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820-00928 CPU Shorted?
- Thread starter Thomas
- Start date
It is trash now.
You've just injected 8V into CPU.
So many times explained on the forum how NOT to inject voltage
...
You've just injected 8V into CPU.
So many times explained on the forum how NOT to inject voltage
...
The CPU was PROBABLY dead, once U7410 caused voltage spike on it.
Now is dead for SURE, as you injected 8V directly, not just a very short time overvoltage.
Now is dead for SURE, as you injected 8V directly, not just a very short time overvoltage.
Probably wasting time; nothing to lose, apart of time.
Thomas
Member
I need to clarify about this repair, when I first started working on it the first thing I did was rule out everything on PPBUS_HS_CPU that could be causing the short besides removing the CPU. Then I injected 8V. I figured that rail was supposed to be around 12V so I started low. That's when the CPU started getting warm.
Anyway actually I got back around to this today, I removed the CPU & what do you know, the short is gone. Now this project will sit until I can find a CPU that I know works. Or unless anyone knows where to get a BRAND NEW CPU, not a pull & reball.
Anyway actually I got back around to this today, I removed the CPU & what do you know, the short is gone. Now this project will sit until I can find a CPU that I know works. Or unless anyone knows where to get a BRAND NEW CPU, not a pull & reball.
Thomas
Member
So you had short on PPBUS_HS_CPU and inject 8V there.
The short was caused because of bad power chip from one of CPU power supplies.
CPU got shorted injecting 8V for sure (maybe already damaged before).
Removing CPU, short disappeared of course.
But you MUST find the bad power chip, or will fry again another CPU.
The short was caused because of bad power chip from one of CPU power supplies.
CPU got shorted injecting 8V for sure (maybe already damaged before).
Removing CPU, short disappeared of course.
But you MUST find the bad power chip, or will fry again another CPU.
Thomas
Member
I'm pretty sure the CPU was already damaged before, which is why I injected 8V. It was the last resort besides replacing the CPU. Now the CPU is removed. SO what your saying is even though the short is gone right now, when I solder on a known GOOD CPU, PPBUS_HS_CPU will have a short there again?
IF SO, then I will not even attempt to power the Board on at all/inject any kind of voltage after soldering on a known GOOD CPU. Before any power is applied I will confirm if the short is present or not. That way IF the short is back the GOOD CPU should not get damaged AT ALL since no power was applied assuming the soldering is perfect. If it's gone I will attempt to power the Board normally. I have already replaced a few of these touch bar processors with success so I have the soldering method perfected.
I have a great feeling that when I solder a known GOOD CPU back on the short will be back.
2informaticos, Could you please take the time and tell me how I would trace down the BAD power supply chip with the CPU off and the short appearing gone?
Or if I need to solder on a known GOOD CPU first to trace down the original issue, if that is the case, how would I approach this knowing a GOOD CPU is soldered on? Would you blame a PCB issue at that point and force me to give up?
IF SO, then I will not even attempt to power the Board on at all/inject any kind of voltage after soldering on a known GOOD CPU. Before any power is applied I will confirm if the short is present or not. That way IF the short is back the GOOD CPU should not get damaged AT ALL since no power was applied assuming the soldering is perfect. If it's gone I will attempt to power the Board normally. I have already replaced a few of these touch bar processors with success so I have the soldering method perfected.
I have a great feeling that when I solder a known GOOD CPU back on the short will be back.
2informaticos, Could you please take the time and tell me how I would trace down the BAD power supply chip with the CPU off and the short appearing gone?
Or if I need to solder on a known GOOD CPU first to trace down the original issue, if that is the case, how would I approach this knowing a GOOD CPU is soldered on? Would you blame a PCB issue at that point and force me to give up?
Just check ohm resistance between I/O pins of CPU power supplies chips; like 8/16 for U7210.
Be aware, there are 6 chips to test.
Where are 2-3 chips with output tied together, lift one pin of the coil.
Be aware, there are 6 chips to test.
Where are 2-3 chips with output tied together, lift one pin of the coil.