Fisher 1266 PART 2

[KingJL]

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.

Found my notes! 1 ohm and 40 ohms. Suitable part, Mouser part # 42TL008-RC.
Regards,
J. L. King

[KingJL]

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

I agree! I am impressed with a lot of the "old" Fisher implementations. Too bad that the new stuff just does not stack up. I like a lot of the "old" Whites implementations also. The Spectrum's are hard to beat.

[ivconic]

I agree.
However; Spectrum&"relatives" do "pull out" rich audio from uPc, hard to make in amateur arrangement - makes those pretty out of range of our interest here. But this audio from Fisher is piece of cake to make.
I am deeply satisfied with what i got from TGSL on real field. Only one drawback - audio. So i tried to improve it many times. Latest audio mod turns to be best so far. But today i took another look on this one and got idea to try it with TGSL. It suppose to give quite new dimension to TGSL. Still early to say anything...but am just about to try it. I do expect some difficulties here, some signal level issues...will see. Better to stop talking for now.
If gain some success i will post my experiences on the other thread.
Back to 1265...well, considering all we talked about here finally i can suspect only pcb or some broken component... transformer is ok, quratz is ok, coil is ok, schematic seem to be ok...pfffff!
These days i will have to sit and recheck all over again from the very start.
Also i will keep on my mind all your hints and datas you offered here.
Until than...
Regards!

[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.

I just noticed that the formatting of the text file changed the columns of the ferrite readings. Here is a corrected txt file with the measurements. The first column of course is the target metal, the 2nd column is the approximate phase shift for the target, the 3rd column is the measurement of the resistive channel demod signal at the testpoint described in the previous post, the 4th column is the measurement of the disc channel demod signal at the test point described in the previous post.

There is a 208 degree phase differrence between the resistive channel and the Disc channel. When the GEB was adjusted correctly (so that ferrite gave 0 volts), the no target signal was leading by 7 degrees (~ -0.12v at the resistive channel test point).
Regards,
J. L. King

[ivconic]

Ha, i knew it! Today i made separatelly 1265 audio stage from schematic above and connected it to TGSL. It is working like hell! Just as i assumed; it is giving to TGLS quite new dimension. Now TGSL audio is extra strong and adjustable, also very rich and it has also sort of "bang" at clear signals!!! Ha,ha,ha! I wasted so many days trying to modd TGSL's audio...but all the time i had ready solution right in front of my eyes! Sheeesh!!
I had fear to meet some signal level isssues here, but i didnt. All is working perfectly from a very start. At TGSL's last stage, LM358 there is 27K resistor goes straight to MPSA13 base. I disconnected MPSA13 and composite signal from 4024, replace 27K with 10K and than connected straight to 1265 audio, and it is working like hell! Excellent! Best audio mod on TGSL so far!
But this experiment has much greater meaning for me; now i can understand much better philosophy of Fisher 1265 too. Actually i thought 1265 has something specially good soluted in previous stages that makes such good audio, such distincive and cognizable specific just to this serie. I was wrong.
Now with this audio stage TGSL is absolute superior in all the aspects to 1265. I will prepare schematic revision and post at TGSL thread...
This was real success..!
But if i wasnt dealing with 1265 last couple days, probably i would never got this fantastic idea....so..again proved that real work,experimenting and hard labour cant be ever replaced with plain philosophy. Proved so many times to me so far....

Now... few questions will remain opened for the future; with setup like this one TGSL will have 2 threshold stages...ha,ha... also 4024 lost part of important role....could be replaced with some simple divider 1/2 to run negative voltage generation stage...
and apetite now grows more; is it easier to achieve audio discrimination (2 tone) etc...etc....huh...neverending story!

[ivconic]

Few other jobs finished so i am back on track again here. 1265 copy i made is still on the bench and waiting. By strange coincidence today i got original 1265 in descent shape. Only one thing miss - coil. Actually with this one came 8" White's (3900) coil!!! Ha,ha,ha! And it is working, but not that good as with original. Now i have almost perfect conditions to recheck all over again, to compare, measure...my 1265 copy simply MUST start to work good in next few days. PCB's were checked many times, there are no mistakes on those. Neither one mistake. So people who's interested in making copy of 1265 can freely use those pcb's...no mistakes at all.
First will recheck and compare original transformer and the one i used...than use scope and measure some signals and later check wirements on front panel...
If discover something wrong i will report here..

[Mikes]

Ivconic!







Best regards!

[ivconic]

Is it? I will check tomorrow.
Regards!

[ivconic]

Yes!

[ivconic]

Just checked. Mikes is right!
Now it is working by the book!

[ivconic]

Ok..one more tip;
instead VP0104N3 and simillars i used ordinary IRF9622! Wow! I get perfect 8.0 volts now with it and all the things came to proper places!
Than applied Mikes corrections - even better! My 1265 copy started to work exactly as original. I can't get only proper phase by now, not yet, simply cose i used inproper coil. I dont have proper coil so i used Quicksilver (CZ5&7) 28cm coil just for testing purposes. But comparing to past situation and now, i see huge differences and huge improvements. Audio is extra loud (due proper 8v) and Sensitivity, Disc and other presets are working now nice and linear!
Everything simply came on its places! Simply as that!
Ha! I never payed attention on those 27M9 inputs!
Huge schematic mistake! Mikes i own you!

[ivconic]

Here are updated pcb files!
Cheers!

[ivconic]

"...Huge schematic mistake! Mikes i own you!.."

I owe you! Not "own"! My damn English!

[ivconic]

Problems! Problems! Problems!

Just few hours ago i took original 1265 coil (8") from my friend to try it with my handmade. Very bad behavior! In Disc mode i got bedlam of cracks and beeps! In Static mode it is calm and working but sensitivity is very low....iron pliers bairly at 10cm in air! And also in Static mode it can not see coloured metals at all! I tried everything! Switched coil pins, switched transformer pins, rechecked everything - no result! Frequency is 4.7xx kHz.
With previous CZ5 28cm coil i got so so behavior, but out of phase....with this one, original...worse behavior much!?
Maybe some ic busted in between? Maybe more mistakes on schematic?
I am giving up of this one! To much wasted time for nothing....

[Mikes]

Hi, Ivconic!
All is very simple. I too have decided to collect 1265 (yours PCB).
When checked your payment has seen this error.
Now I do a design and the coil. Electronics works normally.
When I will finish completely a design 1265 I will write about all "reefs" at myself on a site http://mikes.front.ru. Naturally there will be references to yours PCB.

Regards,MikeS.