Aviation Forum / General / IFR / September 2008

I agree it probably isn't ATC radar. I have flown through countless
ATC radars and none TMK did any harm.

However, looking at the KS27x servo design defect in the current limit
circuit, I cannot rule out the possibility that a *brief* current
limit condition might get prolonged (because the current limit circuit
is not stable as a control loop) until the whole lot burns out. More
likely however, a continuous upset lasting the required few seconds
would be the cause.

You would not need much power to upset the servo. I looked at the
schematic of the input amp (will update the website soon with that)
any RF above ~ 1MHz will go straight in - there is no passive
filtering at all. Really negligent design.

The thing about the $2 pot is just a standard problem in avionics. If
there is no authorised repair procedure, you have to replace the whole
instrument. I have just been quoted $1350 for a LCD for a KLN94. The
KLN94 is beautifully built internally, with excellent design practices
(loads of filtering etc) and normally they are very reliable, so it
was a shame to see this. But I had bought a spare one a while ago.

You could have bought a refurb KC225 for far less than $3k - I have
just bought two of them.

There is an STC for the STEC 55x but speaking to avionics installers
who fit them, they have as much trouble with them. Apparently, pitch
instability is a common problem. Also, the STEC servos have the cable
wrapped around the servo pulley so changing the servo (e.g. to service
the motor brushes) needs that to be undone - a lot of work.