In May of this year, my business partner gave me a not-dimming E550 machine after well repaired. Today I came across the same errors with the same machine. So I can say it’s like a common error issue. Thus I would like to share this with you guys.
Title: E550
Model of Motherboard: NM-A221
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Error: no dimming, without stand by voltage 3V and 5V, total power supply is normal. When switch it on, voltage is normal. Sometimes it can be triggered by electricity, but power off after a while.
Repair: firstly I found it’s not stand by, normal main power supply, normal linear power supply, stand by 35V, no short circuit.
It was triggered by electricity. I switched it off. After a while, I switched it on, but it failed. Repeated but still failed. Check EC conditions, ensure power supply, reset, ACIN, LID, on/off, EC_ON are all normal.
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Switched on EC_ON to supply stand-by chip, which is controlled by MAINPWON_EC.
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After cutting off control,MAINPWON_EC has still no voltage. Check MAINPWON_EC further.
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Followed one instruction mentioned on a repairing forum, tearing down PU2, but it’s still not working. Then tried to tear down PD2 and cut off temperature control, then it worked.
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No need to change circuit, tear PD2 down directly.
Summary: MAINPWON_EC is controlled by temperature control resistance. There will not be any trigger without MAINPWON_EC, even there’s stand by.
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