Thanks to all who chimed in. Lol.
Anyways, everything is working fine now. I replaced the 6R199P with a ST 24N60M2 and put a slightly overspecced diode in place of the bad one. replaced the HDD with an SSD and i'm installing Mac OS now.
mat2k
Member
Last Activity: Today, 10:56 PM
Joined: 03-28-2021
Location: Buenos Aires
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Components arrived, I replaced the MOSFET and found a shorted diode (diode between PFC coil and MOSFET), replaced that too. The power supply worked fine for about 5 minutes, iMac turned on and worked, but the new diode (same model as original) went into short after that, and MOSFET may also be bad (did not remove and test yet, but it measured 250 ohms between drain and source in circuit). What could have caused this?Leave a comment:
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iMac 2017 PSU - shorted PFC mosfet
I am trying to fix an iMac 2017 PSU, initially came with a blown fuse and shorted PFC MOSFET (6R199P). After visual inspection and some measurements I replaced the FET with a P20NM60 and tested with 100w series lamp, and it lasted 1 second before going into dead short. The PFC controller chip (NCP1605BG) and its passives appear fine (passives measure OK), but I do not know if there is a simple way of testing the NCP1605 as I wouldn't like to blind-replace it.
There was some slight blackening of the solder on the PFC controller passives so I reflowed them all with some flux. I am waiting... -
One more thing to add - I kinda have access to a thermal camera now. Do you think it would be worth it to inject 1v through the 1.05va rail and take a look? It's a relatively high resistance for that voltage, but it could be worth a try.
I am more concerned about everything else (no syson voltage etc.) so I would like to know what you think about those missing signals.Leave a comment:
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1.05v - 3.2 ohm
1.35v - 1.3k ohm
1.8v - 1.4M ohm
3.3v - about 17k ohm
5v - 100k ohm
GFX_CORE - 138 ohm
CPU_CORE - 400 ohm
all on the coils. I'll take a look at the switched rail side later. Thanks for the helpLeave a comment:
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Lenovo 300-15IBR - No SYSON, no SUSP#, bunch of missing voltages
Hello, I've been struggling with this one today. I'm troubleshooting a Lenovo 300-15IBR (board BMWC1/BMWC2 NM-A471) that turns on the power LED and does a bit of fan spin but nothing else. 3v3sb and 5vsb present, no 1.05v, no 1.35vddr, no vcore, no 1.8vsb.
BIOS has been reflashed with one I found here, supposedly tested OK by someone else. I don't have an EC programmer unfortunately.
I looked around and SYSON is 0v, SUSP# is 0v too. Forcing them to 3v3 enables the 1.35v rail, but the 1.05v and 1.8v rails are still missing (generated by PU704). EN_1P05A signal is 3.3v, and IN_1P05A... -
oh well, i still don't trust it and would definitely disable it if I could, but it doesn't seem to be possible. I was considering trying random memory ID bits, but I doubt they do anything at all in this board.
I didn't know that's the way RAM is laid out, makes sense. In any case I was able to install Windows without issues, and if the bad pages come back I guess I can just add them to {badmemory} with bcdedit...Leave a comment:
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Of course, I used leaded solder, sufficient flux and a heatgun to move them, and then I measured all of the connections from other pads using the boardview. All of them measured very close to 10k.
The reballing seems to have fixed it. I was extremely skeptical that it would, because the issue was just a few bits but in two different pages. Since the issue was around the 150mb mark, I just reballed the 1st and 4th chip (because I didn't know which of them would be the first gb) and tested a few minutes afterwards, no errors. now i left it overnight so it cooled to ambient temp (around...Leave a comment:
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I guess I'll try, but I would still prefer to disable the RAM to avoid any issues. Btw, I have also tried to set the three bits to 1 (shifting resistors to 178, 179, 180 - I tried this since some other Acer models seemed to use this scheme for no onboard RAM) and nothing changed - exactly the same behavior as with all the bits set to 0, or with the original configurationLeave a comment:
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Thank you, I missed that entirely.
Unfortunately it doesn't seem to work, after moving RU178 to RU186 (the others were already set in 188, 187) the BIOS still reports the onboard 4gb and i can access them from Memtest. I suppose the "no onboard memory" code could be something else, or it isn't even coded in?...Leave a comment:
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Disable faulty soldered RAM on Acer A315-22
Hello, I've been googling for some pointers on this but couldn't find anything that applies to this board. I have an Acer A315-22 (board NB8607) with faulty RAM between 142 and 174mb. I just wanted to disable the onboard RAM altogether, but this one doesn't seem to have any memory down ID resistors or strap in order to disable it. I'm attaching the schematic I found, the boardview for it also seems to be available somewhere in this forum but I still don't have a use for it lol.
How would I disable the RAM on this PC? Thanks for the help.
[B][MOD EDIT] LINK to boardview + schematic[/B]... -
Hi, I'm Matias from Argentina. I'm an electronics engineering student, fix laptops and consoles in my free time.Leave a comment:
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