help needed with old detector

[Davor]

The larger battery holder looks exactly like a PX19 one

This detector is very odd.

[keith777]

here is some more pics..........

[Digger429]

One quick bit of reverse engineering later.

The burnt out resistor of unknown value is on the left.

Unfortunately without knowing exactly what the white wire is connected to, its not clear what the function of the resistor is, or what value it is supposed to be. It it was me, I'd just stick a 33k resistor in there and see what happens. Probably just a pull up biasing thing, value not critical.

https://i.imgur.com/S4UYcY4.jpg

Edit - white white goes to pin 3 of the larger board. I guess somebody else can reverse engineer all that.

[keith777]

i have just had a quick look at the wires in the detector.

[Davor]

One quick bit of reverse engineering later.

The burnt out resistor of unknown value is on the left.

Unfortunately without knowing exactly what the white wire is connected to, its not clear what the function of the resistor is, or what value it is supposed to be. It it was me, I'd just stick a 33k resistor in there and see what happens. Probably just a pull up biasing thing, value not critical.

https://i.imgur.com/S4UYcY4.jpg

Edit - white white goes to pin 3 of the larger board. I guess somebody else can reverse engineer all that.

The first transistor is a PNP, and 3 ohm resistor is actually 30 ohm. It is a 100x amplifier.

[6666]

K777 if you cannot work out the value for the damaged resistor from the colour bands if you have a look around the pcb for other R's with ether exactly the same combination of colour bands OR if other R's have the same individual colour bands somewhere on the body as the damaged R, by measuring those other R's you may be able to work out the colour scheme if all the paint has aged the same, for example RED paint can start to look orange or brown but if you have several R's with the same colour you can measure them and see what colour makes what part of that value, get it ?

[keith777]

i have now put a replacement resister on the small board.
there is something that i noticed whilst i was doing it. i remembered when i first took the detector apart and not long after i was first looking around inside, a yellow wire had came off and i thought it looked like it came off were i had put it on the headphone jack. what a dummy i am. it could of never went were i put it. it was never going to give off any sound were it is. (both speaker wires on the same headphone jack pin) assuming it does go on the headphone jack. which pin has it came off.

[homefire]

There seems to be a bit of wire protruding from the pin with the Orange wire on opposite side. The Head phone jack opens the contacts to the speaker when a plug is jacked in and deverts the signal to the Head phones. You need to see what pins are doing that. I think if you use a Ohm meter between the Gray wire and the Orange wire you will find that's the case when a plug is jacked in.

[keith777]

homefire thanks for that.
the yellow wire had came off were the orange wire was soldered on. the orange wire to me some how looked different to the yellow wire. so what i done was i un-soldered the orange wire and strait away i could see that it was a solid wire. so i rubbed the soldering iron around on the headphone pin and bingo. there was loads of small loose wires floating about.

here is a photo of the inside of the machine now. it looks the part but that's all. i did hear a couple of crackle sounds coming from the speaker at the point when i was pushing the main board back in to it's slot.

i am at the stage now of giving up on it. i wish i new more about electronics but sadly i don't. i would of loved to of seen this wounded soldier up and fighting again.

i never thought of showing a pic of the coil. here it is just in-case any of you guys are interested.

[homefire]

You give in too easy. It would just take you some time. I think if you move ether the Gray or the Yellow wire to the other side of the Jack the speaker would work.

[keith777]

hi again homefire.
i did try that but i did dot get any sound either. there must be something else going on. i have been testing it using 4.5v as another member suggested it was a px19 battery that it used because of the battery terminal sizes. so i was using a AAA flashlight battery holder for the power source. see pics.

[homefire]

Did you use both batteries ? The Odd Ball 4.5 and the 1.5 ? Can you tell me the numbers on this transistor ? I think it's the audio output transistor. I seen a ZENER Diode on the small board that could be a voltage regulator set up.

[keith777]

yes i had both connected up.

[dbanner]

From the picture of the coil indicates a T/R(Transmit/Recieve) detector and not a BFO(beat frequency oscillator) type detector. One can clearly see the recieve coil(small circle at centre). This type coil is known as omega coil design. I see five wires plus a ground wire going to the coil, I suspect there might be additional circuitry in the coil housing but i could be wrong. Assuming you have the correct power supply connected, you should check all transistors and diodes on the main board and the small board. Post some more pics of the wiring between the various boards and controls etc. so i can see more clearly whats going on. If there is no additional circuitry in the coil housing then this will be a straightforward fix.

[homefire]

He only has a limited electronics back ground. This one is going to be challenging.

I think that 2N4403 is your Audio Driver. Photo's of it and all it's connected to would be good. We may be able to determine if it is or is not infact producing a tone even with the speaker / headphone wires botched.

You said you have a VOM ?