Hi, I am interested in electronics as a hobby. I need help with something.
I have a EBD USB Discharging Load Resistor (Link) and I've been using it almost two years. Recently my pc recognize it but the application did not fulfill its functions. Only it can connect EBD tester device but doesn't work start, stop, adjust and read voltage/amper functions. Also it drain more current (400ma) on usb. After then i dissasamble heatsink etc. I check resistors and all of them okey. But SE8533 Voltage regulator is very hot i measure it 105 degrees. I pull it out and test it. I saw it give 3.3v and nothing wrong it. I add some circuit photos. I will be grateful if you could help me.

 

Have you been able to find a schematic ?

 

Have you been able to find a schematic ?

Thanks for reply. I couldn't find any schematic. I just find source code (link). Also i send mail zke company, unfortunately they didn't return.

 

Have you checked the mosfet?
Also try getting a Vgs of the mosfet reading.While it may be pwm controlled it can help see it's state.
Also try to measure the output of the mcp6002 opamp.Maybe it reports false current readings to the micro?
But first try to see it's gain....
Either the mosfet is burned,opamp sensing trouble,or something else.
On that 3.3 V rail something is eating excessive current.See what devices it feeds.

 

Have you checked the mosfet?
Also try getting a Vgs of the mosfet reading.While it may be pwm controlled it can help see it's state.
Also try to measure the output of the mcp6002 opamp.Maybe it reports false current readings to the micro?
But first try to see it's gain....
Either the mosfet is burned,opamp sensing trouble,or something else.
On that 3.3 V rail something is eating excessive current.See what devices it feeds.

Thank you for reply.
I don't know how to checked mosfet but circuit draws same current with mosfet or without mosfet. Can it be still faulty?
And other things you said more complicated for me. Besides i found some short circuit on regulator pins (Ground and Vout). I will add pinout photo datasheet and my checked pins. I pull out Mosfet and it s continue the same way.


Anybody help?

 

check your decoupling caps... it's possible they failed short.

 

Anybody help?

Without a schematic and measurements will be hard.It's better to understand the circuit's working principle.
You have a current sense circuit that reports to a microcontroller.
The micro then sets the load current.It can do this trough 2 ways : PWM or continous using a DAC/Filtered PWM/other methods.
If your MOSFET went bad you can tell by checking it's behaiviour outside the circuit.
A MOSFET has 3 terminals(G-gate D-Drain S-Source).Depending on the MOSFET type(p or n) you will need to either polarize the gate negative with respect to source or positive.Start by putting an 1k resistor in series with the mosfet's drain.Connect the source to ground and the resistor(other end to +5/9/12V).When you connect the gate directly to source the voltage drop on the resistor should be (close to) zero.If not you found a problem.Then if you do gate drain you should see a voltage drop on the resistor.Will be significant and close to your supply voltage.
As someone said caps maybe went bad ,but usually caps don't fail so easy....electrolytics do ,but ceramics shouldn't just burn out.
We know something on your 3.3v line went bad.Just try to see what other things get hot...3.3V at 0.4A is enough power to heat things up.
Other than that sorry.
Start with cheching all the components on the 3.3v rail.Look for the IC datasheets online and measure their supply voltage at input.Also check for unusuall heating.
Other than this things get messy.

 

Without a schematic and measurements will be hard.It's better to understand the circuit's working principle.
You have a current sense circuit that reports to a microcontroller.
The micro then sets the load current.It can do this trough 2 waysWM or continous using a DAC/Filtered PWM/other methods.
If your MOSFET went bad you can tell by checking it's behaiviour outside the circuit.
A MOSFET has 3 terminals(G-gate D-Drain S-Source).Depending on the MOSFET type(p or n) you will need to either polarize the gate negative with respect to source or positive.Start by putting an 1k resistor in series with the mosfet's drain.Connect the source to ground and the resistor(other end to +5/9/12V).When you connect the gate directly to source the voltage drop on the resistor should be (close to) zero.If not you found a problem.Then if you do gate drain you should see a voltage drop on the resistor.Will be significant and close to your supply voltage.
As someone said caps maybe went bad ,but usually caps don't fail so easy....electrolytics do ,but ceramics shouldn't just burn out.
We know something on your 3.3v line went bad.Just try to see what other things get hot...3.3V at 0.4A is enough power to heat things up.
Other than that sorry.
Start with cheching all the components on the 3.3v rail.Look for the IC datasheets online and measure their supply voltage at input.Also check for unusuall heating.
Other than this things get messy.

Thank you very much. I looked for any heated component but same as I said before (SE8533 105° and BS103F3P6 55°). This way draw 450mah and 300mah current. After than i pull out BS103F3P6 IC and now draw only 3mAh. So faulty component is this IC or can it still be another component?

If only this, IC i searched it and I came across very few sources. I found only one datasheet maybe it's right. I will add this.

 

Up!