IDX-PRO+VDI

[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.

[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]

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.

[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]

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]

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.

[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?

[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.

[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

[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.

[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

[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.

[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]

cheers I am testing with 2 factory coils 8 inch that ground balance fine on a 6000d. Tried with 2 types of ferrite and the ground all ground balance fine but at around 30K. Played with VR3 thought it only affected a display set at 1K the sens pot is working correctly now unless I have knocked something. Volume is very low in pinpoint mode but fine in disc mode. Will do some more testing. Disc mode is great much better than a genuine Classic.

[golfnut]

In PP you need to advance the sens pot to just below tone boundary. If you dont it will be quiet.

S