Electronics > Repair

34461A white screen cannot start

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晓看风云:
Hello everyone, I have a 34461A that needs to be repaired. At first, its fault was a white screen, but later it turned into a black screen. After reading the forum and maintenance manual, I found that the FPGA power supply voltage was very low, and the DS200 on the motherboard kept flashing. I suspect it may be due to the power overcurrent protection caused by a short circuit in SPEAR320S-2.

We replaced the SPEAR320S-2 with a brand new one, but it turned on with a white screen and the FPGA indicator lights turned on normally. The DS200 only turned on the left half of the yellow LED.

Now, I have found that there is a CR327 capacitor behind the MCU motherboard that is short circuited. I think it is not a capacitor short circuited. I want to know where one end of the capacitor is connected to GND and the other end is connected to? If you can help me, thank you very much!

u666sa:
It would be nice to see how this one ends ups.  :popcorn:


Take your meter in ohms mode and go over each and every single one of caps. Whatever looks __ off __ blow off with air and check again with LCR meter.

coromonadalix:
once again 

sad to see this problem  ...   

Does the mcu have busted  because it was getting too hot ?

Voltage lines problems,  spikes  etc ...

or the bga's / solder balls are not fully soldered ??  but you said  there is some shorted caps ????

晓看风云:
I applied 1.4V/1A to both ends of the short-circuit capacitor, and the results obtained from thermal imaging showed that the line from tps65070 to the short-circuit capacitor was heating up, about 30 degrees Celsius. As the voltage and current I applied were not significant, I was worried about burning the line. Upon inspection, it was found that 44/45/46 (AD_IN2/3/4) of tps65070 was connected to GND, which should be the foot position of the touch screen. However, all three outputs of tps65070 are very normal, with 1.2V/1.8V/3.3V being normal.

Thank you very much. I think I will try blowing off tps65070 when I am at a loss. I am worried that too many things will be dismantled, leading to the expansion of the malfunction. I am still a novice in the hot air gun.

coromonadalix:
you have low temp  chipquick solder paste in a syringe

just need to order a stencil .... or not ??

http://www.chipquik.com/store/index.php?cPath=400&osCsid=vr6jdra3dqjnl7nl0p6ggget03

yeah expensive ...

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