This is a continuation of my previous post regarding 4 Metal detectors which I have purchased that need some attention to get them working.
This post will be about the Micronta 3001 Metal Detector which is more of a toy in the world of metal detecting. The unit was manufactured by Radio Shack a division of Tandy. Sadly both Tandy and Maplins are no longer in business in the UK, this is very sad as there really are no shops like it anymore.
I am of the belief we will shops like this come back as I do think there will be a big shift to repairing old equipment, we really do need to save broken and faulty equipment where possible instead of the throw away and buy new mentality.
Here you can see the case with the knobs removed to allow the PCB to be taken out.
This unit just beeps when it is switched on so there is some kind of fault in the circuitry. I did manage to find a schematic of the unit which is shown in the next picture.
I really don't understand this schematic and need to further my knowledge of electronic circuits. I removed the PCB board and checked for obvious signs of component failure but I cannot see any.
Here is the underside of the PCB, I checked the Pots and they were all OK.
Here is the component side of the PCB, relatively few components. The Electrolytic capacitors all look good and I measured the coil resistances and they checked out as per the schematic.
Unfortunately I don't have an oscilloscope and that is something I am hoping to add to my collection of instruments, the diagram shows some expected wave forms and it would have been good to have verified these.
So my only option is to do the very brutal method of component swap outs until I find the faulty part. I have ordered replacement Caps and Transistors and will start with these when I get them.
I do have a Transistor checker but will wait till I get the parts and I will do a test and swap out of each component. My initial thought was that Q5 was faulty as that would turn on the sound circuit, but of course also it could just be doing its job and the fault lies in the previous part of the circuit which detects a metal object.
I have watched some videos on metal detectors and how they work and have a better understanding of that but not enough to help with the fault finding here, I need to to a bit more research into the various types of circuits.
If anyone has any tips or tricks for fault finding these types of circuits I would be most interested to hear them.
