WQNR-FM HT-5FM Transmitter Load Tuning Mechanism Repairs, Replacement of Front Panel Circuit Breakers, and Telephone Wiring Repairs – September 27, 2021

During recent work and tuning on the WQNR-FM Harris HT5FM transmitter, the factory installed U-joint which links the front panel “Load” adjustment control to a linkage rod broke. I had to purchase an aftermarket replacement U-joint, bore it out to 1/4″, and install it in the transmitter. I also replaced three front panel circuit breakers which had become “flaky” with age, which is a common problem. I also had to make a quick run to a machine shop to get a custom linkage rod fabricated, which you will see and is explained in the photos below. The recent lightning strike damage had burned-out the telephone line wiring coming into the building and damaged the telco interface box on the outside of the building, so I finished up the repairs on the phone wiring during this same on-site work.

Power output on the WQNR-FM Harris HT5FM transmitter had dropped to around 68% after some burn-in of the recently replaced 4CX3500A PA tube, but due to the broken U-joint in the load tuning mechanism, I couldn’t peak the tuning for full TPO.
One of the ears on the factory U-joint which connects the front panel “Load” tuning knob to a linkage rod had broken off.
View of the other half of the broken U-joint. This photo shows the part of the U-joint which is attached to the back of the “Output Load” tuning knob/dial.
Front panel “Output Load” adjustment knob/dial, which would not function due to the broken U-joint assembly.
The rod on the left is a replacement 1/4″ diameter stainless steel rod, which I had to run to a machine shop in Montgomery, AL to have fabricated. I had to get a new, longer rod made because the aftermarket U-joint I had to install was physically shorter than the original one, causing the original rod to be about 1/2″ too short.
Circuit breaker front panel section of the Harris HT5FM transmitter partially removed for circuit breaker replacements. The Bias, IPA, and Screen circuit breakers had become troublesome with age, which they are well known for doing. Because they had become mechanically weak, intermittent contact failure within the breakers was causing occasional transmitter shutdowns and problems with restarts.
Rear view of the circuit breaker panel on the Harris HT5FM transmitter while partially removed for access in order to install three replacement breakers.
Almost done with the replacement of three of the circuit breakers. It’s not really a difficult task from a technical perspective, but it is a bit time and labor intensive removing the old breakers, keeping the wires and terminals sorted out, and reattaching them all to the new breakers.
Now that’s more like it! With the load tuning mechanism repaired and new circuit breakers installed, getting the transmitter tuned up and back to 100% TPO only took a couple of minutes after letting it run for about 30 minutes for the tube to warm up and settle-in a bit in terms of tuning.
Telephone wiring punch block inside the building. I finished permanently rewiring the line, including the MOV surge/transient protector which can be seen attached along the left side of punch block. We had been waiting for the telco provider to install a replacement interface box on the outside wall of the building. The old box had a couple of problems. One was the fact it had gotten burned-out by the recent lightning strike at the site, which had also totally blown out the telephone wire coming from the telco I/F box into the building. I had previously run a temporary piece of wire from what was left of the telco box; however, the box had then been ripped completely off the side of the building and physically demolished. I can’t say with total certainty how that last damage had occurred, but I think I have a pretty good idea. See next photo.
I have a strong suspicion that this characters had a hand in demolishing the telco interface box on the outside of the building. Oh, the joys of sites located in working pastures. I’m not really saying it was a long workday, but I definitely worked ’til the cows came home… and then some.