Fisher 1265 Revival

[KingJL]

As I have stated before in another thread, I have aquired a 1265X that is somewhat distressed. It had been swallowed/drowned in brackish water by hurricane Ike.

Initial checkout revealed all potentiometers (Disc1, Disc2, Volume, and Sensitivity) need replaced. Speaker, mode switch, battery check switch, coil connector, headphone jack check out serviceable. PCBs look pristine.

Oops, someone has soldered a wire to pin 4 (-4V, chassis gnd) of the PCB edge connector. The wire has a paper clip soldered to the end. To what end, I do not know.

Removed all controls from front panel, separated PCBs. Hooked up 8 cell AA rechargeable battery pack to pins 7 & 8 of ribbon cable socket. WE HAVE LIFE!! Well, sort of. Voltages are acceptable (-3.96V & +3.89V), so power supply/voltage regulator working. Without coil connected, the TX oscilator output is 81kHz and unstable. With coil connected, TX signal looks terrible. Only abot 3Vpp; very unstable looks like 4kHz & 5kHz intermodulation.

Troubleshooting with coil disconnected reveals same signal on pins 1 & 2 of U101 (LM339). With coil connected pins 1 & 2 look like outputs are ored together. Removed and replaced the LM339. Fired back up. Oops, no output; Positive rail at 5.8V, negative rail at -3.98V. Inspect my solder job and notice excessive flux on board and LM339 pins. Off to the sink; scrub the board gently with small brush, soap, water. Rinse and let dry.

Fire back up. Violla! We have a stable oscilator oscillating at ~77kHz. Oops after about 1 minute, oscillations become erratic; Positive rail is 4.5V and increasing. Re-inspect and see that a couple places are still damp. Let sit and dry for 2 hrs.

Fire it back up. It works again! Rails are -3.96 & +3.89. This time everything remains steady for more than 5 min. Decide to hook up coil. Fire it back up. Tx signal looks super! Nice clean sinusoidal 12Vpp signal.

Now to check out Rx. The demodulator gates look good. Output of pre-amp is about 100mvpp and is very near to in phase with TX (coil in air). Iron taken near the coil causes the phase to remain the same and signal increases. A quarter brought near the coil changes phase, decreases signal level; As it is brought nearer it shifts phase past 180 degrees and then increases in level. It appears that Fisher coils are not nulled in signal level (there is a 15 Meg resistor connection between TX and RX coil in the coil head) at the input to the preamp. I suspect that the coils are nulled without the 15M connected. The resitive channel demodulator output is null when no target present. The Disc channel demodulator output is negative with no target present.

The static channel, resistive channel, and 1st stage of Disc channel all check out.

Cannot check out remaining circuitry until I get some replacement potentiometers.

THE BEAST IS COMING TO LIFE!!!!

To be continued...

[ivconic]

What a coincidence!? Few days ago i got one 1265 on service. In working condition but "depth" is so low. Bairly detect 1e coin at 15cm. Disc works good, audio good, all the pots&switches are good...coil and cable in excellent shape so as jacks.
So i opened it and tried to adjust trimmers inside.No results...
Voltages are proper, TX is ok...at RX i get right signal and shape??
What the heck is this?
So i started to suspect some of capacitors. Damn, lot of job to check them all.... I dont have proper voltages and levels on paper to compare with this device....so i could easilly locate bad component.
I can gain some more sense with thresh trimmer but than it starts to be much sensitive on hot rock and ferrite rod.
What is different here than at TGS is quite different Disc stage. Very interesting to compare with TGS.
In case you have some measurements (test points), voltages and oscillograms from accurate 1265 than please post those here, would help me much!
Best regards!

[KingJL]

What a coincidence!? Few days ago i got one 1265 on service. In working condition but "depth" is so low. Bairly detect 1e coin at 15cm. ..... In case you have some measurements (test points), voltages and oscillograms from accurate 1265 than please post those here, would help me much!
Best regards!

I will take some pictures in the next few days and post. Also when I get my parts so that I can put it back together, I will document and take pics. I think I am going to add external adjustable GB.

What is the level of your TX at the collector of Q102? What coil are you using, the 8.5"? This thing seems pretty responsive (from the changes that I see on scope) but will not know for sure until I get the potentiometers in. It would be nice if someone had the alignment procedures for the static threshold, disc bias, and threshold.

Regards,
J. L. King

[Merc]

Fisher 1265

Oops, someone has soldered a wire to pin 4 (-4V, chassis gnd) of the PCB edge connector. The wire has a paper clip soldered to the end. To what end, I do not know.

I have a Fisher 1212X with the same paper clip on a wire arrangement. It connects the PCB ground to the foil lined paper along the inside surface of the control box. It's shielding. They used the paper clip because it's a little hard to solder to aluminum foil.

Merc

[KingJL]

I have a Fisher 1212X with the same paper clip on a wire arrangement. It connects the PCB ground to the foil lined paper along the inside surface of the control box. It's shielding. They used the paper clip because it's a little hard to solder to aluminum foil.

Merc

Thanks. That is good info!
Regards,
J. L. King

[ivconic]

I will take some pictures in the next few days and post. Also when I get my parts so that I can put it back together, I will document and take pics. I think I am going to add external adjustable GB.

What is the level of your TX at the collector of Q102? What coil are you using, the 8.5"? This thing seems pretty responsive (from the changes that I see on scope) but will not know for sure until I get the potentiometers in. It would be nice if someone had the alignment procedures for the static threshold, disc bias, and threshold.

Regards,
J. L. King

Now when you mentioned it...; sheeesh!!! I didnt expected such low power there!!?!?! Bairly over 2vpp !?!?
Is it normal?
I am using approx. 20cm diamm. coil (closed enclosure) with it.
I checked transistors and resistors there..seems to be ok. But wait!
Somebody previously changed transistors...not 2N5087 anymore? Now those are BC307 !?!?
Ha,ha,ha...you helped me with your question! I think i solved my problem...

[Qiaozhi]

As I have stated before in another thread, I have aquired a 1265X that is somewhat distressed. It had been swallowed/drowned in brackish water by hurricane Ike.

Initial checkout revealed all potentiometers (Disc1, Disc2, Volume, and Sensitivity) need replaced. Speaker, mode switch, battery check switch, coil connector, headphone jack check out serviceable. PCBs look pristine.

Oops, someone has soldered a wire to pin 4 (-4V, chassis gnd) of the PCB edge connector. The wire has a paper clip soldered to the end. To what end, I do not know.

Removed all controls from front panel, separated PCBs. Hooked up 8 cell AA rechargeable battery pack to pins 7 & 8 of ribbon cable socket. WE HAVE LIFE!! Well, sort of. Voltages are acceptable (-3.96V & +3.89V), so power supply/voltage regulator working. Without coil connected, the TX oscilator output is 81kHz and unstable. With coil connected, TX signal looks terrible. Only abot 3Vpp; very unstable looks like 4kHz & 5kHz intermodulation.

Troubleshooting with coil disconnected reveals same signal on pins 1 & 2 of U101 (LM339). With coil connected pins 1 & 2 look like outputs are ored together. Removed and replaced the LM339. Fired back up. Oops, no output; Positive rail at 5.8V, negative rail at -3.98V. Inspect my solder job and notice excessive flux on board and LM339 pins. Off to the sink; scrub the board gently with small brush, soap, water. Rinse and let dry.

Fire back up. Violla! We have a stable oscilator oscillating at ~77kHz. Oops after about 1 minute, oscillations become erratic; Positive rail is 4.5V and increasing. Re-inspect and see that a couple places are still damp. Let sit and dry for 2 hrs.

Fire it back up. It works again! Rails are -3.96 & +3.89. This time everything remains steady for more than 5 min. Decide to hook up coil. Fire it back up. Tx signal looks super! Nice clean sinusoidal 12Vpp signal.

Now to check out Rx. The demodulator gates look good. Output of pre-amp is about 100mvpp and is very near to in phase with TX (coil in air). Iron taken near the coil causes the phase to remain the same and signal increases. A quarter brought near the coil changes phase, decreases signal level; As it is brought nearer it shifts phase past 180 degrees and then increases in level. It appears that Fisher coils are not nulled in signal level (there is a 15 Meg resistor connection between TX and RX coil in the coil head) at the input to the preamp. I suspect that the coils are nulled without the 15M connected. The resitive channel demodulator output is null when no target present. The Disc channel demodulator output is negative with no target present.

The static channel, resistive channel, and 1st stage of Disc channel all check out.

Cannot check out remaining circuitry until I get some replacement potentiometers.

THE BEAST IS COMING TO LIFE!!!!

To be continued...

Here is the setup procedure for the 1265-X:

Front panel controls:

• Disc 1 and 2 to "0".
• Sensitivity knob pulled out and turned fully clockwise.
• Turn VOL on and fully clockwise.
• Press battery test button to insure good battery voltage. A loud audio signal indicates adequate batteries.

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.
• There may be a trimmer for the frequency on some models - set it anywhere.
• 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.

Frequency Adjustment

• If the audio at this point is rhythmic and pulsating, adjust frequency pot to minimize the sound. Some models do not have this adjustment.

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

• Pull the trigger switch into the static mode position, and while holding the trigger switch, 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 trigger switch and listen to make sure that the threshold sound level is about the same. If it's not, pull the trigger and readjust the Static Threshold again.
• Set the panel sensitivity control to the 12 0'clock position (straight up). There should be no audio in the motion mode. Now pull the trigger switch. 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 12 o'clock position with the knob pulled out. Hold a ferrite pot core a considerable distance away from the front surface of the loop. Pull the trigger 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 trigger 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.

The 1265-X is now adjusted.

[KingJL]

Here is the setup procedure for the 1265-X:....

Qiaozhi,
That is EXACTLY what was needed. Thank you ever so much.

BTW: Any suggestions where I might obtain a ferrite pot for testing?

Regards,
J. L. King

[KingJL]

Now when you mentioned it...; sheeesh!!! I didnt expected such low power there!!?!?! Bairly over 2vpp !?!?
Is it normal?
I am using approx. 20cm diamm. coil (closed enclosure) with it.
I checked transistors and resistors there..seems to be ok. But wait!
Somebody previously changed transistors...not 2N5087 anymore? Now those are BC307 !?!?
Ha,ha,ha...you helped me with your question! I think i solved my problem...

I think you are in the right area of your problem. I went back and measured Q102 Collector voltage accuratly. I have 15.2 Vpp!

Attached is a zip containing pictures of TX signal:
I have included 2 pictures of Q102 Collector signal: 2V/div-50usec/div & 2V/div-100usec/div.

I have also included picture of Q102 Base signal: 0.2V/div-50usec/div

Regards,
J. L. King

[Qiaozhi]

Qiaozhi,
That is EXACTLY what was needed. Thank you ever so much.

BTW: Any suggestions where I might obtain a ferrite pot for testing?

Regards,
J. L. King

I use a ferrite tuning slug from a tuned coil, similar to one of these:
Just remove the core and throw the rest away.

[KingJL]

1265 sensitivity control

I cannot find a direct replacement for the 1265 sensitivity control. This appears to be a Honeywell, conductive plastic, series 388 100K w/pnp swtch, M7 bushing, .125" shaft. I cannot find it from any of my known suppliers. How many other Fisher models use this type of sensitivity control?

Rather than ruin my original 1265 control box and faceplate trying to mount a substitute, I am currently going to mount everything in a generic plastc box enclosure and use a substitute for the sensitivity control.

If anyone has ideas concerning finding a replacement sensitivity control, please let me know.

Regards,
J. L. King

[KingJL]

Disc1 & Disc2 potentiometer check

Ivconic,
Could I impose on you to check the Disc1 and Disk2 potentiometers. Mine have bad spots on them, but I want to verify their taper. Mine act like they are logritmic (audio) taper (at 12 o'clock position I measure ~1k pins 1 & 2, ~4K pins 2 & 3). Also mine measure 5K from end to end, not 10K as specified in schematic.

Thanks in advance.

Regards,
J. L. King

[ivconic]

Ivconic,
Could I impose on you to check the Disc1 and Disk2 potentiometers. Mine have bad spots on them, but I want to verify their taper. Mine act like they are logritmic (audio) taper (at 12 o'clock position I measure ~1k pins 1 & 2, ~4K pins 2 & 3). Also mine measure 5K from end to end, not 10K as specified in schematic.

Thanks in advance.

Regards,
J. L. King

Of course you can!
Give me half an hour to do that. Have to go to my workshop and do that.
Be here in ...let's say one hour..

[ivconic]

So... Disc1 and Disc2 pots at this 1265x are the same; 8.9k linear...!?
I guess those were 10K and lost some of preferences during time and various objective working conditions like moisture etc...
But those are identical on measurements ; 8.9k ...??? Strange?

Oh yes; i had to unsolder wires cose when wired up those gave values 3.8K each... end to end.

Reffering my problem; i havent solved it yet. 2N5087 are put on places and still TX amp is bairly over 2vpp!? 1ohm resistor in serie with coil is ok. Everything else is ok..??? Could it be coil? I dont have right now another to check...damn!
What bugs me mostly is shape of signal - saw??? The heck!
Cheers!


P.S.
Sorry i am late. Took me more...had some troubles..

[KingJL]

So... Disc1 and Disc2 pots at this 1265x are the same; 8.9k linear...!?
I guess those were 10K and lost some of preferences during time and various objective working conditions like moisture etc...
But those are identical on measurements ; 8.9k ...??? Strange?

Thanks. That clears up that little discrepancy. It is strange though, both my Disc1 and Disc2 measure 5K and both show logrithmic taper. I will replace with 10K linear.
Thanks again.

Reffering my problem; i havent solved it yet. 2N5087 are put on places and still TX amp is bairly over 2vpp!? 1ohm resistor in serie with coil is ok. Everything else is ok..??? Could it be coil? I dont have right now another to check...damn!
What bugs me mostly is shape of signal - saw??? The heck!
Cheers!

In some of my modeling I have encountered that saw shape. It could be coil. It is showing integration of square wave. What was the frequency of the saw waveform? I just went over to LTspice and fed a 1265 Tx circuit with 6.5KHz squarewave. Got a 2Vpp 6.5KHz saw waveform! 8KHz gives extremely sharp saw waveform of 1.5Vpp. I think your TX is wrong frequency or coil is for a 2KHz 12xx.

Dissconnect coil and check the feed to the 4025 (actually check LM339 U101 pin 2. It should be ~77KHz square wave. If it is not, check out U101 (and be sure that you are not getting feedthrough of another section of U101; I was getting feedthrough from pin2 to pin 1 and vise-versa). Also check that the output of U102 (4025) is divide by 16 (4.8KHz).

P.S.
Sorry i am late. Took me more...had some troubles..

I thought you did extremely well. Especially since you went out of your way to do this for me.

Thanks again,
J. L. King