removing lm1117 regulator glued/affixed to pcb...

Hi guys,
like many other MOTU 828mkii units, mine finally burned the lm1117 voltage regulator up (resulting in intermittent dropouts); I've started to replace the lm1117 (thanks, mouser!), but it looks like MOTU glued or otherwise affixed the regulator to the pcb. To be more clear, the bottom of the lm1117 is its heat sink, and that is what specifically is not wanting to come off of the pcb. At this point, I've destroyed the bad lm1117, so just the heat sink is left on the board (the picture shows the bad regulator intact, prior to destruction), and I've tried an xacto knife and a flathead screwdriver to pry it up, but no luck. Do any of you guys have better suggestions?

Using force, you risk damaging the board. I'd probably just improvise something. Unsolder and remove/cut the existing connections (if you haven't done so already). Install the new regulator - possibly vertically - it looks like you have the headroom. Improvise an alternative heatsink - see if you can adapt some clip-on type to fit.

Alternatively - is the remaining bit of heatsink flat/smooth? Lay the new one on top and improvise downward pressure (using that nearby screw).

The cooling tab of the regulator is soldered to the pcb.
Why not just cut the 3 connections to the regulator and desolder the cooling tab?
Or alternatively: cut the 3 connections and install a new regulator with a separate heatsink?

Krumlee,
I agree, force risks damaging the board. The remaining heatsink is a flat piece of metal; I tried heating it up a bit to see if that would be enough to remove it, but it did not move at all. Then, I tried soldering a new lm1117 to the 2 connection pads and to the existing heat sink, verified that it really is connected (so additional downward force unneeded), but that didn't result in a working unit either. In the process of playing with that, I'm pretty sure I lifted one of the two pads, as well.


RuudNL,
I think you're correct that the cooling tab is soldered to the pcb; however, I think (but can't verify at the moment) that the solder point may be the heat sink itself (since in the lm1117 assembly the heat sink is connected to or otherwise part of the tab). The problem here is that the heat sink - which is the only thing remaining of the lm1117 - is *firmly* attached to the pcb (perhaps soldered, as above). The two pin connections are cut already. If that's true, shouldn't heating the heat sink up with the iron allow for removal? If so, maybe I'm not being patient enough with heating the heat sink up.

I appreciate both of your input, and this makes me appreciate really good design decisions allowing for repair (contrasted to this)!

Fire up your soldering station at a relative high temperature, so you can heat the heatsink tab quickly.
Also they may have used lead-free solder, so in this case you will need a somewhat higher temperature anyway.
As long as you work quickly, there is not a big chance that you will damage the PCB.
As soon as the solder melts, move the component sideways (with the tip of a screwdriver for example).
Afterwards you can always clean the area where the cooling tab used to be with solderwick.
I did this several times with success.

well, no luck; the good news is that the pcb is actually really thick. The bad news is that not even letting the iron sit on the heat sink for a good while resulted in the heat sink being able to be moved. I think the iron is hot enough - it's supposed to be 450C.
Oh well, I think this will be sold for parts. Cheers

I suppose your soldering iron doesn't have enough power.
15 Watts is certainly not enough!

ha, you're probably right. 

the likelyhood is that the heatsink is soldered down. (solder paste was used, and reflowed).

you'll need an SMD hot air gun, and a lot of patience. you'll need to bring that entire area up to 450 or so,  and also be careful not to disturb other passives etc. that can be tough with a  hot air gun.

/R

thanks, Rochey. I'll have to ask around to see if I can borrow someone's hot air gun.

If the old regulator is being discarded you can probably cut away the molded plastic top part of the package to directly apply heat with a conventional iron to the heat sink.. be careful to trash the old regulator without hurting the PCB.

JR

Maybe you could add and heat some solder to the soldered tab in hoping to help heat transfer

Yes, that usually helps!
(It sounds a bit controversial, to add solder at the moment you want to remove something, but indeed it helps to transfer the heat better.)

I hope you've gotten the LM1117 off the board by now. It's soldered and requires enough heat to get the solder flowing to pop it off. If the regulator has given up the ghost you might also want to check the input voltage. Mine has been going slowly bad, I replaced it and found the voltage on the input was slightly over 9 volts. I think the LM1117 works with voltages up to 15 v but the higher the voltage the more heat generated and I think that's why it's getting hot. I replaced the LM1117 and soldered a 5mm by 25mm strip of copper to the output tab to remove some of the excess heat. The strip can't touch anything else (like the case) because it's attached to the 3.3v output.