Chosen Solution
I am working on a Bluelab Guardian a TDS and PH monitor for aquariums and hydroponics. Total device power is 5v 1 amp. I suspect the previous owner hooked it to the wrong power supply and fried it. No response when supplying the correct 5v 1aNo visible damage on the PCB to make things easy. Many parts of the circuit have active voltage when plugged in which gives me hope it’s not a total loss. While checking the board with power supplied I noticed that the main 44 pin Microcontroller was getting quite hot - measured as high as 170F which seems high to me for such a basic chip.This chip’s model number is “PIC18F2423” - and trying to search through the documentation I couldn’t seem to find anything about expected operation temperature so was hoping someone with general knowledge of basic chips like this would have an idea if that level of heat output might be an indication that it’s fried. Any thoughts? Since it stores the programming, if it’s dead then there’s nothing else I’d be able to do with this circuit so this seemed a reasonable place to start. While investigating the circuit I did find a DC to DC converter which seems to be dead - has 5v coming in and no output. It’s a 4 pin model with no “enable” pin so I believe I should have voltage out. I can definitely replace it just don’t want to start swapping components throwing good money after bad if there’s a chance the main microchip is fried. Any advice or suggestions appreciated. Photos of the circuit attached.
Being that it’s a microcontroller, it’s not surprising to me that it might get rather warm. If you dig all the way to the bottom of the data sheet to the product identification system for that chip, it does list some temp ranges. It looks like there is some variability since the data sheet is for a few different variants of this microcontroller, but it lists temp ranges potentially as high as 125 ℃ (~255℉). And even the variant which has lower expected operating temperatures, tops out at 80 ℃ (~175 ℉), which is within the range you gave, even if only just. That doesn’t mean it’s okay, but it’s not running hotter than it’s rated anyways. If you’re going based on the theory that it could have been damaged by improper voltage, I would think your best bet is to see where that incoming voltage goes. What might it have gone to/through. It’s hard to tell from the pictures,especially with the large display readouts. But these green PCBs usually have traces that are pretty easy to follow (unless they go to other layers of the board). Check with continuity mode on your multimeter if need be. But there’s a chances that that main line goes to the DC to DC converter. In which case, it being damaged is definitely possible. I would concur with @oldturkey03 though, that having a short in the circuitry seems like a strong possibility, especially if it is getting toasty.
