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Help installing discriminator tap on pro-51

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Bill2k

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I want to install a discriminator tap on an old pro-51 scanner. The IC I need to connect the tap to is surface mounted and in a very tight area. I'm pretty handy with a soldering iron but I don't trust myself with this task.

What would be the best way to attach a wire to pin 9 on the IC? Is there any type of glue or epoxy I can use instead of solder?

Below is a pic of the pro-51 opened up with an arrow pointing to the pin I need to connect to. Any suggestions are greatly appreciated.
 

jlh

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bill, if you're handy with a soldering iron, you can do it.

get a low wattage iron and some wire-wrap wire ( because of its small diameter ) and a mounted magnifying glass.

trim a 1/2 inch of insulation off the wire and hold the end of the wire to the solder point on the target pin. using the other hand, use the iron to heat the stripped wire lightly. the solder already on the pin will melt slightly and the wire you are hold will attach.

i've done this process several times and it always works.
 

SCPD

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Bill,

I tapped my BC760XLT myself and it was pretty tight as well. What you might want to try is tinning the wire first. This requires putting a small amount of solder on the wire first before trying to attach it to the IC. This may help with the solder moving to the IC connection without toasting the chip.

Also make sure you're using the right power on the iron for the solder you're using. You really don't need a lot of heat in order to get the solder to flow. It will follow the heat.

Good luck.
 

Al42

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Looks like a tight spot. It can be done (jlh's idea of using wire-wrap wire is a good one) but, if you have a schematic, you might try finding where that pin is connected and tapping that point instead.
 

Bill2k

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Thanks for the suggestions. I never thought about a magnifying glass but I'm sure it'll be handy. I was already going to tin the leads before soldering, good looking out! Do you guys know if rosin core 60/40 solder is ok to use?

I was hoping to avoid using an iron, but I think I'm gonna have to do it. What size iron should I use? 5 Watt?

Edit: I found an alternative spot. Its an actual hole through the board filled with just solder. I'm trying to find a suitable ground now. Should I shield the disc. wire?
 
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jlh

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bill, no shield required. pick the ground point closest to the jack you install.
 

DickH

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Good Grief! Doesn't anybody have the answer? You solder to the BOTTOM of the board, not the top.
 

Bill2k

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DickH said:
Good Grief! Doesn't anybody have the answer? You solder to the BOTTOM of the board, not the top.
Its surface mounted....... But I found an alternate mounting point anyways. ;)
 

SCPD

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DickH said:
Good Grief! Doesn't anybody have the answer? You solder to the BOTTOM of the board, not the top.
It’s not really that difficult soldering a wire to the pin on the IC. Why dismantle the scanner any more than you really need to. Sometimes the older the scanner the more problems you encounter when trying to remove the circuit board from the plastic case. I’ve soldered directly to the IC pin many times with no problems.

But then again...it looks like you've provided the answer...
 
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kb2vxa

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Hi Bill and all,

Careful now, you must attatch the "ground" to signal low, not just any old ground. Quite often what you're looking for is not common ground, a careful examination of the detector portion of the schematic will reveal whether the return path is the low side floating or actually the main circuit ground. If you ground to the wrong spot you may cause a short or ground loop introducing hum and spurious noise.

BTW, a lighted magnifyer is a must for fine work. Mine is a crane that clamps on the edge of the bench, the head is a circle flourescent with a lens in the middle. Another must is a temperature controlled soldering station, mine is a Weller WTCPS with a tip for every occasion. Each is a different point and temperature making selection easy. Don't forget a dab of liquid or paste rosin flux, NEVER depend on the core and always prep the work or no matter what tool you use you'll overheat the work. I've done professional soldering for many years and that's the best advice I can give, if you can't make a clean connection in one second or less you're doing it wrong.
 

jlh

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bill i don't know about the schematic, but the 15w should be fine, i did mine with higher wattage than that
 
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