cs6pi setting up (cct board pot tweaking and checking )

[martinkayak2000]

I have just bought an old c scope cs6pi , I wish to improve it with mods I have found on this site , but first I want to give it a 'tune up' , i.e make sure it is working as it should , I have the circuit diagrams etc (from this site) , and test equipment , I just need the procedure , can anyone point me in the right direction. TIA
Martin

[kt315]

"Do any members have any thoughts on this as a starting point to modifying the 6PI? It would be good to get some feedback and maybe some moral support that I am heading in at least the right direction."

Russ,

The CS6Pi is a low power pulse detector. Do not try to make a high power unit out of it as you will fry the small 4-pin MOSFET IRFD113. Note there is a 39 ohms resistor in series with a 10 ohm CS6PI coil made with 30 turns of AWG 30 wire. This coil is designed to work at about 15 to 17uS delay only. If you want any faster delay you will need to remake a new coil with about 19 turns like in my Fast coil article on thsi web site.

Obtain a solder sucker or a desoldering gun to suck out the solder and not damage the board.

Remove LM709 the first amplifier and install an 8-pin scoket and install an NE5534, a low noise op amp.

Reduce the gain by changing the 1M feedback resistor with a 470K resistor.

Remove both compensating caps 10pf and the 3.3pf cap.

Increased C7 1000uf to a larger value like 3300uf to 4700 or some value that would fit the same footprint. Do this on other large electrolytic caps also.

Change both electrolytic caps in the +/- 5V power supply to Tantalum caps 10V about 47uf. Observe polarity!!!

Reduce the two 47 ohm resistors to about 27 ohms to provide a little more voltage at the amplifier stage.

Add a 4-pin mic jack and plug to connect a new coil. The cable strain relief comes out leaving a hole that will fit a chassis mount connector.

Only make the new coil coax cable length about 32" long so as to reduce the TX circuit capacitance.

On the 555 IC change the 1nf or 1000 pf cap to about 680 pf (use a mica capacacitor only) to increase the pulse frequency range to a max of about 10K PPS this will get your delay down as the frequency control adjusts the pulse width and delay at the same time the frequency is changed. At about 10KPPS, the delay is about 10uS.

Before you make any mods, check that the CS6PI is working. Look at the pulse on the coil connector inside the control box with your scope. The peak flyback voltage is about 80V.

Read Carl's Hammerhead construction article as the circuits operate in a similar manner using a 555 chip to produce the pulse and an NE5534A for the first amp stage.

Then make the changes one at a time and continue to verify that the CS6PI is working.

If you raise the frequency after changing the 1 nf cap and the coil stops responding using the stock coil, that is normal as you have reached the limit of the stock coil's delay range. Just reduce the frequency to mid point and it should start working again. If you go to the trouble of increasing the frequency range you should consider making a new coil to match the new lower delay range of the modified CS6PI.

With these mods, you should be able to detect a nickel at about 14".

The audio circuit in the top handle box, has a large value resistor (a few hundred ohms) to limit the audio volume to the headphone. There are some rules in Europe to protect hearing from loud noises. This has the consequence of limiting the audio sensitivity. Just visually trace out the circuit connection to the headphone jack and look for the resistor that limits the headphone volume using an ohm meter and bridge a 47 ohm resistor across it. That should allow you to have a little more audio sensitivity.

I was able to fit a 10 AA battery pack in the battery compartment sideways by obtaining longer metric screws to hold the cap on. Rechargables are rated at 1.2V each so you need 10 to look like 8 regular 1.5 V AA batteries at 12 V.

Remember, high frequency pulse induction metal detectors make up for the lower power by supplying more pulses and having the potential to sample sooner, with a lower flyback voltage, where the signal is stronger on low conductive targets like gold and nickles.

I was able to get my CS6PI to operate at about 13K PPS (Pulses Per Second) with a delay of about 7.5uS. I believe I used a 480 pf mica cap for my last mod.

The final tweak is adjusting the 1K damping resistor for the best damped signal after the preamp (observed with a scope). See the Hammerhead article as the procedure is the same.

This should get you moving in the right direction.

bbsailor

[GeoMax]

Hello martinkayak2000,

Could a better photo of the front view of the CS6PI detector be posted here—one better than the image below? While there are numerous photos of the CS6PI's internals available here, I have never seen a good, high-resolution photo of the control panel that clearly shows the controls and labeling. This is the best image of the control panel I could find online.
Thanks.

[eduardo1979]

The detector isn't mine. The photos are from Google.

[ivconic]

I have this, attached, it is nice little design, pretty much straightforward.
Never made it. Intedned to.
Now looking at its schematic again; I am tempted to make it.
Don't have any first hand experiences with that model.
If its for any help:

[kt315]

The CS6PI is similar circuitry to the Beachscan, both of which were made some years ago now. A later development is the Goldquest which has also gone through two or three versions.The major changes since the CS6PI is the ability to sample at 10uS, the addition of a variable SAT control, and a switchable two stage autotune filter, plus you can use DD coils for all but highly mineralised ground. What you need therefore is the addition of ground balancing to the latest Goldquest system. Hmmm!

See the latest Goldquest SS v3 details by clicking on the Surfscanner banner above.

Eric.