repair GTI 2500 problem on function Imagin

[luigi cataldi]

this is another complicated repair, this GTI 2500 has problems with the imagin function, with another GTI working I found the problem on the 3 PCB, I changed 6 integrated

1 - LM 393
1 - op 37g
2 - lmc 66
1 - 4016
1 - 103/1121

after this change it worked perfectly for a week, after a week the problem returned, the function imagin working only for 3 minuts, after no working plus

[WM6]

Did you try with another Imaging coil?

[luigi cataldi]

yes Guru the coil original 9,5" and the coil 12.5" imagin on other GTI 2500 it works perfectly

[WM6]

If you gently knock on housing using screwdriver nothing changed?

[luigi cataldi]

with a screwdriver on electronics
not using a screwdriver on the electronics are delicate, if it goes in the short run we throw it metal

[Qiaozhi]

If the fault is heat-related, you could try using some freezer spray to isolate the problem ->
https://www.maplin.co.uk/p/maplin-fr...ay-400ml-n68an

[kt315]

check all soldering point on smd's by magnifer glass 10x zoom.

[luigi cataldi]

I've already tried with the technical spray and heating with the desoldering station to verify the temperature limits for each integrated, changing the markings marked with the marker the imagin function works for only about 1 week, there must be some strange input that overloads the ones integrated

I for electronic spare parts I get it from here
https://www.reichelt.com/de/en/

[Sean_Goddard]

The GTi has TWO Rx paths and TWO Rx coils (one smaller than the other). It uses the relative signal strength of the two to determine the size/depth of the target. You have lost one channel by the sounds of it. If depth is the problem then the LARGER outer coil channel is the problem. If the imaging is the ONLY fail then it will be the INNER smaller coil signal path.

Have you checked the supply rails? Maybe one is out of spec due to a faulty regulator and this is over stressing the amplifiers? Highly unlikely that things just "die" in electronics then die again when replaced unless there is a something a LOT more serious at fault and my FIRST INSTINCT would be to check the supplies (which you ALWAYS should - FIRST THING to do in fault finding).

[Qiaozhi]

... check the supplies (which you ALWAYS should - FIRST THING to do in fault finding).

This is very true. I don't have enough fingers and toes to count the number of times I've seen someone jump straight in with the scope, only to find later that the power supply is faulty, or the battery is flat.

[luigi cataldi]

good morning guys
if they were batteries or power I would have noticed
here the problem is on the 3° pcb, all data are correct (compared to another GTI 2500 working)
as soon as I discover the cause I will update you

[Sean_Goddard]

Thanks Qiaozhi. Good luck Luigi. I hope you gt it fixed. the GTi 2500 is a VERY good machine.

Personally I can't think of anything which might cause a repeat failure unless you have a faulty component on another board which is loading the output of an amplifier and then causing a cascade failure. though if this is the case then I would point a VERY stiff finger at anyone who called himself a Design Engineer and didn't protect the inputs and outputs of the stages in his circuit.

[luigi cataldi]

yes, in fact, the problem is a little bit particular in the first minute everything works correctly, just after this time, the imagin function is no longer available, the next step I will take is to use the GTI 2500 working and the GTI 2500 defective, connect them to 2 oscilloscopes and 2 meters and try to pick up in that little minute of time what kind of variations there are that could cause the malfunction.

one question:
is it possible to upload videos to the forum?

[Altra]

Some times electrolytic and tantalum capacitors can cause hard to trace problems. These capacitor with age can degrade. One affect is an increase in ESR which causes heating. What you are describing sounds like something is slowly heating and then failing. Your circuit board has quite a few tantalums. Since you replaced all the semiconductors it's worth looking at the caps. With a ESR meter it would be a quick check.

My 2 cents

[Sean_Goddard]

I wonder if it's one of the tants breaking down and going "short" thus pulling a supply rail down.