Fisher 1266 PART 2

[KingJL]

Also i established one more thing; we spoked about MPSU51 and it's role there? So...listen me; i am 100% sure it MUST be involved in working modes at 1265. MUST! I remember that you found out it was shorted (with momentary switch in working mode) at your device, but i am ready to swear that it is mistake.Trust me. Than in batt.check mode it could be shorted. So if you found out it was shorted in working mode at your device than i can only presume that somebody else, previously modded that and made mistake.

I was under the same opinion as you. The first indication that this opinion might be wrong occurred when I happened to obtain (before I obtained my real 1265) the hand drawn schematic (included in my zip in previous post) of the external contols. In studying this hand drawn schematic, I just assummed this to be a major mistake. How could this be, it must be wrong, I assumed. Then i obtained my 1265, and low and behold, it was wired hust as the hand drawn schematic. I don't put a lot of faith in coincidences. It may be just a coincidence and be in fact wrong, but my 1265 works perfectly with great sounding audio.

How i know this? Simply, in working modes without MPSU51 we gonna get pretty "smutty" audio without distincive 1265 "bang" at clear detection.
But if you involve it in working mode, acting as current limitter it will smooth and limit current to MPSA13 and when incoming signal reach certain level it will release full current and MPSA13 will produce very nice and smooth "BANG" at clear detection.

Mine has distinctive bang with clear detection.

I realized this just few minutes ago experimenting with it.
And i am 100% SURE on this. Please do some experiments and test this, than let me know.

Thinking on this , it actually makes sense to use the MPSU51 in the battery check mode. As the battery discharges down to close to 8-9V, the MPSU51 current will decrease and give weaker audio, but with fully charged battery will limit current during battery check and keep from "blowing" ears and speaker.

Regards,
J. L. King

[ivconic]

Yes i am using factory coil 8". Few minutes ago i tested it with another coil (24/25cm for CZ3) and same thing i got, same problems.
About other things...i respected schematic 99.99% (maybe instead 40k i put 39k on 2 places and that is all).
One more thing bugs me now...; i choosed transformer among dozen simillar. It is modulation transformer. 1.1ohms at one side and 2x22ohms at other. Maybe this is the only cause of all problems?
Also i established one more thing; we spoked about MPSU51 and it's role there? So...listen me; i am 100% sure it MUST be involved in working modes at 1265. MUST! I remember that you found out it was shorted (with momentary switch in working mode) at your device, but i am ready to swear that it is mistake.Trust me. Than in batt.check mode it could be shorted. So if you found out it was shorted in working mode at your device than i can only presume that somebody else, previously modded that and made mistake.
How i know this? Simply, in working modes without MPSU51 we gonna get pretty "smutty" audio without distincive 1265 "bang" at clear detection.
But if you involve it in working mode, acting as current limitter it will smooth and limit current to MPSA13 and when incoming signal reach certain level it will release full current and MPSA13 will produce very nice and smooth "BANG" at clear detection.
I realized this just few minutes ago experimenting with it.
And i am 100% SURE on this. Please do some experiments and test this, than let me know.
About other of your notes...many thanks i will check them all..
Best regards!

[KingJL]

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??

ivconic,
Is you pre-amp (U201) circuitry exactly as in the 1265 schematic. The phase shift caused by R203 and C204 is fairly critical for the GEB circuit (C205 & R205) to be in working range with the factory coil (I seem to remember that you are using the Fisher factory coil). You need to have the R205/C204 combinations specified by the 1265 schematic (or for higher pre-amp gain, the combination specified in the 1266 scematic).

If you are not using the Fisher factory coil, then that brings on a whole other set of issues as it is not simply nulled to minimum signal to the pre-amp.
Regards,
J. L. King

[KingJL]

You are right! I will recheck some other areas later on today. I think there were others. They were minor errors if you were troubleshooting a 'factory' board, but could lead to problems if you were creating a board from the schematic.
Regards,
J. L. King

I have re-checked and can't seem to find the other errors that I thought I remembered. Oh well, memory isn't what it used to be!

Oh BTW, for maximum sensitivity, S403 is closed.(shaft pulled out on actual factory unit). Are you using the setup procedures given by Qiaozhi? To pre-set GEB, I used a scope at the junction of R223 & C210 and adjusted GEB for 0v to ever so slightly negative. Then followed Qiaozhi's procedures.

Regards,
J. L. King

[KingJL]

Maybe this could be the point of confuse;
it cleary says "9" but i think must be a "5" ? Right?
When i draw those pcbs's i connected this with 5. pin not 9.
Am i right? Or not?
To connect with pin 9. doesn't make any sense? Right?

You are right! I will recheck some other areas later on today. I think there were others. They were minor errors if you were troubleshooting a 'factory' board, but could lead to problems if you were creating a board from the schematic.
Regards,
J. L. King

[ivconic]

Maybe this could be the point of confuse;
it cleary says "9" but i think must be a "5" ? Right?
When i draw those pcbs's i connected this with 5. pin not 9.
Am i right? Or not?
To connect with pin 9. doesn't make any sense? Right?

[ivconic]

Thanks!
Those i compared...hmmm..i dont see anything suspicious.
Back to pcb checks again!?

[KingJL]

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

The original 1265 that I had was way too big to upload here (36Mb bmp file). I had converted it to a gif (it was still too big at 2Mb). Then I let Outlook change the file size to get down to a size that I could send. I guess it took out too much!

I re-converted the original 1265 bmp to a gif (with Photoshop). Changed number colors down to 8 (after all it is only BW), and got the size down to where it is comparable with the 1266 schematic. Now it will fit in zip without blowing the upload size limit.

This zip contains a higher resolution 1265 schematic!

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/showthread.php?t=14422&page=2

[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

[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?

[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]

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

[KingJL]

Now is -15 degrees in my workshop !!!

Now, That is depressing!!!

[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!