Re-soldering a PC board

Discussion in 'General Electronics Chat' started by JulieMor, Aug 29, 2012.

  1. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    I have a Pioneer Elite rear projection TV that is about 10 years old. Yesterday I heard a pop and then the screen went dark. No picture, no sound. It turns out two fuses on the power supply board blew.

    I have it on fairly sound advice that the power supply board in these TVs were made with weak solder joints and you either replace the board (about $300) or re-solder the board to beef up the joints. I've opted to do the latter before plunking down $300.

    I have a Hakko FX-888 soldering iron that I've used for little projects but have never taken on an entire circuit board. Well, maybe that Radio Shack strobe light kit I built in the early 70's counts? :rolleyes: The iron is 70W and has a temperature range of 392-896°F.

    Anyway, I was wondering what temperature I should use for re-soldering the board? I have 60/40 rosin core solder (.062 dia - 376°F melt point) that I plan to use for this work. Is that the right solder?

    Any help is appreciated. Thanks.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I use 63/37 solder but yours will work too.. and have that same iron.. I set it at 350 deg C and go go go... Most important thing.. Don't heat up the pads too much/for too long. They can lift up and your are basically screwed then.
    I would put a bit of solder on the tip just to get better "bridging" from tip to solder joint and as soon as it starts to melt add a touch more solder and remove the iron.
     
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  3. paulktreg

    Distinguished Member

    Jun 2, 2008
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    If it's ten years old it would be a good idea to replace all the electrolytic capacitors while your at it!
     
  4. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    Thank you! When building up the solder, should I do anything with the solder that is part of the circuit board (like the part circled in the pic)? I was thinking I'd leave that alone but that may be part of the problem I've read about.
    [​IMG]
     
  5. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    Now you're talking Greek to me. I wouldn't even know where to begin!

    A self proclaimed Pioneer guru said he re-solders the PW boards and that's the only weakness of these TVs. (fingers crossed!)

    This is the power supply board. The red arrows in the middle point to the fuses that blew.
    [​IMG]
     
    Last edited: Aug 29, 2012
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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    You probably don't need much solder, just flux.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    melt a good size drop on the tip of the iron and rotate to cover the whole tinned surface, use a piece of coarse steel wool, or better yet, a slightly damp sponge and wipe the tip across it twice. Once for each side of the tip, or just rotate the tip as you wipe. A few seconds after a nice light toasty bronze color can be seen on the shiny tinned tip. This is the sign that every thing is just right! :) If the tip never gets to the light yellow look, but stays silvery and shiny for a long time, it is too cold for anything but micro sized pads and leads.

    start by putting the tip at a 30-60 deg angle and lightly pressing into the solder. It should melt in 1 sec or so. Immediately at this time touch the tip of the solder wire to the tip and pad together and again immediately withdraw. This will add fresh rosin to the surface as you remove the iron, leaving a shiny smooth finish. You don't really want to add much if any actual solder to the joints. Just remelt and flow them. Wipe the tip frequently and relax and enjoy the smell of freshly roasted pine rosin!
     
  8. #12

    Expert

    Nov 30, 2010
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    The capacitors are those tall, brown things, and some of them are blue. Any suspicion, whatsoever, and you replace them. Suspicion: swelling (especially at the top), leaking, corrosion, wobblyness to a gentle finger wiggle.

    Electrolytic capacitors contain liquid. They go dry, they corrode, they swell up. They are the least reliable part in modern circuits, except maybe the solder joints. The only real proof that they are all good is that the circuit board works, and sometimes the circuit board can cripple along in spite of a weak capacitor. Always keep a jaundiced eye on the capacitors.

    If someone gave you a 50 year old guitar amplifier, you would replace all the electrolytic capacitors and THEN plug it in to see if it has problems.
     
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  9. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    I was going through the service manual and found this:
    [​IMG]
    Fuses FU202 and FU204 are blown but I don't have the equipment to do the tests recommended. If the circuit board has weak solder connections, would that create high loading on the conversion amp?
     
  10. crutschow

    Expert

    Mar 14, 2008
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    I'd think that, if the fuses are blown, it's more likely a bad electrolytic, then a bad solder joint. As paulktreg noted, take a close look at all the electrolytics. But it's certainly possible that a bad joint could cause the power supply to go into some mode that would blow the fuses.

    As others have noted, do not apply the heat for too long when resoldering. You just need to remelt the solder and then let it harden. Often all you need is a second or less of heat.
     
  11. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    The "guru" says most likely the ICs are bad and need to be replaced. He said some owners do this themselves. My problem is where do I get these parts and are the parts on the power supply board or on the convergence amp assembly?

    This is a picture of IC901 & 903 on the power supply board:
    [​IMG]

    But those same IC numbers are also found on the convergence amp assembly but they are a different part #, both STK392-110, so, in the conv. amp assy. both ICs are the same part. Can something that goes bad on one board blow a fuse on a different board?

    BTW, that assembly runs $280 and when you consider there's the slightly newer, and working, model (630HD) selling on Ebay for $150, it makes you wonder.
     
  12. paulktreg

    Distinguished Member

    Jun 2, 2008
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    The IC numbering scheme is probably the same on each board so there's probably several IC101 etc.

    Problems on other boards will blow the power supply fuses.

    Try replacing the suggested IC's and disconnect everything from the power supply board, apart from the AC of course and see if the fuses blow.

    I don't know your location so it's hard to suggest a source.
     
  13. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    I thought the numbering would be consistent across the boards but it's not. This is the board layout (partial) for the convergence assembly. On the bottom are IC901 & 903. They are the same part but very different than what IC901 & 903 look like on the power supply board.
    [​IMG]

    Since I don't have the ICs, I'll run your test with new fuses and see if they blow. If so, then the problem must be in the convergence assembly?

    I'm in the Chicago area but have no idea where to begin looking for these ICs. Thank you for your help.
     
  14. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Digi-key have the ON3171 opto-coupler and MCM have the MIP0253SP.

    Hope that helps.
     
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  15. JulieMor

    Thread Starter New Member

    Aug 29, 2012
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    I ordered the STK392-180 and the other IC from MCM as well as some fuses. I read on MCM that Pioneer is recommending using the 180 over the 110 for the STK as the 180 is 18 watts to 11 for the 110.

    I was told the ICs on the convergence board are most likely shot. That seems to be what the manual says too.

    I've been working on beefing up the solder joints on the power board. I just hoping I'm not laying down TOO much solder. I'm using 63/37 solder but don't know if that makes any real difference with the cold joint problem.

    That's some neck wrenching work! I can't imagine how anyone can do that for a living without becoming hunch backed.
     
  16. #12

    Expert

    Nov 30, 2010
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    A question to consider: When MCM recommends a different chip, is it a straight, plug-in replacement, or do they mean you should use the higher wattage chip if you're designing from scratch?

    Too much solder is when it blobs over and shorts something out. 63/37 or 60/40 makes very little difference. They mix well together and don't fight. The only significant difference is a slightly different melting temperature.

    and yes, resoldering is a young person's game. Besides the hunching, it requires good eyes.
     
  17. Rleo6965

    New Member

    Jan 23, 2012
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    If it hard for you to source the IC901 or MIP0253SP. How about isolate first the blowing fuse problem. By removing IC901 form the Power Supply Board. I think its a pwm ic. Use half capacity or ampere of the original fuse. This is to avoid more damages of components if short still exist.

    If fuse still blow. Then it's not IC901 was defective. Use mulitimeter to identify shorted Varistor, bridge diode, power fet and capacitors, open resistors. This components will be easier to source. This will save you time and money in repairing
     
  18. JulieMor

    Thread Starter New Member

    Aug 29, 2012
    12
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    Here's what I "know" so far:

    1. From the Pioneer guru: The convergence ICs are gone and need to be replaced. The supply board has problems with cold solder joints and needs to be re-soldered. $350 to replace the ICs on the convergence board and $275 to re-solder the power supply board.
    2. From JustAnswer.com: These TVs have problems with cold joints, especially on the power supply and deflection boards, and should be re-soldered.
    3. From a supplier of new boards: Odds are 90% it's just the power supply, 10% it's something else that blew the fuses. A new PS board runs $280 and is at least 60 days out for delivery.
    4. From the service manual: If fuses FU202 & 204 are blown, look at the convergence ICs then at the potential between the convergence ICs
    5. From Pioneer: a new power supply board is $280, a new convergence board is $294.
    6. From Ebay: someone is selling a slightly newer version of my TV for $150, and they say it works fine.
    I'll finish the re-soldering on the power supply board, making sure I don't bleed any solder over, and test just that board. If no fuses blow I'll replace the STK ICs on the convergence board. If that doesn't work I'll :confused::(
     
  19. JulieMor

    Thread Starter New Member

    Aug 29, 2012
    12
    1
    Well, the power supply board is re-soldered. Besides damaging your posture, the smoke just loves to find your nostrils!

    Some of the areas were so small I was using magnifying glasses with a fluorescent magnifying light to see what I was doing. Even with all that magnification I can't be 100% positive there was no bleed over. Some of the gaps are about as wide as a knife edge.

    Now I'm hesitant to plug the board in (without connecting it to anything else) because I don't want to see it melt. I'd need intense therapy if that happened.

    I received the ICs yesterday. Now it looks like I'll need some sort of desoldering tool. The larger ICs have 18 pins that are thin wires. Oh what fun!
     
  20. KJ6EAD

    Senior Member

    Apr 30, 2011
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    A small fan strategically placed will disperse solder fumes away from your face. All you need is a slight breeze.

    If you're not trying to save the IC, often you can cut all the leads close to the body then desolder one pin at a time.
     
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