Desolder and Solder in of an STK391-020 Conversion IC From Zenith Projection TV

Im just asking what power soldering iron I should use for this job, is a 20w iron sufficient? What precautions should I take to ensure i dont mess up the new IC circuit (by burning it up) .If this job is just a standard job that needs no other precautions than listed in the FAQ then let me know. Im just curious how hard it is to burn something up doing this. Thanks

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VoRTeX
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I replace these hybrids all the time using a standard Weller TCP series 50 watt magnastat iron. I've never had a problem. The trick is to get the old one out cleanly, without damaging the print. Run new solder onto the old joints first. Then remove the old solder using a solder sucker or desolder braid. When you've got the old hybrid out, clean all of the old paste from the heatsink, then put a thin layer of new paste on the back of the new hybrid. Feed the legs carefully into the PCB holes, and make sure that they've all gone through properly. There's nothing worse than getting 3 joints from the end, and finding that a leg has twisted up behind a resistor, where you can't get at it ...

Screw the device to the heatsink, before soldering. Make each joint reasonably quickly ; 2-3 seconds is fine. You shouldn't then have a problem.

If it doesn't work when you've done the job, check for any low value feed resistors on the supply rails being open.

Arfa

Reply to
Arfa Daily

20w iron sufficient? What precautions should I take to ensure i dont mess up the new IC circuit (by burning it up) .If this job is just a standard job that needs no other precautions than listed in the FAQ then let me know. Im just curious how hard it is to burn something up doing this. Thanks

Only yesterday I used a hot air gun to desolder such a hybrid output device, no dislodged tracks, didn't even have to clean up the holes afterwards. Clean,quick, easy and cheap and a tool with multiple uses , unlike a de-solder tool.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
n cook

Good for those of us " in the trade ", but I'm always reluctant to recommend it to 'have a go' interested non professionals ... d;~}

Arfa

Reply to
Arfa Daily

a

mess

job

recommend

I find it a bit galling that I own a proper vacuum pump assist desolder station and a more basic blug in a Weller base hand vacuum one but rarely use either. Hot air gun is so much more efficient and less colateral damage, lifted tracks etc, even for desoldering SM ICs after shrouding off surrounding comps.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
n cook

That's the trick to it, though - masking off surrounding components, and making sure that there's no plastic nearby ...

I also have a Weller vacuum desolder station that I use on a daily basis for general work, and twice or so a week on large batch commercial board repair work, and I have to say that it is absolutely excellent at the job, and I have never damaged any print with it. The only thing that I would say is that it needs 10 minutes a week spent on maintenance - cleaning and replacing filters, cleaning out the solder channels and receiver glass etc, and as soon as the nozzle starts to become tight at getting the cleaning wire into, it's time to replace it. I have to fit new O rings to the receiving glass about every three or four months, and about once a year, I strip the vacuum pump, and clean or if necessary replace the flap valves, and clean out the vacuum pipes, that get flux fume residue in them, even though the vacuum system is filtered.

Arfa

Reply to
Arfa Daily

.

Tell me more about this. In my profound ignorance, I've never heard of such. I would like to know the device, and the procedure. Thank you.

David, on the Illinois prairie.

Reply to
dharrisfc

device. . .

Scroll down to the 2 hints and tips files on the URL below

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
n cook

Hey Smitty, how's it going ?

The IC in question isn't a surface mounter - it's one of those gi-normous output hybrids with a single line of through-the-board pins, so normal through board removal techniques are all that's required ( after first splatting some liquid flux on, of course ... d;~} )

Arfa

Reply to
Arfa Daily

iron sufficient?

Not even close. If you /must/ desolder the original chip, you should use a professional station (eg; Weller TCP) with a heavy tip. But it's easier & quicker to snip the legs away from the body of the failed chip & remove them one by one with an iron & a pair of tweezers.

Once you've done the above & cleaned up the holes + pads, soldering in the new part is pretty straightforward.

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Lionel

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