help needed with old detector

[dbanner]

That's O.K. your potentiometer is working. By the way are there any numbers on the potentiometer you can make out? Well the remaining four black tranistors(2n363 will have to be checked.

[dbanner]

I don't know how that smiley face got in there. I never use them.

[keith777]

the potentiometer says on it. 10k then a little horse shoe image. LN RTC ABD4 CTS

[dbanner]

Thats good because you measured it at 11.2K so its within acceptable limits for its purpose. At least you know it isn't fried internally. Now I'm afraid you will have to check those for remaining transistors. Dont bother removing base leg, just check them as they are with the meter set up for transistor test and follow same procedure as you did with black transistor on small board. I posted the datasheet so you can identify the base leg. They all should test similar to one another as all are the same transistor 2n3638. If any of them shows a short(meter goes to zero like when checking a wire) then you.ve got a problem.

[dbanner]

Remember place black probe on base leg and touch other two legs one at a time with other probe. Take readings and post.

[keith777]

all read a number.

532/533
525/530
531/536
524/530

[dbanner]

These are all good transistors. So far everythings checks out good. Join these two terminals together on volume control using a small piece of wire and turn on detector. Wave a big piece of metal(like a pot) at search coil. Is there any sound at all?

[dbanner]

Also, while detector is on, adjust treshold control(the 10K), is there any sound?

[keith777]

no sound with either test.
what i can hear is though. if you leave the volume control fully up. then switch on the machine, you hear a click sound come from the speaker.

[dbanner]

O.K. You have to take some voltage measurements while detector is on. At this point I am suspicious of coil, but I wil be back with a drawing of where i want you to measure.

[keith777]

thanks mate.
i really hope you don't mind all this hassle.

[keith777]

i for got to say that the speaker defiantly works. i de-soldered the wires and hooked them up to a audio cable to a mp3 player. it played music just fine.

[keith777]

Hi again dabanner.

i have managed to get a hold of another metal detector made by the same company as the one we are testing. it has the same type coil and the main board is setup in the same way, just some of the components are a bit different. guess what. this one uses a regular 9V battery.
this one works....

i wonder if someone changed the battery terminals on the faulty one for some strange reason?

[dbanner]

WOW! That's really nice. It's in fine condition too. My internet connection just started working again. This detector is a bit more advanced than the other one. Check the coil wires and see if they are the same as the other one. If they are, then you can compare measurements to determine if the other coil on the non working detector checks out good. Does this detector have a small circuit board like the other one did?

[dbanner]

AS for the battery terminals, I don't think anyone changed them since the battery holder is definitely not for typical 9V battery but rather some round, circular battery. The 30K on small board still bothers me. I think it should be 10K(brown, black, orange). I see a lot of 10K resistors on other detector circuit board but i haven't seen any 30K resistor used anywhere else on any board on both detectors.