Bought this receiver as the amp for my keeping room home theater system sight unseen "...unable to test all functions." Well it was DOA and resetting was of no use. Read that the DTS chip was the usual culprit since the speaker matrix did not display on the front panel and the cure was to rework the chip. So I bought some liquid flux and I already had a hot air rework station (thank you AliExpress!) which I'd never used except to shrink tubing. So I applied the flux to the edges of that chip and with the unit off, but still plugged in, I applied heat at about 340C and all of a sudden it turned on by itself, the speaker matrix was displayed, and playing. However this was short-lived and I've done it a couple of times more with the same result (except it didn't turn on by itself) and if it's on but dead heating the chip edges would make it go live again. Do I need more temp on the air; do I need to bite the bullet and completely remove and resolder the chip? Anyone with some experience here or suggestions? Thanks!
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I surmise you’re repairing a chip with gull-wing leads. That’s promising—- at least it’s not a ball-grid device.
I assume the chip is well registered on its pads, not askew. If it is askew, you’ll have to remove the IC and clean the chip leads and wick pads and footprint clean.
You need good lighting and a temperature controlled soldering iron with a fine tip. You need patience and a light touch, and magnification—- eg. a stereo Zoom microscope ideally, or a “mag light” at minimum. If you have to resort to the mag light, rest you chin against the lens and ring light, so both hands are free. It sounds comical, but it works.
You can use a dentil pick to test the integrity of the solder joint at each lead. The tip of a Xacto blade can also work. Nudge or pry gently to determine if the joint is intact. When you find a loose joint, use solder wick to clear the joint of old solder. Often solder wick is skimpy on flux, so add liquid flux if needed. Use fine rosin core, leaded solder. Avoid lead free. Use dentil tool or knife to press lead against board surface while soldering if necessary.
If you are forced to remove the IC, use solder wick and flux to wipe pads clean and generate a uniform coating of solder. Clean the site with alcohol. Try to remove excess stale solder from the IC leads. To remount, hold IC in position and solder a corner joint. Then solder joint on diagonal corner. Reflow original joint if it seems stressed. Then work your around the perimeter one lead at a time, as above.
Good luck!
I assume the chip is well registered on its pads, not askew. If it is askew, you’ll have to remove the IC and clean the chip leads and wick pads and footprint clean.
You need good lighting and a temperature controlled soldering iron with a fine tip. You need patience and a light touch, and magnification—- eg. a stereo Zoom microscope ideally, or a “mag light” at minimum. If you have to resort to the mag light, rest you chin against the lens and ring light, so both hands are free. It sounds comical, but it works.
You can use a dentil pick to test the integrity of the solder joint at each lead. The tip of a Xacto blade can also work. Nudge or pry gently to determine if the joint is intact. When you find a loose joint, use solder wick to clear the joint of old solder. Often solder wick is skimpy on flux, so add liquid flux if needed. Use fine rosin core, leaded solder. Avoid lead free. Use dentil tool or knife to press lead against board surface while soldering if necessary.
If you are forced to remove the IC, use solder wick and flux to wipe pads clean and generate a uniform coating of solder. Clean the site with alcohol. Try to remove excess stale solder from the IC leads. To remount, hold IC in position and solder a corner joint. Then solder joint on diagonal corner. Reflow original joint if it seems stressed. Then work your around the perimeter one lead at a time, as above.
Good luck!
Thanks; I was hoping also for some suggestions about using a hot air rework gun. Does the fact that after cooling, after the chip was working properly, that the receiver again malfunctions could that indicate an internal problem in the chip and the chip itself may need to be replaced? I do have some inspection scopes I could use but the legs are so tiny I'm not sure I'd see any that were loose.
If you’re watching through a microscope, you can see a loose joint move when you nudge it. (X10 to x30 power)
We never had much success with hot air soldering, but perhaps we never found the correct technique. We would occasionally hand apply solder paste and reflow with a hot plate when we had to solder a hidden thermal pad on the underside of an IC.
We never had much success with hot air soldering, but perhaps we never found the correct technique. We would occasionally hand apply solder paste and reflow with a hot plate when we had to solder a hidden thermal pad on the underside of an IC.
Some chips have thermal pad underneath for some heat dissipation. These can break connections sometime and also stubborn to reflow. Normally 420-480 deg c works great(coz these are pb-free solder with higher melting point) for large chips with underside thermal pads, should reflow properly after a minute or so. Also make sure you have good amount of flux(BGA or rosin also fine) applied before you start reflowing the chip. I would just take chip out entirely, clean the pads with wick and IPA. And then prepare the pads with low melt solder, position the chip, reflow again with some more flux. If you positioned the chip to align all the pins close enough, it should just pop into position automatically when your solder melt completely. And then when you gently push and release on the side of chip a little(not more than 0.5mm🙂), when the hot air still on, it should pop back into position due to viscosity.
I would not attempt it as a first project. So if you are not confident doing this entire process than just apply generous amount flux on all pins and run solder blob over the pins with a fine tip. Just wick the excess or any bridges. But if you have bad contact underneath the chip then it will not fix it. If you don't have any microscope you can use some camera magnifier apps on your app store.
This video demonstrates a bit.
I would not attempt it as a first project. So if you are not confident doing this entire process than just apply generous amount flux on all pins and run solder blob over the pins with a fine tip. Just wick the excess or any bridges. But if you have bad contact underneath the chip then it will not fix it. If you don't have any microscope you can use some camera magnifier apps on your app store.
This video demonstrates a bit.
Not sure why someone would want to rework with the unit plugged in, especially again and again ...
The hot air gun is definitely not a soldering iron with leakage current but the repeated making / breaking of contacts with current draw could cause surge voltages above normal and possibly damage the electronics. This is one of the reasons (besides the usual "shock warning") why repairs need to be carried out with the power completely off and preferably after any bus capacitors have discharged.
Thanks! I’m supposed to get a board-warming plate today then I have to remove the board; I’ll look with my inspection scope to see if I can detect any loose arms.
Got out the inspection microscope (see, honey, this thing I bought did come in handy; IYKYK😉) and looked at all the arms on the chip and I poked them all with a static-free tweezer and no obvious movement. There is a problem in the construct as it goes normal temporarily with heat. I've removed the board, bought a cheap preheater, and I'm going to try and reflow with some bottom heat to augment the top heat. Can the board, which is of course double-sided, sit directly on the preheat plate or do I need to prop up the edges to keep it off the heater surface? At this point I'm using this receiver as a trainer; if it works great; if it doesn't I'm learning a new skill.