I need Help with Surf PI 1.2

[Tepco]

So you have some weak tone near the coil, and despite some instrument problems, at least some change between coil and no coil connected, it can be assumed that TX part works. You have audio, so timing, or at least part of it also works. I assume (please confirm ) that your threshold control works too, so you can adjust continuous tone at some point with threshold pot and set below threshold, just not responding to metal. Voltages around U3 should normally be around zero, not abnormal to indicate some obvious failure. U7 switches are most probably good, one is used for audio, chip failure is unlikely. Even with partial failure, all this will respond at least to some degree. At this point, usual scope issue appear, with scope this is 30 second work, but without it, multimeter is almost useless. Some fault around U2 input amp is most likely, you can adjust offset to zero, chip may be good, so try this first:


Carefully check component values for proper placement of R7,8,9,12,13,14, it is very easy to make mistake especially with metal film resistors, say, 1K and 1M is only one color band difference. Good idea is to recheck entire board for misplaced components. Also check D1,2, first for correct orientation (if by chance, one diode is misplaced, so both oriented in same direction, this can cause damage to U2). Unsolder one end and test diodes with multimeter on “diode test” mode for possible breakdown, should read 0.6-0.7v in one direction, infinity in another. Solder them back before you turn on detector again, or U2 will blow.


Two more useful things you can do: first make well focused photo of your board under good light condition, bottom side too and post it. Also, try to obtain any piezo element (buzzer, tweeter), can be removed from any electronic junk, any type and for any purpose, just must be piezo crystal, not dynamic (magnetic) type with wire, like in headphone, must measure infinity in ohm test. This can be effectively used like some sort of “blind man's oscilloscope”, if you can't see it, you can hear it, very useful troubleshooting tool. Will add more on this, may be interesting for anyone having trouble with Surf, last few problems reported here would be solved in matter of minutes using it. Simple go-no go test, but in most cases this is only thing needed.


Some sort of well documented “Surf 1.2 troubleshooting guide” document is badly needed here. Or offering assembled and tested PCB's.

[yako84]

[yako84]

I chek and the placement of R7,8,9,12,13,14 are OK, the orientation of D1 and D2 OK. And buzzer works, because if I take the board with the Hand, it do a very High Beep. Thank you
I don´t know what else do

[Tepco]

From pictures posted above, no obviously visible problem or misplaced component, no idea what can be wrong (lot of things can be). Do you have threshold tone adjustable? Need to get continuous tone at one point turning threshold pot, is it OK? Also see my next post.

[Tepco]

Blind man's scope

Blind man's scope: very useful thing for troubleshooting, in absence of real oscilloscope. Try to find one of these: piezo element, buzzer, very common, cheap and easily available component. Can be of any size or appearance , just must be piezo type, not magnetic. If your multimeter is equipped with continuity tester that beeps, most probably you have one inside, can be removed temporarily and used for testing. Very limited but better than nothing, points can be probed where DMM reading alone is useless. Only output pins on some chips can be probed this way. Connect one end to GND (battery -), use other end for probing, in about this order:


First connect to pin 3 on U1 (555), you will hear relatively loud signal, to establish some reference, this may vary with piezo type, in your case this point is OK. Next probe coil signal (Mosfet D), you will get even louder response. Test C of Q1 (from now, bit quieter) to eliminate usual Q1 issues. Next important points are pins 3,4, 10,11 ofU4 (4093), signal at pins 3 and 4 should sound identically, also check U7 pins 5,13 for same signal to eliminate eventual PCB issues. This can verify timing circuit operation, now it pays off, DMM is useless for this. Preamplifier output, U2 pin 6 (5534) can be probed, you will get audible tone, with large enough metal near the coil you can actually hear some change. Even at pin 3 (input), very weak but still audible signal can be found. Rest of the circuit, around U3 cannot be probed this way, nothing audible there, just slowly varying voltages, but DMM can measure them. Blatant improvisation, but can save hours, or some random component replacement. If piezo is not available, use ordinary headphone intended for detector, and 1K resistor connected in series.

[Pete B1]

Thanks for that useful info Tepco, it's helped me understand how the circuit works much more clearly.
I get a loud signal on pin 3 of U1 but a barely audible signal on mosfet drain and collector of q1.
Anyone any idea what i can check?

[6666]

See here as well

http://www.geotech1.com/forums/showt...-386-audio-amp