PI-190DTLB 5v earthing out

[SuperDuty]

Re: PI-190DTLB 5v earthing out

Checked all the diodes, nothing wrong there.

Is it normal that when I check the voltages directly at the AC-in pins on the PCB, I get little to no voltage ? Tried with different wall plugs but it made no difference.

Can I replace the varistor with a wire temporarily to see if it's the problem ? Could the start up capacitor be so bad it won't even let a little bit of power flow ? Same for the other capacitors ?

[jetadm123]

Re: PI-190DTLB 5v earthing out

Since you say that your board has a different layout, now may a good time to post some photos of it. Take them similar to the ones shown on post #1 of this thread.

Not sure where you are measuring the AC input, but if you measure across the large 450V cap, you should see approx:

220VAC x 1.414 = 311 VDC , assuming the AC voltage in France is 220VAC.

[sabre504]

Re: PI-190DTLB 5v earthing out

I had forgotten all about this board i had gotten busy on other work and had put it away in a box this post has reminded me .
I shall have to get it out and finish it

[vasst]

Re: PI-190DTLB 5v earthing out

Please help me... what is it this part >> ZD204!!!

[budm]

Re: PI-190DTLB 5v earthing out

ZD204 shown in the diagram as not used (not installed). Do you have that on your board?

[vasst]

Re: PI-190DTLB 5v earthing out

ZD204 shown in the diagram as not used (not installed). Do you have that on your board?

MAG T906W (model 900W)
Power Supply Backlight Inverter 860-AB0-190DTLB-PCH
IC201=LD7575, Q201=8N60C
R215=2kOh, ZD204=??? is installed

[SuperDuty]

Re: PI-190DTLB 5v earthing out

ZD should be a zener diode right ?

[budm]

Re: PI-190DTLB 5v earthing out

ZD = Zener Diode, not sure if the diagram as shown in this thread matches the board that VASTT is asking about ZD204 since the diagram as shown in this thread as NOT USED.

[SuperDuty]

Re: PI-190DTLB 5v earthing out

I have nothing on mine at ZD204 either.

[sabre504]

Re: PI-190DTLB 5v earthing out

Vasst
post a picture of both sides of your board and try a close up of ZD204

Maybe that will help us help you

[SuperDuty]

Re: PI-190DTLB 5v earthing out

Allright here are the pictures of the boards :

[SuperDuty]

Re: PI-190DTLB 5v earthing out

Ok I have done several tests, and it seems like the AP431 shunt regulator (IC203) is shorted according to this test : http://www.jestineyong.com/how-to-te...gulator-tl431/
I'll see if i can find one in my scavenged parts.

BTW, I'm getting around 318V at the big capacitor, so it's close to what jetadm said.

EDIT : YES ! THAT WAS IT ! The shunt regulator was shot. Found another 431 in my stash
LED light lit blue, now to test it with the flat panel on and on a computer !

EDIT2 : test failed...led won't turn on anymore, the shunt regulator is fine :/ Nevermind, one trace was broken, just needed a little solder.

[SuperDuty]

Re: PI-190DTLB 5v earthing out

Well the screen is acting weird, seems like there's a short somewhere. When I plug it with the bare board with or without the screen, it works...randomly. If I put the shield back on, it won't work at all. It feels like it needs to drain all the power before being able to start up again.

[budm]

Re: PI-190DTLB 5v earthing out

TL431 testing:
As you can see in the spec sheet, the Anode and Cathode is just a NPN transistor driven by the comparator IC. so Anode (Emitter) and Cathode (Collector) should show open circuit.

[sabre504]

Re: PI-190DTLB 5v earthing out

Have you checked R233 and R234 seems to be heat marks around them

[SuperDuty]

Re: PI-190DTLB 5v earthing out

I had checked them and one of the two is showing 1K ohms more than it's supposed to. The heat marks also show on the back of the board. I've changed them with standard resistors of the same value, and no change.

The original TL431 had current going between the anode and cathode, while my other 431 don't. Yet I've changed it again with another 431 I had, no change.

I hear a slight "pop" coming from the speakers when I turn the switch to on.

[sabre504]

Re: PI-190DTLB 5v earthing out

Not sure if you have checked these do you have any voltage at the output pins on the power board ?

[SuperDuty]

Re: PI-190DTLB 5v earthing out

I'm getting a very small voltage on the +14V, and it's slowly going down, and nothing on the +5V pins.

[sabre504]

Re: PI-190DTLB 5v earthing out

Ok i am going to dig out my unfinished board and notes on these and see what i can do next to help
On another point when you test the main large cap does the voltage stay stable or is that dropping off at all ?

[SuperDuty]

Re: PI-190DTLB 5v earthing out

No it's stable at the main cap, at 319V-320V.

The problem is really odd, yesterday I swapped the 222M Y-cap next to the transformer with an identical one, and it worked on the first test until I unplugged the cord and plugged it back, then no power again. I was thinking the 817BN optocoupler could be bad, I found the exact same one on a modem card, but the problem remains. Now I'm wondering if the transformer could be bad, but I have no idea how to test them.

The voltages seem normal before the transformer stage/y cap/817BN optocoupler, then I get no voltage to very low voltage, and it's slowly going down where I find some (at the +14V pins for example).