TESORO GOLDEN SABRE

[ivconic]

AAAARRRRGGGHHHHHH!!!!!


Finally problem is SOLVED for real!!!!!!!
But i have to admit - without oscilloscope (even obsolete) i would never find out what was the real problem!!! Also i have to thank to all of you on great support and efforts involved here!

Problem WAS damn %&^%$#@%$^%$$@%$% 100pF capacitor C9 at LF353!!!
I bought 10 of those brand new from same supplier! Even checked each of those with capacitance meter!? Each showed 105-115pF on meter!!!
I would never have any doubts more on those.....but after all possible doubts i decided few hours ago to take oscilloscope probe and "trace" signal after each component....without much of a concept...And i founded it! Damn $%$% capacitor. Out of circuitry it is acting like good one. Included in circuitry it is not good at all. I simply replaced those with first came handy to me - ordinary ceramic capacitors....and it is working PERFECT!
Like Max stated; now i can adjust Sense at Maximum and Disc at minimum.......no chatters, no "beep's"....Calm and silent like stone!
Also in All Metal mode with Sense to Maximum....working PERFECT...no false signals at all!!!!
On coins depth remained same but on larger items...like Cola can depth (distance) raised for 30% more !!!! It can detect Cola can over 80cm in the air now, with 27cm coil. Havent checked yet distances with larger Eliptical coil 32cm...To tired...i'll continue tomorow with testing...
Now i can adjust everything by the book! GEB trimmer is now adjusted right in the middle...everything else same as Max described earlier...Huh!!!!

Damn local suppliers....thieves!


Again, people, thank you so very much for suggestions and efforts here!
Best regards!

[ivconic]

Now, this one is more like it !!! 'Beast" in small package! But with double price...
I have 10 days to rethink on this....

[ivconic]

Good question. But i have limited budget for now. 2 channel scope will cost me much more money...

This one looks sharp tome;

http://www.chocbar.demon.co.uk/

But i took only skim look on it...Dont know if i can find all components for it?
Also need pc to be attached. Dont know?

If i find some 2 channel second hand than for sure i'll buy it...
But i dont like desktop devices any more.... Must be something handy and cheaper to suit our needs here?

[Qiaozhi]

You could always make your own.

http://www.chocbar.demon.co.uk/

[Qiaozhi]

Intend to buy this one. Any suggestions...?

Don't really know. Never used one.

I notice that it only has one channel though, which would be a problem. How are you going to measure any phase relationships, such as TX versus RX, or sample pulse versus sync demod output?

The one good thing I like is the storage facility and the cheap price.
Have a look here -> http://www.maplin.co.uk/module.aspx?...doy=19m10#spec
There's a couple of videos as well, but the first one is crap. The presenter is so monotonic, that you almost fall asleep with disinterest. You can also download the complete manual.

[ivconic]

Intend to buy this one. Any suggestions...?

[ivconic]

Plain truth!

But after box of beer, my head can be used as pretty good scope at least day or two after...

[Qiaozhi]

"...Ivconic - now go and buy a decent scope. .."

If this solve my problem than i'll first buy huge box of beer and honestly get "wet".....later comes scope and stuff...

But wait first to be sure...

But the good thing about buying a scope is ... it's still there tomorrow!
With beer, you never buy it - you only rent it.

[ivconic]

"...Ivconic - now go and buy a decent scope. .."

If this solve my problem than i'll first buy huge box of beer and honestly get "wet".....later comes scope and stuff...

But wait first to be sure...

[Qiaozhi]

Ivconic, the reason that the pin 1 waveform is so out of control, is because you have removed the original GS notch level 10k potentiometer
that was directly paralled with the 100k discriminate pot. By removing the notch circuit, you have increased the gain of the opamp - at
the same time as you also increase the likleyhood of oscillation because of the higher feedback resistance.

Either change to a 10k Disc pot, or parallel a 10k fixed resistor across the 100k pot, and see what happens. It will very likely cause a different curve
to the Discrimination potentiometer effect (to be more like the original), but things should smooth out.

The LF353 is not a rail-to rail opamp. By having raised the circuit's gain, you have run out of dynamic headroom!
It feel stupid for not realizing this sooner.

Hi PorkLuvr!
Well spotted. That's just what this forum is all about.

Ivconic - now go and buy a decent scope.

[ivconic]

If that will turn as main source of problems....than i'll feel stupid even much more!!! What to say? Either you right or wrong, thank you very much for effort. I will obey your suggestion and report here in hour or two...Right now i have some guests...wait they to go

[porkluvr]

OOh, ooh!

Ivconic, the reason that the pin 1 waveform is so out of control, is because you have removed the original GS notch level 10k potentiometer
that was directly paralled with the 100k discriminate pot. By removing the notch circuit, you have increased the gain of the opamp - at
the same time as you also increase the likleyhood of oscillation because of the higher feedback resistance.

Either change to a 10k Disc pot, or parallel a 10k fixed resistor across the 100k pot, and see what happens. It will very likely cause a different curve
to the Discrimination potentiometer effect (to be more like the original), but things should smooth out.

The LF353 is not a rail-to rail opamp. By having raised the circuit's gain, you have run out of dynamic headroom!
It feel stupid for not realizing this sooner.

[ivconic]

ApBerg do you have ocassional beeps as i described? Or it is working stabile?
Is it Goldy pcb or larger one?
Regards!



Come to think again; large pcb is working just fine, i put LM308 in plastic case on it.
Goldy pcb is not working fine, i put LM308H on it...?! On all 8 pcb's...
But this wrong oscilogramme is measured at LF353..not at late stages...?!

About metalic case of LM308H; is it connected somewhere in internal wirements? Have to look datasheet....
If not than i'll connect those to gnd...if yes than...!?
Front end with LF353 is so simple...i dont understand.I put very same components at all 8 pcb's, same as on large pcb..?

[Qiaozhi]

Hello Frends.

Qiaozhi, in the past I had some problems with wire wound pots, when replaced by a 'normal' pot the problems were gone, can it be that there is an L function ?

Well made some screenshots, transmit sinus is 2 v p/p also the 353-1 is 2 v p/p for the r25 and r26 signals it is 0.2 v p/p ( I hope..... can be wrong )

First is LF353-1 then two from r25-q7 then two r26 q6

Ap

Yes - these all look as expected to me.

Ivconic - study these waveforms. This is what they should look like.

[ivconic]

Yes - there is a problem with the sampling in the DISC channel (fet #2), but at least it's sampling in the correct place. I think the double pulse is happening because the sample pulse has that strange instability.


Why do you think a wirewound DISC pot would cause any problems?

Damn! You are right! And i suspected scope!? It is obsolete and very old so sometimes it is doubling ..gramms when turn one switch on it. But this time i am sure it is not a case, cose i cleaned that switch to avoid internal scope hums...Damn!