I damaged the heatsinnk of my Technics SU-v8. I am replacing the output transistors and the screw is causing issues so i used a saw and did damage where the IC sits scatches look bad? sandpaper where the IC sits maybe?
? thermal compound fill the scatches, but heat will not disperse enough?
An externally hosted image should be here but it was not working when we last tested it.
and the screw is causing issues so i used a saw and did damage where the IC sits scatches look bad? sandpaper
where the IC sits maybe?? thermal compound fill the scatches, but heat will not disperse enough?
The sink surface must be machined quite flat to be effective. These scratches will likely cause shorts and/or thermal failure.
sounds bad Rayma thanks for the reply. I was looking what if i invert the heatsink and get new holes drilled for the ICs to sit?, as heatsink is the same inverted
drilled for the ICs to sit?, as heatsink is the same inverted
Make sure that the other surface is machined flat as well as the original surface was. Usually only the surface used is machined,
and the rest are left as originally extruded, which does not work nearly as well. If it is ok, be sure to deburr the new holes.
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Scratching is the essence of polishing, that's why toothpaste is abrasive.
If I had to fix something like this in a simple manner I'd get a clean sheet of wet and dry sandpaper and lay it flat, abrasive side up on a hard flat surface and place the heatsink down on it and make gentle figure eight motions while holding it with fingers a little away from the middle so it remains flat throughout, as opposed to causing the corners to dig out.
You may lose the anodising. If you can get the scratches down evenly enough and fine enough, some silicone grease should take up the difference.
Oh. The next best thing could be to use a level block with the paper wrapped around it. Keeping your strokes rounded and smooth can help to prevent galling caused by sudden stops at the ends of the stroke.
Watch if the block is larger than or will go over the edges of the heatsink that those edges dont have a raised bank on them, and you dont tilt over them.
edit: don't try to go too fast on aluminium.
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I think you got good advice - the majority of the surface area is not disturbed by the scratches. You simply want to ensure that there are no raised ridges etc. so that the device can lie as flat as possible onto the unscratched metal. You just need to smooth down the area under the actual device but of course a small flat block with sandpaper wrapped around it will need some space to move around so you'll end up cleaning a broader area. Make sure the metal particles are all cleaned away, they can cause shorts if they get stuck between a power device and the heatsink.
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1) **don't overthink it**
2) sand those scratches down, but not holding the "sandpaper" between your fingers, you want to sand that area flat , not dig a trench there
3) so use a sanding block: a piece of flat wood is enough.
A piece of MDF will be way flatter than any random piece of wood.
4) you need to sand the "peaks" flat, don't worry about the "throughs" wich all together amount to , say, 1% or 2% of the contact surface and to boot will later be filled with thermal paste.
5) don't scratch it more than it is now: use wet-or-dry emery paper , with *a drop* of water as lubricant, in this order: 100 grit > 200 grit > 400 grit.
Just a minute each, whatever's necessary for your fingertip to feel the surface smooth.
6) wipe the surface clean, also clean the screw threads with a Q-tip, reassemble, solder, enjoy.
EDIT: just read what bigun posted: yes, that's the point.
Your surface will end up being flatter than typical extruded aluminum ... which is already flat enough.
2) sand those scratches down, but not holding the "sandpaper" between your fingers, you want to sand that area flat , not dig a trench there
3) so use a sanding block: a piece of flat wood is enough.
A piece of MDF will be way flatter than any random piece of wood.
4) you need to sand the "peaks" flat, don't worry about the "throughs" wich all together amount to , say, 1% or 2% of the contact surface and to boot will later be filled with thermal paste.
5) don't scratch it more than it is now: use wet-or-dry emery paper , with *a drop* of water as lubricant, in this order: 100 grit > 200 grit > 400 grit.
Just a minute each, whatever's necessary for your fingertip to feel the surface smooth.
6) wipe the surface clean, also clean the screw threads with a Q-tip, reassemble, solder, enjoy.
EDIT: just read what bigun posted: yes, that's the point.
Your surface will end up being flatter than typical extruded aluminum ... which is already flat enough.
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There's a lot of scaremongering going on here. You only need to get rid of any ridges that might perforate the insulating washer.
A perfectly polished finish is ideal but is unnecessary as the thermal goo will fill any light scratches.
First and foremost you want the area to be as flat as possible.
A perfectly polished finish is ideal but is unnecessary as the thermal goo will fill any light scratches.
First and foremost you want the area to be as flat as possible.
Thanks Biggun , best to concentrate on the one transistor rest are fine thank god, still worried, as the Technics SU-V8 is a warm running beast
Thanks JMFahey, what ive been doing worrying myself sick as i really love this amp, nicely set out steps for me also thank you
Thanks KatieandDad, my concern is stress on that transistor, i can try to get it as smooth as possible, however the scratches are pretty deep, i do get i need to flat as possible, i got mdf blocks i can cut to just do that area, yep i am scared and worried as the Technics SU-V8 is a great amp, running very hot and friend uses the Sankens as it runs cooler , i will clean and reuse the old plastic pads and all old solder will be removed
Thanks JMFahey, what ive been doing worrying myself sick as i really love this amp, nicely set out steps for me also thank you
Thanks KatieandDad, my concern is stress on that transistor, i can try to get it as smooth as possible, however the scratches are pretty deep, i do get i need to flat as possible, i got mdf blocks i can cut to just do that area, yep i am scared and worried as the Technics SU-V8 is a great amp, running very hot and friend uses the Sankens as it runs cooler , i will clean and reuse the old plastic pads and all old solder will be removed
use wet or dry paper.
It is available in grades from about 180 (pretty coarse for fast removal) to about 1200 (very smooth for very fine finish).
Wrap a strip, 2" to 3" wide, of wet or dry (try 150 or 220) around a flat wood (or similar) block and rub until all the high points around the scratches are REMOVED. I think wet or dry is silicon carbide and this is harder than glass or sand and does slowly remove metal, even steel, but it is slow. Emery is too hard and generally not available in the very fine grades needed to finish.
Then change to a finer grade (try 220 or 300) and remove all the scratches left by the coarse grade.
Then change to a very fine grade (try 400 or 600) and remove the scratches left by the finer grade.
If you rub in two orthogonal directions you can see the previous scratches gradually being removed a bit easier. If all the rubbing is done in the same direction you can't see the deeper scratches and so don't see the improvement.
The deepest of the original scetches will not be removed, but the surface around them will be smooth.
The thermal goop must FILL all the air spaces in the thermal interface. You want the thermal goop as thin as possible to minimise the thermal resistance. That is why "smooth" is so important. Smooth allows less goop.
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Most soft Thermal pads are use once and then throw away.
Gets very expensive during amplifier development.
Mica sheet can be re-used often, until they get cracked, or broken.
Alox can be re-used often.
Someone even stated recently that a cracked Alox pad can be re-used !
But I wouldn't.
BTW,
I OFTEN use 3M scotch tape and other cheap imitations during amp development where I can keep an eye on Tc & Ts.
These thin tapes are not suitable for higher temperaures. It is my blinkered (penny pinching) view that they make suitable low voltage electrical insulators, particularly when the devices are clamped and the tape is not holed for through bolting.
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Thanks Allen for the reply and help. I cant just fix the one area where I scatched it? has to be uniform across the whole heatsink, only IC pad I managed to scatch, seem to have bad luck today with accidents
There's a lot of silly panic in this thread
Simply sand the affected area with glass paper (as my woodwork teacher used to say, sand paper is for budgie cages
) and a block (to keep it flat). Then a thin layer of thermal compound will proved perfectly good heat conduction.When you're 'sanding' what you're trying to do is remove the upward ridges, the thermal paste will fill downward ones. You should be able to feel this with your finger tips.
Hi Andrew,
Thanks for the reply and advice. I would assume, if iam luck the Sanken transistors I bought might come with mica pads. The old plastic pads? would be mica. I'll get some of those grades of sandpaper
Thanks KatieandDad, I might get new ones as these are 30+ years old
Thanks Nigel, yes i am still concerned about the heat dispersion. Glass paper? I will have to google that product. I just get the jaycar thermal paste, low odor. Ive seen some fancy ones like Wakefield etc.
Maybe grease the heatsink first, wipe way so i can see the scatches filled them apply grease to IC and Mica pad and install?
Thanks for the reply and advice. I would assume, if iam luck the Sanken transistors I bought might come with mica pads. The old plastic pads? would be mica. I'll get some of those grades of sandpaper
Thanks KatieandDad, I might get new ones as these are 30+ years old
Thanks Nigel, yes i am still concerned about the heat dispersion. Glass paper? I will have to google that product. I just get the jaycar thermal paste, low odor. Ive seen some fancy ones like Wakefield etc.
Maybe grease the heatsink first, wipe way so i can see the scatches filled them apply grease to IC and Mica pad and install?
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