help needed with old detector

[keith777]

Hi again dabanner.
sorry for the late reply. i was keep refreshing page 2 for a new post and not realizing there was a new page 3 added with your reply on. sorry about that.
anyways i tested that part you asked me to and i got a reading of. depending on which way i put the meter pins on which way. 467 and 540
should it matter which way round i put them?

[dbanner]

O.K. No problem. We'll go with 30K as replacement for now. Next I want you to check this transistor for me. Set up meter as shown and place probes as shown on picture. what does meter read?

[kt315]

KT is this any good for you.....

thank you. now you can draw a schematic

[keith777]

Hi dbanner.
i have done what you said and i can not get any kind of reading what so ever.

[dbanner]

looks like correct value resistor but just to be absolutely sure i would like you to measure the resistance of old resistor. Set up your multimeter as shown in picture then clean ends of old resistor with some abrasive thing and place multimeter probes on each end as shown in picture( any probe to any end, it doesnt matter). Read resistance on meter. What does it read?

[keith777]

Hi again dbanner.
i replaced the resistor with the one in the pic bellow. i sill have the toasted resistor. so i had a good look at it with a magnifier eye peace. plus looking at the photos i had taken of it before it fell apart. i think i got it right.
also thank you again very much for the help. what a great bunch of guys on here.

[dbanner]

Keith 777 thank you very much for your drawings. It's exactly what I needed. Tomorrow I will examine in more detail. I will show you how to test each transistor without having to remove them from circuit board. It actually very simple using the multimeter. And also the diodes. What value resistor did you use to replace the damaged one?
I am sure you will be able to fix this detector with a little help but we will have to take some measurements with the multimeter to see exactly which component
Has failed. It's late over here now.

[keith777]

KT is this any good for you.....

[keith777]

kt i haven't getting around to it yet. give me half an hour and i will take it out and take a photo for you......

[kt315]

ignore?

do i have to initialize your answer??? i need a pic of pcb back side.

[keith777]

O.K I need better pics of wiring in this area only.

i have done a drawing of the wiring on the inside. would this help you any better?

[keith777]

thanks guys. i really appreciate the help.

[dbanner]

Yes. This is multimeter. Testing wire for brakes is what i mean by "testing for continuity". Setup your meter as shown in pic.
The selector switch is set as shown, the black probe connected to COM as shown.

With multimeter setup like this, you are now ready to test for continuity or test diodes and transistors.

[kt315]

reconnect negative black probe on COM/MON socket.

[keith777]

We need pics of wires coming from coil cable attached to mainboard connector strip and better pics of all internal wiring. The idea is for us to be able to see specific wires and where they are connected so we can work out generally how this detector is put together. Then we will know where to look for the fault. If you know how to use a VOM to check for continuity then its easy to check each transistor and diode. There are five PNP transistors 2N3638A(the four black top ones on mainboard and one on smaller board), one 2N4403 PNP( the small one on mainboard) and another transistor on smaller board which i cant see the number on it, plus a few diodes. All these components are easy to check for integrity with a multimeter(VOM). Even you can do it without much any knowledge of electronics.
I think this metal detector is quite rare and worth fixing, but this is just my opinion.

this is the only multimeter that i have which i only know how to test voltage and testing wire for brakes.