NESRGB Power Issue

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Ben Boldt
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Re: NESRGB Power Issue

Post by Ben Boldt »

I had an idea. What if you test the other 74LVC541? Are all the same pins shorted to GND on that one too?
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ShredderN64
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Re: NESRGB Power Issue

Post by ShredderN64 »

Thank you for the extensive help, Ben. Went ahead and ordered some sockets and pin strips along with a few extra ICs and figured I may as well grab a fresh power filter cap while I'm at it. Definitely getting some overtime at work this week, so if I do have to make another order for more components, I'm not too bent out of shape about it.

If I don't win the coin flip on this one, what other components might be suspect?
Ben Boldt wrote: Thu Jun 23, 2022 8:06 pm I had an idea. What if you test the other 74LVC541? Are all the same pins shorted to GND on that one too?
Here's the guy on the right. Same as before, red goes to GND.
PXL_20220622_115604835~2.jpg
Obviously I'm not an expert, but this one appears to be working as intended.
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Ben Boldt
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Re: NESRGB Power Issue

Post by Ben Boldt »

That is very interesting. This definitely points to the first chip being bad. Actually, the 2 /OE pins on the second chip may be intentionally shorted to GND by the circuit board anyway, so what you are seeing on the second chip does look completely normal.
vcc_gnd.png
What you will want to do next is remove the first chip, since we almost definitely know it is bad now. Then test the second chip again and see if the VCC -to- GND short is still there, or if it went away. If the short goes away, that is great news. If it is still there, we keep looking to find it.

It is really important not to lift any traces when removing the chip, as that will make additional work way more difficult. The best way is to use a heat gun and hold onto the chip with a fine tweezer with very light pressure until it just lifts off. No pulling or prying, trying to wedge something under it, etc. When it is hot enough, it should come right off with zero force.
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ShredderN64
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Re: NESRGB Power Issue

Post by ShredderN64 »

Plop! With some heat from my trusty Chinese clone 858D and the slightest tap of my tweezers, the troublesome chip jumped right off.
PXL_20220624_194927722.jpg
VCC no longer shorts to GND, nor do A2 or RST. I suppose all that's left to do now is wait for the mail. :beer: 8-)
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Ben Boldt
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Re: NESRGB Power Issue

Post by Ben Boldt »

Cool!

It still worries me what could have broken that chip in the first place. Be sure to let us know how it goes putting in the new chip!
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