help with surf pi kit no sound

[Qiaozhi]

ok i wish mine was that simple new q1 resistor back in place and still the same made no difference and tried a new coil as well

If you're sure that Q1 is OK, then the next thing to do is replace U4.

Are you located in Europe?

[alcartraz]

hi iam in england and the other kit should hopefully be here tomorrw i ordered it tuesday could just swap it over

if that works i proberly will not build the other one i will whant to get out and play do i run the risk of blowing the new chip if i just swap it ?

[Qiaozhi]

hi iam in england and the other kit should hopefully be here tomorrw i ordered it tuesday could just swap it over

if that works i proberly will not build the other one i will whant to get out and play do i run the risk of blowing the new chip if i just swap it ?

I am also in the UK. If you would like to post the non-working board to me, I'll gladly fix it free-of-charge.
Send me a PM if you're interested.

[alcartraz]

hi i just built the second kit and it works straight of the mark just need to tune it it up a bit detects small gold ring about 7 inches from coil but seems very erratic outside think the delay is to slow
i will post the other one tomorrow ! thank you for all your help

[Qiaozhi]

Alcartraz - Your Surf PI board is working!

To start with I probed the signal across the coil with a scope, and this was found to be as expected. Next I looked at the collector and emitter pins of Q1, and discovered the signal to be low in amplitude. Since you had already replaced Q1, and it appeared to be inserted correctly, I examined R4 and R5. These were found to be 100k instead of 100R. After replacing these resistors, the waveforms were correct, but there was still no sound from the speaker. The sample pulses at pins 5 and 13 of U7 looked correct, so clearly at least 3 of the gates of U4 were OK. I then looked at pin 7 of U7 (which is the audio tone) and that was also good. Hmmm, but still not sound. The signal at TP2 was behaving normally, as were the signals at pins 2 and 4 of U7, which meant that sampling was taking place. Pin 7 of U3 was providing a good strong response to a metal target, but pin 1 was very weak. Then I noticed that R22 was 100R instead of 100k. But, after replacing R22, there was still no sound; even though the output at pin 1 was giving a good strong response. Now, suspecting that both the 100k and 100R resistors had been swapped over, I looked at R35. Ahah! ... it was 100R. And .. guess what? ... after changing to 100k, still no sound. The bias voltage on the base of Q6 was being pulled up in the presence of a target, leading me to think that Q6 was kaput. I didn't have an MPSA13 in stock, so I replaced it with a BC517, which is also a darlington pair. The pinout is different on this device, so be aware that it doesn't match the PCB silkscreen. Lo and behold ... still no sound! There was only one last thing that could be stopping it working fully, and that was U7D. To prove this I shorted pins 11 and 12 of U7 together and the detector produced a loud audio tone. Replacing U7 (4066) fixed the final fault.

Lastly, I adjusted the null offset of U2 to zero volts, and set the delay to match the test coil.

Working perfectly!

[Koala]

Nice work Qiaozhi. Never easy when there is more than one fault. Alcartraz will be a man.

[alcartraz]

thank you very much cant see how i got the resistors mixed up who knows but its working cant thank you enough

[Luuk]

Thank you for your dedication and problem solving on this project

[methanolcat]

Hello guys, I'm new here on the forum. I've been reading threads for a few couple months now. Long story short, I bought 2 detector kits from silverdog, surf-pi and idx-pro. I have some electronics background (analog), I put them both together (still need to make coils for idx-pro, so its untested), the surf-pi was working fine and then something happened while I was putting it all in a plastic box, normally this is something I wouldn't have much trouble with but this really has me stumped.

When I turn it on, U5 (regulator) gets warm and I have almost no sound anymore, very faint. I have read through this thread as it was similar to my problem. I checked all the supply voltages on all the IC's positive and negative and they all seem right but something must be overloading U5 somewhat causing the heat.

I did notice that somehow P1 got broke so I replaced it, didn't help. I thought maybe a problem with U5 so I replaced it, didn't help.

I also changed out D6 and Q1 with no change. I have an oscilloscope and have confirmed tx and rx to be working with the waveform changing as metal nears the coil and thats when I hear the faint beep.

Since I have an idx-pro board some of the IC's are the same so I swapped out U2, U3, and U7. I also had another U4 (4093BE) in my IC box, so changed it too. Still no changes.

I have checked all of the solder joints, checked both external mounted pot's.

I'm running between 12 and 13 volts on my power supply and the circuit is drawing 50ma idle with coil hooked up. Here is something odd, with the voltmeter (set on 20vdc range) black on GND, red on pin 11 of U7, I get a more audible tone from the piezo, which makes me think the sound stage is all working.

Any help in getting this working would be greatly appreciated.

Matt

[Qiaozhi]

Let's debug this logically:

1) Monitor TP2 with the scope (coil disconnected) and adjust P1 to get the DC voltage close to zero.
2) Still monitoring TP2 ... connect the coil and confirm that the output reacts to the presence of metal. Use something large like a cola can
3) Take out U3 and connect the junction of U3a-1 and R23 to +5V. Check for a loud audio response.

Did you get a response at the output of U2 (point 2), and an audio tone (point 3)?
If yes, then the input and output circuits are ok, and the fault lies in the middle section, which means there something broken in either the sampling circuits or the integrators.

[methanolcat]

I did like you said and with the scope on TP2 the waveform changes in the presence of metal can, so that part seems to be working.

I do not get an audio tone from (point 3) with +5v applied, I do get a noticeable pop/ crackle when making connection but no tone.

[Toros]

If you use the analogy of MPSA13, as KSP13 it should know that they are with different pinouts=

[Qiaozhi]

I did like you said and with the scope on TP2 the waveform changes in the presence of metal can, so that part seems to be working.

I do not get an audio tone from (point 3) with +5v applied, I do get a noticeable pop/ crackle when making connection but no tone.

Can you check whether the sample pulses are present?
Put channel 1 probe on U7b pin 13 (main sample), and channel 2 on pin 5 (Earth field sample).

Also, let's look at the output of the integator stage by putting the scope probe on U3 pin 1. Does this change in the presence of metal?

[methanolcat]

OK, so I started probing U7 when I noticed that sometimes (whenever I put any kind of pressure on U7) I would get a tone, sounds like it is suppose to, loud. I kept messing with it and determined the socket was bad, it never would make good connection and stay, unless I put pressure on U7.

I changed the socket, put U7 back in and turned it on, was then getting a constant tone, it would not stop, so I get to messing with it and noticed that jiggling wires around the tone would stop and go, further investigation showed that I had a wire break going to P2, wire had broke at pot terminal (most likely from all this messing with it). I fixed the broken wire, then tried it out. It has erratic behavior at this point with no movement whatsoever, I can even leave the room and it will start going off, I even took it outside away from everything and no change.

U5 still heats up so something is not right with one of the IC's, I checked Tp2 and my waveform looks much different than when it was working right.

I can get it to work (detect metal) but only if I adjust P1 to a voltage around 4v+ and the detection distance is very short with large object.

If I take out U2 then U5 doesn't heat up so I guess what I am going to do is order some new IC's, they are cheap so I'll get several of each.

Thank you very much for your time and helping me, I appreciate it, I will get back to this once I get more IC's.

[langleylocator]

Hi Guys, Yet Another NOOOOB to md'ing And electronics. I can solder quite well,and decided to make the PI 1.2. however i am another one with similar problems NO audio . I have tested the U1 U2 U3 U4 & U7 pins as suggested in an earlier post and have similar results yet still no audio or signal ( I have managed to score a scope {FREECYCLE IS A WONDERFULL PLACE} don't really know what i am supposed to be looking for with it) any HELP would be greatly appreciated.
I have also meterd out all of the resistors and found 1 that is the wrong rating namely R5 Is listed 100 Ohm but i have found that i have inserted a 100k (I have no idea where this came from as i counted all of the items in the bag And found the diodes missing. quick trip to maplins sorted that little problem) would this be the cause of my problems?
H-E-L-P.
DESPERATE of slough Uk.