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Killed an MDD logic board

Nixontheknight

Well-known member
A few months ago, I was trying to overclock my MDD (rev A from 2002) from 1.25GHz to 1.5GHz, so I could get DiscordPPC to run properly, but I accidentally overvolted the CPU card and killed the logic board. Can this logic board be saved or should I just buy a working one?
 

Byrd

Well-known member
How do you know the motherboard is toasted? It might be perfectly fine if you just fried the CPU daughtercard.
 

Nixontheknight

Well-known member
How do you know the motherboard is toasted? It might be perfectly fine if you just fried the CPU daughtercard.
I turned it on with a 1GHz CPU card and the light just flashes and fades away, then it's silent, then the fans ramp all the way up
 

Byrd

Well-known member
Have you done the motherboard CUDA reset, also pull PRAM and PSU wiring leave it be for ~ 24 hours. Is the PSU known good (knowing these aren't great to start with in any MDD)?
 

herd

Well-known member
I think the single 1GHz MDD board was from the 133MHz bus version of the MDD, and all of the 1.25GHz boards came from the 167MHz version. So if you plug a "1GHz CPU card" into a 1.25GHz machine it will try to run at 1.25GHz, where it might not be happy with the overclock. I would suggest either changing the multiplier on the CPU card or on the MDD logic board so that the CPU runs slower and see if that works.
 

Nixontheknight

Well-known member
Have you done the motherboard CUDA reset, also pull PRAM and PSU wiring leave it be for ~ 24 hours. Is the PSU known good (knowing these aren't great to start with in any MDD)?
The PSU is known good, I have not done a PRAM reset but I believe the bus clocks are different from the card to the motherboard, and that's probably what's tripping it up
 

Nixontheknight

Well-known member
I think the single 1GHz MDD board was from the 133MHz bus version of the MDD, and all of the 1.25GHz boards came from the 167MHz version. So if you plug a "1GHz CPU card" into a 1.25GHz machine it will try to run at 1.25GHz, where it might not be happy with the overclock. I would suggest either changing the multiplier on the CPU card or on the MDD logic board so that the CPU runs slower and see if that works.
I'm gonna try changing the bus speed on the 1GHz card
 

k24a1

Well-known member
MDD... nothing of value was lost. /J
Hopefully you can get it working, jokes aside. I had one but now I feel better about my dual QuickSilver machine since that's far more reliable despite running slower than some dual MDDs...
 

mmu_man

Well-known member
I suppose nobody has schematics for those… I also have an MDD which doesn't start and was given to me in this state…
 

waynestewart

Well-known member
The logic board is a 1.25GHz board so it's going to be 167, and the 1GHz card is 133MHz bus
The card isn't anything, it runs at multiples of the logic boards bus speed.
It should have a 7.5 multiplier for a 133MHz bus
When you put it into a 167 bus it's running too fast
If you change the cards multiplier to 6 then it'll run at 1GHz on a 167 bus
That way you keep the higher bus speed with all it's benefits.
 

Nixontheknight

Well-known member
The card isn't anything, it runs at multiples of the logic boards bus speed.
It should have a 7.5 multiplier for a 133MHz bus
When you put it into a 167 bus it's running too fast
If you change the cards multiplier to 6 then it'll run at 1GHz on a 167 bus
That way you keep the higher bus speed with all it's benefits.
I'm ok with the risks as long as it gets my MDD working
 
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