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Old Aug 07, 2009, 10:04 PM
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Torrance
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how to remove SAW filter from 900 rx's?

Hey guys, just wondering how you've been removing the SAW filter from the 900mhz rx modules?

I've tried an 80watt iron and cannot get the solder to melt on the board. should I try grinding it off?
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Old Aug 07, 2009, 10:57 PM
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High risk of damaging the board by grinding.
Plus, all the grinding debris would be a pain to clean from the board, and how would you be sure you got it all cleaned out?

I guess it could be done, but I sure would not want to.

I think someone else got the filter out by crushing it with pliers first, that made unsoldering it easier.

Again, not a technique I would try, but that's just me, I'm chicken...

FWIW I used a Weller 120W soldering gun. You know, one of those great big heavy "transformer in a pistol" things.

I was concerned that the AC field from the transformer and the tip of the gun might cause... I don't know... some kind of damage to other parts on the board.

Well, It worked! and after soldering in the new filter the Rx worked just great.

BTW
I did NOT use the soldering gun to install the new filter. Just my 45W soldering iron
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Old Aug 07, 2009, 11:10 PM
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I also used one of those big pistol grip soldering irons that gets the tip
glowing red hot. I used a suction type de-solderer and it worked on
the two small pins but not the ground pin (which dissipates all its heat
through the whole case). In the end I put the whole thing in a
vice with rubber grippers, with the old filter facing downward,
grabbed the filter with a pair of pliers and then heated up
the ground pin on top until the solder finally melted, while simultaneously
pulling hard on the filter all the time. It eventually popped loose.

I've used that on two 900Mhz Rxs so far. I destroyed
the tracing for one of the small pins so I had to jumper a wire completely
over the bad spot.

I did more recently pick up a solder wick (fine strand mesh that's
pre-fluxed) which is supposed to suck the solder into itself once
it's hot enough. I'll try that on the next Rx (I've got two more 900Mhz
Rx's and two 1.3Ghz Rxs that I really don't want to mess up).

On a pedantic note, I'm pretty sure the filter we're taking out
is not a SAW filter. That's sorta the point. One the we're putting in, is.

ian
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Old Aug 07, 2009, 11:14 PM
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I got it out in a four step process.

Step 1- try to cajole someone else to do it for you. This process sucks.

Step 2- use a solder sucker and solder wick to get as much off of the pins as possible.

Step 3- Use pliers to crush the metal can and remove it. This gives you access to the metal base.

Step 4- While heating the metal base with as big an iron as you have; Pry it up with a small screwdriver.

The first one took me several hours. The second about 20 minutes. I dread doing #3 and will wait for a rainy day with no good tv on.

-good luck- Ken

PS: Radio Shack sells a desoldering iron with a heating element and a big rubber bulb attached. It works great.

PPS: While you are in there find the RSSI pin and solder wires to it. Now you can use a voltmeter to decide which antenna is best. It's the pin which voltage changes when you turn your transmitter on. (usu 7 or 9)
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Old Aug 07, 2009, 11:36 PM
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why take out the saw filter?
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Old Aug 07, 2009, 11:38 PM
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Oh yeah... Daemon made a good point that I forgot to mention....

When I used the big soldering gun, I also used solder wick to suck up the solder, and that really helped for getting the old filter out.
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Old Aug 08, 2009, 12:45 AM
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Quote:
Originally Posted by David22
why take out the saw filter?
As I mentioned above, we're actually removing a non-SAW (or very crappy
SAW) filter and replacing it with a good narrow band SAW filter.
There's a long thread about it elsewhere, with pics of the procedure
and some sample videos showing how much it can improve the performance
by rejecting out of band interference, that the stock filter passes right
through.

It's basically replacing a really cheap component with a high quality one.
Better filtering is why most 2.4Ghz gear has better
range than 900Mhz and 1.3Ghz even though the latter two should
be able to provide longer range at lower power levels.

ian
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Old Aug 08, 2009, 03:49 PM
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Torrance
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OK I got it out with a 140 watt gun iron. the solder wick is definatly needed.

My next question is why are there only 3 legs, on the filter when the original had 4?
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Old Aug 08, 2009, 04:10 PM
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Yay! you got it out!

Got a pic of the filter with the extra pin?

I'm not sure, but I think it is just an extra ground pin.
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Old Aug 08, 2009, 04:25 PM
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Quote:
Originally Posted by JustinONE
OK I got it out with a 140 watt gun iron. the solder wick is definatly needed.

My next question is why are there only 3 legs, on the filter when the original had 4?
Post some pictures of module and old saw filters legs.
Does it look like this? F480-2

http://www.alldatasheet.com/datashee...G/SF480-2.html
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Old Aug 08, 2009, 05:33 PM
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what does SAW stanad for, and what does it do?
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Old Aug 08, 2009, 06:32 PM
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Quote:
Originally Posted by JustinONE
OK I got it out with a 140 watt gun iron. the solder wick is definatly needed.

My next question is why are there only 3 legs, on the filter when the original had 4?
I never did 0.9GHz/SAW filter mod TX but having a lot of experience with electronics I hope you've made a typo as anything more than 40W for longer than 5 sec will overheat and lift pads on your PCB.

Once this happens you need a lot of skill to reconstruct destroyed/missing pads/traces (mind you you are working on microwave device with PCB utilizing micro strip technology) or final result may be not as great as expected or the worst case scenario - dumpster.

Wish you luck!
Homer
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Old Aug 08, 2009, 10:46 PM
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Torrance
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Quote:
Originally Posted by miso111
Post some pictures of module and old saw filters legs.
Does it look like this? F480-2

http://www.alldatasheet.com/datashee...G/SF480-2.html
I got it from these guys

http://www.dpcav.com/xcart/product.p...cat=252&page=1

yet the picture shows 3 pin, but there are 4 pin holes in the board to accept the 4 pin SAW
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Old Aug 08, 2009, 10:50 PM
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Torrance
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Quote:
Originally Posted by Homer_Simpson
I never did 0.9GHz/SAW filter mod TX but having a lot of experience with electronics I hope you've made a typo as anything more than 40W for longer than 5 sec will overheat and lift pads on your PCB.

Once this happens you need a lot of skill to reconstruct destroyed/missing pads/traces (mind you you are working on microwave device with PCB utilizing micro strip technology) or final result may be not as great as expected or the worst case scenario - dumpster.

Wish you luck!
Homer
Homer, I tried a small propane soldering iron and just wouldn't melt any solder from the board, niether did my 80 watt iron.
I had to go to the 100/140 gun with a wick, but there is no fear in lifting the pads as the tracings are very robust, and it's only 3 pin holes that required heating up to soak up all the residue solder.

easy japanesy, the hard part is soldering in the filter, now I need to find a smaller iron.
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Old Aug 09, 2009, 12:38 AM
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Quote:
Originally Posted by Homer_Simpson
I never did 0.9GHz/SAW filter mod TX but having a lot of experience with electronics I hope you've made a typo as anything more than 40W for longer than 5 sec will overheat and lift pads on your PCB.

Once this happens you need a lot of skill to reconstruct destroyed/missing pads/traces (mind you you are working on microwave device with PCB utilizing micro strip technology) or final result may be not as great as expected or the worst case scenario - dumpster.

Wish you luck!
Homer
Since you have never done the mod, you wouldn't know... And BTW it's the RX we are changing the filter on.

It takes a lot of heat to get these filters out. Large metal can, and soldered directly to a very large ground plane.

A 40W iron won't even begin to melt the solder on this thing.
A 40 watt iron has nowhere near enough thermal inertia, you need a big hot iron to do this job.

I used a 120W gun on mine and it was barely enough.... and guess what?
No damaged traces...
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Last edited by galaxiex; Aug 09, 2009 at 12:43 AM.
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