replacing parts on printed circuit

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wizardofheinz
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replacing parts on printed circuit

Post by wizardofheinz » Thu Sep 07, 2017 8:56 am

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!

gerty
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Re: replacing parts on printed circuit

Post by gerty » Thu Sep 07, 2017 10:24 am

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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haklesup
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Re: replacing parts on printed circuit

Post by haklesup » Thu Sep 07, 2017 5:27 pm

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.

dyarker
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Re: replacing parts on printed circuit

Post by dyarker » Fri Sep 08, 2017 5:10 am

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,
Dale Y

wizardofheinz
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Re: replacing parts on printed circuit

Post by wizardofheinz » Fri Sep 08, 2017 11:32 am

Welder 140 watt. Cleaned tip, etc. Nothing!

dyarker
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Re: replacing parts on printed circuit

Post by dyarker » Fri Sep 08, 2017 12:16 pm

Does it get hot?

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

wizardofheinz
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Re: replacing parts on printed circuit

Post by wizardofheinz » Sat Sep 09, 2017 7:19 am

Temperature at tip: 125+

dyarker
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Re: replacing parts on printed circuit

Post by dyarker » Sat Sep 09, 2017 10:04 am

60/40: melts between 183–190 °C (361–374 °F)

Not even close! You need a new iron.

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Dale Y

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Lenp
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Re: replacing parts on printed circuit

Post by Lenp » Sat Sep 09, 2017 1:09 pm

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.
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

wizardofheinz
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Re: replacing parts on printed circuit

Post by wizardofheinz » Sun Sep 10, 2017 8:13 am

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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haklesup
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Re: replacing parts on printed circuit

Post by haklesup » Tue Sep 19, 2017 2:49 pm

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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