National SemiConductor QC Replacement Tips

[bucko170]

It has been a good few months since I last had a go at replacing a QC and although my previous attempt was successful I don't know how much of that success was down to beginners luck, so to prevent potentially destroying an otherwise good module I thought I would consult with the experts beforehand.

I have what I believe are the correct tools, a soldering iron (low wattage) solder, liquid flux, good quality QC's and a heat sink plus a couple of NS modules which are currently displaying a single digit.

Couple of initial questions
1. Where is the best place to attach the heat sink, if I place it on the leads from the QC it makes the soldering fiddly as it gets in the way but would it still be effective if it is placed on the QC casing?
2. What is the best method to bend the leads from the QC to position them correctly without causing any damage to the QC?

It would be great if someone could post a step by step account on how this should be done correctly preferably with photo's.

I know this is a basic operation but hey we all have to start somewhere.

[Led-Time]

Mick,

I've changed plenty of these without using a heat sink and never damaged a crystal or module, the only advice I can give is don't keep the heat on any of the components too long a quick dab is all thats needed. When the two crystal wires are soldered to the module gently bend back the crystal so it will fit inside the carrier where the original module sat and thats it...

[bucko170]

Cheers Klippie, sounds like I was trying to make a simple task difficult, I will give it a whirl.

[Led-Time]

Give me a shout if you run into problems...

[retroleds]

Not sure how the clamp gets in the way. Small, smooth-jawed alligator.


3 Suggestions - using tweezer or one of those clamps, carefully bend the wires before soldering, particularly the one that needs to swing under the crystal. Do that as two bends and then make a small third bend at the end, creating a "foot" to place firmly against the existing solder.

Don't bother unsoldering old crystal, just snip off fush with existing solder.

Clean leads by gently scrapping sides with a razor before bending.

BTW: the IC is on other side under the rightmost battery contact "wings", so the heat is rarely a problem, if you do it quickly. Shouldn't take more than .5 seconds to hit that with a small drop of solder and achieve good melt. Pull off and blow! And may the Force be with you!

[bucko170]

Thanks for the tips chaps What is the fail rate for the new QC's or are they usually pretty reliable?

[bucko170]

Changed three this morning and all are working as they should...... thanks for the tips. I found it a very easy job to do, it was just a case of having the confidence to give it a go

Also replaced the QC on the one that I previously tried but this one is still displaying a constant zero so I suspect it has another problem elsewhere.

[Led-Time]

Also replaced the QC on the one that I previously tried but this one is still displaying a constant zero so I suspect it has another problem elsewhere.

It could be the trimming capacitor thats at fault try replacing it with one from another module to see if it works...

Check the time keeping on the modules they should be very good now since modern Q.C's are in there.