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Hello all, I need some experts help I have an old Teknetics G2 that used to work fine but lately it just won't work or even show anything on the screen. It was giving some random beebs before and got weaker and started basically detecting from a smaller distance, I did read somewhere that it could be a crystal or a capacitor but haven't troubleshoot it as it used to work fine sometimes but often goes crazy as I described above. I can probably eliminate the coil as faulty but I'm not sure of anything. Anyway the issue now is the machine is dead and any help will be much appreciated. I have a component that's getting hot which turned out to be a voltage regulator with the number 2951 (8 pin smd ic). When I removed it and gave it around 12v on pins 8 and 4 it's not getting hot at all but when I soldered it back on the board it gets hot. The only major change I did was replace the 9v battery with 3x3.7 lithium battery in series and the detector worked fine after that for a while so I don't think there's an issue between 9 and 12 voltage. I will attach a photo of a similar board I found on the internet I hope I can get some help solving my issue and thank you all again.
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It sounds like you have a dead short somewhere. Does the 2951 get hot when the coil is disconnected? -
Thank you for your reply Carl, yes the 2951 gets hot without the coil. I have been testing without it already. I test it when powered on and the 2951 gets hot fast, output is around 1.5v on gnd and pin 8, input is around 10v and no short circuits so far in the capacitors and resistors that I've tested. Also no other components getting hot that I know of and the regulator doesn't get hot when I removed it and feed it 12v and tested outside the board. I did read on the internet that it should output 3.3v and 5v or one of them... Something like that. Thank you again Carl and the Geotech community.Originally posted by Carl-NC View PostComment
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With the pins 1 and 2 of the 2951 connected to the capacitor above it and to pin 3 of the 2426i which is the input only carrying about 1.5vComment
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Here's the power supply schematic:
Try removing R36 to kill power to the TX driver. If U10 still gets hot, remove R33 which also kills power to the analog circuitry. Removing R34 kills power to the micros. If U10 still gets hot then the only thing left is U11.Comment
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Yup, R33 seems to do it. You're the best Carl I really appreciate the help. Now I can see the message "overload" on the screen and battery indicator showing low battery warning with continuous short beeps and I'm not sure if the missing resistor is the reason so I'm investigating into that.Originally posted by Carl-NC View PostHere's the power supply schematic:
Try removing R36 to kill power to the TX driver. If U10 still gets hot, remove R33 which also kills power to the analog circuitry. Removing R34 kills power to the micros. If U10 still gets hot then the only thing left is U11.Comment
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For now it doesn't recognize the coil and regulator input is 10.6v the output is 4.9v and it's not heating up. So now I have to check around the analog circuitry, what would you recommend starting with?
https://files.fm/u/2nknws73vpComment
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Sounds like a short on the +5VA supply. This powers the analog circuitry: U1,U2,U3,U4,U5,U6, and U8. I would start by ohming +5VA to ground to see if it's shorted. If it is, then do a careful inspection to see if there is a physical short, maybe a small piece of solder came loose and is shorting a supply pin. On U1 +5VA is pin 6, on U8 it's pin 10, the rest it's pin 5. Also look at traces. If you can't find anything, then you have to start removing chips. If you're good with a soldering iron, lifting the +5VA pins of the chips will do the job.
If ohming +5VA to ground does not suggest there is a short, then it could be the output of U1, U2, or U3 has a short (all pin 1). Do the same as above to find the problem.
If you're adventurous, power up the circuit with R33 removed and apply the +5VA with a bench power supply limited to about 1 amp. Do it very briefly (about 1 second) and see what heats up. Or, apply it longer and see what smokes.
BTW, overload is normal, the main ADC is no longer working. But the battery check should still work.Comment
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OK back with some updates, I have traced the 5v as suggested and removing U6, U5 doesn't have an effect but U4 removal got the device starting, the battery indicator is working now and it seems to work normally but it doesn't detect the coil still and it either works "normally" (doesn't detect coil but normal behavior) or it gives short continuous beeps so now I'm at U4 which is marked JC5R and according to my research it's an analog switch (TS5A3157DBVR) if I'm not mistaken. Not sure yet if it's the bad IC or I should put it back and continue tracing and I did not have it in any old boards to salvage it from or know any alternatives. Still working on it and hopefully it will be fixed soon. Any tips or advice regarding the issue will be helpful and much appreciated. And thank you Geotech and Carl without your instructions and information I wouldn't have gotten this far.Originally posted by Carl-NC View Post
https://files.fm/u/wke3jamukaComment
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That part number is correct. If U5 and U6 are still off the board then try putting one of them back to U6 and place the other to U4 (all 3 are the same part). Leave U5 empty. If the power is still working then it suggests the U4 chip went bad. And now the detector should work (beep on targets) but all targets will look like low foil (~40). If you like, you can now press the bad chip down on the U5 pads (use a pencil eraser) and see if it again shorts out the supply. If it does, you'll need to buy a replacement. If it does not, then it's possible that the chip is OK and maybe there was a hidden metal short.Comment
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