Surf PI Constant Beep - No Detection

[yedla]

Hope you experts can help me. I have built the Surf PI circuit and coil.
When I turned it on, I'm getting constant noise, no matter if I attached coil or not!
And, the PIN 6 of U2 voltage shows -4.4, but I couldn't bring it to zero - I have turned OFFSET all the way up and down as well (click to click, about 25 turns).
I have attached pics. Please help.

[Freediver]

Hi Yedla,

Not sure if your problem is the same as mine but I also had a constant tone from my surf pi when I finished it last week. I found it was due to a low supply voltage. My batteries were weak and only giving 10.5V. I connected new ones giving 12V and straight away it started working. However I did not have the problem with the offset not adjusting the voltage on pin 6 of U2. Maybe someone else here has more knowledge of this circuit.

I built a similar coil to yours and I get 16cms with a 1 euro coin. If you manage to resolve the problem with you board let me know how much you are getting.

[yedla]

[/SUP]

My battery pack voltage shows 11.7v. I'll recharge and test.

What is your coil resistance and inductance?
my coil shows 2.7 ohms - no way to check L.





is the same as mine but I also had a constant tone from my surf pi when I finished it last week. I found it was due to a low supply voltage. My batteries were weak and only giving 10.5V. I connected new ones giving 12V and straight away it started working. However I did not have the problem with the offset not adjusting the voltage on pin 6 of U2. Maybe someone else here has more knowledge of this circuit.

I built a similar coil to yours and I get 16cms with a 1 euro coin. If you manage to resolve the problem with you board let me know how much you are getting.[/QUOTE]

[Freediver]

My coil is similar to yours in geometry and number of turns but my coil resistance is only 1.3 ohms. I used 24AWG enameled copper not insulated braided wire. My internal diameter was 120mm and outer was 175mm. I don't have an inductance meter either but I used the calculator that I found on this website http://deepfriedneon.com/tesla_frame6.html to calculate it to around 245 uH. There are some useful calculators on that site.

I notice on your circuit board you have added some wire bridges that are not required as the points are already joined on the board beneath the silkscreen. eg the bridgeto the left of the pins for the 1000uF capacitor in your picture. It should not make any difference of course your joining them again but I cannot see all of your board. Maybe you have joined something that should not be joined? There are only be two wire bridges required to be added to this board.

[yedla]

Can someone please help?

My coil measures 1.5 ohms - 30 turns of speaker wire, starting with DVD diameter.
C13 voltage: 4.98V
C14: 2.45 V
C15: 4.75 V
C2: 12.3 V


The pin 6 of U2 shows 4.40 stable - it doesn't change no matter how much turn (end to end) on P1 offset pot.
I still constant noise from speaker. I couldn't get 0V on PIN-6


Can someone help me how to debug? What other voltages that I need to check?

Thanks

[neptune769]

Hi Yedla,
I know this is kind of old but did you figure out the problem yet? I had the same problem. It turned out the be that Q6 was a 2N3906 PNP not a 2N3904 NPN. It was with the Silverdog kit. I would check that. I'm not trying to bash Silverdog. I like his board and kit. Mistakes happen.

Regards,
Dennis

[Pete repeat]

Hey Yedla, if you're still around, try fixing those solder bridges, by soldering them from the top of the board, they might not actually be contacting how they are, judging by your picture. That could probably explain why you are getting -4.4v continuously on pin 6 of U2 even when you change the offset.
Good luck.
Pete.

[kenny444]

Time has moved on, but Just built a Silverdog Surf PI pcb and have 4.4 volts on the output of pin 6 (U2)? I have changed to socket and waiting for a replacement IC 55534. Any clues or cures please. Thank you.

[silverdog]

start with checking voltages - U6 the 7660S, check poins 5,8 - you should have near +5v and -5V

What are your coil specs, wire type, diameter, no of turns

Check Q1 is a 2N3906

[kenny444]

Hello Silverdog nice of you to reply and support, the 7660 voltages with reference to GND are 4.9 & -4.7 I am running from a PSU so current is not a problem but its between 48mA and 60mA depending where the tuning is set. The coil is one I have been using with the other boards, 200mm, .5m enamelled single copper, spiral wound for stability in free air, 22 Turns. The voltage on U2 pin 6 (TP2) is 4.4v with the coil, I suspect the 5534 because the cermet is part of the negative feedback loop gain (AFAIK) and it is not adjusting. I have a couple in the post along with an LCR meter. I have visually compared the resistors and capacitors. I wonder if the 2n3906 is working? I can swap it, but not tonight, my transistor box is in the loft.

[mohandes]

Hope you experts can help me. I have built the Surf PI circuit and coil.
When I turned it on, I'm getting constant noise, no matter if I attached coil or not!
And, the PIN 6 of U2 voltage shows -4.4, but I couldn't bring it to zero - I have turned OFFSET all the way up and down as well (click to click, about 25 turns).
I have attached pics. Please help.

[ATTACH]21686[/ATTACH][ATTACH]21687[/ATTACH][ATTACH]21688[/ATTACH]

please take photo under board(soldering)

[kenny444]

Hello Silverdog. I pulled the 2N3906 and its gain measured 242 on the PNP meter.

[Firebird]

Hi, did this problem get resolved as I have the exact thing, I checked what Silverdog said check U6 the 7660S, pins 5,8, pin 8 has -5v but pin 5 has 0v... Help needed please

[kenny444]

Looks like you need to pull all the IC's except the 7660 then check voltages, if you still have no -5v, nominal, more like 4.67.

[kenny444]

Sorry that was not finished. with only the 7660 in situ you should have 12v from your main supply, +5 and -5v on the other IC sockets depending where the voltage pins are on the 14 pin IC's you should have 10v across pin 7 & 14 (Not with regard to GND) and do not forget the two long iC's have there pins 1 and 14 in the middle of the pair. Kenny444