Thinkpads Forum

Yesterday, the screen on my 600X went out for no apparent reason. It was just sitting on my desk, I tried turning it on, and I couldn't get the LCD to show.

After swapping parts around with my brother's 600E, I could see that the LCD and LCD sub card were fine. So I started testing the motherboard fuses with my multimeter. I came across fuse "F3" located about 1/2" to the left of the right LCD cable connection, and I wasn't getting any continuity with my tester. So I de-soldered the fuse and put a very short loop of wire there instead, and the LCD works again.

My question is, what kind of risk am I taking to bypass the fuse like this? I don't know what caused this to happen, so maybe it could happen again.

Has anyone ever had this happen to them before?

Unfortunately no... after reading your comments, I immediately tested the fuses on my T21 mainboard, hoping I could find a reason for the backlight failure (not due to the LCD panel, the cable or the inverter), but no such luck. All the fuses I could find (F1, F3, F7, F8 ) were OK.

As to your question, I'd feel uncertain and nervous too, but unless you can find a replacement fuse and solder it in (the ones on my T21 board are labelled 1x1 and 7x7, so possibly you could cannibalize a nonworking board for this), the only thing to do would appear to cross your fingers and hope for the best. Maybe the fuse failed because of age, corrosion, thermal expansion/contraction plus a bad solder joint or something not connected with any electric overload.

I haven't had an LCD fuse blow before but I did get a T23 system which had a bad main fuse:

http://forum.thinkpads.com/viewtopic.php?t=32656

Follow-up: and to answer the other questions, the risk of bypassing the fuse with a piece of wire is that if the reason why the fuse blew in the first place was due to excessive current being drawn, then if it happens again, something other than the fuse might be damaged. Most likely the fuse protects the inverter board. I'll dig out my 600X donor/testbed motherboard and see if I can identify what it is and where you might be able to get a proper replacement.

rkawakami wrote:I haven't had an LCD fuse blow before but I did get a T23 system which had a bad main fuse:

http://forum.thinkpads.com/viewtopic.php?t=32656

Follow-up: and to answer the other questions, the risk of bypassing the fuse with a piece of wire is that if the reason why the fuse blew in the first place was due to excessive current being drawn, then if it happens again, something other than the fuse might be damaged. Most likely the fuse protects the inverter board. I'll dig out my 600X donor/testbed motherboard and see if I can identify what it is and where you might be able to get a proper replacement.

I appreciate the trouble, thanks!

Hopefully I'm not causing more damage with this temporary solution. I haven't noticed anything out of the ordinary with it yet, but it's only been one day.

Maybe it was something else that caused it to go, like Robby said. I have been tinkering with it a lot lately, but I wasn't doing any surgery when this happened.

I found the F3 fuse on my 600X motherboard. "It's dead, Jim" .

I bought this thing (600X motherboard and bottom case) last year specifically to practice installing my external WiFi antenna mod. I never powered it up but as far as I can tell by measuring it with an ohmmeter, it's open. There's no markings on the top side so I'm going to take it to work tomorrow and see if I can remove it without doing any damage to it.

I checked the DigiKey catalog and there might be a Littelfuse part that matches the physical size. I just need to figure out the current rating. Does/did your F3 have a slight purple/periwinkle color to it?

rkawakami wrote:....Does/did your F3 have a slight purple/periwinkle color to it?

Yes, it did. And it was white on the bottom.

Weird. I suppose this could be a fairly common problem, but this is the first time I've ever heard about it