help needed with old detector

[dbanner]

[keith777]

Hi again guys.

i have decided to give the detector a knock on the head now.
i really appreciate all the help that i have been given with trying to sort the machine out. my biggest appreciation goes out to dabanner how has given up so much of his time to help me out. as i have said before. what a great forum this is and what a great bunch of guys this forum has on it.

[dbanner]

yes, good to change out old caps.

[Polymer]

I wouldn't trust those old electrolyte capacitors anymore, after 40 or so years & unknown storage conditions. They might have gone funny inside.
Put in new ones if you can. Shouldn't be too much work.

[dbanner]

try changing the 30k for a 10K

[keith777]

Hi again dabanner.

i tried that adjusting capacitor and all i got was a very, very tiny amount of extra sensitivity.

[dbanner]

you are right. Those tracks look terrible in post #110, especially the one running along the bottom of board.

[nickel_n]

Looking at pic two on post #110 I think your PCB tracks, may be broken /corroded and measure Hi resistance.
I would get some methylated spirit and a small paint brass and give them a good clean. I would do that to all PCB’s.

Then I will just measure the resistance of the tracks make sure that is NOT hi or broken

I think will make a difference.

Give it a try.

[dbanner]

Something tells me a 10K resistor is more likely appropriate. But i not sure. If you are 100 percent sure about 30K then thats fine.

[keith777]

Hi again dabanner.
thanks very much for replying back again.

i haven't tried the adjusting capacitor yet as i have just seen your post. the resistor replacement that i put in was a 30k

thanks in advance.......

[dbanner]

What value resistor do you currently have in the small board(the one you replaced)?

[dbanner]

Something I just remembered. The resistor you replaced on small board now becomes critical since you assumed you replaced it with the correct value resistor. A wrong value would affect the sensitivity of detector.

[dbanner]

Hello there, sorry for taking a while to reply. That is good news. At least it,s working, sort of. Sounds like your null of search coil is a bit off. There is an adjusting capacitor i think on the main board. Mark the original position with a marker pen so you'll know where to set it back to its original position, then try adjusting it for better sensitivity(null) of search coil. Other than that, it may be your threshold potentiometer(control) is bad. Could be other things as well, but you can try these things first.

[keith777]

Hi again dabanner. sorry to bother you so soon.

i decided to buy a new replacement part for the circuit board. i put it in tonight and was surprised when i checked it against some metal. this is what is happening.
i am picking up my fridge door at about 2" 1/2 inch. when you turn the volume potentiometer whilst the search head is picking up the metal. the volume/sound doesn't kick in until you are just about at full turn. basically it's not a gradual volume, it pops on at full turn.

least i am picking up metal now but,,,,,why the lack of depth as well.

[keith777]

let me know when your ready to have another bash at it.
thanks a lot mate for all the help that you have already given me. it was so much appreciated.

keith