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04-02-2021

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X220 repeatedly blowing backlight fuse

2021-04-02, 1:17 AM

Greetings,

 

I picked up an X220 and separately a (apparently low quality) charger. After working fine for about a week, one evening I heard urgent beeping from the other side of the room coming from the X220, with the power status LED irregularly flickering. The beeping and flickering stopped as soon as I unplugged the charger, and the laptop seemed fine on battery power. But the next day, the screen wouldn't illuminate. I could tell with a flashlight that graphics were being rendered, but with no backlight.

 

(I've since gotten an OEM charger)

 

I did some troubleshooting and discovered that fuse F1 was blown. I soldered on a replacement and double-checked electrical connections, but after reassembling everything and powering up, the screen still wouldn't light. F1 was open again, so I replaced it a second time, verifying that the screen did light up. And it worked again. I verified with a current-limited supply that nothing was drawing the 3 amps needed to blow that fuse.

 

Working until today, that is. Same symptom--dark screen but graphics faintly visible with a flashlight. I haven't taken it apart again, but I'm thinking it's F1 again, and that replacing it won't solve whatever the underlying problem is. What do repair-oriented folks here think? Is this likely caused by a problem in the screen itself? Or should I troubleshoot the board more?

 

Where would you look for trouble spots in this situation?

 

Much appreciated! -m

 

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12314 Posts

01-02-2010

United States of America

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Re:X220 repeatedly blowing backlight fuse

2021-04-02, 3:24 AM

I am assuming you do not have some weird aftermarket screen that draws a lot of current.  I cannot really diagnose without seeing it, but my experience has been that defective screens that cause similar problems were more common on older screens with CCFL backlights.  I would look for a blown capacitor near the LCD connector.  There may be a capacitor to ground and a fused resister together.  The capacitor will absorb a surge at power up.  If it is blown (open, not shorted), all the current goes through the fuse.


Rich


I do not respond to requests for private, one-on-one help. Your questions should be posted in the appropriate forum where they may help others as well.

If a response answers your question, please mark it as the accepted solution.

I am not an employee or agent of Lenovo.
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12314 Posts

01-02-2010

United States of America

40504 Signins

427349 Page Views

  • Posts: 12314
  • Registered: ‎01-02-2010
  • Location: United States of America
  • Views: 427349
  • Message 2 of 3

Re:X220 repeatedly blowing backlight fuse

2021-04-02, 3:24 AM

I am assuming you do not have some weird aftermarket screen that draws a lot of current.  I cannot really diagnose without seeing it, but my experience has been that defective screens that cause similar problems were more common on older screens with CCFL backlights.  I would look for a blown capacitor near the LCD connector.  There may be a capacitor to ground and a fused resister together.  The capacitor will absorb a surge at power up.  If it is blown (open, not shorted), all the current goes through the fuse.


Rich


I do not respond to requests for private, one-on-one help. Your questions should be posted in the appropriate forum where they may help others as well.

If a response answers your question, please mark it as the accepted solution.

I am not an employee or agent of Lenovo.

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2 Posts

04-02-2021

United States of America

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  • Message 3 of 3

Re:X220 repeatedly blowing backlight fuse

2021-04-25, 22:01 PM

Thank you for your help (and apologies for a delayed response).

 

When I went back in, to my considerable surprise, I found that mainboard F1 was still fine, as were nearby F2 and F6. But the backlight was definitely out, and the screen otherwise working. This is an original Lenovo LED screen. I dug further, and found inside the display unit, on the LVDS driver board physically attached to the LCD, another fuse marked F2 (and labeled TK -- 3.5A?) that was blown.

 

You mentioned before to look for blown components near the LCD connector. I'm still looking, but now broadening my search to include this driver board.

 

Would you think it prudent to try replacing the entire display assembly? Or would this risk blowing more fuses (either in the new display, or on the mainboard)?

 

With appreciation,

 

-m

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