burnout – Engineering Radio

The breaker keeps tripping…

This is yet another addition of the “Burned up Sh*t” collection:

It is a breaker from a 5-ton AC compressor. Back in the bad old days when I was the Director of Engineering for a 28-station group Headquartered in Harrisburg, PA, I received a phone call from one of the local engineers. He stated that the studio AC unit compressor had burned out again and the breaker kept tripping. What did I think, asked him. I thought perhaps he should dig a little deeper and determine why the breaker was tripping before throwing another AC compressor at it. When are you coming to town again, he cheerfully inquired.

Okay, I get it.

I started by calling the HVAC company to inquire what had gone wrong with the compressors. Winding shorted to the case for both units was the answer received. It being July and mighty hot out, the various worker bees in the studio were feeling inconvenienced by the sweat in their eyes and dripping on their work, etc. I called the local manager and asked for a hotel room, I’d be up tomorrow. Then I called the HVAC guy back and asked in to meet me at the studio tomorrow afternoon.

Upon arrival the next morning, I found the fifth-floor studios to be hot, as reported. I trip to the roof location proved to be hotter still. I tested the voltages at the compressor unit with a DVM and everything looked good. A trip down to the utility room found the electrical panel in reasonable shape. Then the local engineering guy chimed in, “Oh yeah, I forgot to tell you, the breaker hums and gets hot when the compressor is on.”

It’s always that little bit of missing information…

I took the breaker out and sure enough, the fingers were all arched and nasty-looking.

I replaced the breaker, the HVAC guy showed up, with a new compressor and the studios began to cool off around 3 p.m.

Since then, I have specified Square D QO bolt-on breakers for new installations, especially for heavy loads like AC units, transmitters, and so on. They are a little more expensive, but in light of two AC compressors, the unscheduled trip out of town, and the grumbling staff, it is better to pay upfront for better equipment than to put up with preventable outages.

Crown D75 monitor amp goes terminal

Happened the other day, took out the monitor speakers too. I am not sure how this happened, but the production director reported that the speakers began making very loud squeals. Somebody finally thought to turn off the amp using the conveniently located on/off switch on the front panel.

Crown D75 audio board burned open resistor

The two-watt resistor is burned open. Also, this got so hot it burned a hole in the circuit board below it. Truth be told, I think this amp was about 25 years old and due to be replaced when the new studios were built out.

I’ve seen these Crown amplifiers self-destruct in the past.

Delta Current Sample Toroid

Another example from my blown-up shit collection, artifacts division:

Delta TCT-1HV current sample toroid destroyed by lightning

This is a Delta TCT-1HV current sample toroid that was pretty well destroyed during a thunderstorm. I mounted it on a piece of plexiglass because I think it looks cool. This unit was installed at the base of the WGY transmitting tower. One June evening, I received a call from the station operator (back when they had live operators) that the air signal sounded kind of “funny.” So I turned on the radio and sure enough, if one thinks a radio station that sounds like a motorboat is funny, then, why yes indeed, it did sound funny.

Since I only lived a few miles away from the site, I jumped in the trusty truck and headed over. Upon arrival, I found the MW50B on the air at full power, with the carrier power swinging wildly from 20-90 KW with modulation. Hmmmm, bad power supply? Turned the transmitter off and tried to place the backup transmitter on the air. Now the old Gates BC5P had never been super reliable in the first place, but it was odd that it would not even run at all.

Then I had a hunch, let’s walk out to the tower I said to my assistant who had shown up to help. When we got to the ATU building it was filled with blue smoke. Ah ha! Somebody let the magic smoke out of one of the components! I was expecting a capacitor blown in half but was surprised to find the copper tubing that connected the ATU to the tower melted in half. Lightning must have caused an arc between the tubing and the toroid and for some reason, the transmitter kept on running while it was arcing. The copper tubing in the picture with the toroid is only missing about six inches, the way the system was mounted at the tower base, fourteen inches of copper tubing was missing, or rather melted into a puddle on the bottom of the ATU.

I quickly found another piece of 1/2-inch copper, cut it to length, flattened out the ends with a hammer, and drilled mounting holes. Luckily I was able to get everything back in order quickly and the station returned to the air about an hour or so after it went off.

Everything has a cause. Investigation showed that the VSWR circuit on the MW50 had been disconnected from the directional coupler. The lead was un-soldered and taped off, so it was quite intentional. I spoke briefly with two of the three prior engineers that had serviced the MW50 over the years, they both blamed the other one. I surmise this; The WGY tower was prone to lightning strikes because of its height. Even if the tower was not directly struck by lightning, oftentimes the guy wires would arc across the insulators, causing the MW50 to momentarily interrupt the PDM signal and drop the carrier for about a second. Some programming people at the station did not like this, it sounded bad on the air, so one of those guys undid the VSWR circuit, and voila! No more momentary outages during a thunderstorm! Brilliant! Except for the 60-90 minute outage one night…

Sometimes it is better to tell the program directors that their idea is not good, then move on.

Harmonic Filter for BE FM-30T

Another example from my blown-up shit collection, pictures archive:

Burned out harmonic filter, BE FM-30T transmitter — Burned-out harmonic filter, BE FM-30T transmitter

The harmonic filter from a Broadcast Electronics FM-30T. This actually started in the bullet connector to the 3-inch hardline on the output side of the filter.

Burned out 3 inch hard line section — Burned out 3-inch hard-line section

Again, I did not install this myself, someone else did. Cutting 3-inch hard line is pretty straightforward. When using a field flange, the outer and inner conductors are cut flush. Both conductors should be de-burred and filed smoothly. It only takes a little thing to start an arc with 30 KW of FM power, so once again, attention to detail is key to avoiding these things.

Fortunately, BE sent along replacement parts for the harmonic filter and the line section was replaced.