Has Anyone Ever Seen Or Had This Metal Detector Before?

[keith777]

Hi again guys.

has anyone any information at all on this metal detector please. " Type C400 MK111 "
also, would you say that in picture 6 the component pointed to is damaged. it has some bulging to the top, but no leaking that i can see.
thanks in advance guys.....

[keith777]

here is the last two photos as i was only allowed to upload ten at a time.....

[Carl-NC]

Never heard of that one but, yes, a bulging cap indicates it's gone bad.

[keith777]

thanks Carl.

am i wright in saying it is a PI machine.
i don't have any C type size batteries to test it out, but i have ordered some AA to C size battery adapter case holders to use. picture 12 shows the inside of ware the coil fitting is wired up. there is three wires soldered on the back. one braid wire and two red wires. i have a PI coil laying about that has just two cables coming from it. would that be OK to use. or would this fitting need a specific type of coil that uses three wires.

thanks.

[ivconic]

No it is probably not PI.
Most probably it is BFO.
Middle '70s or so.

[Carl-NC]

I agree, it's most likely a BFO or something similar. I would hook up a 1mH coil (or inductor) to it and see what happens. If you get a sinusoidal oscillation then it will be a matter of trying different inductances until you get something within the tuning range.

[keith777]

thanks guys.
this is the damaged cap in the photo. i assume it means that it is a 100uf 16v when replacing it. does it mater about the diameter sizes of the replacement cap. or as long as the values are the same is that ok.
as for "I would hook up a 1mH coil (or inductor) to it and see what happens. If you get a sinusoidal oscillation then it will be a matter of trying different inductances until you get something within the tuning range" i am not sure what that means. or is.

thanks again guys....

[Carl-NC]

Replace with a 100uF, 16V or more, physical size doesn't matter.

A true BFO is designed to work at a particular frequency which is determined by the inductance, and won't work unless you find the correct inductance so that it will tune. This will likely be difficult unless you can find the reference oscillator and measure its frequency. If it is instead an energy theft design, then those will work across a wide range of frequencies.

[keith777]

thanks again Carl........
would i be better of changing both the caps just to be on the safe side.
so would you suggest that i am probably better of just replacing the damaged part and selling it on. hopefully to someone in the know how......thanks.

[Qiaozhi]

I've never seen this detector before either.
It must be quite old, as Stanford-in-the-vale is now in Oxfordshire, not Berkshire. The change happened in 1972.

[keith777]

well, i have swapped out the two caps with new ones now. i am getting an audio tone now through the headphones and the needle moves on the meter. without a coil i can not do any further testing.....

[kt315]

BFO has two gens, one exemplary, with fixed non-changed frequency, second with search coil. so you need to measure the frequency to find up a coil L via calculation .
output signal is iteration of the two, in audible range - maybe approx 800Hz-2kHz.

[kt315]

[keith777]

thanks for the info Kt, but i think i will just sell it on and let someone with the know how take the rest of the challenge on.....

[Yourownfree]

I personally have not seen this diagram before but it is a simple BFO metal detector using CMOS chips. CD4022(H2 in diagram), CD4011(M1) and CD4013 (M2). The diagram is hard to make out but the chips are K561TH2,K561TM2, K561TM1, K561TM2. The CD 4000 series came out early 70's and the Russian part numbers most likely early 80's. CMOS was almost everywhere you looked when you wanted to build something. Thy were the cats meow. Does the crystal (ZQ1) have a frequency stamp on it? if you have that we can redraw the circuit where we can read it and make sense. I didn't study too much but definitely a BFO. The fixed frequency could be being divided by the first chip and also by the flip flops. figure that out then you can figure out what the search coil inductance should be and the variable cap marked with an asterisk. The whole thing looks like somebody was tying to improve the BFO (good luck) somewhat back then. Looks to me like somebody had someCD4000's on their bench and wanted to get rid of them and maybe all they had was certain size crystal which may have been too high in frequency so they divided it down or just used the internal blocks of the chip to use the inverters. notice how they utilized them in the audio area.