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Author Topic: TE Systems Repeater Amplifier Not Working  (Read 15420 times)
W4JST
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« on: February 13, 2013, 06:13:10 PM »

I have a TE Systems amplifier.

The back panel says it's a 1552RAS. The board inside says "TE Systems 1454" so I'm not sure if they use the same board in different amps or if this was a 1552 but now has a 1454 board in it?

This is a repeater amplifier. No front panel, no on/off switch etc.

I connected power to it and had about 10 watts input and nothing (not even the 10) at the output antenna connector.

Pictures:

http://i46.tinypic.com/wl7vgm.jpg

http://i46.tinypic.com/25kltmx.jpg

http://i45.tinypic.com/2n8aasp.jpg

http://i49.tinypic.com/6zrlhw.jpg
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K8AXW
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« Reply #1 on: February 13, 2013, 06:26:23 PM »

Do you have a schematic?  No?  Get one!

Usually, the first thing is to make sure the fuse hasn't blown.

Next you measure the voltages at the power transistors to see if they're getting power.

I'm assuming at this point that the RF is indeed getting into the amplifier because you have zero output.  (If the amp isn't switching, you should read the input power at the output)

What have you done so far?



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KA4POL
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« Reply #2 on: February 13, 2013, 10:17:37 PM »

If you didn't measure using a dummy load it might be an SWR problem.
TE says you need to check the input voltage. If it drops below 13.6 V you'll experience degradation.
The pictures do not show any suspicious coloration.
The board may be used in different amps, therefore the number. They had a 1454 70W in 350 W out as well.
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W4JST
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« Reply #3 on: February 14, 2013, 06:27:13 AM »

I looked online for a schematic? Where can I get one? I contacted TE also but have not yet heard back.

It doesn't look to me like there is a fuse.

Which tabs on the transistors should have what voltage?

You mention the amp switching. I don't believe this one has a relay. I believe it has to have DC power to have output but I am not sure.

I measured 10 watts or so at the input and there's 0 at the output of the amplifier.

Voltage is about 14 volts DC into the amplifier.
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KA5IPF
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« Reply #4 on: February 14, 2013, 08:50:07 AM »

It's a repeater amp, there is no relay switching or power switch.

On the transistors the top of the "M" points to the collector. With no input power hook up the power supply and note the current draw. It should be very low. Measure the voltage on the collector and base (opposite side) of each transistor. There should be 14v on each collector and zero on the bases. Beyond that will require more test equipment than a voltmeter.

Clif
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WB2WIK
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« Reply #5 on: February 14, 2013, 09:31:16 AM »

Of course it needs a source of DC current to work.

Did you check to see if the 14Vdc going to the amplifier power terminals remains 14Vdc after you drive the amplifier with 10W?

Did you check to see if the 14Vdc is arriving at the transistor collectors?

The photos show no signs of overheating or obvious abuse; of course, transistors can fail without any telltale external signs (a fast transient might do that), but with RF amps like these, they "usually" fail over time from overheating, and that leaves some signs which aren't evident in your photos.
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K4JJL
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« Reply #6 on: February 14, 2013, 10:48:35 AM »

A problem I've had with GE repeater amps is the ground bond failing between the boards in the amp.  Over the years, heating and cooling will make the tab tying the boards together break.  You might also check that the RF is actually getting through the coax connectors and to the board, as well.  Those can break off, too.

Sometimes you can get hairline cracks in the traces, too.  Although, this happens more often to ceramic boards than fiberglass.  Ohm them out to make sure everything is still connected.
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WD8AJY
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« Reply #7 on: February 14, 2013, 01:23:24 PM »

I found this at the TE web site under pager amps
                  IN            out      volts      amps                          Cost
1552RA    10-25    350    +13.8    54    UHF    CD/fn    1340

73 bob WD8AJY
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WD8AJY
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« Reply #8 on: February 14, 2013, 01:25:53 PM »

This is the link

http://www.tesystems.com/comml-2-way-paging.htm

73 Bob WD8AJY
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W4JST
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« Reply #9 on: February 14, 2013, 01:34:10 PM »

The current meter doesn't move on my power supply. So current draw is very low, not just without input power, but even with input power to the amplifier.

There is 14 volts on all 5 collectors (above the M) and 0 on all 5 bases (below the M).

I am pretty much seeing the same reflected as forward power at the input, SWR is very high.

Now, I checked for positive voltage at the collectors with the ground lead attached to a known good ground connection (negative input of amplifier).

I am thinking maybe what K4JJL said:

Bad ground somewhere or bad antenna connection.

Thanks everyone. Please keep helping.
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W9GB
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« Reply #10 on: February 14, 2013, 03:27:09 PM »

Your RF transistors are MRF247 - 12.5 Volt, VHF to 175 MHz, Output: 75 watts
http://www.datasheetcatalog.org/datasheet/motorola/MRF247.pdf

Power Gain = 7.0 dB Min
Efficiency = 55% Min
--
Greg, KJ6KO no longer repairs the TE Amplifiers, BUT here are his comments:
http://users.innercite.com/kj6ko/te.htm

I have yet to find a correct TE schematic.
2 Meter (VHF) TE Amplifier models:  25W IN, 350W OUT
If you have or buy one of these amps, Do this simple test before extensive use on SSB.
The 2m model uses a driver (MRF-247) that is designed for around 10-15W input for max out, around 80-100W.
The final stage uses 4 of the same MRF247 transistor.
With this much gain, it usually does not take more than 10-15W to achieve full output.
==
Amplifier "Do It Yourself" Testing and Repairs
http://users.innercite.com/kj6ko/doitursf.htm#Amp%20Repairs
« Last Edit: February 14, 2013, 03:39:39 PM by W9GB » Logged
AC2EU
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« Reply #11 on: February 14, 2013, 05:23:37 PM »

One quick test is to test the tabs that connect to the broadband transformer. Those are sure to be the collectors and should show DC ( Vcc)  there. If not a fuse or fuse link has blown, Before replacing said fuse, turn of the power, and test for a sort or very low resistance with respect to ground. You may have a bad final. So-so ones or one open PA will usually result in SOME output.
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W4JST
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« Reply #12 on: February 14, 2013, 06:20:17 PM »

AC2EU,
I had 13.8 volts or so on the collectors (above the M) on all 5 transistors if that's what you mean.
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AC2EU
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« Reply #13 on: February 14, 2013, 07:44:13 PM »

AC2EU,
I had 13.8 volts or so on the collectors (above the M) on all 5 transistors if that's what you mean.

Sorry, missed that.
The thing is so dead, my instinct was to start there.

The circuit is very simple, so now that we know not much current is drawn and the PA has power, it's time to "back up" toward the input.
Verify that there is quiescent bias on the PAs approx 0.4 to .6v. If it is something in that range move on back to the driver stage.

An Oscilloscope or rf meter would be a great tool to verify where there is signal and where it stops.

You mention that the swr to the input is high. Is the input supposed to be 50 ohms? Sometimes the are oddball impedances used. ( the meter assumes 50 ohms) I never assume anything. If it is 50 ohms, then perhaps there is a problem in the first stage?
I would have had the problem figured out by the time I finished writing this if it were in front of me, but fixing something on a forum is very difficult...
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K8AXW
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Posts: 3761




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« Reply #14 on: February 14, 2013, 08:36:11 PM »

2EU, I was thinking as you, if the input has a very high SWR and the reflected power is the same as the forward power, there is a problem in the input circuit. 

Most (I always hate to say "all.") amplifiers have close to a 50ohm input to match the industry standard 50ohm output of transceivers/transmitters.

I suspect the input transistor first and then a failed component in the input circuit second.  A scope would be great to see if the input transistor is amplifying the exciter RF.

Since you don't have test gear (Scope) you might have to simply start substituting transistors.



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