Any one got a mod/ advice for avoid hot rocks on a Minelab SD

[mario]

Hi, I have a 2100V2, running 7.5V/Audio amp/11.5 Mono coil (everything custom). I really am getting frustrated with digging those hot rocks. Does any one know how to avoid them? I know the 3500GPs have a much better time coping with them. Is there a chip that I can replace?

I've tried discriminating them out with a more aggressive ground balancing, but they sure stick out.

I would greatly appreciate any advice. I could also post pictures of the pcbs if needed.

[detectormods]

Basic detectors like the 2200V2 do not have the filtering circuitry that the gp and later series detectors have to reduce the response to hot rocks. You can try speeding up the detector to transmit shorter pulses in order to excite minerals a lot less or increase the receiver turn on time to allow for the hot rock signal to decay in amplitude. You may be able to tweak the pulse timing so that the decay curve from a hot rock sits on a detection timing hole.

[mario]

Thank you so much!

I probably should have researched my detector a little more before deciding on the purchase. I was under the assumption PI units were less prone to hot rocks compared to VLF detectors.

Nearly all the hot rocks in my area are a faded orange, which is what i'm beginning to look for during my recovery. They give a weak signal, and if I see an ugly orange rock I'm moving on.

Let me ask you something, by the below quote, are you referring to adjusting the pot settings on the pcb? if so, which pot "speeds up" the detector?

...You can try speeding up the detector to transmit shorter pulses in order to excite minerals a lot less or increase the receiver turn on time to allow for the hot rock signal to decay in amplitude...

In this photo, is the adjustment done to any of the 3 pots on the upper left ?



Or does the adjustment has to be done to the pot on this other photo below (the one on the upper left)?

[detectormods]

The Pot by itself adjusts the tone.

The 3 in a line adjusts ground cancellation and earth field nulling. I do know a guy who fiddled with the 3 pots and had a hell of a time getting it right. You may be able to cancel common types of hot rocks by dare i say ...adjusting the pots. if you want to play with them , write down the resistance value of each one from the middle wiper pin to the 2 outside ones so you can put them back exactly where they should be if you make a mess of the ground balance or earth field settings. To adjust Earth field short out 2 and adjust the one not shorted by waving a plastic sheet fridge magnet near the coil at normal sweep speed and null the response. You can also move a coil vertical and horizontal to receive the earth field and null it.

I have done this on SD2000 detectors but have not tried it on later units, when we change the timebase in the 2000 we realign the trimmers to get the detector behaving nice.

[mario]

pot settings

Good thing you advised me to write down the default resistance values before tinkering with them!

I have not really had time to properly adjust the pot settings because of too much in-town-interference, but I do definitely notice a pronounced coil response when playing with them. The third one from the top has much to do with ground balance, while i assume the first one probably with the earth field settings. I was shorting out the first one from the top, when i noticed no target response when the coil was at ground level. Also, my home made coil now grows loud as i bring down the coil down to 3 feet and then eventually stabilizes at ground level.... I have to play with the middle pot to see what type of response I get.

I'm going to try and short out two and null out a plastic magnet like you advised...also, I'm trying to replace the LM394 chip on this detector, however I can not find it....I'm going to assume it uses 797s?