Fisher 1265X

[nalag46]

Have just purchased one of these in a "butchered" state.
All components on both boards are clean and there aren't any signs of having been/removed replaced. However, all the controls have been rewired wrong.
Some of them are broken and the leads from ribbon connector are hanging loose or no connected at all. Even the battery connectors are missing so needless to say it is
in a non working condition.
I really need a clear circuit diagram to be able to sort this mess out and I know
some of you have these. Can anyone please be kind enough to let me have a copy?
I will be most obliged.
Ton

[Qiaozhi]

Have just purchased one of these in a "butchered" state.
All components on both boards are clean and there aren't any signs of having been/removed replaced. However, all the controls have been rewired wrong.
Some of them are broken and the leads from ribbon connector are hanging loose or no connected at all. Even the battery connectors are missing so needless to say it is
in a non working condition.
I really need a clear circuit diagram to be able to sort this mess out and I know
some of you have these. Can anyone please be kind enough to let me have a copy?
I will be most obliged.
Ton

Try this -> http://www.geotech1.com/forums/showp...3&postcount=62

[nalag46]

FISHER 1265X METAL DETECTOR

Have just purchased one of these in a "butchered" state.
All components on both boards are clean and there aren't any signs of having been/removed replaced. However, all the controls have been rewired wrong.
Some of them are broken and the leads from ribbon connector are hanging loose or no connected at all. Even the battery connectors are missing so needless to say it is
in a non working condition.
I really need a clear circuit diagram to be able to sort this mess out and I know
some of you have these. Can anyone please be kind enough to let me have a copy?
I will be most obliged.
Ton

Cheers Qiaozhi. Much appreciated.

[nalag46]

FISHER 1265X METAL DETECTOR

Hi there,
I live in UK and urgently need to obtain the miniature push/pull potentiometer as used in the Fisher 1265/6 for the Sensitivity adjust.
I believe the model no. is VA388 - 100k.
Can anyone point me to the right place to purchase this item please?
Best wishes
Ton

[nalag46]

FISHER 1265X METAL DETECTOR

Me again,
Also found that Transistor FET VP104n3 needs replacing but cannot find it in any component catalogue.
Has anyone have a data sheet of this transistor or know of good reliable equivalent that may be used in lieu please?
Much appreciated.
Ton

[amtech2005]

Me again,
Also found that Transistor FET VP104n3 needs replacing but cannot find it in any component catalogue.
Has anyone have a data sheet of this transistor or know of good reliable equivalent that may be used in lieu please?
Much appreciated.
Ton

Hello . It is actually a discontinued VPO104n3 P-channel FET . So NTE326 should work . Look at the pdf data folder and also a nice clear schematic from this forum already !! Other opinions are welcome .

Best Regards...........Eugene

[nalag46]

FISHER 1265X METAL DETECTOR

Hi Eugene,
Thank you very much for the info.
I think the NTE326 or other equivalents should be ok to source now that
I have the data.
I am very grateful.
Regards
Tony

[nalag46]

FISHER 1265X METAL DETECTOR

Hi again,
I have found a replacement FET for the VP104ne used on this detector. However, it does not work and think I might have connected it wrong?
From the pin out data I have obtained, the NTE326 shows a sequence of S-D-G for the pins; Source going to the positive rail of the circuit. The VP104, as fitted, has Source to + but the centre pin is the Gate, the Drain being the outer pin as opposed to above.
Am I right or wrong?
As I could only get one NTE326 (difficult to obtain here) I have found that the 2n5480 fet has very similar specifications so has anyone tried it and does it work?

[nalag46]

Hi again,
I have found a replacement FET for the VP104ne used on this detector. However, it does not work and think I might have connected it wrong?
From the pin out data I have obtained, the NTE326 shows a sequence of S-D-G for the pins; Source going to the positive rail of the circuit. The VP104, as fitted, has Source to + but the centre pin is the Gate, the Drain being the outer pin as opposed to above.
Am I right or wrong?
As I could only get one NTE326 (difficult to obtain here) I have found that the 2n5480 fet has very similar specifications so has anyone tried it and does it work?

Oops! made a mistake, I meant 2N5460 FET transistor 40v. 10ma.

[porkluvr]

Oops! made a mistake, I meant 2N5460 FET transistor 40v. 10ma.

Bad news:
The VP104N3 is enhancemode mode MOSFET. NTE326 and 2N5460 are depletion mode JFET. These are different function devices and are not interchangeable.

Depletion mode devices are normally ON with zero volts input and get turned OFF with a voltage lower than the source pin (using absolute numbers). Enhancement mode devices are normally OFF with zero volts input and get turned on with a voltage higher than the source pin (using absolute numbers), more like a BJT transistor.

I say "absolute numbers" because when describing P-channel operation, negative numbers are normally used. That can get ambiguous and confusing.

VP0106
VP0109
TP0606

These are all P-channel enhancement devices and should all work to one degree or another but I am not prepared to say which one would work best. Leaded devices (through hole) are getting harder and harder to find with the advent of SMT.

Supertex, NXP, and Vishay are good sources for information (and parts, depending on your location).

Don't guess. Check the pinout (and function) on a manufacturer's data sheet before installing a replacement.

[nalag46]

FISHER 1265X METAL DETECTOR

Interesting info.
I have owned and repaired Fishers now for over 20 years and never had any problem when it came to replace transistors of any type using closed available replacements.
The Fisher 1260 on which the 1265 platform is based on, uses a simple 8v. Voltage Regulator that works extremely well and could never understand why go for this elaborate array of npn and pnp transistorised circuit to just provide a stabalised 8v. rail.
However, the VP0106 and similar from same maker are just impossible to obtain and some alternative had to be found.
The NTE326 that I connected -wrongly- by taking for granted the pins layout would be the same as the VPO, had been damaged but I am sure it would have worked well, was substituted by the cheaper and easily obtainable 2N5460 and I now have a full working circuit with all voltages stages as they should be.
All I need now is the also obsolete push/pull sw with 100k variable pot used in this ancient design and the detector will be up and running in no time. I am waiting for a contact to find out whether there is a possiblity of a "scrapped" one from an old spare machine but failing that, I have decided to simply use a miniature 100K pot and a separate two way toggle switch (if space can be found on the front panel) to activate normal and enhanced sensitivity.
If parts are not easily available or as in this case impossible to obtain, there is always a second best alternative and this is mine.

[amtech2005]

Yes it is an enhancement mode mosfet . VP1008L . Same as used on 1280x [see parts list] . Here is the correct data sheet pdf below . I am still looking for correct substitution . Always a work in progress until it is fixed .

Best Regards........Eugene

[porkluvr]

I used to think that this 1265 power supply was sucky because LTspice showed poor load regulation. That was my mistake.

I've corrected my errors and repaired the simulation circuit and have to say it looks great. No joke.

You can have near perfectly symmetrical, well regulated 4V outputs even as the battery drops to 8V. After that the rails droop symmetrically.

Of course my version is only a simulation, but it's good. Maybe that's why Fisher went to the trouble of developing such a complicated circuit, and not just because they had extra parts lying around... big boss walks in and says, "we have extra parts lying around. Somebody needs to use them".

BUT
if you don't use the prescribed enhancement MOSFET for Q506 (or a reasonable substitute) and instead use a JFET, although you might have power it will not be the same. For that matter you could use a jumper for Q506 to save trouble and $$$. That's my two cents.


edit: In all honesty I did make some minor adjustments in the power circuit before I got it working 'freakin' good. I did it through empirical means; trial and error. I am hardly qualified to modify the circuit because I do not understand how it works.

I removed the comparator pull-up resistor ( R508 ) and installed another capacitor alongside C501, connected to +4V. I don't know if these mods would be so very great in real life, but they look good on my PC.

edit 2: That's not all. I also relabeled +4V 'ground', and ground became -4V (which wouldn't make it work any better but it does makes it easier for me to detect asymmetry, or operational anomalies).

[nalag46]

FISHER 1265X METAL DETECTOR

Thanks Eugene,
I have a working circuit and will play with it until I can get better substitute DMOS Fet transistors. Not an easy task here in UK and sourcing them from the States is a non starter as no supplier ships these in small quantities and shipping cost make them prohibited.
On a different topic; have a faulty CZ70Pro. Problem seems to be around the audio stages but this is a different beast altogether and a clear schematic is a must. Apart from most of the circuitry being surfaced mounted, I notice it uses several of these Cmos enhanced transistors both N and P channel, so I may be looking for the same susbtitute all over again.
Has anyone have a schematic for this model. It would be greatly appreciated.
Best regards,
Tony

[amtech2005]

Hello . They may of had problems on the 1265x , could that be why they used IRFD9213 for q-506 on the newer 1266x machine ?

Regards.........Eugene