Controller board for IPL laser

[Ole]

Hello,

I'm trying to fix an IPL laser machine (generic nobrand from China). The problem with the machine, is that the LCD touch screen has no image, it's totally black. Without the LCD touch screen, the machine and laser is unoperable.

So far, after pulling everything apart, I found a burnt LCD driver chip on the LCD screen, so I have purchased a new identical screen (received), which I have mounted and tried, and still nothing but blank screen.

So I'm on to the controller logic board, looking for errors. Can't see any burnt components nor busted capacitors, but what I've noticed, is the LM1117 3.3v voltage regulator with heatsink that gets very very hot (maybe 60-90c - just a guess) within 2 seconds of plugging the AC power in. The LED light which I suppose should light up (marked with 3.3v) when power is connected, does not light up either.

Any ideas where to look for errors, how to measure, suggestions? Would be fair to assume that the LCD screen is powered by the 3.3V, and the problem is around that area...?

Thanks! Sorry, I'm quite green when it comes to electronics, but I'm trying to learn as I go

 

[kellys_eye]

Have you measured the voltage coming out of the regulator to see if it actually is 3.3V? Use a multimeter and measure the voltages at each of the pins on the device.

Also measure the voltage of the green battery. This likely retains various system settings which may be lost if the battery is flat.

 

[Ole]

i will try that now will not be connecting LCD screen through 40 pin connector on the backside of the board, just powering on the controller board itself.

 

[Ole]

ok, so I measured the 3 pins of the 3.3v voltage regulator with a multimeter in dc20 settings. pin1 = 3.12v, pin2 = 0v, pin3 = 1.10v. the heatsink on the regulator gets so hot, it's actually too hot to touch, and this happens within 2-3 seconds. (notice that the board has 3 red LED lights. the LED for the 3.3v is not lighting up, like the LED for the 5v is - and the 3rd LED light - im not even sure what is...))

the green battery measured at 0.85v. it's rated as 2.4v, 60 mAh.
ive attached more pictures of everything thanks so much for replies!

 

[kellys_eye]

Sounds like there's a short somewhere on the board.

Unless my eyes are deceiving me the (black) capacitor (smaller of the two) in this picture seems to be swollen.....


can you confirm? Better still, replace it anyway......

The one behind it doesn't look too chipper either.... replace that too.

 

[Ole]

ive got no clue, but to me - it looks like the cap isn't? ive attached some more pictures of the cap you're referring to

also, just to clarify what ive seen so far, and how things are connected.

the LCD screen that normally is connected through the back of this controller board, has a blue colored pcb with minimal components on it, and it's located between the LCD screen and this controller board. see pictures for reference the LCD screen has by the looks of it, had it's LCD driver chip blown, and there are heat marks on the blue pcb board that would indicate that the LCD driver chip has overheated. am i correct in assuming that...?

im not sure what uses 3.3v and what uses 5v, to be honest. LCD touch panel maybe uses 3.3v...? and the LCD screen panel uses 5v...? im not sure where to look anymore or what is actually wrong

ive purchased and tested with the new LCD screen (with new driver board) that is identical to the previous one (7"), but not showing any sign of wanting to work. should I just replace every capacitor on the controller board...? replacing voltage regulators...?

thanks for any help! any help that gets this up and working again, would definitely get beers. hehe

 

[Ole]

another pic of the controller board

 

[kellys_eye]

The section of board shown below forms a small SMPS that delivers a 5V supply to the board. Mains comes in at the right hand side, is rectified and smoothed, switched via the 8-pin IC that drives the transformer (blue) and rectified (two diodes and a couple of capacitors) to give the 5V that lights the LED marked as such. W1 allows some variation in setting the output voltage which itself is derived from the reference IC T1 (KA431Z) via the opto-coupler (4-pin device to the right of it) feeding back to the controlling IC.



Check that 5V is properly present at the output of the SMPS and fault-find if it's not there.

Assuming it IS present, the 5V feeds to the LM1117 - a simple linear regulator that drops the 5V to 3.3V. Your previous pin measurements at this IC don't show a 5V input which can either be because the 5V supply is dodgy or the LM1117 is dragging it down. Remove the LM1117 and test for 5V again. If it is now measured to be 5V then fit a new LM1117 and test for the 3.3V again.

If 3.3V is still not present then the output of the LM1117 is being dragged down by something - potentially the LM1117 is providing the charge voltage for the battery which may be dud......

Just a few things to be getting on with!

 

[Ole]

Ah, this is getting dangerous for a total newbie
Where would I measure the 5V output exactly?

 

[kellys_eye]

Keep your hands/fingers away from the 'naughty' bits (mains voltages) and it's not dangerous!

The 5V (and 3.3V) may be available at the 'bottom end' of the resistors adjacent to the specific supply LEDs. Measure the voltage at these resistors with respect to 0V (ground) and report back.

I can't tell from the images you posted but the pads marked S3 and S4 may be the relevant test points for them anyway......

 

[Ole]

Hello,

I tried measuring the voltage from between the resistor and S3/S4 pads.
The S3 pad (closest to 3.3v) measured 0 volts.
The S4 pad (closest to 5v) measured 4.85-ish volts.

Also, why is there a 12v input on this board as well? I've tested the output of the Switching Power Supply, and it shows around 17.5v.

So clueless around all of this, sadly :/

 

[kellys_eye]

Assuming it IS present, the 5V feeds to the LM1117 - a simple linear regulator that drops the 5V to 3.3V. Your previous pin measurements at this IC don't show a 5V input which can either be because the 5V supply is dodgy or the LM1117 is dragging it down. Remove the LM1117 and test for 5V again. If it is now measured to be 5V then fit a new LM1117 and test for the 3.3V again.

If 3.3V is still not present then the output of the LM1117 is being dragged down by something - potentially the LM1117 is providing the charge voltage for the battery which may be dud......

Just a few things to be getting on with!

 

[Ole]

I will be ordering a new LM1117. Should I at the same time order capacitors? Battery? Anything else I might as well order? thanks dude, you've been very helpful.

 

[kellys_eye]

If parts availability is suspect then by all means order a battery too..... but without getting to the nub of the problem you could be purchasing 'dozens' of parts that may never get used.

 

[Ole]

true so I've been on this for some time now. This is just so weird, and so many different results.

1. The s4 pad measures 5v. The 1117 5v input pin still measures approx 3v.

2. I disconnect the 4 x 12v cables from the controller board. The s4 pad now again measures 5v. Then rapidly increases to 6v and 6.5v before I shut it down.

So clueless

 

[Ole]

Should I try to find a replacement board instead..?

 

[kellys_eye]

I disconnect the 4 x 12v cables from the controller board. The s4 pad now again measures 5v. Then rapidly increases to 6v and 6.5v before I shut it down.

What "12V cables"???

The fluctuating 5V is a problem. It should be steady regardless of the load.

Your two issues seem to be:

1. dodgy 5V supply line
2. missing 3.3V supply line.

If the 3.3V is being derived from the 5V line then that might explain why you have a 3.3V issue.

We need to see the board traces - close-up, in focus and hi-resolution - to trace the 5V supply which may be the root cause of your problems.

Equally I only ASSUMED that the SMPS section was the source of the 5V supply as there doesn't appear to be any other (on board) source for the 5V. A close-up of the area might reveal more details.

 

[Ole]

Ok, I tried to get some video and more pics of this. Sorry, I'm a total newb

Please see attached link for vids/pics.

thanks!

https://drive.google.com/open?id=1YmLqnEq0N7BmXe0JVu7uWIYrsHzqjACa