Surf Pi Post assembly checks?

[Lefizz]

Hi i have just finished getting my Surf pi together with a home made 23 turn coil made out of some 28awg enamlled wire.

I plugged on the battery and nothing, well not quite true, if the speaker gets close enough to the coil i get a slight hum. I imagine that means that pulses are being created in the coil.

Is there anything i need to do after soldering everthing up to get a working detector? Do i need to adjust the pots or do they simply tune the device?

I am a bit tired today and have to make dinner but any ideas greatfull recieved

[Lefizz]

Well dont all speak at once

Gone over all the component placement and cant find anything wrong. Soldering looks fine underneath.

Regarding my homemade coil, its got a resistance of about 2.8 ohms does that sounds about right? Waiting on an ebay LCR meter so cant test inductance but i cant see it would be way off after using the calculator on the site.

[silverdog]

I think 28awg will be too thin and too high resistance

try for 22-24awg and about 1.6ohm

[Lefizz]

But that would stop it working totally?

[woodbob123]

Just finished my first one during construction tested each R and C before soldering powered up board before inserting ICs, cleaned and checked joints for bridges, coil was just 20 turns of hookup wire held together with spiral wrap direct to board. As a final check compared mine against pictures on forum, trans &ICs in correct, set pots to centre removed 2 and used meter to check as difficult to feel ends. Powered it up 9 then 12v and it detected a pair of snips. Changed R18 R22 over and much better. now making a better coil and will do any final tweeks with coil, cable,stem and box fitted together. Hope that helps anything more technical will have to wait if you need can give you details of coil. what part of Spain are you next surf will be waterproof for next stay in Alcocebre Bob

[Lefizz]

Thanks Bob,
Very similar to me, checked every resistor n cap, compared everything to pictures before powering up. Checked all solder joints. Maybe its the coil but seems odd to me. I'm in Madrid less bathing in the sea than other areas of Spain

[woodbob123]

reading previous post surf seems to work with a range of coils do you have a scope happy to compare with mine, check cap's are correct and think that speaker has a + side I ordered 2 kits so had spare ic's etc may be able to go through circuit with a multi meter with you , if it comes to it i have free calls to Spain

[silverdog]

Thanks Bob,
Very similar to me, checked every resistor n cap, compared everything to pictures before powering up. Checked all solder joints. Maybe its the coil but seems odd to me. I'm in Madrid less bathing in the sea than other areas of Spain

The coil can make a huge difference and stop audio working
I played with some ferrite rod coils once and a couple with too high resistance/inductance caused the problem you have
A simple coil from 7 strand equipment/hookup wire works ok to test with

[Vortxrex]

Both my Surf PI's worked the first time I tried them w/o setting the offset, all pots in the middle. I think triple-checking all components made a difference. If it is not a coil problem, you will need to post scope pics of the test points.

Dave Frank

BTW EVERY coil I made for this detector worked . The 18-20 turn ones worked the best. (22 gauge & 10" diameter)

[Lefizz]

First off all thanks for the responses, I'm very grateful indeed.

My calculated inductance is exactly the same as yours dave, obviously the resistance will be higher because of the smaller diameter.

I dont own a scope unfortunately, so i will try going over the board again to see what is wrong.

Actually i am also going to post some pics and if anyone can spot anything obviously wrong I would very very grateful.

[Lefizz]

pcb

here it is acually i think i might be better to take photos tomorrow. cant get the ligh righ and too much flash glare

[golfnut]

you have

C13
C15

The wrong way round + - / - +


steve

[6666]

What GN said, fix them then check your + and - voltages
the position of the tune pot will stop it from working to

[homefire]

Looking at your photo, it looks like you followed the Old Visual Aid.

Check R18 and R22.

R18 is 47K

R22 is 100K


The old Visual Aid had them Reversed.

[Lefizz]

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