Re: iMac A1312 820-2828-A only led one lit
Power button is testing fine. I've got the PSU and MB out of the machine anyway. The solder looks fine in the connector. I've just been shorting the two pins together, not using the actual power button.
I don't have another PSU. On the MB, connector J600 the only voltage present is pin 11 at 12.09, and pin 13 at 4.29.
Q610 has the 4.29 on ping 3, I believe that pin 1 (PM_EN_P12V_SO_FET) should get 12v to turn on the PSU. I have 0v on that pin regardless of the power button state.
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bellyacres
Member
Last Activity: 01-15-2021, 03:19 PM
Joined: 05-14-2019
Location: Mansfield Ohio
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iMac A1312 820-2828-A only led one lit
I'm stuck staring at the schematic.
PP12V_G3H is 12.02
PP3V42_G3H_REG measured on the output of L7900 is 3.38. The schematic indicates that is should be at 3.425. I'm not sure if that is causing my problem or not. Somewhere I have it in memory that it needs to be 3.425.
I have 3.39 at the power button also.
Any pointers most welcome.
Thanks
Using the schematic and boardview from this post.
[url]https://www.badcaps.net/forum/showthread.php?t=60644&highlight=820-2828-a[/url]I'm stuck staring at the schematic.
Last edited by bellyacres; 07-02-2020, 11:31 AM. -
Re: Samsung 245BW BN44-0019A
Fixed!
CM809 was obviously bad upon opening this thing up. The trace on the bottom of the board was gone. I had jumpered it to fix that. Upon closer inspection it looks like one of the jumpers in that area was able to arc over and cause the short. I re-worked that with some insulated wire and a bit of heatshrink. Also cleaned up the carbonized area as much as I could. It would probably be a 12mm hole to get it all gone. Replaced RM801 and QM801/QM802 and all is well again.
Thanks for the help and getting me looking at the right...Last edited by bellyacres; 06-01-2020, 11:47 AM.Leave a comment:
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Re: Samsung 245BW BN44-0019A
Okay
I've got 385 Vdc across CP801.
RM801 and QM801/QM802 are still out of the circuit.
TM802 was pulled and had some issues due to glue. One secondary was reading high, cleaned up more, the winding wire came free due to corrosion. That is resolved. No shorts or opens on TM802. All the diodes and resistors are good in that area.
I'm at a standstill as I don't want to blow another set of mosfets...
Still staring at the schematic, but I'm missing something obvious I'm sure!Leave a comment:
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Re: Samsung 245BW BN44-0019A
Right, my bad. Just checked again I'm getting .022 across both RM812/RM814. That was the reading I got on both RM811/RM813. I'd say RM812/RM814 are both open, if the transformer was open I wouldn't see the .022 from RM811/RM813...
I'll have to see what I can scavenge up tomorrow to replace those two. My eyes are done for now and the boards that were handy don't have any 473....Leave a comment:
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Re: Samsung 245BW BN44-0019A
Yes, the diodes all test right around there, no shorts. The 473 resistors are reading nearly open, the 220 are bang on....Leave a comment:
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Re: Samsung 245BW BN44-0019A
DM851 and DM852 show forward drop of .199 DM853 .176, in circuit.
If they are ok I suspect all the gate drive zeners & resistors are bad. When the fets short they supply 160~385vdc to the gate circuit, there is no way those poor little zeners survive.
The gate zeners are DZM80[3456] and the surrounding resistors?Leave a comment:
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Re: Samsung 245BW BN44-0019A
Those numbers are from the board. I'm going to double check, but those resistor values were both 100K by the color codes if memory serves. They were open though. They had the infamous glue on them.
As to the voltage on CP803 I've never seen above 160 vdc. If I understand the circuit right the mosfets should be handling the PFC to get the voltage to the 385 vdc.
There is the rub, if I put in the mosfets they go bang! Along with RM801...
Edit due to missing part of last post.
I'll check those diodes and...Last edited by bellyacres; 05-28-2020, 05:54 PM.Leave a comment:
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Samsung 245BW BN44-0019A
Hello all,
First time post here. I've searched here and used up my know-how. I'm at a loss on how to continue with this. I really don't want to blown another pair of mosfets!
[url]https://cdn.badcaps-static.com/pdfs/37e40dc6e13bb8b5d00b1cf8a620fd8c.pdf[/url]
Is the schematic that I've been using, not an exact match, but I believe that it's close enough for this board as a guide.
Here is what was found on initial inspection.
CM809 47pf obviously blown open on initial examination
QM801, QM802 FQPF5N50C shorted
RM801 0.22 1W... -
Re: New Members - please post your introductions here
Hello all,
Just another computer tech, trying to get a little bit deeper understanding of electronics.
MikeLeave a comment:
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