Fisher 1266 PART 2

[Qiaozhi]

No, it is not voltage issue here, at my handmade. I desoldered all the supply parts out from pcb. Than made another on small pcb, providing regulated +4.5 and -4.5 . Handmade is acting the same!? In nonmotion mode it is working excellent (same as original) but in Disc mode detection is weak and phase looks out of range to much. On iron acting like detecting hotrock and no detection or very poor detection on some coloured items. Turning GEB trimmer i can achieve some so so detection on masive colured item with famous Fisher 1265 "bang" in audio, but than it is not detecting other types of coloured metals. For example if it detects masive bronze washer than it is not detecting 2cm coin or Al plate...etc...
Back to nonmotion mode it is detecting nicely all the metals!?
More and more i am sure that there is some mistake on pcb. Need good concentration and to recheck pcb's again and again. I am kinda "used" to these pcb's so it is hard for me to spot the mistake. Need to take few days rest from it...
All other thing seems to be ok, power drain is approx. 40mA, voltages are as noted....in nonmotion mode audio is pretty ok while in Disc mode it is a bit silent..?
Huuuh!

P.S.
Like i assumed; fully simmetrical supply is not needed here. I alredy measured (long time ago) +6.35 and -3.89V on one accurate and good 1265 which worked excellent... So.... kind a returned back to the place where i started!?? Right? Sheeeesh!

Hi Ivconic,

Rather than just blindly checking the PCB, may I suggest that you check whereabouts on the RX waveform that the DISC channel is sampling. This should help to point you in the right direction. It might also be worth checking the GEB channel as well.
Please let us know what you find.

[ivconic]

Schematic of simple supply i made for this check...

[ivconic]

Hi Ivconic,

Rather than just blindly checking the PCB, may I suggest that you check whereabouts on the RX waveform that the DISC channel is sampling. This should help to point you in the right direction. It might also be worth checking the GEB channel as well.
Please let us know what you find.

I might do that. But more and more i am sure there must be some mistake in pcb draw. It is not just "blindly" checking, i collected many references during last couple of years, especially servicing several 1265/66's so far. This is just not right - handmade behavior. Something is mistaken HUGE here.
Anyway..thanks for advice...problem is i dont have scope here by me...
Scope is "conservated&preserved" and packed somewhere in the house and it is painful for me now to find it and bring back to workshop...dont ask me why!
(it is cold winter, i dont have heating in workshop, so i packed and removed all the expensive and sensitive tools from there....scattered those across all the warm and dry places in da house! yup!)

[KingJL]

I might do that. But more and more i am sure there must be some mistake in pcb draw. It is not just "blindly" checking, i collected many references during last couple of years, especially servicing several 1265/66's so far. This is just not right - handmade behavior. Something is mistaken HUGE here.
Anyway..thanks for advice...problem is i dont have scope here by me...

Even with a scope, it is extremely difficult to get any real comparisons of the signals in the motion channel. Reason... They are motion channels! The HPF's have a corner frequency of ~7Hz. I have found the only way to check the motion channels, is to have a target on a string hung from the ceiling (about 7ft pendulum) swing over the coil. Then I can consistently observe the changes occurring in both of the motion channels.

As for the power supply (the new design in a previous post), does it work?
Regards,
J. L. King

[ivconic]

Yes, like i said; connected and providing +4.5 and -4.5 vots... 1265 drains approx. 40mA...everything cool...nothing bad with supply.
Considering this...even when i discover the problem..i am thinking to adopt this supply and integrate it in 1265 instead original...cose damn fat is not possible to obtain here in local shops...

[KingJL]

Yes, like i said; connected and providing +4.5 and -4.5 vots... 1265 drains approx. 40mA...everything cool...nothing bad with supply.

Cool

Considering this...even when i discover the problem..

Oh yes the problem. Well there are some misleading things on the schematics. You need to verify these.
1: The dual momentary pushbutton battery test switch; The normal connections (not in battery test mode) are one side open (connected to pins 10 & 13 of the 16 pin header and connected to the 22K) and the other side closed(connected to pins 6 & 11 of the header and across the MPSU51 ec). Since you mentioned weak battery test audio, I would check this. Also in that section as well as the, the grounds on the schematic are are chassis ground, (-4V) not analog ground. There are quite a few areas where one can confuse these. You need to look at them carefully.

2: I seem to recall that some sections of the quad IC.s have been mislabeled. Although, I believe that the pin numbers were correct. When I was troubleshooting mine, I kept a device data sheet handy to crosscheck the schematic

Wish you luck!
Regards,
J. L. King

[ivconic]

No...wait!? You are confusing me now..
At battery check should both switches (both parts of momentary switch) be closed - connected 6 and 11 as well as 10 and 13. MPSU51 is current limiter for MPSA13 and in normal mode (working modes) 6 and 11 are not closed, only in batt. check mode..right?
Also you missunderstood me, i never wired battery test here at my handmade. I was saying that i gained weak audio in Disc mode while in nonmotion mode audio is almost descent, louder than in Disc mode...yet i have feeling it is not loud as on original 1265...strange!?
About pin numbers...hmmm...i never doubted in posted schematic...hmmm...i must check that again !!
Thank for hints!

[KingJL]

No...wait!? You are confusing me now..
At battery check should both switches (both parts of momentary switch) be closed - connected 6 and 11 as well as 10 and 13. MPSU51 is current limiter for MPSA13 and in normal mode (working modes) 6 and 11 are not closed, only in batt. check mode..right?

Wrong! That confused me previosly also. In fact I wasn't sure until I traced out my 1265. In normal operating mode, the switch is closed across the mpsu51, The mpsu51 is only operational in battery test mode. That surprised me also! But it is true. Go figure!!!
Regards,
J. L. King

[ivconic]

Indeed???! Wow! That solved audio level issue, i am sure! Despite several units i've been inspected so far, never occured to me to perform detailed checks and tracings on those switches and pots..really!? Usually i respected same old routine as on any other detector. Now i see drawback of getting to much in "routine" and not using brain much in simillar cases..
First thing tomorrow for me is to check that. Now is -15 degrees in my workshop !!!Also is to late and i am tired...
Ok... one problem less...many thanks to you and your hints!
After that i will continue to search for other problem...
Thank you very much and regards!
See you tomorrow here!

[KingJL]

Now is -15 degrees in my workshop !!!

Now, That is depressing!!!

[ivconic]

Am i enthusiast or what!?
But.... i am not that enthusiast...to tell you the truth!
Cheers!

[ApBerg]

1280

Hello Friends.

Some time ago I made in Sprint Layout a pcb from the famous 1280, it is some brother from the 1265-1266 ( I think) . Had some doubts if I had to post it….. maybe it can be useful to somebody. There is made one working proto , however there was not a good coil that could be used …so how good it is working ??

So….. there can be errors in it ! !

Regards.

Ap

[ivconic]

Nice work!

Reffering MPSU51..yes KingJL is right, makes difference in audio strenght when E nad C are shorted - louder audio.
About other...i havent find mistake yet, i spend whole day trying to locate problem, no success.
I guess must be something arround U301-U303. Disc pots are not making any changes there....huuh!
What really confusing me is certain "discrimination" even in nonmotion mode (static mode)???
Iron pliers and Al plate are detected well but masive brass washer is not??
Other hand in Disc mode all three items are detected now...with no differences?
There are some obscurities in schematic... i am not really shure if i connected some spots properly there..
Is there any other accurate schematic of 1265/66 available?

[KingJL]

There are some obscurities in schematic... i am not really shure if i connected some spots properly there..
Is there any other accurate schematic of 1265/66 available?

The most accurate that I have found (or been given) are 1266 Rev E and 1265 Rev F. I have included these in the attached zip.

Also included in the zip is a hand drawn schematic of the components external to the board taht are connected by the 16 DIP header. Be careful and cross check the pin connections with the Fisher schematics as I think I remember a mistake.

Regards,
J. L. King

[porkluvr]

1265

KingJL - the 1266 you posted is terrific quality (thanks!) but the 1265 in your zip is only 36kb.

There is a very nice copy of the 1265 on page 2 of this thread, posted by Eugene52 (it's named scan0001.GIF, 314kb). I see no need to repost here.

http://www.geotech1.com/forums/showt...t=14422&page=2