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| Digital Angle Gauge won't reset after battery change... |
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| DavoDavo:
--- Quote from: AdeV on June 07, 2012, 07:01:07 AM ---I don't think it's any reverse voltage that's killed it, that voltage regulator (small black chip next to the power wires) should have protected it. It might be worth briefly shorting the two pads at the top RH corner (with no battery connected), that should discharge the black capacitor, give it 5 mins for any other capacitors to discharge, short it again (for luck), then re-apply power & see if it's fixed. Chances are it won't, there may be some reset pads somewhere, but TBH it's looking like it's toast. The sensor will amost certainly be an itty bitty chip underneath that blob of black plastic, you won't be able to salvage it without destroying it, and even if you did save the chip, it'll be max 3mm square and impossible to solder by hand... (don't ask me how I know this)... --- End quote --- Yes, you're probably right about the reverse voltage. I have already shorted the + and - wires together but no luck. I need to find my good multimeter and have a poke around before I go any further, the positive (red) wire is connected to one of those pads and it looks like the other pad is connected to the black cap so that might be a possibility, maybe shorting the wires together was not enough to completely discharge everything. The black blob will be the brains of the thing (CPU), if I knew what type or chip number it is I might be able to look up the specs for it and see which pin-out is the reset line. I think I'll get my magnifying glass and have a good look at all the components. Ah... I just turned the picture upside down and, guess what? Screen printed just below the CPU is "RESET" so I wonder which track it refers to? Looks like there's a choice of two tracks that relate to it, one goes to R8 which then goes to (2 legs of?) Q5 (2TY chip) and then to U3, the other goes to a solder pad. But it's anyone's guess what tracks are on the other side of the board or sandwiched in it. :poke: |
| AdeV:
My guess it's the one that goes to the solder pad. Simple way to check it - short the solder pad to GND with the device powered up. You won't do it any harm, the worst case scenario is that nothing happens. If it needs a high to re-set, then short it to V+, but on the circuit side of the voltage regulator NOT the battery, I'm guessing it's a 2.8v circuit, but it might be less... |
| kwackers:
--- Quote from: AdeV on June 07, 2012, 07:01:07 AM ---The sensor will amost certainly be an itty bitty chip underneath that blob of black plastic, you won't be able to salvage it without destroying it, and even if you did save the chip, it'll be max 3mm square and impossible to solder by hand... (don't ask me how I know this)... --- End quote --- The sensor is the silver topped 6 pin device. A Memsic D2125E accelerometer. Plenty of info on the web for reusing it. :dremel: |
| DavoDavo:
--- Quote from: AdeV on June 07, 2012, 08:00:48 AM ---My guess it's the one that goes to the solder pad. Simple way to check it - short the solder pad to GND with the device powered up. You won't do it any harm, the worst case scenario is that nothing happens. If it needs a high to re-set, then short it to V+, but on the circuit side of the voltage regulator NOT the battery, I'm guessing it's a 2.8v circuit, but it might be less... --- End quote --- Hmmm... In the (very) old days, power up CPU resets were done with a cap/resistor combo that held the reset line high or low, as the case may be, until the voltage stabilised. I'm leaning towards U3, it's a small EEPROM and maybe the R8/Q5 combo does the reset thing on that? As far as I can make out, Q5 is a transistor of some sort, maybe that's gone belly up. More online research needed, I got sidetracked finding out about the accelerometer and how it works - amazing technology! See the link... :jaw: http://www.memsic.com/technology/sensor-components.html |
| Noitoen:
It seems that you are not the only one with the problem. If you Google around a bit you will see the same problem with other devices even of known brands. Couldn't find a solution though. :scratch: |
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