Problem with TGSL edu

[Tauc]

Hi all!
i started building TGSL edu this winter but then got busy with studies and havent done much since. im now starting where i left off, having soldered the entire board and made a coil but it does not function properly. im trying to do nulling and taking some measurements with oscilloscope but it looks kind of strange?
im measuring at these points:

http://www.geotech1.com/forums/attachment.php?attachmentid=31353&d=1412208437

heres my tx signal:


and heres U101a, pin 7:

its a really weak signal (could be correct) but it has those spikes that reach twice as high voltage as the rest of the signal. any idea what is causing that?

when i measure directly at rx:

it has similar spikes and its also a relativly weak signal, but maybe this is as it should be.

now to the issues, when i was trying to null the coil (by making a difference of 20 degrees between tx and U101a, pin 7) they were following each other, so i can adjust it a bit but it stays around 60 degrees if i remember correctly (forgot to take an image of it). how is it that they are following each other? and do the other images look correct?

i get a few beeps from the detector when im touching the cables to the switch and pots, but it does not really react when i move metals over the coil. guessing this is because i dont yet have it in a grounded case, just got the card on its own.

[homefire]

Do you have O Scope in Auto Trigger ? Trigger off the Tx signal .

[Nandor]

Hello. Try to null your coils with the GEB pot in middle position that will automatically give you the 20 degrees phase shift between TX and RX than move Tx to achive the best null. Also ground your cable shielding and pot's too, its important! While nullind sens at minimum disc off and Geb at middle position.

[Tauc]

Hi, thanks for helping me out.
i had the coils losely attached to a casing but decided to unattatch them to make the nulling easier, and i noticed that despite moving the coils away or closer together, they still have the same difference in phase. when they were moving earlier and "following each other" it was because i was changing the shape of the coils a bit.
i set the GEB pot to middle and sens at minimum, tried disc off/on but nothing really changed. this is weird cause i remember that before i took a break with it this winter, i remember that the position of the coils were affecting the difference in phase between rx and tx, but when i move them now, nothing happens.

looks like this regardless of how i position the coils, or how i turn GEB:

tx lagging 70 degrees after rx.

[Nandor]

The problem must be with the coils. Tx coil has to be in opposite direction(winding) than Rx coil. If you have a good PCB than you must search the problem in your coils. Try to swap your Rx coil relative to Tx maybe that way you can get proper phase shift. Good luck!

[Nandor]

Try this way maybe you can make it work.

[Tauc]

Try this way maybe you can make it work.

thats how i have it now. but i found the fault, or at least one of them! the connector from coil to pcb didnt seem to connect properly so i changed it. now it works but it works very badly. getting only 10 cm on pliers and 1-2 cm on a silver chain. even a pretty big steel rod used for mounting a bicyle saddle gives only at most 15cm.
thinking my coil may not be good, or maybe the shielding on the coil?
will look more into it later but i dont have access to an oscilloscope over the summer, the only one i can use is at my university and its closed during the summer.

[Nandor]

I made mine without an oscilloscope and it works, just be careful with the making of the pcb and the placing of the components! The coil is also important but bad shielding won't make your detector sensibility that low it would only chatter. There should be something mechanical problem or misplaced component. I had the same problems with my first detector and by finding these problems will help you very much on understanding what you have mistaken. Learn from these mistakes so you won't make these again in the future. Check the preamp stage, the comapartor LM393 or maybe the audio. I dont know what to say, are you using new components? BF245 is placed in a good way? check your transistors! Have luck

[CDI]

I made mine without an oscilloscope and it works, just be careful with the making of the pcb and the placing of the components! The coil is also important but bad shielding won't make your detector sensibility that low it would only chatter. There should be something mechanical problem or misplaced component. I had the same problems with my first detector and by finding these problems will help you very much on understanding what you have mistaken. Learn from these mistakes so you won't make these again in the future. Check the preamp stage, the comapartor LM393 or maybe the audio. I dont know what to say, are you using new components? BF245 is placed in a good way? check your transistors! Have luck

For PNP and NPN, if they are in the plastic case, need to be rotated for 180 degrees, except for BC547, they are in right position.
For FET's, i don't use BF245, now is MPF102, also rotated comparing to BF245 type.

[Tauc]

I got my kit from silverdog and it has metal 2n2907 and 2n2222.
BC327 pnp (next to the BC547) is plastic.
BF245C is plastic and called BF245A.
right now i have not rotated anything, all is like silkscreen shows. do you think i have to rotate the BF245? i have doublechecked most of the components but i dont see anything wrong. both of the LM308 are TL071 but that should work fine i think.

[Nandor]

Check BF's Pins C E B maybe the plastic BF245A has B E C. I used J106 it works fine but need to be reversed!

[kt315]

look #1 post http://www.geotech1.com/forums/showt...2-Chinese-toys
this wonderfull toy will give you absolutely right understanding on any transistor.

[Toros]

Check BF's Pins C E B maybe the plastic BF245A has B E C. I used J106 it works fine but need to be reversed!

BF 245 - G, D, S

[Nandor]

Toros is right it's a junction field effect transistor I forgot (gate source drain)