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Author Topic: TE Systems Repeater Amplifier Not Working  (Read 15239 times)
KA4POL
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« Reply #15 on: February 14, 2013, 09:44:04 PM »

The high SWR at the input is the first thing to check out.
You can solder a makeshift RF test head by soldering a diode and a capacitor together to connect to your DVM. 10 W is very high, may be you can reduce the input power a bit.
Some of these amps do have a RF vox to automatically switch between TX and RX. However, I could not find a relay on your pictures.
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W4JST
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« Reply #16 on: February 15, 2013, 06:21:13 AM »

AC2EU,
Can you tell me specifically where to check for 0.4 to 0.6 volts DC? I'm guessing one of the tabs on the transistors but I don't know which one.

I guess the reason the SWR is high is because the power is not coming out of this amplifier. It's like it's "open" somewhere. I'm measuring 10 watts at the input and nothing at the output.

I have a WaveNode sensor attached directly to the input antenna jack and one attached directly to the output antenna jack.

SWR's not like 2:1 I think it's infinite, I think reflected power about = forward power if I'm not mistaken.
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AC2EU
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« Reply #17 on: February 15, 2013, 07:01:27 AM »

AC2EU,
Can you tell me specifically where to check for 0.4 to 0.6 volts DC? I'm guessing one of the tabs on the transistors but I don't know which one.

I guess the reason the SWR is high is because the power is not coming out of this amplifier. It's like it's "open" somewhere. I'm measuring 10 watts at the input and nothing at the output.

I have a WaveNode sensor attached directly to the input antenna jack and one attached directly to the output antenna jack.

SWR's not like 2:1 I think it's infinite, I think reflected power about = forward power if I'm not mistaken.

There is no output, apparently because there is no drive, not because of the finals themselves.

Bias voltage is on the the bases. those are connected to the small drive transformer. Easier yet, measuring the tabs, the only voltages you will find are the bias and vcc.
I really suspect that the problem will end up being on the input side of things from what you have been reporting...
If you are lucky, it may only be a blasted transistor...or it may be something much more subtle, then will need some test equipment. Do you know how to "diode check" transistors? Before you do, look up what type they on line using the number on the device.

It may just come down to you needing the proper tools to do the job. 
What you are trying to do is like an auto mechanic without a socket tool set!
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W4JST
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« Reply #18 on: February 15, 2013, 07:34:13 AM »

I seem to have 13.8 volts or so on the collecter (above M) but nothing on any of the other tabs.

Both sides of this transistor are emitters, right?

I know this is an NPN.

So should I have continuity from base to emitter (either side) but not from emitter to base? Anything to check on the emitter tab? Do this on 200 ohm scale or on diode check or what?
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AC2EU
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« Reply #19 on: February 15, 2013, 08:51:14 AM »

I seem to have 13.8 volts or so on the collecter (above M) but nothing on any of the other tabs.

Both sides of this transistor are emitters, right?

I know this is an NPN.

So should I have continuity from base to emitter (either side) but not from emitter to base? Anything to check on the emitter tab? Do this on 200 ohm scale or on diode check or what?

Are you sure there is nothing at all on the bases? Perhaps there is a problem with the bias regulator or maybe one of the PA s have a base=emitter short. Low resistance may be OK but dead short is not.  "In circuit" transistor continuity checks are often of little use.
You may be in over your head at this point...
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W4JST
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« Reply #20 on: February 15, 2013, 09:14:42 AM »

I have continuity from base (below the M) to emitter (either side) on all 5 transistors.
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WB2WIK
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« Reply #21 on: February 15, 2013, 09:23:21 AM »

My first guess after reading the latest dialog on the symptoms is the input isn't even connected.

See if you can trace from the RF INPUT connector to the base of the driver stage; I'd guess something's open (or possibly shorted).

I see TE used a "regular" amplifier PC board for the "repeater" version, and simply omitted the relays, preamp, RF sensing circuit, etc -- and substituted jumpers and coupling caps and stuff in place of the "normal" relay circuitry.  Something might be open there.
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W4JST
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« Reply #22 on: February 15, 2013, 09:41:37 AM »

I don't see a problem following the trace from input up to the driver transistor.

Please look at these new pictures, following the input trace, and see if you can see a problem or maybe tell me what to check.

Thank you.

http://i49.tinypic.com/2gsiv08.jpg

http://i45.tinypic.com/334nt4g.jpg

http://i49.tinypic.com/6z30p4.jpg

http://i49.tinypic.com/2cn9tmh.jpg

http://i50.tinypic.com/c5kdf.jpg

http://i47.tinypic.com/2n9jktu.jpg
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KA5IPF
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« Reply #23 on: February 15, 2013, 01:16:23 PM »

I have continuity from base (below the M) to emitter (either side) on all 5 transistors.

It's a Class C amp which has zero bias on the base, usually connected to ground thru a choke, ergo connected directly to the emitter which is at ground. With almost zero current draw none of the transistors are shorted but there could be an open base or collector, most likely on the first driver. If the first driver were working you would have some current drawn (1-2A) when input power is supplied. Lift the base of it and use the diode checking scale (B-E is just like a diode to ground). If open that would also account for high SWR on the input side.

Clif
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W4JST
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« Reply #24 on: February 15, 2013, 01:35:09 PM »

According to my cheap multimeter on the 10 amp current scale I am seeing:

0.75 A when power is switched on to the amp

It actually goes down to

0.4 A when I key the transmitter and provide about 10 watts input to the amplifier.
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W4JST
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« Reply #25 on: February 15, 2013, 05:11:51 PM »

I lifted the base (below the M) and checked for continuity between it and emitter (either side) and I don't seem to have any continuity (it checks open). I switched the leads, knowing it's like a diode inside, still checking open, no continuity.
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KA5IPF
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« Reply #26 on: February 15, 2013, 05:58:17 PM »

It doesn't sound good, or it does, depends on your point of view. Now lift another base and see what reading you get.

Does your DMM have the diode check function? If so more than likely the base is open. The other transistor check will verify it.

Clif
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W4JST
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« Reply #27 on: February 15, 2013, 06:28:26 PM »

It does have the diode function, I also tried the resistance on all the scales and couldn't get a reading regardless.

I only checked the driver one.

I should lift one of the other four and do the same thing? It was kind of difficult to get the base tab lifted completely off the board.
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AC2EU
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« Reply #28 on: February 15, 2013, 06:58:41 PM »

I have continuity from base (below the M) to emitter (either side) on all 5 transistors.

Continuity on ALL five B-E junctions?HuhHuhHuhHuh? No way! In-circuit resistance, maybe, but not continuity!
Your measurements are too imprecise to diagnose anything.
I suggest that you find a local person who can help you with the diagnostics.
It takes a minimum of 2 years of tech school to be even a mediocre electronics tech. It's expecting a bit much to get up to speed with a forum thread.
If you want to proceed at the risk of doing further damage, before proceeding i would suggest googling some of the following topics.

electronic repair soldering/desoldering techniques
Basic rf amp theory
bi-polar transistor diode check.
Rf troubleshooting 101

If you want to repair your own stuff, that's great, but get some test equipment and learn how to use it.
Without you having some basic knowledge and equipment, I doubt that we can help you unless you get lucky.



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K8AXW
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Posts: 3737




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« Reply #29 on: February 15, 2013, 08:20:42 PM »

JST:  At this point you might want to find a source of these transistors or try to find a substitute.

I checked Mouser and RFParts and neither list the MRF247.  No doubt there are substitutes but you'll have to find it.

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