My Mission Today

It's not often I get to have a "planned outage" on one of the full powers, but this morning is one.

In an hour I'm shutting off a 100,000 watt classic rock FM (the one my employer just bought -- I'm now chief engineer for THREE full power stations).  My Mission? To pull the multiplexer board out of the exciter to replace 8 dried up electrolytic caps, and re-install.  Not to serious, but a pain in the butt.  Of course getting to the transmitter requires driving through a muddy farm field, LOL. Because FM transmitters are NEVER easy to get to!

Why? Because one of the caps is known to dry out and allow the power supply to oscillate causing a very high pitch whine, or whistle in the audio. Gates has a service bulletin for this, which the previous owners decided to never both with, so it's been driving people nuts for a year and a half. We received calls and emails --  would the new owners PLEASE fix the whistle!  So that's my mission this morning.

Trick is -- I, myself, can't even hear it! My old man hearing that has been abused with loud rock and roll in the headphones for 45+ years, andplayins in bands for a combined 20+ has left me with little hi frequency hearing -- so I never have heard it.  But my adult kids can, and the rest of the staff can, and most important the owner/boss can!

I'm off on a mission!



Carl Blare's picture

Knowing what the problem is makes the mission much more friendly than if you had no clue what was wrong.

Many technical problems I've known about were caused by "unknown reasons" and that makes solving them go through a longer period of search, discovery, repair.

I sometimes think I have a problem but it hasn't yet made itself known so there's not yet anything to look for.

Carl Blare

mighty1650's picture

I got lucky with our FM site, gravel all the way to the tower building. Can't say the same for our AM site which turns into a swamp when it rains. Luckily its behind  hospital so I have a place to park, still gotta walk though. That said, I've gotten stuck at both sites and almost got the wrecker stuck trying to pull me out at the AM tower. A rear wheel drive pickup from the 80s just doesn't handle mud well.

Radiodugger's picture

Thanks, Tim, for that. I am not an electronics tinkerer. I can build stuff. The SSTRAN, etc...but this is new to me. Replacing caps. My old Orban 424a Comp/Limiter is misbehaving lately. I suspect the caps. 

Am thinking about buying a Compellor or something similar, but there we go again, OLD caps! I use my Orban for recording, not just for broadcasting. I wonder how difficult finding replacement caps and determining which ones get replaced. Tim, at least you know which caps to preplace and where they are. Solder sucker, FOOP, FOOP, FOOP...and ya done!

I've never had the hood up on my Orban. I need basic tools. I also need a light/magnifier, as my sight is poor. I might buy a single channel Orban and make this a summer project...and then re-cap the single channel down the road. Again, never done it before. I don't even know how to tell if a cap is bad.


mighty1650's picture

Capacitors are pretty easy to come by and the vast majority are still manufactured by somebody or have a direct equivalent.

Bad caps are usually pretty easy to spot, look for bulging at either end of the cap as well as leaking or the fairly obvious exploded cap.

Most engineers I talk to tend to just replace all the caps in old gear to be on the safe side since caps are so cheap. Personally I just wait for the thing to explode or buzz and then replace them, not encouraging this practice I'm just lazy.

Rich's picture

Tim:  Hope that you got the audio whine/whistle in your Harris DIGIT FM Exciter fixed, per the Field Bulletin that was issued years before you recently became involved in its care.

FWIW, I was a member of the product development team for that exciter, which was the first in the world to use totally digital processes to generate a fully-modulated, standard FM broadcast waveform with considerably better performance than analog FM exciters.


Rich (Harris Broadcast Division FM Product Line Applications Engineer, 1980-1999)

rock95seven's picture

If i lived close i would take you to the muddy transmitter shack, Jeeps hardly let people down unless they are just abused or the driver is a total nimrod. Thankfully i am none of those things. lol Not that your present vehicle can't do it , just saying if i was close by i would help out just for the adventure.

 Barry of 1200 AM BBR - WQYY 664

timinbovey's picture

Rich: There's always a surprise waiting when one takes over a new station.  

I shut the transmitter down and went to pull the exciter out of the rack (it's on rails, as you know) It  would only pull out maybe an inch -- it was hanging up on something.  Turns out that something was the top cover that had NO screws installed, so it wasn't sitting flat and was catching.  I used my pocket knife to hold it down and was able to slide the unit out. 

Upon opening the hinged top I noticed several of the nuts that hold the cover over the multiplexer board were missing.  Once I got it off and the board out I noticed the capacitors had been replaced once before! I could tell due to the horriffic soldering job.  Oddly, the top cover was still in stock condition. With this project one is instructed to drill five 1/4 inch holes in the top edge, and 5 more on the top of the cover to allow increased airflow.  This was not done.  You could also obtain a new cover from Harris that already was modified with the additional air holes. I had brought a new cover with the additional air holes from Harris with me.  I took the board home to switch out the caps. One cap had one lead that wasn't even soldered.  I could easily wiggle it as it was held in place with only one lead. 

Got them all replaced, got back out there, fired it up, all was good. Stuck around for half hour hour or so just to be sure everything was good.  Took off, and about a mile from the transmitter it went off the air.  Got back, exciter was shutting down.

I noticed the cooling fan wasn't running. I could open the lid and simply blow on the board behind the left hand side of the front panel and poof, it came on, and ran fine.  For about 15 minutes. Then it shut down again. I quick little puff of breath was all it took to cool it enough to start up again (the PLL was unlocking).  Fan was kaput. I suspect it was running sluggishly before I shut down for repairs and just wouldn't start up again.  Left it off the air, ran home got a roll of duct tape, a mic stand with a goosneck, and a small, cheap desk fan.  Taped the fan to the gooseneck, positioned it perfectly to blow on the chassis where the real fan would be blowing, and it's been running fine since Sunday morning at 10 AM. With the exciter out, top flipped open, and a fan blowing in it LOL!  New fan is on the way from Harris (actually Gatesair now). 

Good news it the boss and my daughter and her boyfriend report the whine is gone! We had complaints from old listeners who said that whine had been going on for well over a year, maybe two. 

We aren't really taking advantage of the digital advantages of this exciter, running analog audio into it.  But who knows down the road!

I wonder if I call my parts guy at Gatesair if he'd know what size the screws are for the top cover? I have no idea but it really should have the top screwed down. Who the heck leaves the screws out, but doesn't leave them laying around someplace?

THEN the station owner and the IT guy mentioned to me when they were out there working on computer stuff (before we took over) they noticed that it had been running with the exciter pulled out of the transmitter.  Of course neither one of them had any idea what an exciter was! I bet it was running warm due to slow fan. 

It's always an adventure.

Now I'm wondering what other repairs or improvements may have been done to the exciter with the same skill level.  The current former engineers claim to have NOT worked on that card.  And looking over the logs there have been several engineers working on it over the past 5 years or so.



timinbovey's picture

Not to worry. I've always had all wheel drive or 4 wheel drive. All these decades as a morning guy and engineer in Minnesota means I have to get to the station in the blizzard so I can tell people school is closed!

Have an all wheel drive Escape right now. Before that a Blazer, before that a Surburban, and before that a Jeep Wagoneer.  I loved the Quadratrac in that bugger!

But it didn't matter.  As the temp had falled to about 26 degrees overnight so the "road" through the field/woods was pretty well frozen, or at least firm!  By later that afternoon it was pretty squishy again!


Rich's picture

From Reply 8 (TIB):  ... Now I'm wondering what other repairs or improvements may have been done to the exciter with the same skill level. ...

No doubt !

The new owners of that station are fortunate to employ you, with your broadcast hardware troubleshooting experience and resourcefulness demonstrated in resolving this problem.

Such skills are fairly rare, these days.

rock95seven's picture

My 2000 Grand Cherokee has Selec-Trac and it does rather well in most weather conditions.
Ice, not so much but really when roads are icy should we actually be on the roads?? lol

4x4 or not, ice is a no-no.

 Barry of 1200 AM BBR - WQYY 664

timinbovey's picture

Back to the scene of the new transmitter today with a replacement cooling fan.

The replacement was fairly painless.  The old fan, if coaxed a few times would indeed start turning.  Very slowly, but turning. Reinforcing my theory that it was on the air with a very slow fan for some time, and when I shut it down to replace those capacitors the fan just wouldn't start up again.  And it was clearly running warm, if not hot before, possibly causing the already replaced caps to fail again, and probably the reason they caught it running before we took ownership, with the exciter pulled out of the rack.

The new fan took off at full speed no problem.  I noticed the fan I removed had a manufacture date of 2014.  So, it wasn't the original -- build date on the transmitter is 2004. Three years out of a fan doesn't seem normal to me!  The replacement was ordered from GatesAir simply because it was handy and I knew it would be the right one, cost $116. I found what appeared to be a fan with the same specs at Digikey, but they were out of stock and figured at least 8 weeks to get one. It was only $37. But again, quality?

No cooling needed in my Part 15.