temp controller problems
Contact your vendor to inquire about the problem. Ask about any similar reliability issues from other operators. Switching vendors is a last resort. It's likely that they'll assign an engineer to assist in troubleshooting the problem. If they don't offer this service, then it's time to replace the vendor. A good vendor will value your business and offer help and a partial credit. I would begin with a batch test on the resitors and diodes they've bulk purchased to overhaul the controllers. I'd also look to see if the affected serial numbers were repaired by the same bench technician (procedure error). Since we seem to be talking about multiple airframes, the problem is likely to be internal to the controller or associated boxes. That is assuming that your fleet has not recently been subject to modifications that might introduce the systems error. Without the ability to review your system diagrams...I'm also suspecting an external high power amplifier for potential problems. The glass is the lowest probability. Good luck.