematic.
Parts replaced by board:
Low Pass Filter Board:
D2,D3,D4,D5,D6,D7,D8 (SOME OF THESE ARE PIN DIODES IN A TO-92 CASE D2 and D3
ARE SPECIAL DIODES SO GET THEM FROM Ten Tec)
R4,R5
LOGIC BOARD:
U14 (MAX232 RS-232 IC)
BAND PASS FILTER BOARD
R10
L2,L3 (THESE ARE SMALL INDUCTORS THAT LOOK JUST LIKE 1/4 WATT RESISTORS GET
THEM FROM Ten Tec)
D7,D8,D9,D10 (PIN DIODES GET THEM FROM Ten Tec)
D12 (SWITCHING DIODE)
I really don't beleive that I could have repaired this rig without the help
of Ten Tec Service. Having had experience with Kenwood and Yaesu (not all
bad but not like Ten Tec's service) I am sure it would have had to be sent
back if it it was from one of those fine companies.
Best Regards
Jim W8IT
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