No power (blackscreen) with MD3021PH -> AI-0088 the reason?

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

@PlainBill
Thanks for your instruction.
D006 (when u move along the "L" from top the first component on the heatsink) from each side to center lead: 2.23kOhm and 3kOhm
D007 (the next one on the "L" track): each lead has 0 Ohm
D008 (the last one and the one you were asking for; Designation is KIA 7812A PI 508): 8.3kOhm and 0 Ohm
What appeared strange to me, when I began measuring the resistance started around 300 Ohm and then increased until the given value limits!

For the schematic, as it is a vectorbased PDF file, you can use your Acrobat reader (or any open source program) and the + Button (magnifying glass) to make the drawing better readable!

[PlainBill]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Unfortunately that schematic is so small as to be unreadable.

PlainBill

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

@retiredcaps
Okay then I don't have to worry about that anymore. I tried starting to locate the evadable shortened diode but seems like it's quite hard. Some are parallel to resistors, some are connected with other parts..
D001 for example has 562Ohm in forward direction and 1664Ohm in reverse direction. At first view it looks damaged for me, at the second view I'm looking at the scheme and getting unsure whether that could be normal...
Should a shortened one have nearly no resistance in both directions?

[PlainBill]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hello,
the last thing PlainBill said, the 'ticking' sound, I can clearly hear that. It's very silent, but has a certain repeating rhytm. The times I checked the board I thought this was normal and doesn't mean anything.
I attached a mp3 of the sound. You have to increase the volume quite a bit until u can hear it.
It seems that is connected with the fluctuating voltages at GND and Pin6. I don't have the possibility of recording the peak and low voltage, but I could measure with my multimeter a range between ~5.8 - 8.3V.

So I should look after the shortened diode?

Or replace the NCP1203D60 first?. I found a trader on eBay Germany, although he is quite expansive. Would you then also recommend to replace the four AO 4606 IC? Or does this mentioned dark spot in my first post mean nothing?

Thank you!

Don't replace the SMPS controller yet. The ticking sound would indicate there is a problem with the load on the power supply. Referencing the picture of the power supply's top side, on the upper left corner is an L shaped heat sink. There are two components attached to the heat sink next to SMPS transformer (the large yellow device). On each of these, measure the resistance from either side lead to the center lead (this is easiest to do on the bottom of the board).

Again, referencing the picture of the power supply's top side, on the left edge, center there is a component attached to the heat sink. It appears to be related to the 12V supply, and appears to have a D??? designation. What is the number on that device?

Also, as an experiment, I am considering having you remove JP28 and JP29. Before we do that. do you have access to a variable power supply?

PlainBill

[retiredcaps]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Would you then also recommend to replace the four AO 4606 IC? Or does this mentioned dark spot in my first post mean nothing?

Some fets will run hot and some browning of the board is normal. If they are not shorted, they are likely okay.

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hello,
the last thing PlainBill said, the 'ticking' sound, I can clearly hear that. It's very silent, but has a certain repeating rhytm. The times I checked the board I thought this was normal and doesn't mean anything.
I attached a mp3 of the sound. You have to increase the volume quite a bit until u can hear it.
It seems that is connected with the fluctuating voltages at GND and Pin6. I don't have the possibility of recording the peak and low voltage, but I could measure with my multimeter a range between ~5.8 - 8.3V.

So I should look after the shortened diode?

Or replace the NCP1203D60 first?. I found a trader on eBay Germany, although he is quite expansive. Would you then also recommend to replace the four AO 4606 IC? Or does this mentioned dark spot in my first post mean nothing?

Thank you!

[PlainBill]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Confirmed. The SMPS controller doesn't start until Vcc (pin 6) rises to 12 volts. The most likely cause is a defective IC. If it rose higher and there was a 'ticking' sound the other possibility would be a shorted diode in the secondary.

PlainBill

[retiredcaps]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi
1) Yes, the voltages are actually fluctuating between the given values. (measured in DC mode). I assume that shoudln't be so?

Correct, they should be rock solid steady DC voltages.

A replacement is around 61 cents to $2.00 depending on which supplier will ship to Germany.

http://www.findchips.com/avail?part=NCP1203D60

I would wait for PlainBill to confirm that this IC is likely bad. He already hinted that these ICs don't have a great reputation.

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi
1) Yes, the voltages are actually fluctuating between the given values. (measured in DC mode). I assume that shoudln't be so?
2) Yes, R044 and R047 both have 27kOhm!

[retiredcaps]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi,
between Pin 4 (GND) and Pin 6 is around 6-8V measured in DC, between Pin 4 (GND) and Pin 8 is around 200-300V DC.

1) When you say "around", do you mean fluctuating voltages between 6-8 and 200-300?

2) Can you verify that R044 and R047, two SMD resistors on the backside, are 27k ohm each?

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi,
between Pin 4 (GND) and Pin 6 is around 6-8V measured in DC, between Pin 4 (GND) and Pin 8 is around 200-300V DC. Measured with unplugged display but power supply connected to 'monitor' board via CN1.

[PlainBill]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi,
okay I will consider 'manage attachments' for my next post with pictures, sorry for that!
The IC001 has the following part number:
20306
PVGF

On the scheme they used the NCP1203D60 as a replacement. I got an offer for that part and the 4 AO 4606. But unsure whether they are really broken and the reason for the blackscreen...

The NCP1203D60 is one of a class of SMPS controllers that generates the startup voltage initially. These are notorious for failing, possibly due to a power surge. There are a couple of quick tests you can perform. Using Pin 4 of the NCP1203D60 as Gnd, what are the voltages on pin 6 and pin 8. Do this carefully - a slip of a probe can have serious consequences. Pinout of the IC is here.

PlainBill

[knurz]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Hi,
okay I will consider 'manage attachments' for my next post with pictures, sorry for that!
The IC001 has the following part number:
20306
PVGF

On the scheme they used the NCP1203D60 as a replacement. I got an offer for that part and the 4 AO 4606. But unsure whether they are really broken and the reason for the blackscreen...

[PlainBill]

Re: No power (blackscreen) with MD3021PH -> AI-0088 the reason?

Please don't post pictures inline, it really inconveniences retiredcaps and annoys me. Instead, use 'Manage attachments' - below the text entry area.

What is the part number for IC001 - the SMPS controller?

PlainBill

[knurz]

Hello forum members,
I'm from Germany and got a Medion MD3021PH 19' LCD Flatscreen. It has been working for many years without any problem, but since yesterday the screen remains black...
If you push the power button there is no response, the power on led stays dark. So I decided to disassemble the display and take a look for the power supply. Here is a picture of the front and the back of the board:



A schematic PDF is available here

In my opinion, the electrolytic condensators look fine. I tried to repeat the steps that PlainBill described in thecicero lcd inverter IC replacment needed thread.
The voltage on the big one, the C001 is around 320V so the fuses and AC/DC components should be still OK. Unfortunately you can't measure any voltage on CN1, neither on +5V and GND nor +12V and GND. When I do a shortcircuit with 10Ohms and +5V and GND also nothing happens...

On the picture of the front I just wonder about the dark spot where the white arrow points to. On the back there is the IC U101 named 4606 BE5B32. Optically I see no damage caused by heat. But is it probably the reason for the blackscreen? I could order some 4606 power mosfet and replace them...

What other things should I try next or what components I should replace?

I'm not really used to electrical complex circuit staff so I would appreciate your help!