K1TTT Technical Reference

Temporary fix for stuck indicator:
From K1TTT on troubleshooting Yaesu G-xxxxSDX control boxes.
unplugging the control cable should cause it to go to the counter
clockwise stop on the indicator.  if it doesn't it probably means the
indicator drive motor is bad.  this is a common problem with the yaesu g
series of rotors, i just had to fix one the other day again.
for a quick check to see if that is the problem do the following:
1. remove the metal cover (2 screws on sides and 4 feet)
2. remove front panel (3 screws on bottom, 2 on top)
3. pull front panel out about 1-2cm and look in to the gear
mechanism on the left side.  you should see a small pulley with
a rubber belt on it.  
4. plug in the rotor power but remove the control cable.  be
careful, there are exposed connections where line power is available
but they are on the bottom side of the front panels on the other
side of the indicator at the switch.
5. turn on the rotor.  with a small screw driver gently try to 
turn the small pulley with the rubber belt, if it starts to slowly
turn the needle it confirms the motor is the problem.  if it doesn't
start operating it could still be the motor, but may also be the
control board.  if it goes back at full speed it might have been
a mechanical jam but i have never seen that here.
what happens is the commutator segments in the motor are too soft
so after a while the metal 'wipes' and powders  enough to get in
between the commutator segments and essentially shorts out the 
motor.  if the controller is left on for long periods in this 
condition it can also burn up the 2 current limiting resistors
and/or drive transistors on the little circuit board behind the
motor.  giving the motor a push gets it past the shorted spot and
at least shows you that the rest of the drive and control stuff is
working, but it won't last.
a temporary fix goes as follows:
1. from the above condition, pull the power plug.
2. remove the small circuit board behind the drive motor (4 screws)
3. with needle nose pliers uncrimp the 3 crimps that hold the
plastic back onto the metal case of the motor.
4. very gently pry the plastic back off the motor.
5. with a needle or other very small type of dental pick tool 
carefully scrape the gunk out from between the segments of the
commutator, you can remove the small nylon washer on top of the
shaft for better access.
6. use a paper clip or small pair of tweezers inserted through
the small slots on the plastic back to hold the commutator brushes
out of the way and carefully replace the plastic back.
7. recrimp the metal back. and replace the circuit board.
this should restore operation for a while, but eventually the 
motor will need to be replaced.  this process is much more 
involved as you have to disassemble basically the whole front
panel to get to it.

Replacing indicator motor:
For those of you who remember the story of the bad motors in the
Yaesu rotor indicators the following is the process to replace
it.  This also shows how far to disassemble to replace the dial
light for those who had asked me about that.
G2800SDX indicator drive motor replacement procedure.
1. Remove 2 screws on top sides of case
2. Remove 4 screws in rubber feet.  Pull case off of control box.
3. Remove 2 screws in top of front panel
4. Remove 3 screws in bottom of front panel
5. Lay front panel down on table.
6. Remove 4 screws with lock washers and flat washers from small
circuit board on back of indicator drive assembly
7. Unsolder red and black leads from motor.
8. Remove pointer cover, pointer, and compass overlay.
9. Unplug cables from large circuit boards to right of drive assembly.
Be sure to mark the two eight pin ones to get them back in the right
10. Remove 4 screws with lock washers and flat washers from 
large circuit board.
11. Remove 4 standoff bolts with lock washers and flat washers from 
the bottom large circuit board.
12. Remove 2 screws from the small bracket that holds the main 
power switch.
13. Remove 4 screws that hold the indicator assembly to the front
panel.  one of them should have a plastic insulator stuck on it under
the large circuit board.
14. Remove 3 screws with plastic spacers that hold the clear degree
dial on the indicator assembly.  (now is the time to replace the 
inducator bulb if that is bad!)
15. Remove 4 screws that hold the large metal plate on to the front
of the indicator drive assembly.
16. Take the rubber band off the motor pulley.
17. Remove the motor pulley from the shaft.
18. Remove the 2 screws that hold the motor to the frame.
Reverse process to reassemble with new motor, just watch out for
the following steps:
17.  Make sure the motor pulley aligns with the big pulley that
the rubber band goes around
15. I think the holes only line up one way.
6. Test repair here, chances are 50-50 that you got red and black
wires on motor reversed.
ALL. watch out for pinched wires or wires with too much strain,
they are probably wrapped around the wrong way.

Rotor turns faster one way than the other:
They told me there was a carbon trace across one of the feedthru caps which explained it to
me...until I measured it and found nothing! However, the bottom of the modul is rusty, so
maybe it IS something that could have come and gone. Anyway,
keen observation and simulation...Tnx 73 JACK
David Robbins wrote:
> i wonder if a ground in that brush noise filter could cause that problem.  in
> looking at the schematic of the control box the power circuit is virtually
> floating.  it is tied in with the speed control but there doesn't seem to be a
> real good common ground between the circuits.  it may be possible that a high
> resistance leak to ground could upset the speed control, and that it could very
> likely affect one direction differently than the other if it was on one side of
> the motor vs the other.
> come to think of it, i can simulate that.... and i did.  and yes it does affect
> it that way.  a 2200 ohm resistor to ground from pin-5 of the connector cuts
> rotation speed in one direction about in half and doesn't seem to affect the
> other direction.  i picked 2200 ohms because that is what they use to connect
> the power ground to the control circuit ground(r38 on page 2 of the schematic
> 800sdx/1000sdx schematic).  this could also explain why it could cure itself, a
> bit of water in the rotor or cable could cause the same problem.  check that
> filter module to see if there is a low resistance from any terminal to a
> mounting bolt or for evidence of worn insulation or water.
> i can see why they might do something like that, but it doesn't seem to be a
> very robust implimentation of the idea.  it would look like they wanted to keep
> the motor circuit floating so there is no path for rf in or out of the motor.
> it would also prevent a single short to ground from breaking the rotor.  as you
> saw a short to ground slows it down one way but doesn't stop it... there are
> probably better ways to design the circuit though (maybe an opto isolator) that
> would avoid the slowdown problem also.
> JACK wrote:
> >
> > It IS working now. They repl the pot (checks fine with ohmeter, a module that filters
> > brush noise from the motor...all components check fine, a plastic gear that looks fine
> > but Maybe hole was enlarged or something not evident...that was 69 cents or something so
> > that doesnt bother me! hi   Also replaced ALL the ball bearings, charged $20 for a box
> > to return it and used a box big enough for a FT1000MP! Oh well...hope you dont have it.
> > W1CKA had the same thing with a 2800 but it went away by itself. I know my tower is
> > badly out of plumb, and ZM suggested that's probably got something to do with the
> > failure...but when I sent the rotor back it did the same thing without any load at all.
> > 73 JACK
> >
> > David Robbins wrote:
> >
> > > but does it work now?  what did they replace?
> > >
> > > i have not seen that kind of problem with any of them here.
> > >
> > > JACK wrote:
> > > >
> > > > Hi Dave. I know you have some Yaesu rotors and was wondering if you ever had a
> > > > problem with turning faster in one direction than the other? I just got one back
> > > > from Yaesu which was repaired, but I dont see anything wrong with the parts they
> > > > returned and dont know what really caused it yet! Tnx 73 JACK...mine are
> > > > G1000SDX...have two