Announcement

**retiredcaps** · 01-29-2012, 04:50 PM

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

Originally posted by knurz View Post

D008 (the last one and the one you were asking for; Designation is KIA 7812A PI 508): 8.3kOhm and 0 Ohm

Okay, for diodes, I usually use the diode check function on the multimeter. Yours has one.

If you retest D008, you should get a voltage reading. A good diode should test between 0.5 to 0.8V one way and you should get a "1" on the left hand side of the screen to indicate "out of range" or "infinite".

**knurz** · 01-29-2012, 05:40 PM

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

Thanks for explanation. I also took a look into the manual of the VC220.
I did a diode check for D006-D008:

Code:

D006
|>-*-<|
+ - + => 158mV from each + to -
- + - => 569mV from + to each -

D007
|>-*-<|
+ - + => 0mV from each + to -
- + - => 0mV from + to each -

D008
(no Diode symbol on board)
+ - + => 0mV from left + to -, 588mV from right + to -
- + - => 0mV from + to left -, 1196mV from + to right -

D007 really has to be replaced... Why can I grab at D006 in reverse direction 569mV? Also damaged?...
Thank you all for your support that far

I really think we can get the LCD back to work!

**retiredcaps** · 01-29-2012, 05:56 PM

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

Originally posted by knurz View Post

I also took a look into the manual of the VC220.

So did I, but I can't read German. At least I could see the specifications. For the diode test, it needs to be > 3V DC in order for the multimeter to display "1". This threshold varies for different multimeters.

D007 really has to be replaced... Why can I grab at D006 in reverse direction 569mV? Also damaged?...

I would remove D007 and verify out of circuit. In circuit readings usually suffice, but sometimes a component has to be desoldered in order to get an accurate reading.

While D007 is out, you can retest D006 and D008 in circuit. Sometimes a shorted component will affect the readings of others while still in circuit.

When you perform the check for D008, can you retest it 3 times in a row? I don't have your lcd, but I have a board here with a similar type of SMD diode and the first time I tested it, I got 0.0V and when I retested it again, I got the expected reading of between 0.5 and 0.8V.

**retiredcaps** · 01-29-2012, 06:37 PM

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

By the way, the schematic clearly shows a D009 with a dotted line.

Does your board have a D009? If yes, you should test that too.

**knurz** · 01-30-2012, 05:20 AM

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

Originally posted by retiredcaps View Post

So did I, but I can't read German. At least I could see the specifications. For the diode test, it needs to be > 3V DC in order for the multimeter to display "1". This threshold varies for different multimeters.

Well unfortunately there is no english translation for the datasheet. But you are right, for voltages higher than 3V DC it will display the '1' for overload. The display shows the forwarding voltage in mV. For the D007 (MBR10100CT) it should be around 500mV for the low testint current.

I would remove D007 and verify out of circuit. In circuit readings usually suffice, but sometimes a component has to be desoldered in order to get an accurate reading.

While D007 is out, you can retest D006 and D008 in circuit. Sometimes a shorted component will affect the readings of others while still in circuit.

When you perform the check for D008, can you retest it 3 times in a row? I don't have your lcd, but I have a board here with a similar type of SMD diode and the first time I tested it, I got 0.0V and when I retested it again, I got the expected reading of between 0.5 and 0.8V.

Okay, I will do that and get D007 out. After that I perform the checks you mentioned.

By the way, the schematic clearly shows a D009 with a dotted line.

Does your board have a D009? If yes, you should test that too.

On my AI-0088 board there is no D009. But the symbol is drawn on the diagram and there is space for the D009 though the component isn't there!

**knurz** · 01-31-2012, 05:57 AM

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

Hello again,
I unsoldered D006, D007 and D008 and performed a diode check.
I have got different values to the ones that displayed while still beeing in circuit.

Code:

D006
LT5207 SBL1060CT
[IMG]https://cdn.badcaps-static.com/image_cache/9fcb273d1459623cc6bc94c1f65456e4.png[/IMG]
+ - + => 186mV from each + to -
- + - => 1 from + to each - (no connection)

D007
LT5208 MBR10100CT
[IMG]https://cdn.badcaps-static.com/image_cache/9fcb273d1459623cc6bc94c1f65456e4.png[/IMG]
+ - + => 254mV from each + to -
- + - => 1 from + to each - (no connection)

D008
(no Diode symbol on board)
KIA 7812A PI508
+ - + => 1 from left + to - (no connection), 1856mV from right + to -
- + - => 600mV from + to left -, 1203mV from + to right -

Unlike my expectations, D006 and D007 seem to be OK.
D008 isn't a diode, so i can't say whether the values are ok and a diode check makes sense.
On the the board with D008 unsoldered, I also checked if there is a short-circuit between the Different pins. Between Pin 1 (IN) and Pin 2 (GND) there is a connection even with unsoldered D008. That was exactly the two pins i measured 0Ohm and accordingly 0V while D008 was on the board.
That shoudln't be so? Maybe C013, C019, C011 or C020 has a short circuit..

Here is again the link of the schematic:
https://cdn.badcaps-static.com/pdfs/...3099a2f00e.pdf

And the extraction of the schematic attached

Attached Files

**PlainBill** · 01-31-2012, 07:10 AM

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

We're getting back to a test I was going to suggest earlier. The readings indicate the diode is not shorted, now we have to figure out why it appeared to be shorted.

Because retiredcaps pointed out the error of my ways, I'm able to view the full schematic (thanks, retiredcaps). First, check the positions on the circuit board where D006 and D007 were installed (5V and 13.8V rails) for shorts. If it still shows that the D007 position is shorted there are a couple of simple tests to perform.

The problem is almost certainly shorted FETs in the inverter, and the way to test is to remove one end of JP28 and JP29. If the 13.8Volt rail is still shorted it is either a shorted cap, solder short, or D008, the 12volt regulator.

More likely the 13.8Volt rail will not be shorted and the load side of either JP28 or JP29 will be shorted to ground. There is no point in determining which of the FET packages are shorted, replace both - the unshorted one was stressed.

PlainBill

**knurz** · 01-31-2012, 10:52 AM

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

Hello PlainBill,
I did as u said:

D006 -> from each side lead to mid: raising resistance to more than 3,3kOhm -> should be no short

D007 -> from each side lead to mid: 0 Ohm -> short-circuit

D008 -> as mentioned in my last post, from IN to GND 0 Ohm -> short-circuit

After removal of JP28 and JP29:
Between every side and mid lead of D006, D007 and D008 there was a rising resistance to several kOhm while I was measuring.
The short-circuits of D007 and D008 IN and GND disappeared.

So when I follow your conclusion, I have to replace the FETs. How can I locate them? With the scheme I made out two FETs: 2SK2645 and Q101 BSS84. Am I right or did u mean other FETs?

Thanks

**PlainBill** · 01-31-2012, 11:08 AM

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

Originally posted by knurz View Post

Hello PlainBill,
I did as u said:

D006 -> from each side lead to mid: raising resistance to more than 3,3kOhm -> should be no short

D007 -> from each side lead to mid: 0 Ohm -> short-circuit

D008 -> as mentioned in my last post, from IN to GND 0 Ohm -> short-circuit

After removal of JP28 and JP29:
Between every side and mid lead of D006, D007 and D008 there was a rising resistance to several kOhm while I was measuring.
The short-circuits of D007 and D008 IN and GND disappeared.

So when I follow your conclusion, I have to replace the FETs. How can I locate them? With the scheme I made out two FETs: 2SK2645 and Q101 BSS84. Am I right or did u mean other FETs?

Thanks

The FETs in question are the pair U101, U105, and the pair U102, U104. You should be able to check which pair is bad by measuring the resistance from JP5 to ground and JP12 to ground. They are AO4606, which are available from a variety of eBay sellers, including this one.

PlainBill

**knurz** · 01-31-2012, 12:11 PM

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

I understand, now we are really again on the beginning with the AO4606...

U102&104: from JP5 to GND R is about 2,24kOhm
U101&105: from JP12 to GND R is 0 Ohm
From JP12 to every Pin of U101 is 0 Ohm, seems to have a short-circuit

actually this seems to be the part which caused the brown spot an the board that i mentioned in the first post

After ur confirmation I will replace U101 & U105.
The other FET pair doesn't need to be replaced?

**retiredcaps** · 01-31-2012, 04:19 PM

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

Originally posted by knurz View Post

actually this seems to be the part which caused the brown spot an the board that i mentioned in the first post

Hmm, I assumed that you tested them for shorts after post #11?

**knurz** · 01-31-2012, 05:01 PM

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

Originally posted by retiredcaps View Post

Hmm, I assumed that you tested them for shorts after post #11?

No I didn't. I just tested the voltages while power was on like Bill described in #4. I then was focused too much on the 'ticking' sound and thought I have to look for the reason somewhere else than with the AO 4606. Somehow I must have overread your first part of second sentence in #11.

Well I am still asking myself whether I should replace all 4 AO 4606 or just U101 & U105. Is it possible that U102 and U104 were also damaged during the short-circuit in U101?

**retiredcaps** · 01-31-2012, 06:05 PM

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

Originally posted by knurz View Post

Somehow I must have overread your first part of second sentence in #11.

Lost in translation!

Well I am still asking myself whether I should replace all 4 AO 4606 or just U101 & U105. Is it possible that U102 and U104 were also damaged during the short-circuit in U101?

It might be prudent to do so. The price difference on ebay for 2 pieces and 5 pieces is only 45 cents USD. So I would get 5 for $4.45 + free shipping and just replace all 4 of them.

**PlainBill** · 01-31-2012, 10:33 PM

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

If you look at the circuit, each pair drives one transformer. U102 and U104 should not have been stressed by the failure. On the other hand, ordering 5 is a good idea. It's your call if you wish to install 4 of them.

PlainBill

**knurz** · 02-01-2012, 04:06 PM

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

Well first I will only replace U101 and U105. As soon as I did that I will test the LCD again. Hope I can give a positive report then

Thanks so far

**knurz** · 02-08-2012, 05:46 PM

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

Hello again,
today I could find the time to replace the mentioned ICs and assemble the LCD. The MD3021PH works now again like it has been for many years. Hope it will continue that again for a couple of years.
Thank you all for your support, especially PlainBill and retiredcaps!

Edit:
I just found out that the right name for this 19" LCD is MD30219PH. Maybe some mod/admin could change the Thread title that other users with the similar LCD and problem can get help.

**knurz** · 02-14-2012, 04:42 PM

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

Unfortunatly I have to ask again for your help... As i mentioned above I replaced U101 & U105 and the LCD was working again.. But as I must experience, only for a short periode of time.
After that the screen became black again and no power sign.

So I disassembled again the LCD and took a look on the power board. I measured the resistance on the 4 AO4606 and again U101 seems to be short-circuit..

Before I replace the part a second time hoping for a longer time of sucess, I want to ask for possible reasons for U101 beeing damaged. Which other parts could have a failure? How to figure that out?
thank you again!

**retiredcaps** · 02-14-2012, 05:23 PM

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

Originally posted by knurz View Post

Before I replace the part a second time hoping for a longer time of sucess, I want to ask for possible reasons for U101 beeing damaged. Which other parts could have a failure?

On Benq made boards, the inverter transformers usually have poor soldering which causes the c5707s to work harder than normal. You may have the same case here?

You can try resoldering all the inverter transformer pins and see if it makes a difference?

**knurz** · 02-15-2012, 03:20 AM

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

Hello,
I did take a look, but the solderings don't look poor...

**retiredcaps** · 02-15-2012, 03:38 AM

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

Originally posted by knurz View Post

but the solderings don't look poor...

The same with Benq boards. Sometimes they don't look bad, but they are. It just cheap enough to try.

Announcement

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

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment