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Old 09-25-2019, 10:57 PM   #1
Amraks
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Default Tops of resistor have seperated

Hey need a temporary solution for a emergency repair on these resistors this will not be long term but it will need to last a weekend in a cross over circuit. as I can't find these 66 ohm 20w valued resistors in Australia. The resistors are reading fine but I'm wondering what type of bonding I can use to stick these back together.
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Old 09-26-2019, 08:00 AM   #2
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Default Re: Tops of resistor have seperated

Usually some sort of kiln fired ceramic is used to attach the two together and it had failed.

If all you have is plastic glues which won't work well at the temperatures we may be dealing with here, I'd suggest you look for a small fan and blow air across them, probably would be sufficient to run a little while - that is if the fan is not physically an option?

(JB Weld might be last resort option... but regular epoxy probably won't work well.)

Last edited by eccerr0r; 09-26-2019 at 08:02 AM..
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Old 09-26-2019, 08:07 AM   #3
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Default Re: Tops of resistor have seperated

thermal adhesive might work .bit expensive though
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Old 09-26-2019, 08:53 AM   #4
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Default Re: Tops of resistor have seperated

JB weld might be a go yet.


would 3x 22 ohm 10w resistors in series work?
to replace the 2x 66 ohms resistors which are in parallel dividing it up to 33 ohm.

then the 10ohm 20w.
could I use 3x 3.3 ohm 10w resistors in series.
I have fixed another one of his crossovers and they done something similar and it seems to be working.

This only has to work for a weekend or two I really do want to refurbish the lot of his crossovers with right spec resistors and must likely keep at least 2 sets of spare resistor in stock, if an accidental drop occurs again.
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Old 09-26-2019, 10:13 AM   #5
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Default Re: Tops of resistor have seperated

test it as-is,
the ceramic is not really going to disapate heat anymore than convection - it's more of a protective cover.
just make damned sure you dont let any wires drape over them!
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Old 09-26-2019, 03:00 PM   #6
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Default Re: Tops of resistor have seperated

Quote:
Originally Posted by Amraks View Post
would 3x 22 ohm 10w resistors in series work?
to replace the 2x 66 ohms resistors which are in parallel dividing it up to 33 ohm.
NO (30W is less than 20+20=40W)!
But you can replace each 66 Ohm resistor with 3x 22 Ohm 10W
Quote:
Originally Posted by Amraks View Post
then the 10ohm 20w.
could I use 3x 3.3 ohm 10w resistors in series.
Yes! (It will only be 1% less resistance than original, but well within the tolerance).

Knowing Australia is a hot weather country and never seen power resistors failing in such catastrophic way
curious to know in what device it's being used? (or are they overrated Chinese ones?)

Last edited by megaraider; 09-26-2019 at 03:08 PM.. Reason: Adding question.
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Old 09-26-2019, 03:23 PM   #7
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Default Re: Tops of resistor have seperated

maybe the bass caused the cement to crumble.
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Old 09-26-2019, 07:40 PM   #8
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Default Re: Tops of resistor have seperated

I don't know if this will work, but maybe worth the suggestions anyways: clay (for potting) from any arts & crafts store?

The dirt we have here in some parts of VA is pretty much straight-clay. Some years ago, I "potted" a piece of NiChrome wire with it in a big can. After it dried, I ran current through it to heat it up. Clay dried up and hardened nicely. I used that for making my first "solder pot", in fact (the pictures are somewhere here on BCN, but I don't remember where and what thread.)
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Old 09-26-2019, 09:06 PM   #9
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Default Re: Tops of resistor have seperated

Quote:
Originally Posted by megaraider View Post
NO (30W is less than 20+20=40W)!
But you can replace each 66 Ohm resistor with 3x 22 Ohm 10W
This is what I meant sorry for the confusion. so 2x 3x 22 ohm we will get 2x 66 resistors.

Quote:
Knowing Australia is a hot weather country and never seen power resistors failing in such catastrophic way
curious to know in what device it's being used? (or are they overrated Chinese ones?)
I am in Tasmania we are in a cold climate down here in the southern end.
the way it broke was it was dropped while it was being set up by someone I guess this part took the brunt of force..
but I believe someone has repaired it with hot glue previously and this time the glue they used has become conductive as I was missing 5 ohm on the 10 ohm resistor testing out circuit.
removed that piece of hot glue and the resistor was right.
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Old 09-27-2019, 04:10 AM   #10
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Default Re: Tops of resistor have seperated

hot glue is no use as the heat will soften it . am wondering if plaster of Paris would stick the ceramic back on .
scrap that idea .looked it up and its not good at thermal conductivity

Last edited by petehall347; 09-27-2019 at 04:16 AM..
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Old 09-27-2019, 05:56 AM   #11
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Default Re: Tops of resistor have seperated

High temperature grout for fireplaces and flues. Comes in 300ml cartridges, 1200c.

Like this https://www.screwfix.com/p/mapei-map...ey-300ml/25153

Last edited by diif; 09-27-2019 at 05:57 AM..
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Old 09-27-2019, 07:22 AM   #12
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Default Re: Tops of resistor have seperated

Quote:
Originally Posted by diif View Post
High temperature grout for fireplaces and flues. Comes in 300ml cartridges, 1200c.

Like this https://www.screwfix.com/p/mapei-map...ey-300ml/25153
will it conduct the heat away from the resistor ?
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Old 09-27-2019, 08:09 AM   #13
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Default Re: Tops of resistor have seperated

probably not.
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Old 09-27-2019, 08:19 AM   #14
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Default Re: Tops of resistor have seperated

If you want to "fix" the resistors, make sure you desolder and set them in with gravity, let the weight of the potting material and the resistor cores to let any air bubbles out.
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Old 09-27-2019, 03:34 PM   #15
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Default Re: Tops of resistor have seperated

Quote:
Originally Posted by Amraks View Post
(...)
I am in Tasmania we are in a cold climate down here in the southern end.
the way it broke was it was dropped while it was being set up by someone I guess this part took the brunt of force..
That explains it all...

btw guys: all suggestions are welcome,
but if @Amraks can't get access to simple power resistors, on a short time and where he is located, how the hell will we find 'fancy' glue stuff
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Old 09-27-2019, 04:08 PM   #16
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Default Re: Tops of resistor have seperated

well he could use "exhaust putty" from a car place - but i wouldnt bother as i said.
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Old 09-27-2019, 04:56 PM   #17
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Default Re: Tops of resistor have seperated

JB Weld (make sure it's the high temperature kind )
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Old 09-27-2019, 09:58 PM   #18
Amraks
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Default Re: Tops of resistor have seperated

Quote:
Originally Posted by megaraider View Post
That explains it all...

btw guys: all suggestions are welcome,
but if @Amraks can't get access to simple power resistors, on a short time and where he is located, how the hell will we find 'fancy' glue stuff
Could of got JB weld. I opted for the option of resistors in series.

Funny thing passive mode works but Bi mode is not working. Its working on all the other crossovers that have had resistors put in series.
I wonder what else is broken now.
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Old 09-27-2019, 10:07 PM   #19
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Default Re: Tops of resistor have seperated

Thanks for all the suggestions.
I opted for the later option of fixing, I ended up making 2x 66ohm resistors by using 3x 22ohm 10w resistors in series for each broken 66ohm.
for the 10ohm one 3x 3.3ohm 10w resistors in series

Last edited by Amraks; 09-27-2019 at 10:13 PM..
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Old 10-06-2019, 10:31 PM   #20
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Default Re: Tops of resistor have seperated

found the problem with the crossover in bi mode someone had cut the bi mode capacitor lead and done a average job on trying to connect it again.
I tinned up a bit of wire and inserted it into its hole and soldered the remaining bit of the lead to it.
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