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Author Topic: TE Systems Repeater Amplifier Not Working  (Read 18833 times)
W4JST
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« Reply #30 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
« Last Edit: February 16, 2013, 06:25:07 AM by W4JST » Logged
AC2EU
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« Reply #31 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

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.
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W4JST
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« Reply #32 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?
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W4JST
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« Reply #33 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?
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AC2EU
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« Reply #34 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.

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KA5IPF
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« Reply #35 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
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W4JST
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« Reply #36 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.
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W4JST
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« Reply #37 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?
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KA5IPF
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« Reply #38 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
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W4JST
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« Reply #39 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.
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KA5IPF
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« Reply #40 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?Huh

Have fun.

Clif

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KE3WD
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« Reply #41 on: February 16, 2013, 04:58:14 PM »

Do yourself a favor and go with the 2SC2782. 

Seriously.


73
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W9GB
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« Reply #42 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
« Last Edit: February 16, 2013, 08:24:42 PM by W9GB » Logged
KA5IPF
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« Reply #43 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
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W4JST
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« Reply #44 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.
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