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820-2936-B - Green light on, Fan does not spin

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vaswaniraj

New member
Hi Group,

I have a 820-2936 -B logic board where when I plug in the charger I get the green light but the fan does not spin. I tried measuring all the components with PPBUS_G3H, and everywhere I get is 12.56 volts. Also on further measuring the power rails I found the following that PP5V_S3 every component instead of showing 5V is showing Zero (0) volts. I presume that the problem is in the S3 power rails. On further troubleshooting I figured out that U7200 chip the voltage on Pin 12 which is a S5 rail it should measure 3.3V but it only measures 1.295V. I presume that the U7200 chip is bad. Again on further troubleshooting I found out that the PP5V_S0 should have 5 volts but does not 5V. Am I correct in my troubleshooting steps. Correct me if I am wrong. Can anyone please advice what further steps is to be taken in order for me to make this board working. Thanks in advance.
 
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dukefawks

Administrator
Check if PP5V_S3 on L7260 pulses when you connect the charger, best seen on a scope, multimeter is too slow. Make sure you use a REAL 60W charger.
Check all coils for shorts to GND.
This usually does not "just" happen, inspect for liquid and ask customer what happened.
 
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vaswaniraj

New member
Hi Duke, Apparently I don't have a scope. I tried checking it with a Multimeter on VDC and there is a couple of changing figures, which finally settles down to 0.0000v. I am using a 85W ORIGINAL Power adapter would that make a difference. I would need more help with your statement "Check all coils for shorts to GND. I asked the customer and there is no liquid damage, neither I see any liquid damage to the board. The customer mentioned that it was working one night and the next day morning it did not want to come on.
 
V

vaswaniraj

New member
Hi Duke, Apparently I don't have a scope. I tried checking it with a Multimeter on VDC and there is a couple of changing figures, which finally settles down to 0.0000v. I am using a 85W ORIGINAL Power adapter would that make a difference. I would need more help with your statement "Check all coils for shorts to GND. I asked the customer and there is no liquid damage, neither I see any liquid damage to the board. The customer mentioned that it was working one night and the next day morning it did not want to come on.
 
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vaswaniraj

New member
Hi Duke,

I was trying to measure voltage on every PIN on U7200 chip and while measuring from Pin 1 and progressing forward, I observed that when I measure Pin 5 by keeping the Black probe to ground and Red probe to Pin 5 the FAN STARTS TO SPIN. If i remove the probe the Fan stops. What does that indicate ? The Pin 5 is P3V3S5_VFB. It sometimes happens on Pin 6 as well.Please advice.
 
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vaswaniraj

New member
Hi Duke, As i mentioned in my chat an 1 hour ago, that when i touch the red probe to one of the pins either 5 or 6 ( not sure ) the fan spins. This is what i did - I connected the logic board back into the computer connected all the cables including the LCD connector. and then went ahead and touched the red probe to one of the pins 5 or 6 ( not sure ) and black probe to the ground. The computer came one with a Chime. So does this indicate that the U7200 is bad or is there something that i need to check. Please advice as what should I do further. Thanks in advance.
 
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vaswaniraj

New member
Hi Duke, I don't know if what I did was correct. I put some flux on the U7200 and heat the chip in little bit. After that now the green light on the charger does not want to come on. Please advice what is wrong that I am doing so that I can fix it and make this board working. Louis, please advice if you feel I am doing something wrong. Regards,
 
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vaswaniraj

New member
Duke, please help me out. Please try to get me the possibilities to make this board working again. I am trying to learn, though I am slow, but your help would make me confident in fixing boards. Regards,
 
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vaswaniraj

New member
Hi Duke, I checked the voltages and all R1800/1/2/3 and they measure 0.42 V except R1801 which measures 0.38 on Pin 2 .
 
Repairable

Repairable

Active member
check voltage on both side and report them. ADD Ohms for each

simple
R1800 pin 1 3,0 volt pin 2 0,8volt.

etc
 
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vaswaniraj

New member
R1800 Pin 1 and Pin 2 - 0.42
R1801 Pin 1 - 0.42V
Pin 2 - 0.38V
R1802 Pin 1 and Pin 2 - 0.42V
R1803 Pin 1 and Pin 2 - 0.42V
 
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vaswaniraj

New member
Hi Duke, I am getting 0.42V at all the 3 caps - C2231/32/33. Also i went ahead and checked the U2800 where the Pin 1 which is VDD_RTC_OUT is showing me 0.42V. Is this correct. Please advice further.
 
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larossmann

larossmann

Administrator
Staff member
Answer aprendiz' question. Also tell me if you have reached any conclusions about what you think is wrong here. stare long and hard at U2800 and PPVRTC_G3H on the power rails page.
 
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