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Old 11-19-2019, 01:57 AM   #41
techtiger
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Default Re: ACER 5742 Dead M/Board

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Originally Posted by John McGivern View Post
Sorry for delay guys, been awaiting part from China. I removed cpu heat sink and cpu also memory. After great difficulty removed shorted chip I am now ready to test for short again but would like some advice as I don't want to short anything else out if possible. Should I reinstall memory and cpu + heat sink? What voltage and current should I apply? I haven't soldered in the new chip yet as I want to see if short is gone. I notice a sort of plastic gasket that surrounds cpu has curled up and hardened with preheat to board, does anyone know what this material is and where to buy a new one or can it be left out? Many thanks.
Upload a pic of Area you have you removed Si7686DP test the resestence to GND All Pads Si7686DP

Last edited by techtiger; 11-19-2019 at 02:10 AM..
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Old 11-19-2019, 05:01 AM   #42
John McGivern
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Default Re: ACER 5742 Dead M/Board

source 18.9ohms, gate 14.5kohms, drain 3Mohms dropping unstable.
See attachment photo. Thank you.
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File Type: jpg Replacement chip.JPG (281.1 KB, 9 views)
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Old 11-22-2019, 02:19 PM   #43
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Default Re: ACER 5742 Dead M/Board

latest update could do with some help.
Replaced chip, cpu,fan so injected 19v see attachments for voltages.
Attached Images
File Type: png voltages.PNG (247.0 KB, 12 views)
File Type: jpg Voltages3.jpg (80.0 KB, 6 views)
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Old 11-23-2019, 09:17 AM   #44
techtiger
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Default Re: ACER 5742 Dead M/Board

If you look back post 32# pic you will understand how the 1st 2 fets working
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Old 11-23-2019, 09:19 AM   #45
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Default Re: ACER 5742 Dead M/Board

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Originally Posted by John McGivern View Post
latest update could do with some help.
Replaced chip, cpu,fan so injected 19v see attachments for voltages.
PACIN is missing that’s why it’s not switching , are you sure PQ52 Drain is 4V ?

Last edited by techtiger; 11-23-2019 at 09:21 AM..
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Old 11-23-2019, 09:51 AM   #46
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Default Re: ACER 5742 Dead M/Board

Techtiger, yes it's 4v.
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Old 11-23-2019, 11:15 AM   #47
techtiger
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Default Re: ACER 5742 Dead M/Board

Was the Battery inserted when you check the voltage if so remove and test again or the PQ52 is faulty what voltage you get PR297 pin 1? PU18A is a comparator it’s not working properly pin3 should be 3.6V

Last edited by techtiger; 11-23-2019 at 11:27 AM..
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Old 11-27-2019, 08:34 AM   #48
John McGivern
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Default Re: ACER 5742 Dead M/Board

Techtiger, no battery inserted, pin 1 = 0v. I will try changing lm393. Then pq52.
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Old 11-27-2019, 09:40 AM   #49
techtiger
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Default Re: ACER 5742 Dead M/Board

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Techtiger, no battery inserted, pin 1 = 0v. I will try changing lm393. Then pq52.
You have to find out Why there is no +19V on PR297 pin1
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Old 11-27-2019, 02:08 PM   #50
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Default Re: ACER 5742 Dead M/Board

Fitted lm393 and pq52 D=5.3, G and S=18.68. PQ 51 D=19, G andS=18.68
LM 393 Pin1=13,14,1.3v fluctuating drawing 55mA
Pin2=10.8
Pin3=13.4
Pin4=14.0
Pin5=13.5
Pin6=13.4
Pin7=14.0
Pin8=18.5
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Old 11-27-2019, 10:57 PM   #51
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Default Re: ACER 5742 Dead M/Board

I doubt your measurements. How can gate voltage of PQ51 and 52 be different when they are tied together??
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Old 11-28-2019, 12:21 AM   #52
John McGivern
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Default Re: ACER 5742 Dead M/Board

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I doubt your measurements. How can gate voltage of PQ51 and 52 be different when they are tied together??
Hi, they are the same 18.68v its the drain that is different.
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Old 11-28-2019, 09:27 AM   #53
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Default Re: ACER 5742 Dead M/Board

I have double and treble checked voltages pq51 and pq52 are the same as post 50.
Lm393 pin1 is all over the place from 14v down to just under a volt sometimes steady at 1.3v I really have no idea what is wrong. I don,t think pq52 was faulty but replaced it anyway so I'am stuck at present. I have a scope if that is worth using but only 20Mhz analogue. Many thanks.
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Old 11-28-2019, 02:58 PM   #54
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Default Re: ACER 5742 Dead M/Board

There is no voltage on Zener diode1 near pin 1 lm393.
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Old 11-29-2019, 11:23 AM   #55
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Default Re: ACER 5742 Dead M/Board

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Originally Posted by John McGivern View Post
I have double and treble checked voltages pq51 and pq52 are the same as post 50.
Lm393 pin1 is all over the place from 14v down to just under a volt sometimes steady at 1.3v I really have no idea what is wrong. I don,t think pq52 was faulty but replaced it anyway so I'am stuck at present. I have a scope if that is worth using but only 20Mhz analogue. Many thanks.
LM393 should work like this pin 1 14V means some SMD protection circuit is BAD
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Old 11-30-2019, 11:52 AM   #56
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Default Re: ACER 5742 Dead M/Board

Techtiger, You where right mate found 19v one side of pr296 other side 0.0v where can I buy 10kohm 0402 5% are they thick or thin footprint nothing is easy with these smd components. May still have more faults very long learning process for me ha ha!
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Old 12-02-2019, 09:22 AM   #57
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Default Re: ACER 5742 Dead M/Board

Hi, pretty sure Pr296 open should arrive tomorrow.
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Old 12-03-2019, 07:30 AM   #58
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Default Re: ACER 5742 Dead M/Board

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Hi, pretty sure Pr296 open should arrive tomorrow.
Arrived today excellent service. Ordered 50 of each value after pinging 4 and losing them while attempting to solder I finally managed to solder one.
Tested with dmm pin 1 is now shorted to gnd and both sides of the new resistor shorted to gnd and PD1 no voltage either way when tested diode mode back to the drawing board. This was the first 0402 component I have attempted I am ok with 0805 but these are really small. When I removed the old resistor I tested the pads they where shorted will try to find what is causing the short.
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Old 12-03-2019, 02:44 PM   #59
John McGivern
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Default Re: ACER 5742 Dead M/Board

Update.
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Old 12-03-2019, 02:56 PM   #60
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Default Re: ACER 5742 Dead M/Board

More Pictures.
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File Type: jpg lm383 a 006.jpg (571.7 KB, 8 views)
File Type: jpg lm383 a 010.jpg (591.1 KB, 9 views)
File Type: jpg lm383 a 011.jpg (427.1 KB, 4 views)
File Type: jpg lm383 a 002.jpg (747.8 KB, 5 views)

Last edited by John McGivern; 12-03-2019 at 03:01 PM..
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