help needed with old detector

[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?

[keith777]

all read a number.

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

[dbanner]

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

[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.

[keith777]

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

[dbanner]

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

[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.

[keith777]

200k test i got 11.2
on turning the potentiometer the reading on a full turn went from 03.9 to 11.2

[dbanner]

Switch down to the 200K scale on multimeter and do the same measurement again. Then place one of the probes on centre lug of potentiometer and other probe on the outer lug where wire was removed. Do this while turning knob. you should see the reading on meter changing as you turn knob.

[keith777]

sorry forgot the .

.011

[dbanner]

Was that .011 or 011?

[keith777]

Hi again dbanner.


the test result i got for the potentiometer test was. 011

[dbanner]

Yes the four black round ones. Here is the datasheet for those 2N3638 transistors. Have a look, the centre leg is the base leg. You may not have to remove the base leg, just do the tests with them soldered in and post results. You should be able to determine which ones the centre leg by looking at the diagram on datasheet. Its the one in the middle of the triangle. But before you get to that, please check the resistance of this potentiometer(refer to picture). you need to remove the wire shown on picture. Set up meter as shown. Place probes as shown on picture. Then post the results before checking other transistors.

[keith777]

which is the other transistors. is them the black round thinks. if so how do i know which is the centre leg.

[dbanner]

This transistor is good. So we have so far eliminated these components that we have checked as the possible cause of problem. Now you can check the remaining transistors on mainboard. You do same test as the last one, remove base(centre)leg and place black probe on centre leg, red probe to each of the other two legs, they should all read similar results as last test. I know its a lot of testing, but at least you will know that all your transistors are good or maybe we will find a bad one.