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Calling All Volt-Modders, 8800 GTS Volt Mod Gone Wrong, HELP - Page 6

post #51 of 68
Damn! the chokes are on the other side of the board by the looks of it, as are the main drivers. The back side there, only has the PWM controller (U501), and the FET driver chips for each phase (U503, U504, U505). C565 C566 C567 may be half of the secondary power smoothing caps (for the GPU core voltage)
post #52 of 68
Thread Starter 
Quote:
Originally Posted by latelesley View Post

Damn! the chokes are on the other side of the board by the looks of it, as are the main drivers. The back side there, only has the PWM controller (U501), and the FET driver chips for each phase (U503, U504, U505). C565 C566 C567 may be half of the secondary power smoothing caps (for the GPU core voltage)

Yes there are some FETs on the other side of the card as well as the chokes/inductors.
     
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post #53 of 68
well The FETs are your main drivers (should be two per phase) and then the choke (one per phase) and then smoothing caps after the chokes. now the FETs that hook up to the phase next to U503 (on the other side of the board) I think were the ones not switching - so that inductor will be doing nowt. its the other two phases doing all the work. if you took the inductors off of those two phases, you'll get no GPU core voltage. smile.gif

If you put them back, it should all be fine though. If you want to use the zombie card as the sole GPU Vcore supply though, I'd remove the 3 inductors from your card, then use heavy wire to wire the supply from the zombie VRM to the supply to the chip on your 8800.
post #54 of 68
Thread Starter 
Quote:
Originally Posted by latelesley View Post

well The FETs are your main drivers (should be two per phase) and then the choke (one per phase) and then smoothing caps after the chokes. now the FETs that hook up to the phase next to U503 (on the other side of the board) I think were the ones not switching - so that inductor will be doing nowt. its the other two phases doing all the work. if you took the inductors off of those two phases, you'll get no GPU core voltage. smile.gif

If you put them back, it should all be fine though. If you want to use the zombie card as the sole GPU Vcore supply though, I'd remove the 3 inductors from your card, then use heavy wire to wire the supply from the zombie VRM to the supply to the chip on your 8800.

The zombie card has 2x phases, so I'd probably use just one of the zombie to replace the one dead one on the 8800GTS.

But I have another suggestion.

I know very little about fets and pwm and what not but can I just link the FETs from all of the phases together? So that the working phase would send the PWM to the other two phases?


Otherwise I'm not quite sure what to do as I'm not quite sure if I can solder those wires onto the 7900GT zombie card...
     
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post #55 of 68
no, because it doesn't quite work like you think....each phase would do the powering out of step with each other, they don't all switch at the same time. in each cycle, each phase is taking a turn a 3rd of the time. so your PWM is really just working 2/3rds of the time.

You can imagine it like a 3 cylinder engine in a car, and cylinder one is misfiring because its not getting the pulse to the spark plug. What you are taking about with wiring the FETS together, is just like linking the "dead" spark plug to one of the plugs on the other cylinders - it would get it to spark, but at the wrong time, and the engine would still run wrong. Its the same with the dead phase, you could get it switching the FETs, but it would be at the wrong time, and cause unstable voltage (probably with a higher ripple).

The normal cycle would fire phase 1, phase 2, phase 3, back to phase 1 etc in that cycle.

By bridging you'd have no phase, phase 1 & 2, phase 3, no phase etc etc

so all you'd do is increase the pulse on the second part of the cycle, as it fired two phases at once, and it would still have the dead spot on the first phase of the cycle. It would probably confuse the PWM controller too, and that could cause things to go funky on the voltage output.
post #56 of 68
Thread Starter 
Quote:
Originally Posted by latelesley View Post

no, because it doesn't quite work like you think....each phase would do the powering out of step with each other, they don't all switch at the same time. in each cycle, each phase is taking a turn a 3rd of the time. so your PWM is really just working 2/3rds of the time.

You can imagine it like a 3 cylinder engine in a car, and cylinder one is misfiring because its not getting the pulse to the spark plug. What you are taking about with wiring the FETS together, is just like linking the "dead" spark plug to one of the plugs on the other cylinders - it would get it to spark, but at the wrong time, and the engine would still run wrong. Its the same with the dead phase, you could get it switching the FETs, but it would be at the wrong time, and cause unstable voltage (probably with a higher ripple).

The normal cycle would fire phase 1, phase 2, phase 3, back to phase 1 etc in that cycle.

By bridging you'd have no phase, phase 1 & 2, phase 3, no phase etc etc

so all you'd do is increase the pulse on the second part of the cycle, as it fired two phases at once, and it would still have the dead spot on the first phase of the cycle. It would probably confuse the PWM controller too, and that could cause things to go funky on the voltage output.

I see...

..And have another question, what exactly are these things that I thought were inductors or coils? This one broke when i originally removed it and I don't think its an inductor or coil or that its even operational anymore:



And here's a bit of a better pic of the VRM's on the GPU side.
     
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post #57 of 68
well its kinda hard to tell with the pic's, but I think they are the inductors each one will be labelled L-something (I think the one that's off was labelled L22? ) If you measure the resistance with a multimeter on either end of each one, it should give you a low reading of a few ohms (could even be as low a 0.5ohms). The ones you have just look like they're encapsulated in plastic. If you think it is damaged, just put the working ones, on the working phases, and leave that one off the dead phase.
post #58 of 68
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Quote:
Originally Posted by latelesley View Post

well its kinda hard to tell with the pic's, but I think they are the inductors each one will be labelled L-something (I think the one that's off was labelled L22? ) If you measure the resistance with a multimeter on either end of each one, it should give you a low reading of a few ohms (could even be as low a 0.5ohms). The ones you have just look like they're encapsulated in plastic. If you think it is damaged, just put the working ones, on the working phases, and leave that one off the dead phase.

Problem is that the one that got damaged is on a working phase.........

Will it still read resistance correctly if I already soldered it back on? Does polarity matter (i have no way of knowing if it was soldered backwards...


EDIT: With a horrible DMM (all I own) I read .06ohm across that broken thing, as well as the other two...
     
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post #59 of 68
well, if you got the same reading, it'll be ok still! smile.gif And what I was trying to say, was even if that damaged one was dead, you could have used the inductor from the dead phase, and put it on the working one. those 3 components are the same.......so they're interchangabe. you'll notice the numbering on top of each one is the same.
post #60 of 68
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Quote:
Originally Posted by latelesley View Post

well, if you got the same reading, it'll be ok still! smile.gif And what I was trying to say, was even if that damaged one was dead, you could have used the inductor from the dead phase, and put it on the working one. those 3 components are the same.......so they're interchangabe. you'll notice the numbering on top of each one is the same.

Oh oh good idea, but I'll try it with the damaged one first because 1. I'm lazy and 2, in order to remove these from their original places, I need to literally break them off because the lead free solder crap is not working with me.

EDIT: just so we all know I broke a TINY surface mount resistor off over by some chips on the backside of the card near the DVI connections (but not on the DVI connections) when the screwdriver slipped off the screw. Hope that doesnt break anything...
Edited by EpicAMDGamer - 5/15/13 at 7:31pm
     
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