help needed with old detector

[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.

[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 ?

[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.

[keith777]

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

[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]

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

[Davor]

The larger battery holder looks exactly like a PX19 one

This detector is very odd.

[kt315]

i did measure even a resistor that was fully burnt. trick is simple. delete a paint from whole resistor. accurately you must do. gently.
measure one whole part to edge of burn spot and another whole part - you get know approx the value. some additional info will give you also unburnt color belts.

[homefire]

As bad as that resistor looks my bet is it's still measurable. Only the Leads are toasted.

[keith777]

i forgot that there was a black clip holder next to the single 1.5v battery holder that i took off. i assume that this is the holder for the other battery.
the gap between the clip over connector measures 8mm and a regular 9v one measures 6mm.
i will take some more photos of the PCB etc in the morning.

[Davor]

There is a 10V electrolyte capacitor on a main board, so I'd say it is safe to exclude anything beyond 9V. There are several possibilities, namely 4.5, 6, (7.5) and 9V. Considering the condition of the rig, powering it up should be attempted with a 50ohm resistor in series with a power supply. And start from 4.5 V. Just in case.

It should be possible to figure out the circuitry of the piggyback board the rusted resistor is on. It could be an amplifier or a voltage regulator. More photos are needed, and especially front and back side of a piggyback board. Whatever is written on the transistors and diodes is useful too. Also the wires - it is not possible from the photos so far to say which one goes where.

[Polymer]

I have just looked some more, being egged on by my childhood memories of oddball batteries.

This modern version might very well fit:

https://www.rapidonline.com/eveready-9v-pp9-battery-18-0249

nostalgia batteries:

[Carl-NC]

Looks either brown-black-brown (100) or brown-black-orange (10k).

The battery snaps are more likely for an old obsolete battery like the PX19.

[Polymer]

Hi Keith777,

Yes, that's the color code you need for a 30k resistor.

I find it hard to distinguish brown from orange in the photo.
Here are the combinations I can come up with for that resistor though:
brown black brown 100 ohms
brown black orange 10k ohms
orange black orange 30k ohms
orange black brown 300 ohms

As to the battery, since it seems vintage (like 60's or 70's) there are quite a few and
many oddball ones from that era with the type or connectors you have shown.

For example this (it won't be this one though):


Hopefully the battery you need might be 9 volts, but its maybe 6v or something in between.

How big is the space in the battery compartment? That might give us a clue more.

[keith777]

hi davor.
i checked the PCB traces. they were a bit powdery in some places but it rubbed off easy enough.
as for checking the value with a meter before soldering it in. i am lucky that i know how to do simple voltage checks with one.