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eHam Forums => Mods And Repairs => Topic started by: W4JST on February 13, 2013, 06:13:10 PM



Title: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: K8AXW 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?





Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA4POL 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WB2WIK 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: K4JJL 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WD8AJY 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WD8AJY on February 14, 2013, 01:25:53 PM
This is the link

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

73 Bob WD8AJY


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W9GB 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU 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...


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: K8AXW 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.





Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA4POL 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU 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!


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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?


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU 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...


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 15, 2013, 09:14:42 AM
I have continuity from base (below the M) to emitter (either side) on all 5 transistors.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WB2WIK 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF 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


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST 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.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU 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?????????????? 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.





Title: RE: TE Systems Repeater Amplifier Not Working
Post by: K8AXW 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.



Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 06:12:50 AM
It looks like they're on ebay from China for about $15 a piece. They have the "M" on them, are they Motorola?

It looks like my input transistor is bad?

What would cause that?

--

Here's two more pictures of how I tested the in-circuit transistors. There's continuity both ways on all 4 of them.

The input transistor, where I lifted the base, it's open both ways.

http://i48.tinypic.com/2qk2khz.jpg

http://i46.tinypic.com/2up8zns.jpg


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU on February 16, 2013, 06:39:59 AM
I found a mod/tip document for a similar model from this company model 1452.
http://www.readbag.com/f1pdx-free-fr-f5dqk-te1452grepairingv2 (http://www.readbag.com/f1pdx-free-fr-f5dqk-te1452grepairingv2)

This one is a 200W amp
there is  bias reg Q3 that should be providing approx .6 to the finals.
the driver should have around .6v on it's base a s well. If not, that may be the problem.
The original design sources all bias through a relay, but on yours the relay is omitted. None the less, there is still a common DC feed point for ALL bias including the driver. If something in that part of the chain opened, no bias. No bias, no amplification.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 07:12:33 AM
I believe the 1452 is the same board, it's a 350-400 watt model.

I don't see Q3.

Did you see it on the pictures of my board?


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 07:15:25 AM
Quote
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.

KA5IPF said because it's class C there is no bias on the base. I think he also said there will be continuity from base to emitter, right?

Maybe the problem is just the open driver? Or what do y'all think?


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: AC2EU on February 16, 2013, 07:55:35 AM
Quote
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.

KA5IPF said because it's class C there is no bias on the base. I think he also said there will be continuity from base to emitter, right?

Maybe the problem is just the open driver? Or what do y'all think?

The schematic shows a bias reg as I originally stated.
I don't have enough good measurement info to make any guess.
I am attempting to guide you to places that need a look and I have explained why. If you want to take wild guesses and replace various components, that may eventually work also.



Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF on February 16, 2013, 10:30:31 AM
Quote
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.

KA5IPF said because it's class C there is no bias on the base. I think he also said there will be continuity from base to emitter, right?

Maybe the problem is just the open driver? Or what do y'all think?

The schematic shows a bias reg as I originally stated.
I don't have enough good measurement info to make any guess.
I am attempting to guide you to places that need a look and I have explained why. If you want to take wild guesses and replace various components, that may eventually work also.


AC2EU
If you look at pg 7 of the document you posted you will plainly see a bias transistor with the associated connections and bias adjustment pot. If you look at the posters first set of pictures that whole area is empty, there is no bias circuit. The 1452 you referenced was designed for SSB or FM and had a bias circuit. His is a repeater amp designed for FM (Class C) only and has no need of a bias circuit.

For a check I would lift the base of one of the other transistors and check for one-way continuity. If it checks as a diode then the driver is open.

Clif


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 12:50:04 PM
Hi Clif,

Just to be clear,

I want to check the tabs I am checking in these pictures, correct?

http://i48.tinypic.com/2qk2khz.jpg

http://i46.tinypic.com/2up8zns.jpg

Just with the base completely desoldered and away from the board?

Right now I am getting continuity both ways but it is still on the board.

Thank you.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 01:17:50 PM
Here's what I get on one of the other 4 when I desoldered the base:

http://i46.tinypic.com/2qmkb9s.jpg

I get a reading just that way, not the other way.

So it looks like the input transistor is open and needs to be replaced? Get a $15 one on ebay from China that says MRF247 and solder it in and that's it?


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF on February 16, 2013, 01:33:32 PM
Bingo, you have an open driver transistor and the one final you tested shows good. That would account for the high SWR also.

On the chinese transistors. I don't care how they are marked (batwings or not) they are clones and may or may not work. That's been my experience with them. I have never used the MRF247's though so don't know for certain about them. RF Parts shows the sub is a 2SC2782 which lists at $40 (probably higher) and I have never had a problem with their transistors working. Your call on that.

Clif


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 16, 2013, 01:44:23 PM
So get another one and solder it in, that's it? Nothing has to be tuned/changed nothing else to do?

I really appreciate your help. Thank you.

Also thanks to the others who helped.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF on February 16, 2013, 01:51:14 PM
Yep.

I looked on Ebay for the MRF247. I have never seen a Motorola transistor with the angle cut emitters as 2 of them have. Strange looking. All I have seen have the full emitters as in item 170475847317. But it has been mounted, look at the screw marks????

Have fun.

Clif



Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KE3WD on February 16, 2013, 04:58:14 PM
Do yourself a favor and go with the 2SC2782. 

Seriously.


73


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W9GB on February 16, 2013, 08:17:30 PM
The MRF-247 usually has 10 - 15W input for maximum output, around 75-95W (VHF frequencies, 2 meters).  
Its case style is: 316–01, Style: 1
It has been used as a driver for larger VHF amplifiers (EME, meteor scatter, etc.)

Freeescale / Motorola datasheet for MRF-247
http://pdf1.alldatasheet.com/datasheet-pdf/view/5259/MOTOROLA/MRF247.html

RF Parts recommends substitution of Toshiba 2SC2782 for the MRF-247
http://www.rfparts.com/pdf_docs/2SC/2SC2782.pdf

Advanced Semiconductor (ASI) has the dies for manufacturing the MRF-247 RF transistor.
http://www.advancedsemiconductor.com/
They may have stock or limited production, datasheet:
http://www.advancedsemiconductor.com/pdf/mrf247.pdf


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF on February 17, 2013, 03:07:45 PM
Only problem with ASI is their minimum order is $500. At least last time I ordered.

Clif


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 18, 2013, 08:44:14 AM
I appreciate it.

Is there much chance of finding one at a hamfest? I was thinking about waiting and seeing if I see one there, but I could go ahead and order one online if y'all think that's pretty much impossible.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WB2WIK on February 18, 2013, 10:38:30 AM
Tip about replacing this type of transistor (irrespective of part number):

Loosen the two machine screws (Allen type, usually, but may be Bristol or Spline or almost anything) that mount the transistor first, before attempting to unsolder the emitter or collector tabs.  This will make the thermal transfer ("heat sinking" effect) from tabs to the heat sink much less efficient, and allow the tabs to be unsoldered pretty easily.

If you leave the transistor firmly bolted down, it takes an awful lot of heat to unsolder the tabs, and that can burn the board or degrade the board and attached components.

When soldering in the new device, I just place the machine screws and turn them in but not fully tight, until after the soldering operations, and then fully tighten them -- for the same reason.

There is likely a tiny amount of thermal grease on the back (flat mounting surface) side of the transistor where it rests against the heatsink.  I'd clean that away, make sure the HS surface is very clean, then apply a small amount of "new" thermal grease on the backside of the transistor before placing it onto the heatsink.  The Wakefield white thermal grease works fine, but there are other choices.  Don't use much -- the layer of the grease should be very thin.

Based on the reported observations, it does seem like the driver transistor failed and the output transistors are still good.  And of course it's true the TE "Repeater" amps use no biasing, they're Class C and intended for FM use only.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on February 18, 2013, 04:20:59 PM
Thanks.

What do y'all think caused the driver transistor to open like that?


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: KA5IPF on February 18, 2013, 05:22:26 PM
Base open = Too much driving power, usually.

I would run about 5-10w of drive and shoot for 200-250 out. If you are driving it with a "regular" 2m radio realize it could have some overshoot at the lower power settings. It depends on the radio and how the mfg handled power control. Driving it with a 50-60w radio turned down may not work too well.

At the least I would pull the PCB from the heatsink and clean all the heat conducting areas and apply new heat sink compound.

Clif


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WV4I on February 27, 2013, 06:05:04 PM
If this really is a model 1552, it will present a very high input SWR on 144-148mhz. If this is simply the "problem", then might be able to retune this amp back down into 144-148 using trim caps usually in input side. Had to do this with a 6m TE amp one time that someone had obviously adjusted for use outside 6m amateur band.

Meanwhile, I've got a model 1410G that may be sick, only 100w out, saturates at about 6w in as expected, thinking a final, if nothing else pans out? Pulls 27A as advertised however.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: W4JST on March 10, 2013, 06:51:58 PM
I replaced the driver transistor and the amplifier seems to be working perfectly now.

Thanks everyone!

Thank you KA5IPF!

I appreciate it very much.


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WB0GAZ on August 18, 2013, 04:33:20 PM
Related to the same model, so including in this thread:

I wish to add SSB bias to existing, working TE Systems 1452RA repeater amplifier. I'm not concerned about relays, switching, etc., but do wish to run the unit in linear mode (so I'd expect to add one additional input, to enable SSB bias.

The big heatsink will be a plus for some long duty-cycle operations I have in mind, so does anyone have reference to info on what components are needed? I gather schematic is not generally available, but perhaps someone knows what-goes-where.

Very tks!

Dave
 


Title: RE: TE Systems Repeater Amplifier Not Working
Post by: WB0GAZ on August 21, 2013, 02:13:59 PM
Found useful information at:

http://www.ham-hyper.com
follow link: Articles Techniques
follow link: Modification des amplis TE-Systems VHF & UHF (2 articles) par F5DQK

or try:

/index.php?option=com_content&view=article&id=85:modification-des-amplis-te-systems-vhf-a-uhf-par-f5dqk&catid=41:amplis--preamplis&Itemid=78

Thanks to F5DQK Marcel!