T23 will not boot

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thomaslp · #1 Post by **thomaslp** » Mon Dec 01, 2008 5:08 pm

Hi,
I have a dead T23. It is not the conductors. I checked them and even tried to replace all of them. I have noticed that there is a beeping sound (not a beep code) when the power is plugged in. I think that the sound comes from the unit with the text 6R8 or somewhere in that area. I tried replacing this unit too but no luck.

The laptop is totally dead. Any help appreciated.

By the way I have been struggling with a T22 that overheated. I found out that the FAN was from an T20. I replaced the fan with one from a T22 and after that temp. goes up to 75C on full system load.....just wanted to share my experience.

#2 Post by **rkawakami** » Mon Dec 01, 2008 6:08 pm

Don't have any of my dead T23 motherboards around me at the moment but 6R8 is a usual designation for an inductor. It is possible to hear a continuous, high-pitching whine or ringing around a powered-up inductor if the windings are loose.

With a "dead" T23, try the following:

- insure that the system cannot be powered up by battery only, AC adapter only, or when placed into a port replicator/docking station
- remove all easily accessible "extra" parts such as hard drive, Ultrabay, battery and especially the MiniPCI card
- if that doesn't help, check all of the fuses on the motherboard; they are typically identified by having an "Fn" marking nearby (i.e., F2, F10, etc.; see image linked below)

Beyond that, then you're talking about troubleshooting the power systems on the motherboard. This could be as simple as a visual inspection looking for something like this:

http://www.rkawakami.net/ibm_t2x/let.jpg

or probing around the various parts with a voltmeter or oscilloscope.

thomaslp · #3 Post by **thomaslp** » Tue Dec 02, 2008 9:30 am

Thank you for your reply. I totally stripped the mobo and soldered a new 6r8 onto the board. I changed the CPU (just in case) and powered on the laptop. Now the fan starts spinning but that's it. Still a black screen. No beep codes or anything. I tried it in a dock and also just using the vga output port, but the result is the same. All capacitors are firmly attached to the mainboard. I checked all the fuses that I can find but I did not find any dead ones.

thomaslp · #4 Post by **thomaslp** » Wed Dec 03, 2008 10:29 am

I was looking at another defect t23 motherboard and I can see that the burned ic on your picture is also wasted on my mobo. I can see the number 4802 on the ic and the last character on line 3 seems to be a A. I have a T40 mobo where there is a similar 4802 ic but it ends with b. Could this ic work?

#5 Post by **rkawakami** » Wed Dec 03, 2008 12:24 pm

I believe that the part is a Siliconix SI4802DY MOSFET. Siliconix has been bought out by Vishay. They have also obsoleted that part and replaced it with SI4778DY. This information was found by plugging in the SI4802DY part number in the search box at vishay.com.

SI4802DY datasheet: http://www.vishay.com/docs/71114/71114.pdf
SI4778DY datasheet: http://www.vishay.com/docs/69817/si4778dy.pdf

The marking code system is here:

http://www.vishay.com/docs/72762/72762.pdf (SO-8 package)
http://www.vishay.com/mosfets/related#markgs (parent listing)

and says that the last character in the third line is a wafer fab code. In fact, everything in the third line should not matter since they are merely codes for where the wafer was processed and when and where it was assembled.

thomaslp · #6 Post by **thomaslp** » Wed Dec 03, 2008 2:38 pm

Hi,
thank you for the info. I tried replacing the ic but when I tried to power on the laptop i still got no reaction at all. I tried it in the dock as well and still nothing.

I tried to plug in the battery and as soon as the battery touched the conectors the exact same ic blew up again

I have a few ic's - but I have no idea why the ic blows up.....any comments???

#7 Post by **rkawakami** » Wed Dec 03, 2008 4:20 pm

I treat those MOSFETs the same as fuses. There's probably a short somewhere else on the motherboard which causes them to blow out. I recently found another T23 motherboard which has the same charred hole in that part as the picture I posted many months ago. At the time I called it a "light emitting transistor" since there was a nice orange glow that came out of it, along with all of the magic smoke that was put inside when it was made

. Unless you have the skill, equipment and time to trace out where that short might be, the best course of action would be to get a new motherboard and save the one you have for salvaging spare parts; inductors, capacitors, resistors, fuses, etc. Basically any of the "non-active" components that are easy to test and not any of the semiconductors (transistors, MOSFETs, ICs).

#8 Post by **RealBlackStuff** » Wed Dec 03, 2008 4:57 pm

You may also have a bad battery...

#9 Post by **rkawakami** » Wed Dec 03, 2008 5:37 pm

I suppose that is possible, as long as the AC adapter was plugged in at the same time (current has to come from somewhere). If the battery is defective enough to register as a short to the motherboard, then it might draw enough current to blow out the MOSFET.

T23 will not boot

T23 will not boot

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