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So I have a replacement on the way (several, actually, just in case), along with some diodes for the Q508 related fix for the QMX.

I have a hot-air rework tool, and have some finer tips on order for it, but was wondering if that is the best bet for removing IC402.

I have also seen suggestions on the group for using a small sharp blade ("carpet cutter") to cut the pins, lift off the carcass of IC402 and then desolder the pins. I have also seen a reference to using a dental tool during the process.

Given that I have a hot-air tool (Yihua), would it make the most sense and just do the obvious and use that to heat up the pins to remove it? Are there other suggestions?

72 JRJ W9IYN

I have removed a few IC402's just hot air and tweezers.? I do use some aluminum flashing to screen off local components from the hot air.
When replacing, I think it was Hans, recommended using Blue Tac to keep the SMD's in place while soldering.?
I find that sometimes a pin is not properly soldered although looks good under the microscope.? I recommend checking continuity between the pad and pin.??
Note the replaced soldering will look uglier than the original. If you look at the PPT needed mod you will see even the QRP-labs change IC402 looks fairly ugly:
https://www.qrp-labs.com/qmx/qmxpttmod.html#galleryd20f63044e-3
I hope this helps, good luck
Chris

I was in your shoes a few weeks ago. I've never done hot air work before so ordered a Yihua rework station and a few IC402 replacements as well and went to town. I started on a pretty low heat setting (500F I think) and held it on the chip for maybe 10 seconds. The whole board and all its components heat up quite a bit in the process, so I was very conservative with the heat application to try and prevent frying anything else on the board. That didn't work so I let the board cool off and then upped the heat. I repeated this process probably 10 times before I was getting to a pretty high heat setting (maybe around 900F) and then was really scared I was going to overheat other components, but the solder still wouldn't melt. Eventually I just went yolo on it with a high heat setting and held it there for longer than I was comfortable with and got the chip to melt off. I think the dual ground planes really pull the heat away from the component. Definitely wait until it's floating on the melted solder to pull it off and don't try to pry it at all or you'll pull the traces off the board and then you have a whole other set of problems.

I just used a soldering iron and the residual solder on the pads to reattach the new chip, adding a tiny bit of new solder where it seemed necessary. Apparently I didn't fry anything cause it's been working fine ever since. Was still pretty nerve-wracking though.

And for the diode I just used the soldering iron. Blasting that area with the hot air gun seemed like a bad idea.

Best of luck!
Brad

Low temperature solder like ChipQuick works well too.?
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73, Dan? NM3A

When I remove these, I cut a square out of Kapton tape and use it as the heat shield. It’s not really needed but it makes me feel better. I don’t pull until the air can make the chip swim. Then I add a tiny bit of liquid solder and drop the new one in.?
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Colin - K6JTH?

On Tue, Feb 13, 2024 at 08:00 PM, Daniel Walter wrote:

Low temperature solder like ChipQuick works well too.?
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73, Dan? NM3A

Another vote for ChipQuick solder. It stays molten for a long time. allowing you to lift the device off easily with no damage to pads.
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Mike G8GYW

A product such as Chip-Quik??or Fast Chip?
will drastically lower the melting point of the solder and cut down on the heat needed for removal.??
But if the part has leads which are accessible to be cut and removed individually that is my preferred method.? This is how we repaired hi-rel spacecraft PCBs.
I find that a #15 scalpel blade works well for this.
73, Don N2VGU

I will just say that Hot air is fantastic once you have the hang of it.? ?

?

Brain surgery on your latest radio is probably not the right way to gain initial experience

?

I used a new heat gun (a decent one this time)? as a chance to collect up all those old broadband hubs, network cards, smart speakers etc that were in the 'chuck or not limbo' pile and amuse myself removing and replacing increasingly challenging components until suddenly after many torn tracks and 'collateral damage events'? it all clicked.? ?Now it works at least 95% of the time for me and I find heat shields etc are rarely needed.

?

I use a lot of wooden cocktail sticks.? They are great for sliding off or flipping hot air heated components out of the way and for holding down SMD components while soldering them in.? Unlike metal tools the board is never damaged and they are less prone to slip.? Furthermore if the cocktail stick starts burning too much I know to ease off a bit ! ?

On Tue, Feb 13, 2024 at 05:13 PM, Bruce Akhurst wrote:

Brain surgery on your latest radio is probably *not* the right way to gain
initial experience

I am NOT new to using hot air to solder SMT. However, removal is something I have only done a couple of times before, on boards that were less dense, hence the request for suggestions.

I like the idea of a wooden stick - I have some that I used for winding the QMX toroids that would be applicable.

73 JRJ W9IYN

The repair appears to have been successful, including adding an SMT diode near Q508.

Photos available at:

So, JRJ, any chance getting one of those diodes? You have a Q508 the right size, too?
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73
Karl
KI4ZUQ