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 Post subject: replacing parts on printed circuit
PostPosted: Thu Sep 07, 2017 7:56 am 

Joined: Sun Sep 03, 2017 7:57 am
Posts: 4
I recently tried to replace two capacitors on a Philips TV 'Backlight inverter board'; however, I could not get the solder to 'melt'. Do I need a special soldering iron? Any suggestions appreciated!


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Thu Sep 07, 2017 9:24 am 

Joined: Mon Dec 06, 2004 1:01 am
Posts: 294
Location: Tennessee
What kind of soldering iron? How many watts ? Is the tip of the iron clean ? A dirty soldering iron tip will not transfer the heat needed to melt the solder. An adjustable one, with the temp turned way down won't work either. When you try it again, try adding a little new solder to it to help make it flow.


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Thu Sep 07, 2017 4:27 pm 
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Joined: Thu Aug 01, 2002 12:01 am
Posts: 2802
Location: San Jose CA
lead free solder melts higher than tin-lead but not that much higher unless it is an exotic uncommon alloy. Your iron could be underpowered for the joint (doubtful on an inverter board) or as suggested some flux or more [flux core] solder to improve the thermal transfer at the tip. I never solder without adding flux (paste or liquid), the time it takes to clean is usually less than the problems that not using it can cause.


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Fri Sep 08, 2017 4:10 am 

Joined: Fri Aug 22, 2003 12:01 am
Posts: 1612
Location: (somewhere), Afghanistan; from Rochester, NY
I argee with Gerty. Wattage and tip size of iron?

You did not specify capacitor type. But the 12W, 1/16" diameter tip I use for soldering IC pins won't touch electrolytic cap leads on wide traces. For that I use a 50W iron with 1/8" diameter tip.

Cheers,



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 Post subject: Re: replacing parts on printed circuit
PostPosted: Fri Sep 08, 2017 10:32 am 

Joined: Sun Sep 03, 2017 7:57 am
Posts: 4
Welder 140 watt. Cleaned tip, etc. Nothing!


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Fri Sep 08, 2017 11:16 am 

Joined: Fri Aug 22, 2003 12:01 am
Posts: 1612
Location: (somewhere), Afghanistan; from Rochester, NY
Does it get hot?

You wouldn't believe the number of times tha answer to "Is it plugged in?", is "Oops, no!" :grin:



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Dale Y
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 Post subject: Re: replacing parts on printed circuit
PostPosted: Sat Sep 09, 2017 6:19 am 

Joined: Sun Sep 03, 2017 7:57 am
Posts: 4
Temperature at tip: 125+


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Sat Sep 09, 2017 9:04 am 

Joined: Fri Aug 22, 2003 12:01 am
Posts: 1612
Location: (somewhere), Afghanistan; from Rochester, NY
60/40: melts between 183–190 °C (361–374 °F)

Not even close! You need a new iron.

Cheers



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 Post subject: Re: replacing parts on printed circuit
PostPosted: Sat Sep 09, 2017 12:09 pm 
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Joined: Thu Oct 26, 2006 7:11 pm
Posts: 1293
Location: Maryland
Indeed your soldering iron is too low in temperature. I use a Weller WTCTP series iron, and the tips are preset to 600,700, and 800°F. Also, smaller tips store less heat so they cool faster on heavy PCB traces. Us old timers used Weller soldering guns, which are still made, and the infamous Ungar ceramic soldering element and 'cigarette lighter'. In the days of point to point wiring, chassis connections were common and a lot of heat was needed. They are still handy to get shields and heat sinks off the board or when soldering ground braid, which is not seen too often anymore.

Side Note:
The WTCTP iron uses a unique soldering tip that has a slug of a special alloy metal attached to its back end. This slug attracts a magnetic switch in the iron handle to turn the iron on and then releases the switch at the slug's Curie point. (Temperature point where the metal loses it's magnetic attraction) The tips, available in many styles, are stamped 6,7,8 for the temperature. It's a great iron, quick recovery and with thousands of PCB connections, and some maintenance, it is still going strong.



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 Post subject: Re: replacing parts on printed circuit
PostPosted: Sun Sep 10, 2017 7:13 am 

Joined: Sun Sep 03, 2017 7:57 am
Posts: 4
Weller WTCTP is little pricey for me.
Anyone familiar with: SOAIY Full Set 60W Adjustable Temperature ON/OFF Switch Welding Soldering Iron Kit


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 Post subject: Re: replacing parts on printed circuit
PostPosted: Tue Sep 19, 2017 1:49 pm 
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Joined: Thu Aug 01, 2002 12:01 am
Posts: 2802
Location: San Jose CA
Hakko is a good alternative to Weller if you want a full featured station with lots of tips to choose from. Probably any 50W or greater iron will be plenty, off brands might not last as long though.


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