Minelab Relic Hawk

[Dominic]

Would anyone have knowledge regarding a falsing problem with this detector. The detector has been unused for several years and now it gives a beep when the coil is ground pumped.
Adjusting the ground balance cancels it for several seconds then it drifts back, this will continue until there is no more adjustment left.
If you air test and tap the side of the coil it also falses even when the sensitivity is set at minimum. It has a new battery and I have changed all the electrolytics , a replacement coil has also been tried.
Any suggestions?

[dbanner]

Have you checked the coil connector at the box end? Otherwise problem may be on PCB with some stupid opamp.27M2 U6 first suspect.
I assume that you measured and have correct PS +/- voltages on PCB. I see +2.5/-2.5 ref. Voltage on schematic( which I assume you have)
Beyond that, oscilloscope.

[ivconic]

"...The detector has been unused for several years ..."

I had exactly the same case.
Bunch of cold junctions.
That's all.
How i solved the problem?
Literally i re-soldered whole main board and especially front panel pcb.
Pay attention on "vias". Small holes which connects top and bottom layers on pcbs.
It is possible that some of those cracks and lose connection too.
Pots also need dismantling and complete cleaning.
Lot of job, several hours.
But than you'll get brand new detector.

[ivconic]

Maybe additional help:

[Qiaozhi]

Would anyone have knowledge regarding a falsing problem with this detector. The detector has been unused for several years and now it gives a beep when the coil is ground pumped.
Adjusting the ground balance cancels it for several seconds then it drifts back, this will continue until there is no more adjustment left.
If you air test and tap the side of the coil it also falses even when the sensitivity is set at minimum. It has a new battery and I have changed all the electrolytics , a replacement coil has also been tried.
Any suggestions?

If tapping the side of the coil causes it to false, then it's probably a loose connection in the coil. Maybe the connection to the electrostatic shield is intermittent.
Have you tried using another coil?

[dbanner]

"...The detector has been unused for several years ..."

I had exactly the same case.
Bunch of cold junctions.
That's all.
How i solved the problem?
Literally i re-soldered whole main board and especially front panel pcb.
Pay attention on "vias". Small holes which connects top and bottom layers on pcbs.
It is possible that some of those cracks and lose connection too.
Pots also need dismantling and complete cleaning.
Lot of job, several hours.
But than you'll get brand new detector.

You are good detective Sherlock Holmes. Of course cold solder joints very first thing to check after long hibernation.
I you are rich man, put PCB in oven for few minutes. just kidding.
Check shield connection to ground.

[kt315]

electrostatic problem. can you give case inside pics i could see the right connection of interior shielding to the ground?

[Dominic]

Hi Guys and thanks to everyone who made suggestions and posted board pictures.
All the solder joints have been redone apart from the via or feed throughs which I will look into. Pots were cleaned and the internal cables to coil and battery re soldered.
The coil has been replaced with another from an Explorer (I know its not the same but it is the only one I had available) it still gave the same problem.
I have now downloaded some circuit diagrams and pictures which will be a great help from your 2008 posts so I can now use this to have another look

I had a similar problem with my Explorer and it was a breakdown in the insulation in the cable from the main board to the coil. New coil cable fitted and its been working well for the last 5 years or so.

[ivconic]

"...The coil has been replaced with another from an Explorer..."

That's generally bad idea. Mixing apples and pears.
Seems like you are crying for hair loss while trying to solve the problem!
...
Looks like cable/connector shielding related problem.

[ivconic]

You are good detective Sherlock Holmes. Of course cold solder joints very first thing to check after long hibernation.
I you are rich man, put PCB in oven for few minutes. just kidding.
Check shield connection to ground.

"...The detector has been unused for several years ..."

These kinds of situation always makes total pessimist skeptic of me.
Such detectors are always pig in a poke.

[dbanner]

Absolutely! Cold soldering is notorious enemy of technicians and engineers. It is like a gentle sleeping baby, too often overlooked as main culprit.

[Dominic]

Now using the circuit diagram although the component numbers on the board do not match those on the circuit diagram, I have found that the +5v and -5v lines ard not correct.
They are -4.9v and +6.75v readings taken at the capacitor (470uf) splitter with the centre ground just after the battery input.
The capacitors have been checked and are ok.
Any thoughts anyone or do I start cutting tracks to try and isolate the area

[kt315]

It has a new battery
---
again you do not wish to share pics. WHAT type of the battery? WHAT voltage on the battery measured?

[Dominic]

I think you are confusing me with another post (Luigi Cataldi) I have never posted on this forum before.

[kt315]

ohhh! you say FORUM! what is the forum? is the forum THE EXCHANGING OF THE INFORMATION IN BOTH sides?