help needed with old detector

[keith777]

there wasn't any wires loose when i first opened it. then one of the speaker wires came off. the battery terminals are the same type fitting as the 9v ones but they are way to big to say on. plus only one would go on at a time.

here is the test results for the transistor. see pic.

[dbanner]

When you first opened up the detector housing, did you find any wires loose?

[dbanner]

You are working with some assumptions, namely:
1- You have correct batteries installed
How can you be sure its not a pp9 battery(9 volts)? Seems like it would fit.
2- Your speaker is good.
Did you check the speaker?
3- Your search coil is good.
we can check this later
4- Replacement resistor is correct vaIue
I cannot find a manual for questor but the fieldmaster 33, which is the next model up, uses a 9 volt battery.

[dbanner]

O.K. Remove base leg of 2N4403(middle leg as shown in picture)from circuit. This maybe a bit difficult, but I'm sure you can do it. Then do same transistor test as before. The black probe goes on middle leg, then test each remaining legs with red probe. Remember to set up meter for transistor testas before.

[dbanner]

This transistor is good! Now i want you to check the 2N4403 on mainboard. you will have to remove the base leg of 2N4403. Give me a few minutes to draw picture to illustrate. I'll be back with you soon.

[keith777]

Hi again dbanner.

i desoldered one leg of the diode and if i have done the tests correctly. this is what i got on the meter. see pic bellow.

[dbanner]

I think the 30K resistor should actually be a 10K. I also suspect this transistor is faulty. Lift up(desolder) one leg of this diode(shown in picture by blue arrow) then repeat the test I indicated in thread #51. Remember to lift up leg of diode(remove from circuit). keep black probe as shown on picture and then switch other red probe to other leg of transistor as shown. what are the results.(the first test is like thread #51, the second test is like thread #51 but with red probe to other leg of transistor)

[keith777]

Hi again dbanner.

i am getting a voltage reading now on testing. the cheap replacement 1.5v holder that i bought is cr*p. the minus spring doesn't connect properly to the solder part. i have sorted it for now but i will have to get a better one.
here is the last two voltage test reading that i get........ see pics.

[dbanner]

Check voltage between these points with detector on. By the way, where is the on switch located?

[keith777]

i have checked every wire on the buzzer sound test and all sounded off.

[keith777]

Hi again dbanner.

i get no voltage at all doing that test.

[dbanner]

Something seems odd about the way the power supply(batteries) are hooked up on this circuit. I think i will attempt to draw(reverse engineer) schematic of circuit using the pictures and diagram posted. This way I'll know for sure what's going on. It will take a little time though.

[dbanner]

These results are what i would expect. So far everything appears to be ok on small board. Now one more test, please set up multimeter as shown and turn on detector, measure voltage between points as shown on picture.

[keith777]

Hi again dbanner.

for the tests i got.

first test 482
second 437
third 451

[dbanner]

Yes, but the reading you got looks O.K. Ideally you should desolder the base leg of transistor(the leg in the centre) in order to isolate it from rest of circuit so it can be checked. I'll be back a little later, have to do something right now. Meanwhile, do same test but on the other transistor as shown in pic. Then test each diode as shown in pic. Remember the color indicates which probe goes where.