compaq cq20 no power

[sasser]

hye all masta and sifoo i got another compaq problem. i think is mosfet is failure but let discuss what need to do. i attach shcematic for this model. i suspect Q10 is faulty because on pin 1234 i got all 19v but no volt on 5678.

mosfet Q10 TPC8121
pin 1 19.41v
pin 2 19.41v
pin 3 19.41v
pin 4 18.99v

pin5-8 no voltage. near this mosfet u1 the power is ok. and u13 all pin no power

tps51120 no vin at pin 22.

[ktmmotocross]

Re: compaq cq20 no power

yep, its bad.

[dj_ricoh]

Re: compaq cq20 no power




no its not!
you need to be 100% sure the gate its ok.

A MOSFET may be thought of as a variable resistor, where the Gate-Source voltage difference can control the Drain-Source Resistance. When there is no applying voltage between the Gate-Source , the Drain-Source resistance is very high, which is almost like a open circuit, so no current may flow through the Drain-Source. When Gate-Source potential difference is applied, the Drain-Source resistance is reduced, and there will be current flowing through Drain-Source, which is now a open circuit.

You need to take it out test it properly

[ktmmotocross]

Re: compaq cq20 no power

wanna bet on it?

[atsio]

Re: compaq cq20 no power

Pin 4 should be low. Check limit signal.

[dj_ricoh]

Re: compaq cq20 no power

Pin 4 should be low. Check limit signal.

Its a P-Channel Mosfet.
It has the VGS on max+/- 25V and its on pin 4
he needs to take it out and test it in diode mode or see if it got short on pads.

[aanan]

Re: compaq cq20 no power

check ADP-EN# point.

[fddizon]

Re: compaq cq20 no power

atsio is correct. at least 0 to 5 volts, p channel will conduct correctly.

check gate protection circuit

cant find the said part from the supplied schematic. all fets are labeled Q10xx
4 digit numeric

[sasser]

Re: compaq cq20 no power

Pin 4 should be low. Check limit signal.

atsio howto check limit signal im sorry im still new in electronic field.

atsio is correct. at least 0 to 5 volts, p channel will conduct correctly.

check gate protection circuit

cant find the said part from the supplied schematic. all fets are labeled Q10xx
4 digit numeric

yes i found label on pcb is Q10,q11,q13. i try read the mosfet q10 the result is same. pin 1-4 around 19.41v then no volt on 5-8.

[sasser]

Re: compaq cq20 no power

Its a P-Channel Mosfet.
It has the VGS on max+/- 25V and its on pin 4
he needs to take it out and test it in diode mode or see if it got short on pads.

i will post the result today. but if i found no shorted howto know got short on pads.

[atsio]

Re: compaq cq20 no power

atsio howto check limit signal im sorry im still new in electronic field.

Page 14 of the schematic, has all the Over current protection circuitry. Limit signal is the input.

[dj_ricoh]

Re: compaq cq20 no power

1 --|__ |-- 5
2 --|__ |-- 6
3 --|__ |-- 7
4 --|__ |-- 8

just put the probe on 1,2 or 3 and then the other on 5,6,7 or 8

select continuity and if it beeps that`s bad

[sasser]

Re: compaq cq20 no power

i have checked the mosfet q10. no shorted i found

[dj_ricoh]

Re: compaq cq20 no power

on fet or pads?

[sasser]

Re: compaq cq20 no power

on fet . i just test mosfet. on pad howto detemine there hav shorted.
on page system power 3v 5v i measure Q33 Q34 Q35 no 5volt there. tps51120 also on pin 22(vin) no volt

[tzoupkas]

Re: compaq cq20 no power

hello my friend I would change the U1 LM393 for start as I don't get the correct voltage at gate pin. Do that if possible and we will see what to do next.

[ktmmotocross]

Re: compaq cq20 no power

just chceck function of q10 with multimeter and replace if failed

[sasser]

Re: compaq cq20 no power

hello my friend I would change the U1 LM393 for start as I don't get the correct voltage at gate pin. Do that if possible and we will see what to do next.

i try later friend coz need to find same code LM393 on another scrap board.
will update after change .im measure no volt on LM393

just chceck function of q10 with multimeter and replace if failed

already check like before the volt on gate still 18.88v also pull out from board and do manual checked and im sure the fet is ok. but why gate got the 18.88v still mysterious

[tzoupkas]

Re: compaq cq20 no power

also U18 might me burned, when you will change the U1 touch with your finger the U18 for overheating.

[sasser]

Re: compaq cq20 no power

also U18 might me burned, when you will change the U1 touch with your finger the U18 for overheating.

hye friend u are right. i got clue from that. when i checked again the LM393 (u1) small damage i see. like burn sign. then i change with another lm393. now standby current got 0.0489. before this 0.0030A.

now i touch what overheat from area U6. will post the result thanks so much all friend to help me here.