Collins TDR-94 transponder/CTL-92 controller

[Gerund]

If anyone can help with this I would be most grateful!!

I am flying a B1900D with Rockwell Collins TDR-94 Mode S transponders with a CTL-92 controller - a pretty standard set up.

There have been intermittent problems with both transponders and they are now on the blink so often that the plane is about to be grounded. Unfortunately, the plane is on contract and fixing the problem is taking forever.

The Test function gives an indication of DIAG 42.

Unfortunately, we don't have a manual here and I have not heard back from Rockwell Collins in the States.

Can anyone help with what DIAG 42 means?

It would be much appreciated...

[Gerund]

Sorry, to bring my own post back to the top but getting a bit desparate here!

This transponder/controller type is VERY common - surely some nice person out there, with a manual lying on their bookshelf, can help me out??

Thank you in anticipation! Still NO reply from the States...

[QAVION]

Sorry, no handbook, Gerund, but surely if you are having problems with both transponders, the problem should be relatively easy to faultfind?

Have you replaced the ATC antenna relays? Have you changed the Control Panel? Perhaps other systems in the same frequency range are interfering with with your ATC? (DME, TCAS) Perhaps a particular system is putting out too many suppression pulses? (Pull these boxes out of the racks to see if this makes a difference)

Have you checked the coax connections on the relays? I can't recall if the relays are solid state, but I suppose you could give them a "technical tap" anyway? ;)

Unfortunately, there's no guarantee that this DIAG 42 will be the cause of your problem.

Cheers.
Q.

[avioniker]

OKAY, here you go...

Straight from the "horse's mouth":

Diag 42 - Bottom Receiver Channel Fault.
Note: This may be intermittantly annunciated for intermittant faults.

Sounds like you have a bad lower antenna coax switch or relay.
If you don't have antenna switches then start looking for a bad ground or corrosion under the lower antenna(s).
If there's only one lower and one upper antenna then you DO have antenna switches.

Good luck.

[Gerund]

QAVION and avioniker

Sorry for the delay in thanking you for your help, but e-mail problems here.

Thank you so much for going to so much trouble to assist - the problems are now being actively investigated using your information.

Once again - many, many thanks.