No discrimination on self made 1210x. Help

[dbanner]

I made 1210x( not the 1220x circuit but unable to edit the title)circuit. Coils are balanced at 4.15 khz. Rx resonance at 4.15khz. I checked and rechecked the circuit board for errors, but can find no errors whatsoever. The all METAL channel working perfectly, very clean with good depth, but can't get it to discriminate. I figured the discrimination channel isn't doing anything, but why, since all is correct according to schematic.
Any ideas?

[Funfinder]

Heeeelp! Err sorry but this describtion is the same like someone is lost in the woods and
don't tell us in what region in the world. *laugh* There can be literally 1000 reasons why.
My help is:
Built it again or / and use a different schematic.
Or do some signal tracing if you know the disc part of the circuit.
Perhaps one of the components is faulty or with wrong specifications.

The fastest way solving this problem is:
Leave it be and go searching without discrimination.

[bernte_one]

I made 1210x( not the 1220x circuit but unable to edit the title)circuit. Coils are balanced at 4.15 khz. Rx resonance at 4.15khz. I checked and rechecked the circuit board for errors, but can find no errors whatsoever. The all METAL channel working perfectly, very clean with good depth, but can't get it to discriminate. I figured the discrimination channel isn't doing anything, but why, since all is correct according to schematic.
Any ideas?

please load sheme and pcb layout

[kt315]

George

asking you to change the subject line from '1220' on '1210'.

TIA

[Qiaozhi]

George

asking you to change the subject line from '1220' on '1210'.

TIA

Done.

[kt315]

thank you Qia.
have to find my sketch of layout. this schema is checked.

[Funfinder]

1210-X - introduced 1985
http://www.silysavg.com/private_dete...gy/fisher.html

https://metaldetectingforum.com/showthread.php?t=76041

Rebuilding a 34 years old MD - wheres the schematic of the Whites 101?
I hope this thread hasn't inspired me now for some longer work. *laugh*

[dbanner]

I built the 1210x as I was curious to explore difference in Rimatron 7mx circuit differentiators. Especially with bandpass filter feedback cutoff frequency, and doing some hand calculations. It is good little circuit to analyze.
Discrimination is now working good. I do some modifications and now is very good detector.
I changed the audio frequency for more pleasant beeps. Also modified discrim channel for a little more gain. Also nulled RX coil for minimum residual voltage. Now I am surprised at how good she works.
Transconductance amplifiers are quite OK for this purpose. This was weekend project. I used 6mH 2D coils, tx with centre tap. Works great! Tx peak to peak 14V. VCC 5.5 volts.

[kt315]

1210-X - introduced 1985
http://www.silysavg.com/private_dete...gy/fisher.html

https://metaldetectingforum.com/showthread.php?t=76041

Rebuilding a 34 years old MD - wheres the schematic of the Whites 101?
I hope this thread hasn't inspired me now for some longer work. *laugh*

i had have two of them and they left good impression. one was unworking but i fixed it easely.
i have to find my sketch of layout i did. will put later.

[dbanner]

I am surprised at depth albeit in normal soil she is comparable to tgsl. She likes silver very much at 4.1khz. Not so good with some other coins, no problem.Nice!
I had to change capacitance different from scheme at 6mH to get 4.1khz. Maybe I make smaller sniper coil for her.
For the simplicity of this design and ease of construction, I give the 1210X circuit a thumbs up.
The 1212X is just about the same.
In few days I will put test video to show.

[kt315]

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
from От: Mary Brady <[email protected]>
to Кому: .lt
wrote Написано: august 24, 2005
subject Тема: FW: Operation Manual on Model 1210-X Metal detector
files Файлы: 1210-X OP MANUAL.pdf
--====----====----====----====----====----====----====----====----====----===--
Dear Sir:

Thank you for your email, forwarded to the Export Office for reply.

Our apologies for the delay. As you may know, we discontinued
production of our 1210-X Metal Detector quite a number of years ago. It
therefore took extra time to convert the old Operating Manual to a PDF
format, but it is attached here.

We hope you are enjoying the detector and wish you many years of fun and
success with it.

Regards.

Mary Brady
Fisher Research Laboratory Export Department
280 State Street
Suite 202
North Haven, Connecticut 06473 U.S.A.
Tel: (203) 288-1638 Ext. 614
Fax: (203) 287-8099
Email: [email protected]




-----Original Message-----
From: KT315 [mailto:.lt]
Sent: Thursday, August 11, 2005 12:54 PM
To: Fisher Lab Service
Subject: Operation Manual on Model 1210-X Metal detector

dear sir,

can you please e-mail me an Operation Manual on model 1210-X Metal
detector in PDF?
what difference is of obsolete model from 1212?

thanks in advance.

regards,
Anatolij,
Lithuania

[dbanner]

thank you Qia.
have to find my sketch of layout. this schema is checked.

[ATTACH]46104[/ATTACH]
[ATTACH]46105[/ATTACH]

One thing I noticed, the supply voltage of 9 volts on last LM324( as shown on schematic) did not work for me. The detector performed poorly. However both Lhar's schematic and rimatron 7mx has +5.5VCC for all op amps. So I changed to 5.5v on last opamp, and it worked perfectly.
Strange thing though, when I had a look at the pictures of the original 1210X PCB, I believe I saw last lm324 use 9volts vcc, so the schematic is correct. Dont know how they did that magic.
The audio response on self made 1210X, VERY LOUD AND DISTINCTLY SHARP RESPONSE TO TARGET at a comfortable 500hertz.
Detecting Kennedy silver half dollar 14 inches in air test with clear sound, 16 inches weak but still audible even without headphones. This is with sensitivity turned down so the threshold is completely silent. the detector is absolutely very quiet and stable. This circuit has surprised me. trans conductance amplifiers are doing job quite good.

[Funfinder]

> it works good

Very nice! Of course it works good, because if you follow the link:
https://metaldetectingforum.com/showthread.php?t=76041
it shows the 1210-X can be easily improved to 1260-X power!
But not with the standard 8'' (20cm) coil, only with 11'' (28cm).