Surf Pi Post assembly checks?

[golfnut]

Slow and steady wins the race

[Comp]

God I feel an idiot about the caps, shows it has been a while since I swung the soldering iron in anger.
I am confused about the resistors, I have already changed them to what I read.

Anyway thanks very much for taking the time to help me out and looking at the picture

The schematic is correct, the PCB etch is correct, BUT the silk screen layout is where the error is,....... R18 ON THE BOARD is where R22 should be,... simply put, the resistor nearest the chip, (marked on the 1.2 Board as R22) should be the 47K one,......

Good luck, Cheers, Fred

[Lefizz]

Can I ask how important are the values of the power supply caps. I'm thinking it may be difficult to desolder mine and put them back. I have loads of very high quality superlow esr 100uF caps, but none in that diameter of anything higher.

Thanks comp for the clarification on the resistors.

[Comp]

Suck it, and see,..... I bet it would be OK,... if not, if you remove the 220pf capacitor, (C17), that will raise the switching frequency, and the 100mf caps should smooth it easy, I would suggest.

Theoretically, the 7660 efficiency will drop a tad, but I have used the same circuit will only 10 mf caps, and no C17, with no problems....


Cheers, Fred

[Lefizz]

Ok caps replaced, i got them out ok, test and within a few percent so i stuck them back in.

New coil built using 0.5mm wire

All solder points checked.

Still dead as a dodo.

Getting a bit pissed off with this. Maybe 10 hrs work so far and nothing. Maybe i need to buy a scope of ebay

[Comp]

Hmmm..... bit annoying, Aint it???? Not too easy to faultfind at this distance, but having had a good look at your photo, it all looks about right,..... can you check current consumption??? Should be around 50 mA (ish). Also, (if you bought your Surf as a kit) check the little speaker supplied, if you have put it in the wrong way round, it wont sound, it is polarity sensitive...... You should get a short beep from it when you apply power.

try that, then post back, but dont panic!!!! I am coming to Bellamadina in a few weeks, will pop over if we are still not sorted!! LOL!!!!

The board is very forgiving of the coil, by the way, It might not work brill, but it will work with a coil to your spec,


Cheers, Fred

[Lefizz]

Thanks for the help.

I have tried the buzzer ever way around, it has never given any sounds unless right next to the coil when it gives a slight buzz. The board is consuming around 45 ma which sounds about right to me. Oh well.

[Comp]

OK, step at a time,... measure pin 6 of the preamp, {U2, NE5534 ) you should be able to set that to 0V using the offset pot, OK???

Fred

Edit to add,... after refitting the Electrolytic caps, have you got your plus and minus 5 volts???? and centre your delay pot, if it is too far down, it will stop the system...

Plus, for a quick, and dirty check of the PI Transmit pulse system,,, switch a radio on to the AM band,.... then switch your metal detector on near it,... you will know if it is pulsing!!! LOL!!!!

[6666]

what voltages are you getting now ?

[Lefizz]

After refitting caps i have plus 5.05 and minus 4.76 and after much turning of the pot i got pins 6 on the preamp to near enough zero.

What next.

Also any ideas how many turns the bourne multiturn pots are, utter **** to find where centre is.

[Lefizz]

Havent got an AM radio in the house (weird) but the peizo buzzer even disconnected from all wires whistles a bit next to the coil so is giving off some kind of EMF

[silverdog]

The cermet pots are 25 turn

Now you have correct voltage and offset, adjust delay pot until you can detect metal

You can monitor for a voltage increase on Ne5534 pin6 when metal is detected, in case you have a problem with the audio generation

Good delay without a scope will be when you can detect a gold ring

You will get there

[Lefizz]

Well, i can get audio tone now on switch on and I can get what seems to be a sort of detecting tone but the whole thing seems a little unstable. It maybe cos i am using a cheap SMPS as a power source because i dont have any 12v batteries. I was thinking that this might beto noisey and this may be causing the instability. Now sure just a hunch.

Still we have progres

As a side not would 15v be too much since i have a 10 x AA pack i could use for testing but I havent got 10 rechargeable AA i would have to use 1.5 v alcalines?

[homefire]

Use the Battery pack and only 8 of the batteries in it! 12V LOL

[Comp]

Probably get away with 15V, but if you want to lose a couple of volts, put 3 or 4 rectifier diodes, (In4001, BY127 types ) in line with the supply,... will be fine to test with.

The instability could be your switched mode PSU, or even flourecent lights/house wiring...


Cheers, your getting there!! Fred