Actual Compass XP-PRO main board rev:F schematic

[DavidB]

Scanner MainXP.pdf

This one is from the pictured unit

[kt315]

DB
what CAD soft you use?

[Nandor]

Very nice work! Thank you for sharing it with us!

[Taktyk]

Where is NOTCH LEVEL, POWER LEVEL and indicator?

Regards

[aothunterpl]

Hello , Do You have wersion PRO-2 (3 tone audio mode)

Regarts

[DavidB]

XP-PRO target ID Notch board.pdf Top board corrected and laid out for easy reading

[Davor]

Interesting. I was about to do something similar for both disc and GB adjustment in new IGSL like what you have here for Disc.
There are a few worthy details to observe, but generally I don't like it. Too slow.
That 430Meg makes no sense. It gives a time constant of about 20 minutes, and I can't see it reasonable for a SAT, or any kind of drift. Perhaps I don't understand its purpose well enough, but so far I'm lost. Heck, 1N4148 have larger leakage current than that. In that sense, those diodes make perfectly no sense in conjunction with 430Meg.

[Altra]

Interesting. I was about to do something similar for both disc and GB adjustment in new IGSL like what you have here for Disc.
There are a few worthy details to observe, but generally I don't like it. Too slow.
That 430Meg makes no sense. It gives a time constant of about 20 minutes, and I can't see it reasonable for a SAT, or any kind of drift. Perhaps I don't understand its purpose well enough, but so far I'm lost. Heck, 1N4148 have larger leakage current than that. In that sense, those diodes make perfectly no sense in conjunction with 430Meg.

It's probably a typo. Maybe a 4.3 or 4.7meg would be more likely.

[DavidB]

Look at the picture, Yellow, Orange, Violet and I checked it with a meter.

[DavidB]

XP-PRO Main corrected.pdfSorry, I saw that before about the diodes and forgot to correct it. The diodes are there to clip large signals. I left off the ground.

[Davor]

...I checked it with a meter.

Either a meter or a resistor must be broken. But now the diodes make much more sense. I don't remember seeing that resistor in a picture, and I can't remember seeing such a resistor in my life. I'm not saying it does not exist, only my honest disbelief that it is actually there. Heck, its paint should have more conductivity than the resistor entrails.
Let me put it a bit differently... If I wanted a 20 minutes time constant, I'd not rely on a component that can be spoiled with a mere sneeze.

[kt315]

[scs]

Resistor colector Q4/c1 to base Q5?

[scs]

Resistor 430M is for lekage compensation in non-motion all metal and is normal.

[Davor]

OK, I believe you. But it still bugs me.
The voltage at its end is well below 1V, and hence the current through that resistor is max ~1nA. With input bias current of a LF444 at 50pA what you say kind of makes sense, but not so much in combination with diodes which suggest reducing the impact of a target on such compensation, and focusing more on the very offset in absence of a target. It looks more like a clever SAT function, and in that case the resistor is too big. If you need only leakage compensation, it would require a potentiometer connected to power rails, and a huge resistor, but no feedback.
I'm still confused.