Fisher 1265X

[Funfinder]

don't know if i understand you right but if your fisher disc 2 switch doesn't work this is simple - i have a fisher 1266x:

switch 1 (no pushing needed, default) is connected to poti 1 (left) and if switch is pushed it connects to poti 2 (right).

first open the detector and look if the inside cables at the switch are not broken off, i had this issue already by too much open-closing-bending the cables etc.

next check where the connection of poti2 leads to the board.

in principle that 2 disc is just a simple "switch between 2 variable resistors" solution and very simple to repair or substitute with something similar:

If poti has 20 Ohm you have allmetal, if poti is at 20kOhm you have silver or vice versa.

but it was a nice solution searching at higher all metal sensitivity and switching to stronger disc level if something was found. this also works as: manual notch-filter.

[nalag46]

Fisher 1265x

Hi Funfinder,
Thanks for your comments. Unfortunately, things are not always as clear cut as they seem. This is not a detector which has suddenly developed a fault, rather a unit I bought in a total non working order because someone had messed it up no end.
I have rebuilt it by replacing all pots, sensitivity switch, mode switch and even the push button battery test switch. Not to mention three ICs and two transistors plus complete rewiring of all leads, the battery terminals and even the control box (needing repair for cracks).
I now have a good working detector, everything works as it should (I have been using Fishers and other makes for over 30 years so I know a thing or two about detectors) so everything works except the second Notch Disc 2. Your 1266x is more or less identical and the mode switch in these models is nothing more than a mechanical way to switch between the 3 modes available. The triggering of the switch from the center off position to either way, only grounds an available voltage at the terminals which in turn, open or close a "logic" switch or switches, which in turn operate the adecuate Disc. circuitry. These logic switches are encapsulated in IC packages and these are the modules which turn on the different phases of operation as required by the front panel controls.
Replacing a broken or "noisy" variable pontentiometer is the easiest task one could wish for, but if any of the logic switches are not functioning properly, no rewiring of the pot leads or any amount of rotating will make any difference to get it working.
My problem then is, I have also checked all the logic states and they are all working according to the Fisher 1265x circuit schematic but my Disc 2 mode does not "come on" when switched in so I am missing something here which so far I have failed to see and this is why I put my "plight" on the Forum, as I know there is always someone out there who might have worked or come across similar problem and possibly pass on a technical comment.
Tony

[Funfinder]

OK, now I understand - you did alot work but the way to get "disc 2" is absolutly easy:

Your disc1 poti is working, right?

If yes, you have already different discriminations depending if you switch it to 1 or 10.

What you need to do now is finding out which poti-wire gets affected (leads more ore less electricity) by turning the disc 1 knob. Cut this wire, add a switch to the disc 2 potis same wire and everything should be fine.

additional explanation:
The chip on the pcb you mentioned creates a different discrimintation depending how much electricty comes from the poti. if you can switch the input of this wire between poti1 and 2 you will have different discrimination. If done this you can set poti1 to 3 and poti2 to 7 and if you find something at usual position (poti1) you can press the switch to the already set poti2 and check if it's still a good signal.

You need no extra disc2 chip on board, it's completly overfluous and if its broken forget about it.

[Qiaozhi]

That's actually a good observation. If you look at the DISC part of the schematic below, you will notice the two DISC pots are selectable by analog switches.

When you sselect DISC 2, what is the result? Does the detector just stop working altogether, or does DISC 1 continue to work? If the latter is true, then presumably the analog switches are not doing their job properly. You should be able to locate the problem by a process of elimination.

[nalag46]

FISHER 1265X METAL DETECTOR

Yes, that is exactly what is happening. When I switch Disc. 2, Disc 1 continues to work in that position, therefore, it would appear the logic switch (IC303 pins 3, 5 and 4 would not be working as it should and so, I replaced the IC but the problem is still there?????????

[nalag46]

FISHER 1265X METAL DETECTOR

OK, now I understand - you did alot work but the way to get "disc 2" is absolutly easy:

Your disc1 poti is working, right?

If yes, you have already different discriminations depending if you switch it to 1 or 10.

What you need to do now is finding out which poti-wire gets affected (leads more ore less electricity) by turning the disc 1 knob. Cut this wire, add a switch to the disc 2 potis same wire and everything should be fine.

additional explanation:
The chip on the pcb you mentioned creates a different discrimintation depending how much electricty comes from the poti. if you can switch the input of this wire between poti1 and 2 you will have different discrimination. If done this you can set poti1 to 3 and poti2 to 7 and if you find something at usual position (poti1) you can press the switch to the already set poti2 and check if it's still a good signal.

You need no extra disc2 chip on board, it's completly overfluous and if its broken forget about it.

Hello Funfinder,
Thank you for your comments above. I can see what you mean when you say one discriminator switched betwen two variable pots. might do the same job. However, I am still trying to work out why the two analogue switches from the IC are not doing the job they are supposed to? I am using a process of elimination but all I have come up with so far is that the Mode Switch in centre position which is the default mode for Disc 1, is working well. When you ground the switch to the Static Mode (pin 13 of IC U303) the voltage at this pin is 0 of course and the Static Mode comes on ok. When that is selected, pins 5 and 6 (Disc 1 Select) are also 0 and pin 9 goes high to select Disc 2 (pin12). That is the logic except that on Disc Select 2, I get the Static Mode, or the same as on the other side of the switch. Like I said previously, I have replaced Ic U303 but the problem is still there.
The two disc. pots are 10k ohm wired up in parallel, therefore the total resitance is less than 5k on both of them. The voltages present at the center tags on both is the same at about 4v. and rotating them only varies this voltage by a max. of l/2 volt. and I know they are working correctly. You are saying to identify which potentiometer is not working properly or gets affected, then to cut the wire/s and add a switch, but where is this switch supposed to go?
Anyway, I still think the fault is a switching fault and I need to investigate further into the whole of the Mode Switching circuit that brings in IC U401 and the other cmos switch IC 402.

[Qiaozhi]

Are the voltages on pins 5 and 12 of U303 changing when you switch between DISC1 and DISC2?

[nalag46]

FISHER 1265X METAL DETECTOR

Hi Qiaozhi,
As explained earlier, in switch default position (center) disc 1 select pins 5/6 are high = 8v. and pin 12 = 0v. so Disc 1 works fine.
Pressing the switch to Static, pins 5/6 are grounded and pin 12 goes high and the Static mode is fine too. But because this same logic (voltages) is present when switching over to Disc 2, I get the Static mode on that side of the switch too instead of activitating the Disc 2 select.
Removing the Disc 1 connection to pot center tag cancels all variable discrimination with switch in Disc 1 or 2 position.

[Funfinder]

nalag46,
the 1266x has a 3 way switch: pull: pinpoint (static), no action: disc1 & push back: disc2

the schematic shows only 1 IC but the DISC input (poti) isn't exactly duplicated.

the simplest way for you is just leave that faulty switch as it is (ignoring not working
DISC2) and add an additional switch so you can select between poti1 and 2 directly.

the way you can see it on my little drawing above.

there's just one discrimination circuit on board and it works either via poti1 or poti2.
just take care that if the signal uses poti1 the second is switched off and vice versa
but most manual switches are constructed to work for such requirements anyway.

btw. here you can find my Fisher 1266x noise reduction mod thread:
http://www.geotech1.com/forums/showthread.php?t=16453
It's really a big improvement if you can adjust those electrosmog sensitive old
Fishers to the best possible background noise <--> signal treshhold level ratio.
Otherwise even the best signal could get swallowed by snaps, crackles & pops.

[nalag46]

FISHER 1265X METAL DETECTOR

nalag46,
the 1266x has a 3 way switch: pull: pinpoint (static), no action: disc1 & push back: disc2

the schematic shows only 1 IC but the DISC input (poti) isn't exactly duplicated.

the simplest way for you is just leave that faulty switch as it is (ignoring not working
DISC2) and add an additional switch so you can select between poti1 and 2 directly.

the way you can see it on my little drawing above.

there's just one discrimination circuit on board and it works either via poti1 or poti2.
just take care that if the signal uses poti1 the second is switched off and vice versa
but most manual switches are constructed to work for such requirements anyway.

btw. here you can find my Fisher 1266x noise reduction mod thread:
http://www.geotech1.com/forums/showthread.php?t=16453
It's really a big improvement if you can adjust those electrosmog sensitive old
Fishers to the best possible background noise <--> signal treshhold level ratio.
Otherwise even the best signal could get swallowed by snaps, crackles & pops.

Hi Funfinder,
I have found the reason for my Disc 2 problem and now everything is working 100%.
I thank you for your advise etc. but I don't need now to bypass the switching IC and I am very relieved to have found the cause in the end (I always do, but sometimes it takes longer than other even when the matter can be so simple??)
Anyway, just so that everyone interested knows, I bought this detector in a sorry state of affairs (completely dead and badly damaged front panel pots, switches, phone socket, broken mode switch, knobs, everything, and not to mention the terrible condition of the connecting cables inside the box).
As I explained in my last one or two posts, my new mode switch was working fine selecting Disc 1 (center position) and Static (to one side of the 3 way switch) but would not select Disc 2 on the other side. The IC responsible for this selection is UC303 and looking at the diagram, Disc 2 Select should only be on (high) when pins 5/6 (Disc Select 1) are grounded by the switch, but it was coming on as well when in the Static mode (grounding of pin 13) so I replaced the IC but did not change anything.
When I reconnected all the loose and other wrongly soldered wires to all the new fitted components, I found I had all the wires except for the two that go to the switch (not counting the ground wire). I thought it to be stranged as no cable were missing from the main connector block, so I soldered to new wires to the switch from the underside of the IC (one to pin 13 and the other to 5/6) and after much checking and searching, I found that the two "missing" wires had been soldered to the battery charger socket right across the bulb (l501). As I had no need for using this socket and since the detector was functioning ok, I never paid any attention to that wiring and assumed to be ok even though there were 5 wires coming out of it, and there you have the reason for having a "high" pin 9/12 (Disc 2) on both sides of the switch.
And the moral of the story should be (yes, I keep hearing it all the time) never take anything for granted, specially after someone else had left their dirty prints everywhere.
I am quite interested in your noise reduction filter and would try that soon.
The Fisher 1266X is no much different from the 1265X, in fact, all components used in the latter are the same but the 1265X has two circuit boards, it is a better layout and much easier to work on as there is more space between components. In the 1266X, Fisher crammed everything on one board and when you need to replace an IC etc, it can be a messy job.
Thanks to everyone who got involved in the thread and passed their comments.
Keep it coming, you are all doing a great job.
Tony

[Funfinder]

Hi nalag46 I'm glad you did it, good job and it's fantastic that persons like you repair those old but in earlier times "state of the art"-detectors so they became "still alive legends" - perhaps not yet but in 50 years very interresting!

Good luck if you also try to mod your 1265x - maybe you'll discover new improvements.

And find some great treasures with your "recovered from overkill" detector, too!