DX50 air flow switch

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sallen
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DX50 air flow switch

Post by sallen » Thu Apr 26, 2018 8:25 pm

Have a DX50 with an air interlock problem. All four fans are running, no blown fuses. Have good air flow through transmitter. Have also removed the air filters to eliminate them. The transmitter is only run during the day. The air indicator will turn from Green to Red and shut the transmitter down. Hit reset and it runs rest of the day. its a 1999 vintage with bulbs in the Hi/Med/Low buttons, not LED

The air switch is S7 on the A19 board if I remember right. Its in the very right cabinet/driver section. Any one have issues with the switch going out? Its some kind of whiz bang solid state device???? No paddle or real air preasure setting, that I could see. And its soldered on the A19 board.

Any one have issues with the air switch on a DX50?

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PID_Stop
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Re: DX50 air flow switch

Post by PID_Stop » Fri Apr 27, 2018 8:12 am

That's strikingly similar to a problem we had with one of our Harris Diamond transmitters (DTV), where the air flow sensor would occasionally cause a shutdown for no good reason. The plastic plunger switch for the rear panel interlock was also flaky, and had the same effect (nothing like having two separate problems causing the same effect!). I figured it out quite by accident after a rather frustrating afternoon of fruitless troubleshooting, which provoked me to deliver an undeservedly mild punch to the side panel (I didn't especially want to hurt my hand)... and discovered that the air flow switch happened to be a couple of feet from the point of impact. It turned out that whenever the HVAC fired up, the duct would make a "BONG!" noise, and the vibration was enough to set off the switches.

Jeff

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RGORJANCE
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Re: DX50 air flow switch

Post by RGORJANCE » Fri Apr 27, 2018 10:56 am

During my "draft dodging days" in the USAF, we referred to that "gentle touch" as " brogan maintenance". Long before those days, while working in radio and TV, I used the "give it a whack alongside the head" technique frequently. It still is a very effective troubleshooting technique I continue to use to this day.

It sometimes is a handy "stress reliever" too, and during those episodes, I tend to really lean into it with a bit more effort!

Fossil

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kkiddkkidd
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Re: DX50 air flow switch

Post by kkiddkkidd » Fri Apr 27, 2018 1:17 pm

Percussive Maintenance or Shock Test was my goto work description while being held hostage in the 2-way world.

Funny story... I got a million of 'em.
One of our 2-way customers had an old tube Motorola base station mounted in a ratty old homemade steel outdoor cabinet that had to be lifted up and over the top of the station. The poor old worn out thing would quit receiving several times per year and would start again while just trying to wrestle the cover off of the pole mount. I tried everything from resoldering every conceivable connection, cleaning tube sockets with a tiny round file to replacing all of the tubes in the RX section. After gently cleaning, soldering, etc, etc, it would work for perhaps a month or two and quit again. Finally one day I pulled up on the hilltop, got out of the van and just kicked the living crap out of the side of the case, called their dispatch on my radio and left. It worked perfectly for months. It quit again, I drove up there and kicked the crap out of it again and it worked fine for many more months. My boss and shop owner one day commented that I had really improved it's dependability by all of my cleaning and reflowing. Not being one to ever keep my mouth shut... Told him that I had stopped it's monthly cleaning 2 years ago and now just kicked the living crap out of it a couple of times per year. He melted down and said that HE would take me over to the site (about 60 miles away) and show me how to properly clean, etc, etc. We went over and spent most of a day cleaning, polishing soldering, replacing, etc, etc.

Not more than a month later it stopped receiving again. I heard him on the phone with the dispatch and cringed when I heard him say that someone would be there that afternoon (Friday) and knew it would be me. He walked back into the tech bay and hung a note on the call board, "Kick the sh_t out of Xxxxxx Water Dept's base". I got paid overtime to drive 120 miles round trip to kick the living sh_t out of an inanimate object.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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kkiddkkidd
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Location: Lawrenceburg, TN

Re: DX50 air flow switch

Post by kkiddkkidd » Fri Apr 27, 2018 1:28 pm

sallen wrote:
Thu Apr 26, 2018 8:25 pm
The air switch is S7 on the A19 board if I remember right. Its in the very right cabinet/driver section. Any one have issues with the switch going out? Its some kind of whiz bang solid state device???? No paddle or real air preasure setting, that I could see. And its soldered on the A19 board.

Any one have issues with the air switch on a DX50?
Harris has used some homemade sensors that were similar to the mass air flow sensors used in automobiles. Some (but I don't think all) of the Gates1 series had a board down in the bottom/back with (IIRC) a resistor and some type of temp measuring device (maybe a thermistor) that measured the amount of airflow by measuring the change in resistor temp as a function of air flow across the resistor. It actually was a pretty slick little circuit.

It had a pizo buzzer that would squeal it's little heart out if the flushing fan quit and IIRC was only mentioned in an addendum or service bulletin.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

ncradioeng
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Re: DX50 air flow switch

Post by ncradioeng » Fri Apr 27, 2018 2:29 pm

It had a pizo buzzer that would squeal it's little heart out if the flushing fan quit and IIRC was only mentioned in an addendum or service bulletin.

Yes it would - and shut off the transmitter. I had to re-cap several of those to stop squirrelly operation. Also a chronic dust bunny will act as insulation and set it off if the air filter is removed.

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kkiddkkidd
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Location: Lawrenceburg, TN

Re: DX50 air flow switch

Post by kkiddkkidd » Fri Apr 27, 2018 7:08 pm

ncradioeng wrote:
Fri Apr 27, 2018 2:29 pm
It had a pizo buzzer that would squeal it's little heart out if the flushing fan quit and IIRC was only mentioned in an addendum or service bulletin.

Yes it would - and shut off the transmitter. I had to re-cap several of those to stop squirrelly operation. Also a chronic dust bunny will act as insulation and set it off if the air filter is removed.
You are correct about the dust bunny but in my case it was more like a dust raptor... The entire board was coated in sage and cottonwood fuzz. Pulling the mute plug off of the board will get the tx back on. I don't recall for sure but I think that you have to short the 2 wired mute plug for the TX to come back on.

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

Kent T
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Joined: Mon Dec 17, 2012 7:29 pm

Re: DX50 air flow switch

Post by Kent T » Fri Apr 27, 2018 7:15 pm

kkiddkkidd wrote:
Fri Apr 27, 2018 1:17 pm
Percussive Maintenance or Shock Test was my goto work description while being held hostage in the 2-way world.

Funny story... I got a million of 'em.
One of our 2-way customers had an old tube Motorola base station mounted in a ratty old homemade steel outdoor cabinet that had to be lifted up and over the top of the station. The poor old worn out thing would quit receiving several times per year and would start again while just trying to wrestle the cover off of the pole mount. I tried everything from resoldering every conceivable connection, cleaning tube sockets with a tiny round file to replacing all of the tubes in the RX section. After gently cleaning, soldering, etc, etc, it would work for perhaps a month or two and quit again. Finally one day I pulled up on the hilltop, got out of the van and just kicked the living crap out of the side of the case, called their dispatch on my radio and left. It worked perfectly for months. It quit again, I drove up there and kicked the crap out of it again and it worked fine for many more months. My boss and shop owner one day commented that I had really improved it's dependability by all of my cleaning and reflowing. Not being one to ever keep my mouth shut... Told him that I had stopped it's monthly cleaning 2 years ago and now just kicked the living crap out of it a couple of times per year. He melted down and said that HE would take me over to the site (about 60 miles away) and show me how to properly clean, etc, etc. We went over and spent most of a day cleaning, polishing soldering, replacing, etc, etc.

Not more than a month later it stopped receiving again. I heard him on the phone with the dispatch and cringed when I heard him say that someone would be there that afternoon (Friday) and knew it would be me. He walked back into the tech bay and hung a note on the call board, "Kick the sh_t out of Xxxxxx Water Dept's base". I got paid overtime to drive 120 miles round trip to kick the living sh_t out of an inanimate object.
Getting paid to kick the living s--t out of transmitters. My ideal of a good fun engineering job. Had the bankruptcy special CCA AM rig from Hades. If it tripped off, you had to kick it in the right spot 3 times, and it would refire. I left a note (it's still there some 22 years later) to kick it in the spot where it's labeled "Kick Me 3 Times" to refire the plates. Percussive Maintenance, the engineer's job is knowing where to kick the s--t out of the offending transmitter and why we get paid.

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