IDX-PRO+VDI

[golfnut]

If you require a different Pot to GEB it ..


Not all ferrite is the same and UK soils - so dont be misled into thinking ferrite is our goal - your machine may balance well on local soils.

You can test this by setting to just geb out ferrite on the bench - then take machine outside and pump the machine over your local soil and they are rarely the same - you will have to geb again.


If you have made your coils - the GEB may not funtion well if the 'E' Screen isnt effective.



If you are using ferrite which is representative of your soil and you do have a build error.

1) Measure the frequency of Tx as it may be out of spec - because the RC phase shifters are frequency sensitive the delay range for GEB CH gating may be in the wrong place.

2) Be certain that the Rx coil isnt resonant too close in frequency to the Tx circuit - In use there will be lots of falses that appear during ground pumps - that look like GEB issues. In fact it is the co tune of the Tx and RX giving erratic large phase changes for reasons well explained on here.


S

[Koala]

Pretty sure I have a small fault in the ground balance channel. Detector is behaving in All Metal Mode like the ground balance is not set. Plus it requires 32K to ground balance out a small ferrite piece.

[Koala]

thanks for the help Aiko satdaveuk and golfnut

The pots I am using have a metal case. I have wired each to the ring that runs around the board the one that the four holes go through. Not made much difference if any. There was an improvement when I connected the coil connector to ground.

Disc mode is absolutely fine no problems at all. Nice loud beep that fades with distance

All Metal Mode works okay rock steady volume is fine close to the coil but fades very very very quickly. Distance isn't too bad if on headphones and almost matches Disc Mode but very very hard to hear.

Not sure how the Sens pot is meant to work. In Disk mode there is an extra inch of detection distance in All Metal Mode can't see any difference. Detector never get nervous even when turned fully up.

Had to add a 20K resistor to the ground balance pot to get it to ground balance

[satdaveuk]

Hi
Interesting because I found with the TGSL project by wiring GEB pot etc with good quality audio shielded cable together with hard wire earth bonding of each pot and coil plug to earth can make a significant difference and diminishes allot of the problems mentioned on here.
Learned allot from that project and since have made a habit of using that procedure together with a complete shielded housing with all projects of these types.
I study the Fisher 1265x and although it first appears to be a basic plastic enclosure, its actually not, the circuit module is wrapped with a card which is penetrated with graphite and everything mentioned above is bonded to earth, very simple and very effective.
The last project I made which was the Barracuda was done in the same way and turned it into a different machine, so maybe that's the way to go, everything to gain and nothing to loose.

[golfnut]

asher - you have osillation, maybe at low rf. my idx was pretty good - i opened it again and moved the pcb and battery and mine does random beep beep also. try twisting the geb pot wires,

koala, you may have oscillation outside of audio band which is killing it.

my igsl did this.

a good friends tgsl does this also.


These units have huge gains, poor decoupling and non optimal layout. As the GEB / Disc pots are not on the PCB edge there is no repeatability in the implementation of these kits. Some are buit in a way where the user has no issues. Others suffer niggly repetitive beeping which drifts ang changes its rate often appearing to stop. Often these units do this when coi is not over ground and when forst turned on. other units turn out to be real stubborn and beep away .


I havent sorted these problems myself - the most sensitive hardware are is neer the Geb inputs to the geb mixer/detector - I guess as its signal has a phase response similar to the Tx signal.

If there was pick up of the phase shifted GEB gate signal plus pick up from the Tx sig direct both could clock the Rx mixer and you may hear a beat note. It could be anything like the preamp hooting at low RF. The comparators hooting, etc .

tryh a ground drain lead wrapped aroungd the Geb pot leads and see if the is a change.


Poke your finger in around the board and you may be able to influence the rate of oscillation - you wont need to touch the parts - just be near them.

You may find ares which are the most sensitive - these are the problem areas.


S

[Koala]

No not connected connector to ground followed the quick connect jpg earlier in the thread that only had 5 wires showing. Connected the shell to ground now and retested. English 2p none magnetic copper coin. On speaker Disc Mode easy 9 1/2" and in All Metal mode 6 1/2" on headphones Disc is the same All metal 10 1/4". If I hold the pot connector that goes to R43 then All Metal Mode on speakers goes to 8" and on headphones 11 1/2" the last half in All metal mode is very very very faint. Tried two factory old white and newer black 8" coils they act differently when close to the coil the black one really overloads easy but over about 4 inches they are the same.

[Aiko]

Cheers Aiko. Was hopping that was it. Measured all resistors with a meter all measure all fine apart from 2 which would have to be removed but the color band are right. Re-checked all capacitors values are correct. At least I know it can't be much as if I hold the connectors it works okay.

Hi Koala, are you sure that the corpus of the coil connector is connected to the ground? What is the detection distance?

[Aiko]

Hello, I have a little problem using my real IDX does not work properly, it creates vibration and beep beep it impossible to use while my internal tests were inconclusive

The most tricky part is the coil. First be sure that the coil is with the exact parameters and it is nulled properly.

[Koala]

Cheers Aiko. Was hopping that was it. Measured all resistors with a meter all measure all fine apart from 2 which would have to be removed but the color band are right. Re-checked all capacitors values are correct. At least I know it can't be much as if I hold the connectors it works okay.

[Aiko]

looking at the parts list on the md4u.ru site it lists C20 C22 and C24 as ceramic I have use Polyester could this be my problem.

Absolutely NO!

[Koala]

looking at the parts list on the md4u.ru site it lists C20 C22 and C24 as ceramic I have use Polyester could this be my problem.

[ashefr10]

Hello, I have a little problem using my real IDX does not work properly, it creates vibration and beep beep it impossible to use while my internal tests were inconclusive

[Koala]

Getting somewhere but don't now where. If I hold the coil connector and the ground pot connector that goes to R43 in the same hand while in all metal mode the detection distance goes up. Changing the LM358s made no differance.

[Koala]

Cheers golfnut 2p is a copper one. In Disc Mode everything is fine. Pot turned fully anti clockwise detects all the way to 10" first 9" fine last inch spitting sound well impressed with this. Slightly better than an original "classic I" with the same coil. In All Metal Mode things aren't so good can't ground balance unless I add a resistor to the pot ground balances fine at around the 32K mark. Distance is less than the Disc Mode but not much less. Digging distance is much less though. Close to the coil the sound is overloaded and is fine to about 5" then drops off very quickly and only audible in headphones I mean very faint hardly noticeable. Threshold works fine. You can go from quite to loud hum. Set to very fain hum the sound is slightly choppy. In All Metal Mode the sens pot has no affect but I have noticed that in disc mode if you have it turned all the way up and don't move the coil there is an occasional pop and crackle from the unit this goes away if you turn the pot to half way there is no detection distance change. Went to get 2 replacement LM358 to test just got home and I have been given 2 PIC chips.

[golfnut]

"volume is very loud when close to the coil but drops of very very quickly and is only very faint for the last 5". Any ideas which part of the circuit I should be looking at."

This is where the sens comes in - It is loud when close and gives the user an idea of the range.

The All metal postion of the disc pot will give more depth - and volume.


Be wary of uk 2P as it may be copper plated steel , so not an ideal test piece.

S