Print

[Jacques]

Furthermore I am a bit stuck since I have to find the caps somewhere in Europe and I don't know with which substance I can replace the white goo, since it is needed to protect against mechanical stress, to prevent unwanted movement of caps closer to heat sources, but also to dampen any kind of coil noise. I had to break the hardened goo in some places and a full clean and re-goo later on has to be done once I have the caps sourced and mounted.

I believe the stuff you are after is called Silicone rubber (RTV). Comes in various grades of hardness but most electronic component suppliers stock the stuff.

[ssp3]

If the PSU is not going on the plane, thain or automobile to get shipped to the other side of the planet, gluing capacitors to the PCB is not necessary.

[robespierre]

ssp3 above is correct. The Silastic or DowSil is for mechanical reinforcement, to withstand shock or vibration such as during shipment. Do not use any RTV: many silicones cure by releasing acetic acid, which will corrode the power supply.

[aBc]

If the PSU is not going on the plane, train or automobile to get shipped to the other side of the planet, gluing capacitors to the PCB is not necessary.

Well perhaps therein, lies the proverbial “rub”. Why not do it anyway?

I’m merely the current caretaker of all Macs that I own. Eventually they’ll all be released “back into the wild” to someone else hopefully. So I use either hot glue from a glue gun or silicone on the clustered group of larger capacitors in the PSUs of MDDs, Quicksilvers, etc. Because eventually these machines may be shipped off to someone else (for the next twenty years of their useful lives).

Previously I did this to reduce any possible effects of harmonic resonance between the larger capacitors (because someone once told me this was why they were originally glopped together in this manner). Now I understand that it’s more to prevent movement or damage. (Because Andy tells me so.)

Quoted below from someone else that has been professionally refurbishing PSUs for now well over ten years. Andy’s definitely the go-to guy for PSUs that I don’t want to refurb myself and I have recommended him to many members here in the past. (All report back with 100% satisfaction.)

The glue is there to prevent components from moving around and getting damaged.  I have seen one or two cases where the glue didn't hold, which allowed one of the large inductors to rub against a heat sink until the insulation on the windings was damaged, creating a short circuit.  I've also seen cases where a heavy part fell off the board.

I've seen both hot melt glue, and silicone used.  I personally use silicone because it sticks more securely, and is more flexible.  Acetic acid isn't a problem for something open to the air like this.  I never seen even the slightest trace or corrosion.

Do not use any RTV: many silicones cure by releasing acetic acid, which will corrode the power supply.

And btw, silicone cures and “gases-off” within 24 hours. So if you’re all that concerend about it, wait a day before reassembly of the PSU to allow any silicone time to cure. And of course, all of this is up to the individual.

And my thanks again to Andy!

[ssp3]

Well perhaps therein, lies the proverbial “rub”. Why not do it anyway?

That's why! Proper stuff is prohibitively expensive and not available in WalMart or in small shops. I'm not talking about the hot glue they use in China.
Purchasing proper compound will cost more than that AcBel PSU or maybe the whole G4. 

Here's good rundown on different adhesives for electronic components: https://www.gluespec.com/


http://static6.arrow.com/aropdfconversion/d59931acb58faa87d10dca26f3092daec75e1215/rtv_ele_e.pdf


P.S. Don't forget to use the proper PCB cleaner after you're done soldering.

[aBc]

So it’s best to not use anything at all, ehh?

Sure, that’s real logic there.

And as I stated... And of course, all of this is up to the individual.

[robespierre]

The original goop is not really expensive. Manufacturers don't create any unnecessary costs, they are trying to profit after all.

It is not an "encapsulant" or potting compound, that would be a different material for a different purpose. It also is not a 2-component material.

As for post-process cleaning, the industry trend is towards aqueous cleaners—not very practical for bench repair purposes.

[ssp3]

Everything is relative. It also depends on where you live.
I wouldn't call EUR 20 + VAT on top of it + shipping inexpensive. 
And, the stuff will be in stock after July 20th.

All this hassle can be avoided by not gluing anything. Like High-End industry have done it for ages. And have shipped their stuff all over the world, btw.

[aBc]

Thanks @robespierre. Seems that now we’re getting closer to what might actually be deemed a “Proper” solution for this specific task / application.

After reviewing more info from the Dowsil 738 SDS, it is also an RTV sealant? And if so, perhaps the Dowsil 748 sealant might be a better alternative for those concerned about acid release during cure - as the 748 is a “neutral cure” silicone adhesive sealant?



As we’ve now nearly beat this horse to death... and as this has veered from the focus of the original thread to a tangent of its’ own... thus the new Topic.

Once again, whether one decides to replace the PSU goo or not (and with whatever they might choose) that is entirely up to the individual. As for me, I’ll continue to use RTV silicone for this.

Many options, opinions and specifics have been made abundantly clear here at this point and any further posting(s) that may be deemed as excessively argumentative or redundant will simply be deleted and this topic possibly locked.

[Jacques]

While i had my machine open last night I applied some rtv to the caps I had replaced. The inside of that psu is so crammed. If you are servicing / cleaning then moving the cable bundle on mine also pushes the three caps from side to side. I’m glad I put some on now. I also applied a pea sized amount touching the top only of the heat sleeve of that resistor (near the fan control board) and the top of the capacitor next to it to ensure they never come in contact again.