BE AM 1A Power meter not working in FWD

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Nathaniel Steele
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BE AM 1A Power meter not working in FWD

Post by Nathaniel Steele » Tue Jun 12, 2018 10:07 am

Reflected power reads fine but forward power is dead. I've not worked on this transmitter before anyone ever encountered this before? Remote power reading still works and seems consistent with past readings. I'm going to suspect the meter itself to be ok since it appears Reflected is reading correctly.

Thanks.

TPT
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Re: BE AM 1A Power meter not working in FWD

Post by TPT » Tue Jun 12, 2018 1:17 pm

Check to see what drives the meter. Not uncommon to find an op amp used as a meter driver--this may be what failed.

kcbooboo
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Re: BE AM 1A Power meter not working in FWD

Post by kcbooboo » Wed Jun 13, 2018 5:54 am

There are no active elements in the fwd/rfl power circuit. There's a directional sampler that outputs both forward and reflected power signals. These feed calibration pots, then the metering switch, then the meter. That's about it. Could be a connector issue, a dirty switch, an open pot, or something defective on the directional sampler board. The AM-500A/AM-1A manual should be on BE's web site for download, about 11MB. It was there two years ago.

Bob M.

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Dale H. Cook
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Re: BE AM 1A Power meter not working in FWD

Post by Dale H. Cook » Wed Jun 13, 2018 8:07 am

If you can't get the manual from BE let me know. I have a copy of revision C the 500A/1A manual that I downloaded from their site some years ago, dated 29-Aug-2011.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
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Deep Thought
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Re: BE AM 1A Power meter not working in FWD

Post by Deep Thought » Wed Jun 13, 2018 11:47 am

The meter switches on that series of transmitter are failure points. Check to see if the remote sample is working, and if it is then it's the switch.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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kkiddkkidd
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Re: BE AM 1A Power meter not working in FWD

Post by kkiddkkidd » Wed Jun 13, 2018 5:42 pm

Ironically I just this week worked on an AM1a that after replacing a couple of RF module fuses, appeared to be operating normally but the power meter only reads about 200w. If the old base current meter is to be believed, it is within a few mils of licensed base current.

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Kevin C. Kidd CSRE/AMD
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KK Broadcast Engineering
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Re: BE AM 1A Power meter not working in FWD

Post by kcbooboo » Thu Jun 14, 2018 4:30 am

There are a couple of cables and connectors involved in the power meter circuit, one coming from the directional coupler sensor, one going to the meter switch. Removing and reinstalling those connectors might fix you up. I wouldn't be surprised if replacing fuses caused the cables to move slightly. There's only a few mA feeding the meter. Any high resistance could affect it. Squirting the meter switch with a good contact cleaner might help temporarily.

Bob M.

Nathaniel Steele
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Re: BE AM 1A Power meter not working in FWD

Post by Nathaniel Steele » Thu Jun 14, 2018 9:02 am

Thank you all. I'll be checking it out in the morning before sign on (it's a daytimer, and fridays I take my wife to work at4:45AM, just a mile from the site....)

The remote reading is working So I'll check the switche first. I have the manual at the site,and a digital copy on my devices.

Thank you!

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Re: BE AM 1A Power meter not working in FWD

Post by RodeoJack » Thu Jun 14, 2018 10:29 pm

I serviced an AM-1A this week that has a power meter that will only go up to about 800 watts. At that point, it hits a wall. You can tap it and move it around a bit, but it pretty much jams at that point. Base readings indicate the transmitter's OK.

By contrast, under normal circumstances, the ref side wouldn't normally go high enough to give you much of a comparison. Could you even get the meter up much by intentionally detuning the transmitter before it would start folding back?

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Shane
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Re: BE AM 1A Power meter not working in FWD

Post by Shane » Fri Jun 15, 2018 1:10 pm

Doesn’t reflected read on a separate meter on the AM-1A? I am familiar with only one of these which was installed in 2003. The top meter reads forward power in two ranges selectable by a switch whose third position is OFF and is the position we generally leave it in when thru with it. I don’t think we’ve had any problems with it so far.

The reflected power meter also has a three position switch which is HIGH/LOW/VAC. I have always wished it had an OFF position, too, but we’ve had no trouble with it leaving it on VAC when done.

This unit has the optional tuner. One can see the variation made in the reflected power easily when adjusting the tuner. We have a non-standard dummy load which will cause the meter to register reflected power and also “tests” the foldback operation. :roll:

For anyone unfamiliar with these, the forward power meter is pretty important on this rig since there are no final stage voltage and current meters and the forward power meter is what you use to measure power indirectly. The only meters are the forward and reflected power. That’s also all that is provided for remote readings.
Mike Shane, CBRE
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Deep Thought
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Re: BE AM 1A Power meter not working in FWD

Post by Deep Thought » Fri Jun 15, 2018 4:13 pm

The forward power meter is at the top with a low/high/off switch. One easy meter test is to set the transmitter at 300 watts (full scale on the low range) and see if the two ranges agree. If there are mechanical issues with the meter it won't go full scale on the low range, but any issues with the range switch or cal resistors can cause the two readings to be considerably different.
5b23f349.jpg
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RodeoJack
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Re: BE AM 1A Power meter not working in FWD

Post by RodeoJack » Fri Jun 15, 2018 5:55 pm

You're right.
My meter's bad, but the scenario doesn't involve REF readings.

Got on the keyboard before coffee this morning. :roll:

50ohmload
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Re: BE AM 1A Power meter not working in FWD

Post by 50ohmload » Tue Jul 10, 2018 5:52 pm

I hope I'm not too late. I have a set of 4 meters (Multimeter, Amperes, Volts, Watts) available. They were pulled from a working retired transmitter (Harris MW 1A) and are still mounted together on their unpainted aluminum mounting plate. I also have spare PA modules that were pulled out for repair but have been collecting dust and taking up space. Please PM me if you are interested.

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Deep Thought
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Re: BE AM 1A Power meter not working in FWD

Post by Deep Thought » Tue Jul 10, 2018 11:30 pm

Pretty sure those aren't going to be much good on a BE transmitter... :lol:
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

50ohmload
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Re: BE AM 1A Power meter not working in FWD

Post by 50ohmload » Wed Jul 11, 2018 4:56 am

So true! And now that you mention BE I see it right in the title over and over. I miss having a working brain on days like this.

As it happens, a BE AM1A replaced the Harris MW1A from which those parts came. Isn’t it ironic?

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