Hp compaq nx7300, power problem.

Measure resistance on pin 2 of L24 and L32
Disconnect all power to the measurement.

Guys I think that you are wasting your time with me.
Since I´m not shure which one is pin 2 ,could you direct me, between what point (picture) should I measure resistance.
Thanks

alternatively measure the resistance of
PAD4 (near C266)
PAD6 Broker (near L32)

Do you mean resistance between PADs or each PAD to ground?

PAD4 and ground
PAD6 and ground
communicate the two values

PAD4
Gnd probe to ground and positive to pad4 =17.8 kohm
Positive probe to ground and gnd to pad4 =0.8 kohm

PAD6
Gnd probe to ground and positive to pad6 =2.2 kohm
Positive probe to ground and gnd to pad6 =0.8 kohm

strange is that if I change measurement range on instrument I get diferent values.
This values is from 20K range on instrument

the meter should be set on the 200 ohm FS
if confirmed values
we are in the presence of a short on the two lines 5 and 3V

-- Tuesday, 25 Jun 2013, 18:08 --

open (remove the pond) is PAD6 Broker and PAD4 and measure the resistance on both sides
measure the resistance of C266, C331

-- Tuesday, 25 Jun 2013, 18:14 --

(probe on the positive side of the capacitor and another to ground)

i don t think there are shorts on pad 4 and pad 6, looking to measured values to ground.

you have just measured the internal diodes in q47, and q57 (lower side mosfet).

different values on different scale maybe depends by differents voltages coming out from your multimeter in different testing condition( selected scale).

shorts are usually rappresented by a low resistence value (depends even from the line nature you are testing) that does not change, inverting the probes.

-- wtorek, 25 cze 2013, 20:25 --

please measure voltage on U31

- pin 29
- pin 12

other tests needs oscilloscope, but, let see if we can do without it

voltage on

- pin 13
- pin 28

As usualy "hard shorts" I search with diode/buzzer range on instrument.
On that way I dont have shorts,elko sound "tik" in both way on each pad ,also between pads ,and lowest value is 122 and no sound for short .I suppose it is ok.Correct me if I´m wrong,please.
No voltage on pad 4 or 6

pin29=5 V
pin12=5V
pin13=4.5 V
pin28=4.5 V

btw
I have working oscilloscope peaktech 60mhz ,unfortunaly I dont use it often.but we could try.

the basic rule is, if you have a short on a line, resistence value to ground must be te same,and low, even inverting the probes.

how much low ? it depends on the nature of the line you are testing, for example, 5 ohms on a cpu vcore line its normal,5 ohms on a v/gpu line it can be normal, 5 ohms on a vin 19 volt line, or on a 3/5volt line is a short.

this is not your case, inverting the probes, you have different readings, so this is not a short.

pin29, pin12 5 volt, this is ok, you have correctly enable to the pwm u31.

let s go haead, pin13 and pin28 , you have 4,5volt... this is good...
seem that pwm chip is working but something appen and the 4 mosfet are not drived properly.

you have an oscilloscope, this is a good thing, so lets play with that...

with oscilloscope

check the driving signal on the pin

pin4 q47
pin4 q39

pin3 and pin8 q57

you must see a driving signal, almost a square wave, or a line with some narrow pulses.

ok,give me some time...

-- Wednesday, 26 Jun 2013, 14:02 --

I try but I dont think that I will be able to check signals since I never work with osciloscope.
One of my friend give me that osciloscope and he explain to me in short how to work but that was few years ago. (:
I try to find user manual ,no lucky.
I hope you will be able ,(in short ,dont waste your time) at least to tell how to configure ranges.
I will keep study how to work with it.

br

if you don t know how to use it, its better to leave it alone for this time.

check continuity from l32 both pin to pad6
check continuity from l24 both pin to pad4

if continuity is ok,

the failure must be in order

q39, q47,q57 so replace all

or, second step, u31, replace it

or ,third step, c331, c266

Hello

continuity from l32,24 to pad 6,4 is OK
I search (I have few MB) and I find ony FDS 6690AS
Is there any replacement for FDS 6900AS , and for 6612N ?

thanks

You can check carateristics on datasheet, Just Google on

Please check the voltage on pins 18, 20 and 23 of U31 (TPS51120). Pay a huge attention if You will measure on pin 23, because the proximate pin 22 (VIN) has a 19V potential - if You make the short circuit between pins 22 and 23, then U31 may explode.

Apart from, i think the TPS51120 may be damaged and You'll need to replace it.

I checked 4 laptop board and PS2,PS3 few lcd invertor.Unfortunately I did not find anything similarly that I need except FDS6690AS.
Since there is no electronic manual for osciloscope that I have, I send mail to them and thay were very kind and promised to send it in paper mould,but It looks like no signal on :

check the driving signal on the pin
pin4 q47
pin4 q39
pin3 and pin8 q57

but I am not shure.
I will check voltages

-- Sunday, 30 Jun 2013, 10:13 --

U31:
-pin18= 4.84 V
-pin20= 4.98 V
-pin23= 4,84 V

replace U31 and mosfet

guys,here's the thing

-manual for scope arrived,but no time for learning scope now...(kids and etc...)
many thanks to peakteach,since there is no electronic manual, thay was so kind and send me paper manual,free of charge
-I order parts that I dont have,so waiting.

is it possible to get schematic?

br

-today fds 6612A (hope it will be good since 6612N is needed from data sheet it should be OK) and
fds 6900AS arrived -:)
-I m still waiting for TPS51120

regards

Hello


guys I have good news
other parts arrived so I decide at first place to replace TPS only and try.
I have some difficulties with hand shaking since I was to excited.
I sucesfully replace it and than I try it.
It work good and it stll work
I`m very thankful to all that try to help me.
For me, without yours suggestions ,it will be very hard or impossible since I dont have schematic.
Thanks again

topic could be closed as solved

best regards