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Old 11-10-2007, 02:15 PM   #1
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Default Step 69 part C - something to take notice of.

Part C says to install Q9 and Q12. These transistors have to sit on mica insulators and have a resistance of greater then 60k ohm between it and the heatsink.

Last night I got done with my build, plugged it in, lights flickered for 10 seconds and died. I started to get really really upset and panicky, I said **** it and went to sleep pissed off. The only thing I discovered last night was that the battery or the adapter got very very hot and there was no power on the cpu socket.

This mornings investigation into the issue lead me to discover that the resistance between the two above transistors was 0. I unscrewed them slightly from the PCB, magically the resistance was 60k ohm and the power returned to the socket.

This lead me further to discover that either the bolt or the tightness is the culprit. I removed both and just pressed the transistor down with the probe on the DMM and resistance was exactly where it was supposed to be.

I have no idea what chamfering is but I have a feeling im going to go grab a drill bit and carefully drill out the metal band in the hole that passes through the pcb for those two transistors. I think it hitting the heatsink and its grounding the transistors.
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Old 11-10-2007, 02:57 PM   #2
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Problem solved.



Did this on both sides.

With a sharp drill bit and my fingers.
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Old 11-10-2007, 03:23 PM   #3
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Never mind, that didnt do it. It worked and then it went out again. Same thing, the resistance is down to 0. I unbolt it and its back to 60.

Im out of ideas.
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Old 11-10-2007, 03:49 PM   #4
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Well ok, now this is just absurd. I moved the mica insulator toward the edge of the pcb and its magically fine again.

This is just funny at this point.
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Old 11-10-2007, 04:07 PM   #5
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http://tinypic.com/view.php?pic=6k79j47&s=1

Its working as of now, gonna leave it on for a while.
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Old 11-10-2007, 09:44 PM   #6
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Why on Earth are the bolts for these transistors metal and the rest nylon? I'm not an EE but i know metal conducts. I'm sure there is a good reason so I didn't swap mine but it seems odd.
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Old 11-10-2007, 10:06 PM   #7
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I would like to know the same thing.
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Old 11-10-2007, 10:15 PM   #8
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There is supposed to be a plastic insert for the bolt also, don't forget to use it too. I honestly couldn't tell you why the bolts for them is metal, but you have to insulate it so the gate of the transistor is not pulled to ground.
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Old 11-10-2007, 10:20 PM   #9
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Maybe with the mica insulator they want metal bolts because they won't stretch or loosen. Maybe the combo of mica + grease makes for a real problematic moutning surface if not held tight with metal bolts and lock washers.
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Old 11-11-2007, 12:37 PM   #10
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Quote:
Originally Posted by cjernigan View Post
Maybe with the mica insulator they want metal bolts because they won't stretch or loosen. Maybe the combo of mica + grease makes for a real problematic moutning surface if not held tight with metal bolts and lock washers.
I highly doubt it has anything to do with a nylon bolt not being able to hold it. The only reason I can imagine it having metal bolts is for heat related reasons.
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Old 11-11-2007, 02:33 PM   #11
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Want the real reason? They have metal bolts because that's what comes with the Mica kit. We didn't spec the contents of that kit out ourselves. Nylon would work just fine which is why we use it everywhere else, and on these two trany's the metal bolt will work just fine if it's properly insulated, but that can be a bit troublesome sometimes. Nylon would do the trick just fine and help prevent the issue...

EDIT:

Going forward (next batch of kits built), we're including a note to direct people to use the metal screws on Q3/Q11, and to use the nylon screws on Q9/Q12. We were going to just put extra nylon screws in the bags but then figured we'd still have to put a note in there to tell people what to do with them, and then decided just the note would do just fine....

Last edited by FoundSoul; 11-12-2007 at 05:43 PM.
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Old 11-11-2007, 03:03 PM   #12
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Quote:
Originally Posted by FoundSoul View Post
What you could do in the meantime, is swap two of the nylon nuts/screws for the metal nuts/screws on components where it won't matter (anything else).
That would be the way I did mine if I recall... I thought it seemed backwards to have metal screws on the the ones that do care and nylon on the ones that don't.
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