Seeking Surf Pi Help

[pberrett]

Hi everyone

I have just built the Surf Pi board (basic , not Pro) and had it working ok. With my spiral coil I was able t detect metal at 22-23 cm.

However whilst rewiring everything to fit inside a box something bad happened and my icf 9640 has become very hot to the point where I now have smoke. Also pin 6 of the

I have ordered a couple of new icf 9640s in case this needs replacing. I expect that to arrive tomorrow.

Can someone please help me in working out what is wrong with my Pi. I have checked my circuit board for shorts and everything appears ok.

I have a multimeter but no oscilloscope.

Hoping someone can help.

Regards

Peter

[Waikiki_Sweep]

First of all add a fuse 0.5A into power supply line. It will save you more IRF9640.
Then turn SurfPI on without coil for first time. Check +5V -5V power.
Check power consumption: 20-30mA without coil, 55-75mA with coil.

Your IRF9640 may be hot because it is in open state all the time or it has broken.
On the gate of IRF9640 there should be voltage near +12V all the time except short TX impulses. So multimeter will show something near +12V.
Try to get sound from the schematic with using buzzer and resistor. If 555 timer works you can find impulses 600Hz that synchronizing all parts of schematic and opening closing IRF9640.

[pberrett]

Thanks

I'll pick up a fuse holder and fuses tomorrow. Where do I check the +5v and -5v power?

Thanks Peter

[Waikiki_Sweep]

Take a look on schematic, opamps and logic ICs powered by +5V and -5V.
Check voltages to ground in any place:
NE5534 pins 7,4
LM358 pins 8,4
CD4066, MC14093B pins 14,7

[pberrett]

Thanks again

I had another look at my components and realised that I had wired C15 (220uf electrolytic capacitor) the wrong way round. This has now been fixed.

I have also unsoldered the IRF 9640 Mosfet and I am awaiting a replacement which should arrive tomorrow.

I then added the 0.5 amp fuse to my power line. In future I will fuse all my projects thus hopefully avoiding needless replacing of components.

I then powered up the board without any coil connected. I found that C13 started heatng up a great deal as did R3 or some other component near it. I found that when I removed the NE555D (marked as TLC555CP) the problem went away.

With the Mosfet out and the NE555D removed the power readings are as follows

NE5534 pins 7,4 pin 7 = -0.68v, pin 6 = 0.65v, pin7= 4.96v
LM358 pins 8,4 pin 4 = -0.68v, pin 8= 4.96v
CD4066 pins 14,7 pin 7 = -0.68v, pin 8= 4.96v
MC14093B pins 14,7 pin 7 = -0.68v, pin 8= 4.96v

I presume that I will need to replace both the Mosfet and the NE555D? Any other components need replacing? It seems that I am not getting 5v negative but maybe it is due to one of the components I have removed?

I am amazed that the project actually worked for a while with c15 in the wrong way.

Thanks Peter

[Waikiki_Sweep]

Probably C13 installed wrong way or broken if it heating up.
To create -5V is used ICL7660 - Switched-Capacitor Voltage Converter.
As I see you have some small negative voltage in the schematic so it works somehow but overloaded.
Negative current leaking somewhere. May be some of chips that consuming +5v and -5v power has been fried.
If you can, remove NE5534, LM358, CD4066 , MC14093B and check that you have -5V on output pin ICL7660.
Try to find why you loosing -5V supply. Who consuming -5V current or if it shorted or ICL7660 malfunctioning or C14,C15 inverted or fried. Without -5V nothing will work at all.
Because your case looks tough I think you need to spent some time for learn schematic diagram for
better understanding how it works because it is unknown how many components have been also fried.

[pberrett]

By the way, before my circuit developed lots of smoke it did work for a while and I had a chance to test my pinpointer idea. I bought a small prewound coil - a LF1308 0.1mH/20AWG and wired it in as the coil. It could barely detect anything but when I put a ferrite rod in it I found I could detect out to about an inch which is just about what I need for a pinpointer. It certainly worked as well as those basic pinpointers you can buy.

[pberrett]

HI all

Here are some photos of my build. I have now replaced a lot of the components in the power supply section but I am still awaiting a replacement irf 9640 mosfet.

With the mosfet out I am now getting the following readings:

NE5534 pins 7,4 pin 4 = -4.70v, pin 6 = -0.65v, pin7= 5.02v
LM358 pins 8,4 pin 4 = 1.49v, pin 8= 5.02v
CD4066 pins 14,7 pin 7 = -4.70v, pin 14= 5.02v
MC14093B pins 14,7 pin 7 = -4.70v, pin 14= 5.02v

Strange voltage on pin 4 of the LM358 or is this normal?

cheers Peter

[pberrett]

By the way a couple of other things. The voltages above were measured without a coil attached.

Also you will see that I have wound 2 coils. I wound a coil with twin lead speaker wire but found it was too heavy so I took only 1 lead of the 2 and wound this into a spiral.

I also wound another coil using 21 turns of 21 AWG copper wire. It will be interesting to see which works best.

I also used some of the copper wire to wind a long coil around the ferrite to see if this makes a better pinpointer. It would certainly be thinner.

A quick supplementary question as well. Does the piezo have polarity and if so how do you tell which side is +?

cheers Peter

[porkluvr]

problem: None of the attachments in frame #8 are visible.


If you have -4.7V everywhere besides the LM358, then look for bad solder or an open trace, and make sure you are pushing hard enough on pin-4 to get a good reading.

[pberrett]

Here we go