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A few days ago I have a rare oportunity to repair and seting this obsolete detector. In order to adjust it after changing a few IC's I used the same method as I do it before with 1266. Tips to adjust 1266 were posted here on Geotech and they were good so I decide to do it with 1235 too. I try and was supprised with result. It works perfect as with 1266. Here are my tips for adjusting 1235 X according to 1266.
Here is the setup procedure for the 1235-X:
-Front panel controls:
Turn SENS knob fully anticlockwise to insure good battery voltage. A loud audio signal indicates adequate batteries.
DISC power ON and at "0".
SENS knob turned fully clockwise.
FREQ knob could be set anywhere.
-Internal trimmers:
Set Ground Comp to any position - doesn't matter.
Set Static Threshold fully anticlockwise.
Set Disc Bias fully anticlockwise.
Set Threshold fully clockwise.
Set Audio in the middle to provide loud sound in the speaker.
No audio should be heard at this point.
Alignment:
-Disc Bias Adjustment:
Turn Disc Bias pot slowly clockwise until you get loud audio, then stop. The sound should be loud and almost continuous, with an occasional click or breakup in the sound.
-Threshold Adjusment:
Slowly turn the threshold pot anticlockwise until audio almost disappears. A slight but distinct audio should still be heard, and it will be irregular or "chattery", having a sound somewhat like electrical interference.
-Static Threshold Adjustment:
Press the PINPOINT button switch into the static mode position, and while pressing the PINPOINTbutton , adjust the Static Threshold pot clockwise until you get a slight audio tone of the same intensity that you had in the motion mode. The sound will be smoother than in the motion mode. Now release the button and listen to make sure that the threshold sound level is about the same. If it's not, press the button and readjust the Static Threshold again.
Set the panel sensitivity control SENS to the ,,5’’ position (straight up). There should be no audio in the motion mode. Now press the PINPOINT button. There should be no audio in the static mode either. If there is sound in either mode, go back the Threshold Adjustment (above) and start again.
-Ground Comp Adjustment:
The objective of the Ground Comp adjustment is to set it so that when ferrite is brought toward the loop, with the instrument in the static mode, there will be a weak response to the ferrite. Note: The Ground Comp pot is a multi-turn pot which may have anywhere from 10 to 22 turns from end to end. You may not be able to feel if you have reached the end.
Set the panel sensitivity control to the SENS,,5’’ position straight up. Hold a ferrite pot core a considerable distance away from the front surface of the loop. Press the PINPOINT button to get the static mode. Move the pot core toward the center of the loop. If there is a distinct increase in audio tone at a distance greater than 3 inches (8cm) from the surface of the loop, release the PINPOINT and turn the Ground Comp pot clockwise. If there is no audio response, or if it does not exhibit a distinct increase in audio until the pot core is within 2 inches (5cm) of the surface of the loop, turn the Ground Comp pot anticlockwise. Repeat the procedure until you reach a setting where the audio starts to increase when the pot core approaches within 2 to 3 inches of the surface of the loop.
-Audio level adjustment:
Set Audio pot at wanted level that is good enough to hear sound in the speaker clearly.
The 1235-X is now adjusted.
I hope this tips will be appropriate for some who need them.
Here is the setup procedure for the 1235-X:
-Front panel controls:
Turn SENS knob fully anticlockwise to insure good battery voltage. A loud audio signal indicates adequate batteries.
DISC power ON and at "0".
SENS knob turned fully clockwise.
FREQ knob could be set anywhere.
-Internal trimmers:
Set Ground Comp to any position - doesn't matter.
Set Static Threshold fully anticlockwise.
Set Disc Bias fully anticlockwise.
Set Threshold fully clockwise.
Set Audio in the middle to provide loud sound in the speaker.
No audio should be heard at this point.
Alignment:
-Disc Bias Adjustment:
Turn Disc Bias pot slowly clockwise until you get loud audio, then stop. The sound should be loud and almost continuous, with an occasional click or breakup in the sound.
-Threshold Adjusment:
Slowly turn the threshold pot anticlockwise until audio almost disappears. A slight but distinct audio should still be heard, and it will be irregular or "chattery", having a sound somewhat like electrical interference.
-Static Threshold Adjustment:
Press the PINPOINT button switch into the static mode position, and while pressing the PINPOINTbutton , adjust the Static Threshold pot clockwise until you get a slight audio tone of the same intensity that you had in the motion mode. The sound will be smoother than in the motion mode. Now release the button and listen to make sure that the threshold sound level is about the same. If it's not, press the button and readjust the Static Threshold again.
Set the panel sensitivity control SENS to the ,,5’’ position (straight up). There should be no audio in the motion mode. Now press the PINPOINT button. There should be no audio in the static mode either. If there is sound in either mode, go back the Threshold Adjustment (above) and start again.
-Ground Comp Adjustment:
The objective of the Ground Comp adjustment is to set it so that when ferrite is brought toward the loop, with the instrument in the static mode, there will be a weak response to the ferrite. Note: The Ground Comp pot is a multi-turn pot which may have anywhere from 10 to 22 turns from end to end. You may not be able to feel if you have reached the end.
Set the panel sensitivity control to the SENS,,5’’ position straight up. Hold a ferrite pot core a considerable distance away from the front surface of the loop. Press the PINPOINT button to get the static mode. Move the pot core toward the center of the loop. If there is a distinct increase in audio tone at a distance greater than 3 inches (8cm) from the surface of the loop, release the PINPOINT and turn the Ground Comp pot clockwise. If there is no audio response, or if it does not exhibit a distinct increase in audio until the pot core is within 2 inches (5cm) of the surface of the loop, turn the Ground Comp pot anticlockwise. Repeat the procedure until you reach a setting where the audio starts to increase when the pot core approaches within 2 to 3 inches of the surface of the loop.
-Audio level adjustment:
Set Audio pot at wanted level that is good enough to hear sound in the speaker clearly.
The 1235-X is now adjusted.
I hope this tips will be appropriate for some who need them.
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