XLT damaged: Help needed

[miliciano]

First : greetings to all from Spain and thanks for your great work on metal detectors.

Second : The Problem ...

Hi , I have damaged my XLT inverting battery polarity ...
It tries to power on but only fast lines appears on VDI then nothings happens.

Can anyone help me to locate wicht component is damaged?

[kt315]

in left bottom corner of the schematic you see a power supply... I give also datasheet of converter IC... you see at pcb this chip near ferrite coil...
try from this...

[kt315]

.... LM2574.pdf

[miliciano]

Thanks mate I wil try to test it today.

[miliciano]

1.8V in output , I will buy a new one : LM2574N5 5volt output ,right?

[miliciano]

Changed but didnt work , powers up , screen light on but nothing appears on it.

Any idea?

[golfnut]

The drawing isnt very clear - so forgive if wrong.. but there appears to be a -ve volts generator on top RHS . 2 transistors fed by oscillator does this give -ve volts out??

[kt315]

seems your skill in electronics is low. try may be find someone around who is able to help. I also, like you, would be want see a lady-at-desk helping everybody and alltime, in mode of non-stop. with all fabric made schematics on every brand model. fine, not only my fantazy... do not know how to help you...

from Lietuva with privet and sveikas

[Silver Dollar]

Nothing on the screen? I would start with verifing +5V for the processor then check the
crystal to make sure it's oscillating. You can do both with a meter if you don't have a scope.
The oscillator should read around 2.5V.

Get the processor and display working first...

Here's a more readable schematic;

[miliciano]

You are right Kt315 I have not skill in electronics because I never have study electronics and the problem is that where I live theres no a quality-electronics-repair only a shop that sells LM317 and carbon films resistors ... I love my XLT and dont wanna to throw it away for this problem.

Thanks Silver Dollar , next week will arrive and simple-cheap-chinese escope (hantek 6022be) and will try to learn to use it , meanwhile I will test with meter voltages and oscillator.
Im thinking that the EPROM is dead...

[Silver Dollar]

I'd guess U14, U16 and Q3 would be the first to go with reversed power. Why they didn't include
a protection diode is beyond me...

[miliciano]

Ok I will test it , today has arrived me a chinese scope

[miliciano]

U14 changed for a new one
Q7 changed for a new one
C31 changed too

Q3 , U16 , U20 , caps and diode seems to be OK but dont boot

[golfnut]

Did you measure the supply rails?


Id get a preowned Golmaxx power and up your finds rate !

S

[miliciano]

12v input on U14 but only 2v output on U14-4 U14-7 , changed again U14 and same measure (1.8v - 2.7v).
Sorry , KT315 is right,I'm trying toremotelyrepair axltandI havenobasic electronic skill...maybe is time to think about say goodbye to my old XLT ...