Help with Minelab GPX4500

[Steefan]

Hello everyone
I have a problem with my gpx 4500. I used contact cleaner for coil and batt connectors and shorted something. Detector didn’t turn on.I open detector and saw what is fried. Its inductance/resistor 0,4 ohm i think(check picture). It’s on/off button circuit.I changed it but as soon i connect battery it is burnt again. Can you please help me with repairing. I have equipment and soldering skills but im not familiar with detector board.

[roshik]

The defective part is replaced and it burns again, the reason is that another part is defective in the same path.
It is better to follow the copper lines connected to the defective part and check the all parts along this path.
you sure another part is defective.

[Mechanic]

Those parts provide 5+ and gnd for the screen. I don't see how applying contact cleaner to the power plug could cause this, but it is happening obviously.
Check that the flexible strip is not damaged, check that the small connector on the screen is seated correctly.
Also try disconnecting the screen and powering on, if the parts don't blow, then likely there is a fault with the regulator on the screen board.

The ferrite bead inductors are 2.2uh and .4 ohm sounds good, looks like they also work as a fuse!

Cheers Mick

[Steefan]

Those parts provide 5+ and gnd for the screen. I don't see how applying contact cleaner to the power plug could cause this, but it is happening obviously.
Check that the flexible strip is not damaged, check that the small connector on the screen is seated correctly.
Also try disconnecting the screen and powering on, if the parts don't blow, then likely there is a fault with the regulator on the screen board.

The ferrite bead inductors are 2.2uh and .4 ohm sounds good, looks like they also work as a fuse!

Cheers Mick

Thanks Mick for describing part!
Machine is working again. What i did is to solder:

INDUCTOR-SMD,2.2UH,20%,2012,0.16OHM,950M

After that i feed it direct 7,6v to power strip with dc power supply. Luckily machine boot up normal. Then tested audio from the machine itself and it was good. So my thoughts are something in the battery/cable is causing troubles. Cable was tested for shorts and its ok. Battery was opened and I did some measurements for shorted caps but nothing wrong. After that i connected everything as it was: battery power cable and detector. This time nothing burned. Machine boots normal.

I have tested it for 3-4 hours and it’s ok. But older problem, for which i used contact cleaner is here again: chattering and something like high EMI. It’s like constant chatter and can’t be reduced with lowering gain. Is there something i can measure or change to make it more stable and quiet again?

[Mechanic]

The power cable can and will fail and cause problems. However, the power cable won't cause those parts to burn. That is most likely the flexible strip and power plug.
If you have a Minelab service agent it is probably worth your while to have the power plug and flexible strip replaced.
Also try a new power lead before further troubleshooting.

For the noise you hear, does adjusting manual tune have any effect on it?
If you run in cancel with a DD does it still make noise?
How about cancel with a mono coil?
Are you away from interference?

There are numerous things that can cause noise, but I won't list them here as it has taken a lot of time to find these things and it is also easy to kill a GPX board if you don't have experience with them. To repair you'd be looking around $160AUD for the noise fault depending what it is and roughly the same to do the power plug and flexible strip(less if it is already here and pulled apart for another fault). I have designed my own custom flexible strips that won't fail like the original ones.

Cheers Mick

[Steefan]

The power cable can and will fail and cause problems. However, the power cable won't cause those parts to burn. That is most likely the flexible strip and power plug.
If you have a Minelab service agent it is probably worth your while to have the power plug and flexible strip replaced.
Also try a new power lead before further troubleshooting.

For the noise you hear, does adjusting manual tune have any effect on it?
If you run in cancel with a DD does it still make noise?
How about cancel with a mono coil?
Are you away from interference?

There are numerous things that can cause noise, but I won't list them here as it has taken a lot of time to find these things and it is also easy to kill a GPX board if you don't have experience with them. To repair you'd be looking around $160AUD for the noise fault depending what it is and roughly the same to do the power plug and flexible strip(less if it is already here and pulled apart for another fault). I have designed my own custom flexible strips that won't fail like the original ones.

Cheers Mick

Hello Mick,
For the noise adjusting manual tune dosnt really help. I have tried manual and auto adjusting frequency. When auto searching there is something like constant noise and cant find clean channel whatever im doing. Also reducing gain do nothing with noise. When i switch on detector there is 5-10 min quiet and stable machine and after that it starting noise. When switch to cancel with DD coil there is improvement. It is more stable and less interference. I am far away from any kind of interference. Also there is old sites searched before and i know machine was stable there. For the power plug and flexible strip i have inspected it and seems nothing wrong.
Cheers Stefan

[Orbit]

Try replacing the batteries on the sd 2000, I noticed that with a certain voltage there is no noise, if the voltage is sometimes too high 7.2v or less than 6v there is noise. That's why I installed a regulator and supply it with a voltage where the noise disappears. I haven't been following the thread so this may not be ok in your case.You could replace the parts for +5V or clean the circuit board around those components with a toothbrush.

[Steefan]

Try replacing the batteries on the sd 2000, I noticed that with a certain voltage there is no noise, if the voltage is sometimes too high 7.2v or less than 6v there is noise. That's why I installed a regulator and supply it with a voltage where the noise disappears. I haven't been following the thread so this may not be ok in your case.You could replace the parts for +5V or clean the circuit board around those components with a toothbrush.

I haven't noticed that the voltage has anything to do with the noise, but I'll try to keep an eye on that. It may not be ok to replace parts that may be good. Board looks good.

[Mechanic]

I haven't noticed that the voltage has anything to do with the noise, but I'll try to keep an eye on that. It may not be ok to replace parts that may be good. Board looks good.

Good stuff! Don't go replacing parts for the heck of it as it is easy for someone who doesn't work on them all the time to make a mess real quick.
Given the symptom I have a pretty good idea what part(s) are at fault. I'll send you a PM.
No amount of cheap Chinese Jamec low esr caps from Madeinchina.com laying all over the board will fix it either

Cheers Mick