| Electronics > Repair |
| Help me find a short on laptop mainboard |
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| Fraser:
I recommend that you view some of Sorin’s repair videos where he uses a thermal camera to identify shorted components…. There are many such videos on his channel ! https://youtube.com/@electronicsrepairschool?si=NLJ-2PS4l8qY4MtD NorthridgeFIX also uses thermal imaging for finding shorted components. https://youtube.com/@northridgefix?si=LJjuOpvxMleZ3YUs Basically a thermal imaging camera can easily identify the areas of a PCB that become hot due to a shorted component. You need to apply a low stimulation voltage of around 1V with a constant current limit of around 1A to 3A, depending upon the situation. Be warned that some lab power supplies do not like working into a short and disconnect their output so little to no current flows in the PCB. Sorin talks about this in one of his videos on buying a power supply. The original power adapter of a laptop will often go into protection mode if a short is present so do not use that to power the laptop. With a constant current of 1A present on a PCB, any shorted component on that power rail will normally reveal itself on the thermal camera. Make sure that you apply the stimulation voltage to the power rail of interest after any LDO or DC-DC converter if they are not part of the investigation. Some heavy duty components, such as large MOSFETs can dissipate a lot of heat to the PCB ground plane so more current may be needed to reveal shorts within these components. You have not stated which thermal imaging device you are using. If it is one of the very inexpensive very low resolution types from China you may find it more challenging to locate the failed component. Anything of decent quality with a true physical resolution of more than 80x60 pixels will work for PCB inspection but 256x192 physical pixels, or more, is a better tool for the job. Thermal imaging cameras have revolutionised the laptop and mobile phone repair industries with respect to quickly tracking down shorted components on PCB’s. It is the time that they save the tech that makes them so desirable in a commercial setting. In terms of cost for a thermal camera…. We have never had it so good ! Well done for wanting to learn about this technology in the PCB repair environment. You may wish to research add-on inexpensive ZnSe close-up lenses, both DIY and commercial, on this forum. If you watch a good few of the videos that Sorin has produced, you will learn a lot about common faults on laptops and the use of the thermal camera where a short or very low impedance is present on a power supply rail. The dedicated thermal imaging area of this forum is a good place to ask any thermal imaging related questions that you may have and for information on making a close-up lens etc. Fraser |
| naujoks:
But I've already mentioned that I've done all those things! I have watched countless Nothridge Fix and Electronics Repair School videos, in particular the ones with voltage injection and thermal camera. My camera is not a cheap one, it has 240x240 pixel resolution and detects low temperature ranges really well, from the looks of it. The search results provided do not actually link directly to the PRO 13 schematics. Sorin and Mo hardly ever have schematics available for their work either. I've increased the amps limit to 1A on the PSU now (remaining at 1V), but still not a single thing gets warm. I checked that the PSU doesn't go into protection mode by connecting my MM to it, and it shows 1V output. The board pulls a maximum of 500mA anyway, so increasing the A limit to 1A wouldn't make a difference anyway. |
| RoGeorge:
If the board only draws 0.5A with the PSU set for 1V and 1A max, then it sees the board+connection wires as a 0.5ohm doh, 2 ohms, not 0.5, sorry. Which means there might be no short at all. The shorted capacitors usually have a lower resistance than 500 milliohm. If by "board is in short" you mean the DMM beeps on the continuity range, that is not a relevant test. The DMM beeps usually at any R under 200 ohms or so, depending on the DMM type. 1. - Where exactly on the Vaio board did you measure a short circuit? Mark the points on the previous picture. 2. - How do you measure? (what instrument are you using and what settings) 3. - Where exactly on the Vaio board did you connect the wires from the 1A/1V PSU? Put a picture of the board with wires. 4. - What voltage do you measure with the 1V/1A source on? Measure V at the board side, not at the PSU side (some wires, for example ready made banana+alligator Chinese wires might be made out of iron instead of copper, so most of the voltage from the PSU will drop on the wires, that might explain why the short-circuit can not draw more than 500mA). |
| RoGeorge:
This guy wrote the schematic can be downloaded for free, the message is from a week ago, so I expect the link is still valid: https://www.diy-laptoprepair.com/forum/Sony-Vaio-Pro-PRO-13-repair-guide-schematics.html Have you tried completing the download puzzle, as it is wrote in the second post there? |
| naujoks:
That schematic download link is a scam. You have to sign up to places with your credit card. No. |
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