Fisher 1266 PART 2

[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

[ivconic]

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

[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?

[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

[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]

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

[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]

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

[KingJL]

About other of your notes...many thanks i will check them all.

A quick check to see if everything in the front end is working correctly, would be to check the junction of R223 & C210 while varying the GEB from limit to limit. It should result with the voltage going both positive and negative with 0v somewhere close to the middle. If this is the case and the components close to the original, then everything in the front end should be ok. With no target, if GEB is set for 0V at the junction of R223 and C210, the voltage at junction of R224 & C212 (Disc channel) should be ~ -0.47V.

This will verify the the inputs to the resistve and disc channels are getting the correct signals.

Regards,
J. L. King

[ivconic]

"...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...."

Yes, agree, that makes sense also. Well...i will distinguish MPSU51 doubt after fixing major problem..not so urgent right now. Pitty i dont have any original 1265 right now at me.
What is your opinion on transformer? In schematic is noted some 800 ohms!?!? Ha,ha!
I dont think is possible to make such small transformer with such HUGE resistance, must be a mistake. What do you think?
BTW what are the resistances of your transformer?

[KingJL]

What is your opinion on transformer? In schematic is noted some 800 ohms!?!? Ha,ha!
I dont think is possible to make such small transformer with such HUGE resistance, must be a mistake. What do you think?

The 8ohm/800ohm are impedance not resistance.

BTW what are the resistances of your transformer?

I think I have that somewhere, I will search. It is a typical audio transformer. I had researched a part that had the right specs when I was anticpating building this (before I came across one at an extremely affordable price).

While on the subject of trouble shooting, I took some measurements of signals of different targets back when I was troubleshooting mine. These signals were the demod outpus for the resitive (R223/C210 junction) and the Disc (R224/C212 junction). I believe (memory may be faulty) that the test targets were 2 - 3 inches from coil. There are in attached txt file.
Regards,
J. L. King

[KingJL]

BTW what are the resistances of your transformer?

As near as I can tell without tearing out my unit the measurements were: low side (TX path), ~1 ohm; high side (comparator inputs), ~40 ohm.
Regards,
J. L. King

[KingJL]

While on the subject of trouble shooting, I took some measurements of signals of different targets back when I was troubleshooting mine. These signals were the demod outpus for the resitive (R223/C210 junction) and the Disc (R224/C212 junction). I believe (memory may be faulty) that the test targets were 2 - 3 inches from coil. There are in attached txt file.

A point to clarify, not all the metals were actually tested. The ferrite, small nail, large nail, gold ring, dime, and quarter were actually measured. The others were interpolated from a phase chart that I have. I adjusted the GEB for 0 volts on resistive test point with ferrite at 3 inches from coil.
Regards,
J. L. King

[KingJL]

As near as I can tell without tearing out my unit the measurements were: low side (TX path), ~1 ohm; high side (comparator inputs), ~40 ohm.

I also remember low side:high side step up ratio was 1:10. You don't want to go above this ratio as you can damage the comparators.
Regards,
J. L. King

[ivconic]

Hopefully not. Seems i picked up most suitable one.
Other things you said - excellent reference, many thanks!
Be back later...

P.S.
Pretty interesting audio we have here...it is starting to itch my imagination !
Was thinking to experiment a bit with this and TGSL...hmmm...