Acer p241w

[Maluko75]

Hello to all,it's been ahwile...anyways i,ve opened the panel and visually checked the boards,nothing sems to be buldging or burnt...The screen blinks for a second and goes blank,so i,ve checked caps,resisitors and so forth and have hit a dead end,maybe someone has found a common problem with these lcd's? Any micro info would help,Thanks

[PlainBill]

Re: Acer p241w

Hello to all,it's been ahwile...anyways i,ve opened the panel and visually checked the boards,nothing sems to be buldging or burnt...The screen blinks for a second and goes blank,so i,ve checked caps,resisitors and so forth and have hit a dead end,maybe someone has found a common problem with these lcd's? Any micro info would help,Thanks

That is often the symptom of a shorted transistor in the inverter. If you can't identify them, read this, and attach both top and bottom pictures of the power supply / inverter.

PlainBill

[Maluko75]

Re: Acer p241w

Ok hope this works..........>>>>>>>

[PlainBill]

Re: Acer p241w

Ok hope this works..........>>>>>>>

Pretty good. The pictures of the power supply are excellent; the ones of the inverter not so excellent.

1. The caps ion both the power supply and inverter are a very good brand. We will assume they are good for now.

2. Are there any components on the back side of the inverter?

3. Measure the resistance between pins 5 and 6 of each of the transformers on the inverter. They should all be very similar.

4. There are two 16 pin ICs on the inverter, I101 and I102. What is the part number of these?

PlainBill

[Maluko75]

Re: Acer p241w

Ok the part number for the ic's
l101 oz9938gn/75hpu.2n/0731e
l102 oz9982gn/t10368.2g/0725c1
it's blank underneath, and pin 5/6 show blank,but if you check 1/6 it shows 958,956,961,962 all about 955-964

[PlainBill]

Re: Acer p241w

Ok the part number for the ic's
l101 oz9938gn/75hpu.2n/0731e
l102 oz9982gn/t10368.2g/0725c1
it's blank underneath, and pin 5/6 show blank,but if you check 1/6 it shows 958,956,961,962 all about 955-964

Hmm, they are driving the primaries of adjacent transformers out of phase. I wonder if that is to produce twice the voltage for each tube, or are they using one tube per transformer or are they using one tube per transformer and simply grounding the other end of each tube?

It would be a real help if you happen to have an oscilloscope and high voltage probe available. How about a spare CCFL tube?

PlainBill

[Maluko75]

Re: Acer p241w

Well i don't have neither at the moment, You think the transformers may have changed poles on neg and pos??

[PlainBill]

Re: Acer p241w

Well i don't have neither at the moment, You think the transformers may have changed poles on neg and pos??

No, nothing so complicated. I mean I don't have a real good idea as to what to do next. I haven't given up, I just have to do more research. Remember, the circuitry usually monitors voltage across and current through each CCFL. The 'two seconds to black' problem can be a failure in the voltage source (the transformer and it's drivers), the load (the CCFL and associated wiring), or in the monitoring circuitry.

Looking at the layout, let's concentrate on T102. C123, R134, and CR102 seem to form a current sense network. C120 may be part of a voltage sense network, possibly involving C123.

In theory this is easy. Measure the voltage at the output of each transformer and the current through each CCFL. Unfortunately, the voltages and frequencies involved makes this difficult. HOWEVER, the components I mentioned above (and their equivalent parts at the other transformers) make it possible to make comparisons EXCEPT that the inverter is only on for a second, and DMMS don't respond fast enough. An oscilloscope would do it; hooking a known good CCFL to each transformer would do it.

There is one more way to do this: Adjust the feedback voltage to the inverter controllers so they 'think' everything is ok, so you have the time to make your measurements. And it will take a few days before I have the time to figure out what how to do that.

PlainBill

[Maluko75]

Re: Acer p241w

Ok i'll jot down those numbers and measure the voltages,if i get stuck i'll get back to you....