cicero lcd inverter IC replacment needed

[rmac@novatone.net]

I'm trying to fix the backlight inverter on a cecero 17" LCD EV-727 Model 700P

The display works other than the backlight, it's fairly obvious what's wrong, there's a bulged cap, some cracked solder joints and a burned out IC.

I'm having trouble finding information or a source for a replacement IC.

The Backlight / Power supply board is a Lien Chang AI-0088.

The failed IC appears to have the part number 4606 and BD4Y25

Pictures atached.

[tiggerific]

Re: cicero lcd inverter IC replacment needed

Seems I looked that part up for someone else on the forum... yup, check out fairchild semi :

Cheers,
Alex

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

Thank you that should help track that down.

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

Replaced the blown IC with a NDS9435a and the board won't power up, some sort of protection kicks in. Removing the part lets the board power up.

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

Compairing the original IC to the replacement, I don't think I have the correct replacement.

The NDS9435a has pins 1 2 and 3 conected together internally the original has 1 and 3 but not 2 conected.

[tiggerific]

Re: cicero lcd inverter IC replacment needed

Hm, I did another googling and found this ebay seller selling the chip for $1 (http://cgi.ebay.com/ALPHA-AO4900-BD4...42.m153.l1262).

Looking at the datasheet (https://cdn.badcaps-static.com/pdfs/...fd452f792b.pdf) you can see that pin 2 is the 2nd mosfet gate. So you would need a dual, not a single. appears to be pin comparable, however it does not have the schottky...

Found one at International Rectifier (the IRF7901D1) but the fets are switched in the package so it might not work.

Found another at Vishay () however it has much higher gate-source voltage (+-20V vs +-12V).

[kc8adu]

Re: cicero lcd inverter IC replacment needed

watch out for that shipping on ebay.
what a ripoff!

[Harvey]

Re: cicero lcd inverter IC replacment needed

watch out for that shipping on ebay.
what a ripoff!

That's typically eBay, ridiculously cheap items but with completely extortionate postage charges.

[tiggerific]

Re: cicero lcd inverter IC replacment needed

True, but if you compare with Digikey or Mouser etc. for a small quantity of items it usually is equivalent if not better.

[Paul S]

Re: cicero lcd inverter IC replacment needed

I looked at my usual places for a replacement inverter board, but that one is not listed. Just in case you want to replace it, I did find one source, from the UK.

http://www.chsinteractive.co.uk/elec...lien-chang.htm

[Krankshaft]

Re: cicero lcd inverter IC replacment needed

watch out for that shipping on ebay.
what a ripoff!

Yeah but I'd rather pay that to UPS on E-bay and get my package on time and be able to get an estmated arrival date.

Rather then deal with the Postal Service and their TERRIBLE tracking system and their "it'll get there when it gets there attitude".

A buyer actually got into a tiff with me over why I use UPS instead of USPS.

Hmmm lets see dropping off my packages at my local Staples or taking forever to find a parking space in front of the PS and waiting in line behind 80 seniors buying one stamp for a letter. I think we call that one a no brainer .

I used to sell alot on E-bay and 7 bucks is UPS grounds base rate for 1 pound and over I believe.

Anyhoo back on topic is that burnt spot around thw high voltage transformer from the IC or is it from the transformer itself?

The reason the legs are tied is because that IC is actually a transistor with 3 outputs.

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

The discolored area of the component side is centered on the failed component on the solder side.

I've got an order going to dijikey anyway so I'm going to try the FDS8984 I'll order the ebay one if this one doesn't work.

Thanks for the additional info.

[Walter_Wpg]

Re: cicero lcd inverter IC replacment needed

I also have one of these Cicero displays with exactly the same problem. I replaced all of the bulging caps with new ones. I also had to replace the 47uF/25V cap on the primary side of the switcher. Now, the +5V and the +12V come up fine.

There are two separate backlight inverter sections, both controlled by the BIT3191. One of the circuits is fine, and the other is blackened, just like the photo that was posted. At least one of the dual-MOSFETs in that circuit is toasted. I have manually traced out quite a bit of the schematic for this inverter circuit. What I haven't confirmed yet is whether the dual MOSFET marked "4Y25" has two MOSFETs of the same polarity (e.g. N-channel), or whether there is a complementary pair - one P-ch, one N-ch. I will do some measurements over in the inverter circuit that is working. Obviously, we need to install the correct polarity device. It would certainly be useful to have a data sheet for that 4Y25 device.

By the way, I also noticed that the inverter power supply (using the BIT3191) has a shut-down function, if it sees disconnected CCFL lamps. The inverter runs for about one second, then shuts off.

More in a day or two...

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

I think the data sheet for the original IC is this one https://cdn.badcaps-static.com/pdfs/...c6e472ae00.pdf

It has one N and one P and Which would explain why the substitution ones I have don't work.

I have some and .

I just noticed looking at all the data sheets that I do have an N and a P version in separate ICs I think I'll try using two ICs since I already have them to see if there's anything else wrong before I order more parts.

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

With the two ICs wired in as a replacement the board powers up but the backlight does not come on. The BL (presumably backlight on) pin on the connector to the logic board has only .25v. I would expect a higher voltage.

[Walter_Wpg]

Re: cicero lcd inverter IC replacment needed

With the two ICs wired in as a replacement the board powers up but the backlight does not come on. The BL (presumably backlight on) pin on the connector to the logic board has only .25v. I would expect a higher voltage.

That's what I also thought initially, but I traced that line over to the BIT3191 chip. I now believe that this is an analog voltage input (driven by the LCD display controller board) that determines the brightness of the LCD backlight. I don't have my hand-drawn schematics here at work, so I can't give you any details right now.

I'm also curious about the one other signal pin on that 10-pin connector (pin 9?).

[Walter_Wpg]

Re: cicero lcd inverter IC replacment needed

That's what I also thought initially, but I traced that line over to the BIT3191 chip. I now believe that this is an analog voltage input (driven by the LCD display controller board) that determines the brightness of the LCD backlight. I don't have my hand-drawn schematics here at work, so I can't give you any details right now.

I'm also curious about the one other signal pin on that 10-pin connector (pin 9?).

Oops...one more thing. On my unit, that BL pin was at about 1.25V DC, and the backlight (when it came on for the 1 second) was quite visible, but not hugely bright. Maybe try the brightness adjustment buttons on the display, see if you can see that BL voltage change? Is it possible that the 0.25V you see means "set the backlight very dim"?

[rmac@novatone.net]

Re: cicero lcd inverter IC replacment needed

I have lables for most of the pins:
1-2 12v
2-4 Ground
5-6 5v
7 BL Which could easily be Backlight Level
8 Ground
9 Ground
10 N/F

I don't know what N/F is but the trace runs through JP4 to a surface mount transistor very close to the burned out IC.

[Walter_Wpg]

Re: cicero lcd inverter IC replacment needed

Success!
I obtained some samples of the Alpha & Omega AO4606, and replaced the one on my inverter board that was toasted (U105, I think, but I forgot to make a note of it; it was in the blackened PCB area). Connected the LCD panel back up, plugged in the AC, pressed POWER, and presto! the power LED went on and the LCD panel, after a few seconds, gave me a nice "NO SIGNAL" image. Connected it up to a PC video output, and the display works fine.

So, to summarize:
- replaced several bad/bulging electrolytic capacitors in the power supply secondary, including C013, C019,C027,C014, which were all 1000uF 25V CapXon KF types. I did not have exact replacements, so I used 470uF 50V caps.
- One of the backlight inverter circuits had also failed (as a consequence of the failing power supply?); replaced complementary MOSFET AO4606 at location U105.

As someone earlier in the thread mentioned, the AO4606 has both an N-channel and a P-channel MOSFET in it. N channel on pins 1,2,7,8 and P-channel on pins 3,4,5,6.

By the way, if anyone is getting ready to repair one of these LCD monitors, and you haven't opened it up yet, there's a trick to getting the front bezel off: Undo the 4 small Philips screws along the bottom edge of the bezel. Then, slide the bezel upwards, towards the top of the screen. This will unhook plastic hooks on either side of the rear of the bezel from notches in the LCD metal frame. You don't have to pry the bezel aggressively. In fact, if you do, you might break those plastic bezel hooks.

Good luck!

[truename]

Re: cicero lcd inverter IC replacment needed

Where did you get the AO4606? I need a few of those and wonder if this will work instead: http://www.newark.com/jsp/search/pro...FC-GB100000001

Thanks...