Tom -
>From the N6TR TS850 page:
Frequency display is all dots - and the radio sends "UL" in morse code over
the speaker (indicating an unlocked condition with the frequency
synthesizer):? This failure might be temperature related - and possibly
show up more often when tuning the VFO in specific places (around 1800 -
1850 kHz is one place I have seen it fail). This is probably the DDS chip
on the carrier board that produces the VFO frequency. The CAR board is
under the bracket that would hold the voice memory board if you had it
(under that door on the top of your radio). Remove the four screws that
hold the bracket and find the CAR board with the four big chips on it. You
can put a scope on the PLL-1-DL01 output and watch the output voltage as
you tune around. On a functioning board, the output level should be pretty
constant as you tune the VFO through a 500 kHz segment. If the output
changes a lot when the VFO jumps from one frequency extreme to the other,
then the failure is probably the IC1 DDS chip. They cost $28 and will
require you to have the right equipment to work with surface mount VLSI
ICs.
One step you should take first is to make sure all of the connections to
the CAR board are good.? Remove all of the cables, and reseat them.
Raspy signals on some bands - maybe no display or all dots:? I had this
problem with one of my radios after taking it to Louisiana for the
Sweepstakes.? The signals on 20 meters all sounded raspy - and broad.? At
first, I thought it was something wrong with the transmitter of the other
station, but when all of the signals on the band had the same problem, I
knew it was my receiver.? I believe my transmitted signal sounded as bad.
It seemed to be temperature related and in extreme cases, the LO1 output
from the PLL board was going away.? And then Dave, NR1DX, hit the nail on
the head with this:
I just finished fixing the second TS-850 in my career with this
problem...particularly symptomatic is the raspy sound which gets worse as
the unit heats up. In both cases TC1 on the PLL board needed only to be
adjusted so that TP2 reads 5.0v. (See the service manual page 98, step 8).
The little trimmer cap TC1 inside the VCO-2 can has been documented as
getting flaky with time. On the first radio the problem occurred at about
year 7 resetting the cap cured the problem and the radio ran fine for
another year without incident before I sold it and upgraded to a TS-950SDX.
I recently came on a bargain ($550) TS-850SAT (10 years old) which was too
good to pass up (including the a 500HZ and 270 Hz CW filters and a DRU ).
It had this same problem only worse in that after setting the cap the unit
would play fine... for a while, then drift back into the same old problem.
I then replaced the cheap Kenwood trimmer cap with a glass piston trimmer
cap which so far after four hours is stable as a rock.. Ill send you a
picture of the mod ( if you want it) as I had to drill a hole in the side
of the VCO-2 can to mount the new trimmer cap.
So check your problem radio's PLL - TP2 when it gets raspy, I'll bet it is
no where near 5Volts, the setting is quite critical.
When I checked the voltage on TP2 (located near the front of the board
right next to the smaller shiny box), it was around 4 volts.? I adjusted it
up to 5V, and things sounded worse...? that was until I removed the lead to
the DVM (it was acting like an antenna and picking up all sorts of junk).
After that, the radio sounded like new.? When I thanked Dave, I got this in
response:
Don't thank me ... thank Cliff at AVVID he is the one that clued me in the
first time three years ago. The guy is amazing Here is the picture of the
modification and the PLL board afterwards.
You will see the little piston cap on the left of the VCO2 can. The little
melt from the soldering iron on the edge of the little blue plastic thingy
was an "aw- $#!^", in trying to clear the holes in the board. Didn't hurt
it electrically...
To do this you have to remove the whole VCO2 enclosure there are about 5
places where the can is soldered to PLL board plus three wires. If you have
never used solder wick now is a good time to learn. Removing the can is
almost as difficult as brain surgery but still not as bad as changing one
of the DDS chips.
Charles Morrison
ProStaff : Documentation Specialist at APC - East Providence
40 Catamore Blvd
East Providence, R.I. 02914 USA
Tel Ext. 6652
charles.morrison@apcc.com
Amateur Radio callsign: N1RR
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