Lost backlight, CF-W2 (little toughbook) - puzzled

OK, this is my first post to NR, I hope I'm not breaking protocol with this question.

I've had my little CF-W2 for several years, and it last weekend suddenly lost it's backlight. No gradual "dimming, change in color, fading" or any other analog degradation, just on Sunday morning when I picked it up the screen was dark.

The display was working, as would an external monitor.
I had it apart, and it SEEMED that the inverter was dead - no apparent output voltage (checked with high impedance scope) so I replaced it today.

New inverter (trust it is good) - backlight still didn't light and no apparent output voltage from the inverter.

I measured the input voltages to the inverter, and I did NOT find one above 3 volts.... I sure would assume that there would be a ~12V power input that would be used to buck up to the output voltage.

So - I opened the case up (ROTTEN job with this little toughbook), and there is no +12ish voltage on the MB power connector for the inverter (5 wire connector).

Hmmm - it's almost like there is a fuse or a "power switch" for the backlight circuit.

So - my questions for the gurus on this site -
* Does anyone know if there is a surface mount fuse for the backlight inverter on a Panasonic Toughbook CF-W2A? Can you share where it is and what it looks like?
* Is there a lid switch/magnetic sensor/thingy that could be stuck and thereby telling the MB/OS to "keep the backlight off, the lid is closed"??

I don't have a backup backlight handy to test with, although that is my next step if you guys can't point me in a smarter direction.

thanks for any ideas or thoughts, and BTW - there are some wicked cool mods that have been posted here! I'm impressed!
best-
timm

 

Tim

Welcome to the forum

I sent some info that might help to your email address


Alex

 

Thanks Tomcat - that was exactly what I was looking for - and sure enough F2 seems to be open, which provides +5v to the inverter. My eyes are getting a bit old, and trying to "spot the SMD parts" without a scope or board layout is challenging!

Unfortunately my parts bin doesn't have many SMD parts, and certainly no 2A fuses that are less than 1*2mm!! I'm inclined to take fly leads and piggy back a "1980's sized" fuse across it and just tuck it out of the way.

Related Q - how common is it for an inverter to fail in a way that causes it to shunt it's supply and therefore smoke the upstream supply fuse? Is a cable fault common?

thanks - you made an obsessive engineer pretty happy!
best-
timm

 

If you read a couple of threads here on the fuse issue with cf-28's and occasionally the cf-29 the fuse failed mostly due to human error when changing the screen
Battery left in or perhaps residual power

The new automotive style in the smaller MINI Fuses might work as they are small

I use a binocular the wrong way to get a macro view lol

Alex

 

You might be on to something, as with a replaced fuse the screen still doesn't light, although I am now sending 5V up the cable.

Either I had multiple concurrent failures, or my fat fingers blew the fuse while testing the inverter that I replaced unnecessarily as it was the bulb or cable that failed originally ;-/

OK, time to button up the case, and open up the display again

 

Mystery solved. Original issue was short in the cable loom which had presumably smoked the fuse. Upon replacing the fuse, and reseating connectors the backlight worked fine......

until I reassembled everything, moved the screen while it was on and lit the cable on fire.

So - a bit of recabling and we are are back in business.

Thanks to Tomcat for great info that solved the problem for me.
best-
timm

 

Gentlemen,
I have the same problem with my CF-T5. I was able to locate two 2A fuses near inverter connector, but have now idea how to test/replace them. Your advise will be highly appreciated.

Cheers, Ray

 

These are easily available; while they are larger than the original, in many cases there is lots of room in a ToughBook to solder solid wire leads on & just piggyback it on top of the blown surface mount fuse. Don't try to remove the blown fuse; you're actually stronger with it in there.

Scrape or sand the ends down to bare brass, solder some tinned leads (I usually just sacrifice a resistor from my kit for expediency's sake) on, then bend the leads down so they line up with the soldered ends of the surface mount fuse & BAM! There you have it.

2A 250V 3.6x10mm Fast Acting Ceramic Fuse (4-Pack) - RadioShack.com

mnem
Good Hacking!