transistor k45 near battery on A7V266-E bad...

  • Thread starter Thread starter MikyZ
  • Start date Start date
M

MikyZ

i looking for the code corrispondent of the transistor K45 near battery on
m/b Asus A7V266-E for replacing, any one help me???
thx
 
"MikyZ" said:
i looking for the code corrispondent of the transistor K45 near battery on
m/b Asus A7V266-E for replacing, any one help me???
thx
Click to expand...

I don't know the actual characteristics of the device, but it needs to
be Schottky (400mV forward voltage drop), so that a 3.0V CMOS battery
can meet the minimum 2.0V CMOS well voltage. The device is undoubtedly
a SOT-23 packaged, dual common cathode diode. I still do not understand
the marking system for SMD components, so I don't know how you work
backwards from the number. The following datasheet is an _example_
of such a device - I don't know if it has the required current rating
or not. Note the BAS40-05 in this doc has a surface marking of "45"
but not necessarily "K45".

http://www.vishay.com/docs/85701/85701.pdf

I've tried a few semiconductor webpages before and had no luck tracking
down an exact match.

Three different models of Asus motherboard I have here, have the same
device used for the diode ORing of backup power for the CMOS. The diode
gets burnt when you clear the CMOS without unplugging the computer.

To see a schematic of how the dual diode is used, see page 67 of
this document. It is 7.6MB in size! This is the spec for an Intel
Southbridge, and I've looked at three of the datasheets and they
don't list operating current, only standby current consumption, which
is useless for gauging diode current requirements. I presume the
current is reasonably low, as writes to the VCCRTC powered CMOS
memory or the RTC will only be happening while in the BIOS or when
changing the time on the clock.

http://developer.intel.com/design/chipsets/datashts/25251601.pdf

A person in this group, who fixed his own motherboard, used some
1N4148 diodes, but these are not Schottky, so the forward drop
would be 0.7 instead of 0.4, meaning a slightly reduced battery
life before getting battery replacement symptoms.

Here is another example of a dual diode, this one having a better
forward characteristic - the 54C has a surface marking of L43:
http://www.fairchildsemi.com/ds/BA/BAT54C.pdf

OK, I just tried a search in Altavista for "K45 diode -relay" and
got this - you may need Acrobat 5 to read this:

http://www.cj-elec.com/ebusiness/product_images/b/cn_b_3_452.pdf
SOT-323 package (a little taller), BAS40W-05 Marking:45.K45

So, looks like it may be a member of the BAS40 family.

HTH,
Paul
 
Thanks very much, you are phenomenal, I will read well and and I will try
the optimal solution, thanks still and long life!
Best regard
cya
 
"MikyZ" said:
Thanks very much, you are phenomenal, I will read well and and I will try
the optimal solution, thanks still and long life!
Best regard
cya
Click to expand...

Make sure to get the "dual common cathode diode", which is the -05
version. Using the wrong version could cause the CMOS battery to
explode. The dual diode is there to prevent the PS in the computer
from charging the CMOS battery, and using the wrong pinout device
is dangerous to the operator.

|\ |
(Power 1 _____| \|__________
Source) | /| |
|/ | |
|___________ 3 (Load side)
|
|\ | |
(Power 2 _____| \|__________|
Source) | /|
|/ |

Paul
 
Back
Top