Technology Forum

http://youtu.be/HTUVNwADXvk

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.



Edited 1 time(s). Last edit at 08/19/2014 11:59AM by draco.

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.



Edited 3 time(s). Last edit at 08/19/2014 12:22PM by draco.

There is a small audio board under the metal plate and is located at the back of the detector. Did anyone try to adjust the pots on that board? One pot sets the lower tone or better called the basic audio tone when no signal is present, and it sounds like there is no lower tone.

Reg

Thanks Reg, the detector sounds like, a long time after being unused. Nobody has touched the knobs.

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

Draco,

If you have any contact cleaner, spray the volume control with it. Ttry to get the cleaner into the front part of the control. The back part is the switch.

Reg

Thanks Reg, I'll buy a contact cleaner. I'll keep you informed.

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

Hi Reg, sorry for the delay, the electronics store was closed for vacation.
Follow the problem, I cleaned the potentiometer contacts and then with clean dry air.

Tank you

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

Hi Draco,

Did cleaning the control help?

Reg

No, nothing has changed.

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

Do you have a digital voltmeter? If so or have a friend who has one and knows how to use it, you might check the voltage on the audio board (top board) where it says IN and GND. This is the location where the signal comes in from the main board.

Disconnect the coil and measure the voltage at the two solder points mentioned. They are located on the right side of the audio board if you are looking from the front of the detector. There will probably be a capacitor soldered to the two locations. The voltage should be 0V or extremely close to it.

The friend who I was hoping would work on your detector says no, he doesn't want to tackle it. So, we will try to fix it ourselves long distance.

Reg

Thanks Reg.
The measured voltage where noted in the photo is approximately -4 volts. (Minus 4 volts)

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

Hi draco,

The -4v is about what I figured. It is supposed to be 0V. So, now we need to figure out what is bad and to do that, you will have to lift up the audio board so you can check a couple of outputs on the last amplifier on the main board on the side the audio pigtail comes in on. Check the last OpAmp and see if it is a LT1112. What is wrong is most likely associated with this opamp.

Before doing that, check the voltage again on the audio board but adjust the gain pot from min to max. The gain pot could also be called the range pot. I think you changed that in your video and it didn't seem to make much difference. So, if this is the case, you will have to measure the outputs of the opamp chip.

On the LT1112, pins 1 and 7 are the outputs. You will need to check both and find out if one or both of the outputs are wrong. Pin 1 can cause pin 7 to read bad if pin 1 is too negative of a voltage. Both should be 0V.

With luck, we will be able to change the opamp and solve the problem. If not, then maybe the offset voltage correction circuit is not functioning correctly. If that is the case, I may be able to fix that also.

Reg

Hi Reg, CN is a 1114 LT.
It is this ?.

Thank you.

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.

I remeasured the voltage potentiometer minimum to maximum, the voltage is the same - 4 volts aprox.

GND + pin 1, - 4.38 volts
GND + pin 7, 0.05 volts

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Used: Tesoro Euro Sabre, Minelab Excalibur, Goldscan 5.



Edited 1 time(s). Last edit at 09/04/2014 12:01PM by draco.

The IC is the 8 pin IC right at the edge of the board. It is the LT1112 and is right under the headphone cable. Do you see the LT1112? If so, double check the pins 1 and 7 again. It should be pin 7 that is -4V.

Actually, measure each pin of the LT1112 and let me know what each reads.

Hopefully, from the measurements I will be able to determine if the IC is bad or some other component is causing the problem.

If you have another dual opamp like a TLO72 or TLO62 and the LT is in a socket, you might try carefully remove the LT1112 and install a different dual opamp. Make sure to get pin 1 in the right place.

Reg



Edited 1 time(s). Last edit at 09/04/2014 12:42PM by Reg.