Remove heatsink screws?

[Axtman]

I am having a heck of a time removing the heatsink screws from the Ampeg SVT 4 Pro that I am working on. The screw is black oxide with a tiny button head with a shallow 1/16-inch Allen recess. I see that on newer amps, Ampeg has replaced those screws with zinc-plated Phillips head screws with integral washers.

There are 10 of them on two heatsinks. The first 10 came out relatively straightforward with soaking with Liquid Wrench penetrating oil. The others I am having a problem with. Recommendations?




On a related note, once I got the screws out on the first 10, I had to pry them off the heat sink silicone pads. They were stuck pretty firmly. Does this mean the silicone pads were shot and need to be replaced?

[The Dude]

Have you tried heat? Maybe hit them with a heat gun for a bit.

[Helmholtz]

Freeze spray might work even better.

[g1]

Sometimes I find a torx bit will bite better, if the size allows a snug fit.

[xtian]

A soldering iron is a way to apply very localized heat (some flux will help). And an inverted can of compressed air makes a decent cold spray. Finally, a well judged tap on the screw head may help it get free.

[tedmich]

Heat cycling often freezes fasteners. While not quite an exhaust flange, putting some anti-sieze on these will avoid them getting stuck again.
Permatex 77134 Nickel Anti-Seize Lubricant, 0.5 oz Tube is about $5 and works well.

The silicone pads can have adhesive for installation, they might be considered single usage but IME can be reused with a little thermal compound.

[Mick Bailey]

I've had these round off - the metal is fairly soft. I find an Allen or Torx bit with any lead ground off used in a T wrench is better than an Allen key. You can apply downward pressure and keep the bit aligned much better.

If it still rounds off, I protect the surrounding area and dremel the sides off with a cutting disk to leave two flats and use an adjustable spanner. There's still a chance that the head will snap off, though.

It's as well to heat the screw with a hot soldering iron beforehand to try to break the bond. My preferred release agent these days is 50-50 acetone/ATF or power steering fluid. It strips paint and damages plastic, so needs careful use.

[Axtman]

Well, the Liquid Wrench penetrating oil did not work. I also tried the freeze spray and it did not work. I heated the screws with a soldering iron (40w, 100w, 200w). Even though I leave the soldering iron on the screw for a while, the heatsinks do such a good job that the screw only gets slightly warm to the touch.

My Plan B is to cut the legs off the 10 FETs and remove the large heatsink. Then I can work on the screw removal safely and possibly break the FETs off. I would really prefer not to do this, though.

[Chuck H]

Well, the Liquid Wrench penetrating oil did not work. I also tried the freeze spray and it did not work. I heated the screws with a soldering iron (40w, 100w, 200w). Even though I leave the soldering iron on the screw for a while, the heatsinks do such a good job that the screw only gets slightly warm to the touch.

My Plan B is to cut the legs off the 10 FETs and remove the large heatsink. Then I can work on the screw removal safely and possibly break the FETs off. I would really prefer not to do this, though.

You could still Dremel a flat head slot into the heads or Dremel off two sides for a wrench type tool as Mick suggested for more secure purchase. Mick indicated these are relatively soft metal so depending on your 'at the bench' experience you're kind of on your own. It doesn't help to say that it's a shame these kinds of problems come up but we all deal with mediocre materials used where they shouldn't be all the time and progressively getting worst for decades now. Good luck with whatever you try.

[Mick Bailey]

To overcome the heatsink issue you could file or machine a dull point on a length of steel rod and heat it to bright red, rather than using a soldering iron. Dremeling a slot may work, but keep it as narrow as you can, otherwise one half of the head will break off when you apply pressure.

[mozz]

I bought these years ago and threw away all my allen wrenches (kidding). They are made of drill bit steel. You use them BEFORE you strip a screw out. Not cheap, i think it's showing they are discontinued, damm. I see generation 2 is out, not cheap close to $20 per size.
https://www.miponline.com/mip-hex-dr...-and-3-32-9501

[Helmholtz]

Heating the screw will make it expand which might make things worse.
I'd try to mainly heat the surrounding metal (heat gun) and then hit the screw with freeze spray to make it contract.

[mozz]

If Loctite was used, you need to heat it. We used to crank up the solder iron with a pointed tip up to 750-850f. Hold for as long as you can. If it is really stripped, i agree with cutting a slot with a dremel tool, also have used a chisel to get it started to spin.

[g1]

Depending on the size, I will sometimes pound a Robertson (squarehead) bit into a stripped allen screw. The combination of the hammering along with the extra bite will sometimes do the trick. Same could be done with a torx bit as mentioned earlier.
The small hand held held 'impact drivers' that you hammer on also help.

[DrGonz78]

I’m not sure that this will help but it has worked for me. A very very long screwdriver is something I have used on my car to remove screws on my air intake valve. I tried impact screw driver and it wouldn’t budge. I pull out my 3 foot screwdriver and lean into it as I turn. It was like butter!!

I can imagine attacking screws on heat sink with the unit lying on the ground and then putting your weight into the screw driver as you turn. Perhaps these are far softer screws and it destroys them. If I was in my shop right now I would try that method. Perhaps this idea is good or not, but the long screwdriver is only like $5 at Harbor Freight.