So my QMX board showed up with the Q103/Q104 short and I figured I would try to fix that before starting on the actual build. Has anyone successfully done this with a soldering iron, as opposed to a hot air gun? I've never done any SMD work, but figured Q103 is big, so maybe I can heat up the large pad and nudge it over, but it wouldn't budge with increasingly aggressive heating. I decided to try and the gate and source pins first, and ... Q103 shattered at the gate pin.

I know this thing is very much in development, but it's frustrating to have a defect like this on a board intended for kit builders. Maybe Hans can offer replacement power boards for some nominal fee since these have been causing so many problems for people? For now I'm setting this project aside.

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I purchased an air gun for this very reason! Applied the airgun and Q103 fell right off the board. I ended up soldering it back in, with my iron.

As a matter of interest, removing Q103 did NOT remove the solder bridge! But I could see it plainly and get to it, at least. Just moving Q103 would not have fixed the problem I had!

I would think the best "iron only" approach would be to use solder wick to remove as much solder as possible from the lead end of Q103, maybe lift them off the board just a bit? Be very judicious, many reports of breaking these leads!

Then flux and heat the tab of Q103, melt the solder there, and lift it gently up--just a bit. Too much will lift the connections on the other end of Q103 (I think!). That may remove Q103 entirely, so you can work in the area freely (good for you!)

Place Q103 back, tack it in place, taking care to keep away from Q104's gate tab. Solder the other lead, and resolder the tab.

(I found putting Q103 back to be quite easy. The way I removed it was surprising to me, I didn't expect it to leap off the board!)

Paul

Sorry that you busted your transistor.? That's been mentioned in other topics; components can't take much physical stress. But you can install a new transistor without too much trouble.? Read on.

For others with the same situation, there are gentler ways to solve the problem so you don't damage either transistor.

Couple weeks ago Keith AG5GW posted this topic
in which he linked
by

Recommended.? Review the video; Mr SolderFix shows very workable techniques for removing components.? I would focus on moving the small transistor, Q104.? You should be able to move the small transistor using his technique of a form-fitted piece of copper wire, which allows you to melt all three legs' solder joints at the same time.? I'll suggest getting all 3 joints melted, then move the small transistor away from its pads toward the edge of the board, and remove the heat-transfer wire.? Then go about soldering the transistor back onto its pads, leaving a gap in between it and the large transistor Q103.

You can accomplish the same goal of removing Q104 (or Q103 if you prefer) using low temperature desoldering alloy.? I have done this on QFP chips, Quad Flat Pack, 32 pins, so I know it can work on a 3-pin device like Q103 or Q104.? The alloy is sold under brand names and on Amazon.
I like low-temp desoldering alloy quite a lot.? Just clean up all the weird alloy from the transistor legs and the board pads, using desoldering braid and flux, before you reinstall the transistor.

Also pay attention to Mr SolderFix' technique of removing solder from through-holes.? You'll need that technique some day.? Desoldering braid and liquid flux and a little finesse --? which this guy shows you -- gets it done.? His YouTube channel is really, really good and informative.

Sorry, I forgot ...
Hans / QRP Labs will be offering the separately.? $10.? They won't be available for a few more weeks though.? Probably in manufacturing.

You can fix your board sooner than that with a new Q103 (big) transistor, and you'll have learned some good new techniques.? Be aware that Q103 has a large copper pad underneath it.? Probably for heat dissipation.? It will take a fair amount of heat to get that solder joint to release.? Again, Mr SolderFix' formed wire technique should do it just fine.? Personally I'd go with the low-temp alloy;? I like to use as little heat as possible for repair operations.? Be gentle on everything and you won't turn a small problem into a big problem; lifting pads for example.

Some components like large ICs have large copper pads underneath them, completely inaccessible to soldering iron techniques.? If you have to repair one of those some day, you'll have to use wide area heat.? The easiest, cost-efficient approach would be to use a heat gun.? I love my heat gun ... everybody who gets a heat gun loves it.? You do have to practice with it though!? Watch a bunch of YouTube videos so you know how not to blow nearby components away!? And practice, practice, practice on junk boards before you attempt your intended repair. Got an old dead cell phone?? Rip it open and take parts off the board one at a time.?Finesse is everything with a heat gun.

Hot air is a good investment. Cheap hot air stations are fine for hobbyist use. I spent less that $50 for a three-channel variant of the usual single 858D stations. Three-channel is a bit of a luxury, which I do enjoy, but single channel will get the job done fine, and they can be had for under $40. Here's one Comes with nozzles and tweezers.

Thanks all for the advice!

Rich: I had indeed watched the Mr. SolderFix video recently, but the wire technique seemed hard to manage in the tight space on the board and with the large drain pad. Thanks for the low-temp alloy and practice suggestions though.

Paul: I think I may have the same situation as you, I'll find out when I can fully remove Q103 (giving in and getting a hot air station,) but the solder bridge from Q104 appears to reach well under Q103.

Hi Eric,

In addition to the hot air station, you may want to get some heat-resistant tape:


Use it to keep the hot air off of parts you do not want to remove.

Just a suggestion.
73
Evan
AC9TU

At what temperature are you setting the hot air gun.? I have one but scared to use it.

Thankfully there is no short on my PS board.. but the components and their associated solder blobs are so very very close.

Thanks

73
Dick
W4PID

Again, watch a bunch of YouTube videos on hot air rework.? They will tell you temperature to use and LOTS more.
Comments in (parentheses) are my opinions, and I Am Not An Expert.

• Temperature (start with 350C)
• How much airflow to use (never the maximum!)
• What direction to point the hot air gun (I usually point it straight down; opinions vary.? I'll say "straight down but incline it toward an area of the board with the fewest nearby components")
• Preheating, then focusing on the component to remove.? (Patience!)
• Use of Kaptan tape or aluminum foil to protect heat sensitive, e.g. plastic parts, or to protect nearby components from the hot air stream.
• How to watch the nearby components to see when unwanted joints are being melted.
• Counting on surface tension of the molten solder of nearby components to keep them from flying away (too much airflow and they will fly away anyway).
• How to gently nudge the part while waiting for all the joints to melt (this avoids lifted pads and traces).
• How to remove the part once all the joints have melted (Tweezers!? Buy a very good tweezer).

I like Louis Rossman, so you might start here:


I also like NorthridgeFix.? He's a working repair tech, not so much an instructor.


Whereas this guy is kind of a klutz:


If other people have favorite videos on hot air rework, please post so we can all learn.
Rich

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I was unsure of my ability to deal with SMD/SMT but got over it by getting a practice kit. ?It doesn’t do anything when you are done so you can’t destroy it. ?Put the parts on and take them off to your hearts content…. you will get the feel of the process.

On 23 Aug 2023 at 22:12, KK4ITX John via groups.io wrote:

Put the parts on and take them off to your
hearts content?. you will get the feel of the process.

If anyone wants old populated boards to practice
with, let me know ... only ask postage for them.

Jim W2JC (nj)

The space between the small transistor Q104 and the larger Q103 does not allow for a form-fit wire of almost any reasonable gauge to fit between the two—much less moving a sharp-tipped iron into that area to heat the wire up—so I don’t think the Mr Solderfix technique is likely to work on Q104. At least this is as far as I can tell.

My QMX kit arrived with the short in place. ?

I removed Q104 (the little one) and the pad was still shorted to Q103’s tab. ?

Using just a soldering iron I first lifted Q103’s two leads. ?Then I heated the tab until I could pull off the part with tweezers. ?

At that point the pads were no longer shorted. ?

I reinstalled the devices at the edges of their pads to increase their spacing. ?All is well. ?

I had no problem with the procedure using just a couple of Metcal soldering tips, one small and the larger one for the tab. ?

Disclosure: ?I did this work using a 7 power stereoscope. ??

Jerry
N6JH