Baracuda problem, beeps once

[barleg]

Fellow metal detecting zealots,

I've recently assembled a Baracuda kit from silverdog but can't get it to work. I'm using a home made coil (25 cm diameter, 22 turn 0,45 mm copper wire) and a 12V battery pack. Whenever I turn the power on the Baracuda emits a clear short beep and then turns silent. The mosfet (IRF510) gradually gets warmer until it is scolding hot after around 15 seconds. If I turn on the Baracuda without a coil I still get a short beep and the IRF510 stays cool. I've also tested the rig with a much smaller coil (10 cm rolled electronic cable, ca 10m in total length) and the Baracuda then emits a less powerful beep and then turns silent, just like before.

I've tried different settings on all the trimpots, looked for component positioning errors, checked and re-soldered some joints but can't find the fault. I would appreciate some advice on how to fault find the Baracuda board. I can get my hands on a multimeter, but so far I've not found a helping Baracuda schematic that I can check against.

This is my first attempt to build a metal detector. I only possess a small amount of metal detecting knowledge and electronic know how, but what I lack in knowledge I make up in endurance and persistence

Pictures of my build
Top side: http://i.imgur.com/mcCIXyo.jpg
Bottom side: http://i.imgur.com/FC2B9JH.jpg

Cheers!

[sinclairuser]

irf510 is the wrong fet,it should be an irf 9640 or tip127 darlington transistor.
at the very least you must have a multimeter, to be honest to set it up properly you need a scope.

[CAS]

The IRF510 is an N-channel Fet where as I think you need to use a P-Channel for the Baracuda - a IRF9640 or similar as Sinclairuser said.

[6666]

It can help the performance if you carefully clean the solder flux off the pcb with soft brush and denatured alcohol.

[bernte_one]

for testing it is better to connect an Audio jack and use headphones

i have looked the most parts lokks not wrong, so Change your irf510 to tip127 or irf9640 re-adjust Offset und delay
and test again

[barleg]

Thank you for your answers! I'll order a new fet and will return with the outcome once I've switched them out and cleaned away the flux residue on the board. The fet was the only component that didn't match the markings on the PCB. I was naive and thought the IRF510 was an okay equivalent to the tip 127/IRF9640. The rest of the components (except the diodes) I've checked on various sites and concluded that they are correct.

[Rizal]

Hi,

I have the same problem but i stick to use IRF9640.. when turn on i got one beep then my baracuda got silent. The mosfet become hot if my circuit connected to the coil but without coil its ok. When i check pin 6 of IC 5534, the voltage is locked at 4.41v event i adjust the potentiometer. Then i found that the problem come from Transistor PN2222 metal body transistor. I change to another transistor (plastic body) and my circuit perfectly function! But please check the position of Emitter and collector maybe different from printed in PCB.

Sorry about my English Hope my experience can help you! Cheer...

[barleg]

@Rizal
Very interesting! I looked at some pictures on the web on the transistor and I must say I'm a bit confused. According to these pictures:

http://upload.wikimedia.org/wikipedi...BJT_Pinout.jpg
http://www.bdspeedytek.com/wp-conten...tor-2n2222.jpg

the 2N2222A has its emitter pin to the left if you place it according to the 2222 transistor outline of the PCB board (http://www.silverdog.co.uk/shop/imag...t-1024x768.jpg).

The 2N2222A I was supplied with looks like in these pictures:

http://upload.wikimedia.org/wikipedi...and_schema.jpg
http://www.electronicoscaldas.com/15...or-2n2222a.jpg

and it has it's emitter pin to the -right- if I place it on the board.

These pictures add up with your story Rizal. If you switched a "metal" 2N2222 to a "plastic" one (like in the pictures) the emitter pins changed places. It doesn't change the fact that my fet is wrong tough. I have to decide if I'll try to turn the transistor right away or wait until the new FET arrive and change that one first. Patience is a virtue, but wow do my fingers itch now when I noticed this...

[6666]

The 2222 transistor unfortunately comes in many different configurations and they must be tested to check which one you have.

[Koala]

The 2222 transistor unfortunately comes in many different configurations and they must be tested to check which one you have.

Yep I have fallen for that one. In the plastic type there is a 2N2222 and PN2222 which share the same pinout but P2N2222 is opposite. There is at least one website that has the pinout wrong which is where I when wrong. From then onwards I pull the original data sheet.

See in the photo the OP has used a metal can type which I believe has only one pinout????

[Rizal]

Yeah.. in my country, we have a lot of substandard and imitation electronic component from Chinna and sometimes it's different from stated in datasheet. Then analogue multimeter and skill to manually identified transistor legs is the best solution... .

[Detectojer]

I have the same problem as Barleg but I don't get the beep when I turn it on. I do have the irf9640 and I checked the 2n2222 and that is in correct. I noticed that I have a large voltage drop on the battery and the irf9640 gets hot. It will drop from 12 volts to 1.5 volts. if I take the coil off then it is fine. As I said before I don't get any sound at all so I will put a headphone jack on and see if that helps. Any help would be greatly appreciated.

[Rizal]

My recents transistor is MPS2222A with position of collector and emmitter is opposite compare to printed on PCB... Detectojer, let me know your voltage reading at pin no 6 of 5534?

[sinclairuser]

i'm starting to wonder if there is a problem with the latest boards, or a bad batch of components, similar problems on the last 4 built is suspect to me.
especially when the barracuda had had i high success rate lately, what's changed?.

[Rizal]

IMHO, i think the baracuda PCB is nothing wrong and it is proven less problem to construct... maybe problem come from the component or method of soldering the component. Previously i had built 2 unit of hammerhead and the same symptoms, mosfet overheat (smokes)... until i found that oversolder ( i mean take a long time to solder every component) also can damage the component (especially transistor).... just my 2 cents..