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Post by mastertech on Feb 13, 2014 21:18:17 GMT -5
Ok, I want you to connect the neg probe of your DMM to gnd but affix it so you don't have to hold it. Solder a wire to the gnd pad if you must and get a good gnd connection. Then set your DMM to diode scale. Now take your positive probe and pick any ic on that board and drag the probe across the pins slowly looking to see if a majority of pins have been shorted to gnd. I would start with the Eeprom(ic83) then the processor. Let me know what you find with those and we can go from there.
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nashou
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Post by nashou on Feb 13, 2014 21:27:09 GMT -5
Ok, I want you to connect the neg probe of your DMM to gnd but affix it so you don't have to hold it. Solder a wire to the gnd pad if you must and get a good gnd connection. Then set your DMM to diode scale. Now take your positive probe and pick any ic on that board and drag the probe across the pins slowly looking to see if a majority of pins have been shorted to gnd. I would start with the Eeprom(ic83) then the processor. Let me know what you find with those and we can go from there. On it! 'One thing is i think i pulled a bit of the pad up from C853, but i think it will be ok. |
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nashou
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Post by nashou on Feb 13, 2014 21:44:26 GMT -5
Ok I think the chips are fine not a lot of shorts. On IC 83 pin 3 and 4 were to GND. Again showing that VCC is shorted to GND. Am I right?
Nashou
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Post by mastertech on Feb 13, 2014 21:51:29 GMT -5
Yes, you are correct. This test does not mean that these ic's maybe good or bad but usually when a chip blows short it takes out most of the chip. So we should keep searching for now. I would next move to ic82, ic84, ic85, ic86 and ic87.
Edit: lets add ic 80 to that list.
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nashou
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Post by nashou on Feb 13, 2014 21:55:04 GMT -5
Yes, you are correct. This test does not mean that these ic's maybe good or bad but usually when a chip blows short it takes out most of the chip. So we should keep searching for now. I would next move to ic82, ic84, ic85, ic86 and ic87. Edit: lets add ic 80 to that list. Ok, I'm on it!!! Nashou |
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nashou
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Post by nashou on Feb 13, 2014 22:09:50 GMT -5
Ic 86 and 87 are not populated. the rest seem ok.
Nashou
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Post by mastertech on Feb 13, 2014 22:12:22 GMT -5
I am signing off for the night so I will leave you with this info if you want to continue.
I have looked over most of the schematics for this board and this power line looks like it only powers what is on that page in the schematics. But not everything on that page either. The remaining ic's I see are ic91, ic92 and ic93. If you go though all these ic's and don't have any with many shorted pins then you will have to lift the VCC pin on these ic's until your short is gone. I just use an exacto knife and a nice pointed soldering tip to just lift it enough to clear the pad. Just try not to break off any pins. See you tomorrow.
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Post by mastertech on Feb 13, 2014 22:15:52 GMT -5
You know, 1 more thing for tonight. I see on a lot of these ic's there are decoupling caps on the VCC line. Example: C805, C805 and so on. You know what I mean. I have see these caps go bad many, many times and they usually go short. So you may want to start removing them and testing before you start lifting pins.
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Post by mastertech on Feb 13, 2014 22:19:09 GMT -5
And when you are looking at the schematic for these caps do not miss the smaller identification for some of the ic's. Example, ic80 shows c813 but it is not shown with the ic basic drawing. It is by itself off to the side. See you tomorrow.
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nashou
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Post by nashou on Feb 13, 2014 22:24:08 GMT -5
Yeh about the decoupling caps, there are 4 on IC81. And those pins are really close.
Removing those caps is a pain , like I said before the high temp solder is not fun to work with.
Especially if there is a huge GND plane connected to it.
I'll go a little further tonight.
Nashou
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Post by mastertech on Feb 13, 2014 22:39:14 GMT -5
Yeh about the decoupling caps, there are 4 on IC81. And those pins are really close. Removing those caps is a pain , like I said before the high temp solder is not fun to work with. Especially if there is a huge GND plane connected to it. I'll go a little further tonight. Nashou Actually there are 5. This kind of work is what separates the men from the boys, lol.  And this is also why I occasionally comment about actual repair shop techs. They don't generally diagnosis to this level so they call it unrepairable to the customer. It still may be a .05 cent part. |
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nashou
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Post by nashou on Feb 13, 2014 22:45:15 GMT -5
While you were researching and I waiting for your response i opened up that Philips Plasma. found two caps bulging on the PS board
So I'll go check the pins on those other chips.
Nashou
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nashou
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Post by nashou on Feb 13, 2014 23:57:35 GMT -5
Ok I thoroughly went through all pins on IC 81. Pin 4 showed a short it is the AMP_LMT pin, also pins 142 and 143 that conect to RN 810 showed a short and on both sides of the resistor
pin 142 goes to. that pin is the NCPU_MISO pin.
Thats all for today.
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Post by mastertech on Feb 14, 2014 11:50:17 GMT -5
Unfortunately this is nothing conclusive. Those pins could be normally low. Until you remove a cap or lift a pin and that short goes away you have nothing to assume upon.
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nashou
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Post by nashou on Feb 14, 2014 11:53:53 GMT -5
Unfortunately this is nothing conclusive. Those pins could be normally low. Until you remove a cap or lift a pin and that short goes away you have nothing to assume upon. Yeah thought so. Just got home and will be here for a couple hours. I think I'll lift one end of those caps before all the VDD pins. Then If they are ok will move onto the pins. This will take a while. I'll need to get a not book too  Nashou |
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And this is also why I occasionally comment about actual repair shop techs. They don't generally diagnosis to this level so they call it unrepairable to the customer. It still may be a .05 cent part. 
