Transponder prob..

Had a strange one today..

While squawking IDENT , our "ident" stuck "on"

ATC confirmed we were continuously "identing"

Cycling the transponder to off then on again cleared the
ident fault.

Pressing the button again locks the ident light on again
until the power is cycled..

Any thoughts?

Switch appears mechanically OK, (clicks when pressed, clicks
when released)..

It is a King KT78 "KT76TSO"

Dave

"Dave" wrote:
While squawking IDENT , our "ident" stuck "on"

ATC confirmed we were continuously "identing"

Cycling the transponder to off then on again cleared the
ident fault.


The service manual sheds little light on the fault. So we start at
the switch, and then if OK note when that momentary switch is
closed, a pin on the big IC chip labeled IDENT is grounded. Could
be the chip, or the capacitor which sets the timing for the indent
to be on. It says this time is variable, suggesting a timing
capacitor somewhere (manual silent on this though). Will be
expensive to fix if the chip is bad, unless jiggling it in the chip
socket fixes it (if socketed).

Fred F.

Yup... more info.. tech here says there is a timing circuit that
gets initialized when switched is closed. I can hear the switch
"click" off when released.. He suspects the IC or something
associated with it...

It is out and off to him now, will report results here when I
get the final result..

Here go more AMU's

Dave


On Sun, 13 Nov 2005 21:57:42 -0500, "TaxSrv"
wrote:

"Dave" wrote:
While squawking IDENT , our "ident" stuck "on"

ATC confirmed we were continuously "identing"

Cycling the transponder to off then on again cleared the
ident fault.


The service manual sheds little light on the fault. So we start at
the switch, and then if OK note when that momentary switch is
closed, a pin on the big IC chip labeled IDENT is grounded. Could
be the chip, or the capacitor which sets the timing for the indent
to be on. It says this time is variable, suggesting a timing
capacitor somewhere (manual silent on this though). Will be
expensive to fix if the chip is bad, unless jiggling it in the chip
socket fixes it (if socketed).

Fred F.

"Dave" wrote:
Yup... more info.. tech here says there is a timing circuit
that
gets initialized when switched is closed. I can hear the switch
"click" off when released.. He suspects the IC or something
associated with it...


The bummer about that the King VLSI chip is absolutely nothing in
function like the 3 gigahertz Pentium CPU in our now cheapie damn
computer, enormous heat sink now and all that. The service manuals
always say to suspect the big IC last. Disheartening, when you see
King's pricing on a 20-cent, common transistor. I was in an
avionics shop once, and spotted a bin of them common transistors.
Does FAA actually allow them to use those? And do they like just
bill $$ that way per invoice? Oh, the joys of owning airplanes
when it comes to genuine proprietary parts, the VLSI, in avionics
boxes we think are all that complicated, but to a good tech guy
really ain't.

Fred F.

You can buy a cheap multimeter at radio shack for about 10 bucks. Put it on
continuity and you are good to go. I know it is not as fun as building it
yourself. Just think of it as a kit with one part.

"TaxSrv" wrote in message
...
"Dave" wrote:
Yup... more info.. tech here says there is a timing circuit
that
gets initialized when switched is closed. I can hear the switch
"click" off when released.. He suspects the IC or something
associated with it...


The bummer about that the King VLSI chip is absolutely nothing in
function like the 3 gigahertz Pentium CPU in our now cheapie damn
computer, enormous heat sink now and all that. The service manuals
always say to suspect the big IC last. Disheartening, when you see
King's pricing on a 20-cent, common transistor. I was in an
avionics shop once, and spotted a bin of them common transistors.
Does FAA actually allow them to use those? And do they like just
bill $$ that way per invoice? Oh, the joys of owning airplanes
when it comes to genuine proprietary parts, the VLSI, in avionics
boxes we think are all that complicated, but to a good tech guy
really ain't.

Fred F.

Well....

Operational check today.. xponder working fine, Ident working
properly

Hopefully the whole thing certed next week

Ah.. joys of aircraft ownership...

Flew 3 hrs today...smooth air, working trip, 2 hrs flying instead of 5
hrs driving...Cher on the CD player....

Makes working on the weekend almost fun!

Dave



On Mon, 14 Nov 2005 18:23:10 -0500, "TaxSrv"
wrote:

"Dave" wrote:
Yup... more info.. tech here says there is a timing circuit
that
gets initialized when switched is closed. I can hear the switch
"click" off when released.. He suspects the IC or something
associated with it...


The bummer about that the King VLSI chip is absolutely nothing in
function like the 3 gigahertz Pentium CPU in our now cheapie damn
computer, enormous heat sink now and all that. The service manuals
always say to suspect the big IC last. Disheartening, when you see
King's pricing on a 20-cent, common transistor. I was in an
avionics shop once, and spotted a bin of them common transistors.
Does FAA actually allow them to use those? And do they like just
bill $$ that way per invoice? Oh, the joys of owning airplanes
when it comes to genuine proprietary parts, the VLSI, in avionics
boxes we think are all that complicated, but to a good tech guy
really ain't.

Fred F.