First major board repair.

[mitch_a]

So I figured I'd post this to show people that with patience and practice board work isn't so bad.

Decided to rebuild the high voltage section on my wpc dmd controller board.

All old parts clipped off, then legs desolder ed, board cleaned, new parts installed, all Flux cleaned off with acetone then and bare traces sealed with clear coat.

 

[mitch_a]

 

[mitch_a]

Always add new heat sink compound

 

[mitch_a]

Done and working 100%

 

[Menace]

Nicely done. Feels great when you bring something back from the dead. (but the inverse is true if it doesn't work!)

D

 

[mitch_a]

I have to say I did enjoy doing it.

 

[brad808]

Sweet. Thanks for sharing. For future reference you may wish to look up some information on thermal paste. It's purpose is to create an incredibly thin layer between the component and heatsink that removes any microscopic air pockets that hinder the heat transfer between the two. By creating a wall of paste so thick it's gooping out the sides you are almost certainly negatively impacting the temperature by lowering the surface area of the two that's touching. Very small amount in the middle is all you need and will give you the best heat transfer.

 

[Menace]

Sweet. Thanks for sharing. For future reference you may wish to look up some information on thermal paste. It's purpose is to create an incredibly thin layer between the component and heatsink that removes any microscopic air pockets that hinder the heat transfer between the two. By creating a wall of paste so thick it's gooping out the sides you are almost certainly negatively impacting the temperature by lowering the surface area of the two that's touching. Very small amount in the middle is all you need and will give you the best heat transfer.

The amount you apply is not important, unless you're not applying enough. Applying too much paste doesn't negatively effect the thermal transfer properties because the amount of "squish" is the same regardless given these parts are screwed to a heat-sink. The only downside to adding too much paste is wasting paste.

D

 

[brad808]

Nope, that's incorrect. There is tons of supporting data readily available online to back up exactly what I've said. This is a very thoroughly researched and documented topic in the PC overclocking community where heat matters immensely. The principles of heat transfer between components using thermal paste is directly transferable. You will find hundreds if not thousands of articles and posts regarding this exact topic. Using too much thermal paste is detrimental to heat transfer and will raise the component temperature above using the proper amount. Using the right amount of thermal paste will be less wasteful, less messy, and will work better. The "squish" theory doesn't hold up in practice using the same force.

 

[Menace]

For CPU's with thousands and even millions of internal transistors yes, I would agree with you as the surface area of those parts is large and thermal transfer is critical. For low level switching transistors with a single junction, I don't see how any of that information is relevant as it's an apples and oranges analogy. I stand by my original statement.

D

 

[brad808]

I respect your opinion but in this case I feel you need to reconsider the evidence and research. It doesn't matter what field the research is done in, the research is done. Using too much thermal paste between two components is detrimental to heat transfer. I fail to see how it isn't applicable in this case specifically or any other. Pro audio transistors are the exact same and you can find the same research in that community.

 

[mitch_a]

Don't think it really matters in this case. The transistor is bolted to the heat sink and bolted tight so most of the paste squished out, it's not like it's being pressed down by a small wire like on a clip on the cpu that can't apply alot op pressure.
Also any is better then none. This was designed to be left on in a arcade for long periods of time originally. In a huo setting this board will last forever.

 

[Menace]

While I can understand the science behind this argument when dealing with CPU's and heat sinks with large surface areas (because lets be honest that argument involves more than the amount of paste but even the type and how it's applied), but when you're dealing with single junction transistors regardless of application I don't buy it for a second unless you have a detailed analysis indicating such that I can review?

I will say that if the amount of paste being applied is so liberal you can't get the screw and nut together that's another issue altogether, but when it comes to reasonable amounts of paste for things like TO220 transistors, it's not that critical. (and from what I've seen here, Mitch hasn't gone overboard)

If you could explain to me how any amount of extra paste will remain between a TIP102 transistor and a heat sink when screwed together other than whatever isn't squished out filling the air gap between the two, I am all ears. Thermal paste is a fluid medium and will be displaced by the force of the screw clamping it to the heat sink, only leaving behind what can fit in the air gap which is determined by the physical space dictated by the heat sink and transistor surfaces.

D

 

[brad808]

Listen, it was meant to be a quick helpful hint for you to keep in mind for future repairs. Whether you choose to use the information or ignore it completely is up to you. Hopefully we can at least agree that there is certainly no downside to using the proper amount of thermal paste and there is no added benefit to using more or less than that. To anyone reading this questioning what the correct amount is and the effects of using too much/too little thermal paste I encourage you to do some research and come to your own conclusions. That's all from me folks.

 

[MultiHack3D]

Nice work! I may have to try the same thing..... if I can order the parts!
There site has issues, preventing me from completing the check out!

Hey mitch_a did you use a de-soldering gun/vacuum?

Id be so worried about ripping of a pad!

 

[mitch_a]

Yup I clip the parts off with small side cutters designed to clip parts off circuit boards, then I use a soldering iron to heat the legs and pull them out using small precision pliers. Then I use my hakku desoldering gun to remove excess solder. Then I use a soldering iron again to solder in the new parts.

Key is the old legs should come out really easy when heated, if you force them out you might damage a trace.