Benq G2255 doesn't power on - amber power light when plugged in

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I'll would rather use a 10k resistor for dimming instead.

Well Dumah, I'll give this a try as soon as I get that diode resoldered (and find a 10K resistor). Thank you for the tip. I'll report back as soon as I have tried it.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I'm adding a couple of diagrams from the MP1009 datasheet and some comments. This is pertaining to my above comment about the signal from the main board. Do you follow what I'm talking about on it?

The mosfets may test differently, the lamps may be suspect, but when you disable current monitoring, both lamps come on immediately without any flicker. We haven't found any bad parts yet, and we've got to consider that there may not be any.

Oh yes I understand very well what you are talking about. Just not sure how to rule this out without getting the main board working....I was able to get the firmware in a zip file for this monitor from a Russian website. Maybe we could try to flash the firmware and see if that fixes it?

I have a Uno board and could unsolder the Eprom chip and try to program it? I realize that it is a big task for which I'm not sure I would succeed, but what the heck! Let me know what you think.

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I'll would rather use a 10k resistor for dimming instead.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

To test the power to the lamp, Budm's method is the best option I've seen unless you had extra ccfl bulbs laying around. Not sure if the bulb you have will work. You would have to get Budm's input on that.

Another thing I'd like his experience on, is what are the odds of the inverter section of the power board, and the main board failing at the exact same time. The only common
links are the enable and dimming connections. Is it possible the driver chip doesn't like the 3.9V that you have jumped to it for dimming. In other words, is it possible the problem we're looking for doesn't exist when proper signals are received from the main board.

There is a user in another thread that says that it would work, but Budm has not responded yet. https://www.badcaps.net/forum/showthread.php?t=19987

Your other point is quite good, in that yes, what are the odds? Unless when the power board went out, it damaged something on the main board? So would a proper test of this is to remove the 3.9V for dimming? I have it connected with a 1K resistor to the 5V, should I try and connecting it to the 3.3V?

Or are you saying we would have to find the problem on the main board first to get it to work?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I'm adding a couple of diagrams from the MP1009 datasheet and some comments. This is pertaining to my above comment about the signal from the main board. Do you follow what I'm talking about on it?

The mosfets may test differently, the lamps may be suspect, but when you disable current monitoring, both lamps come on immediately without any flicker. We haven't found any bad parts yet, and we've got to consider that there may not be any.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

To test the power to the lamp, Budm's method is the best option I've seen unless you had extra ccfl bulbs laying around. Not sure if the bulb you have will work. You would have to get Budm's input on that.

Another thing I'd like his experience on, is what are the odds of the inverter section of the power board, and the main board failing at the exact same time. The only common
links are the enable and dimming connections. Is it possible the driver chip doesn't like the 3.9V that you have jumped to it for dimming. In other words, is it possible the problem we're looking for doesn't exist when proper signals are received from the main board.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hi Will,

I understand that we are getting wild results, but it may be because of putting the original mosfet back in (as for the underrated one, my mistake was to not keep it, I assumed it was blown and threw it out, but because the original was the original I kept it).

Could it be that if there is a bad lamp (when they light up, they look normal to me, but it is only a white screen, so it's hard to tell if they are both perfect), is it getting worse with the tests?

Maybe we should go to the lamp route, and use Budm's method with one of the F13TT lamps I have. I could plug it into the CN801 and see if the lamps go out?

What do you think?

Edit: Also, I am not sure that my oscilloscope is very precise, sometimes it gives me results that I cannot replicate, so please bear with me and thank you for your patience.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

This is where we were:
With pin 2 lifted, meaning that we are not using the LI1 monitoring circuit, the lamps would light without jumping pin 5. You could invert the lamp plugs and both lamps lit without hesitation as long as they were only monitored by LI2 (p3). This is very important, because it ruled out a bad lamp.

This is where we are now:
With either pin lifted, the lamps come on sometimes, and sometimes they don't. It doesn't matter if LI1 or LI2 is doing the monitoring. This indicates that it could be a bad lamp. It's like we're teetering on the edge of pass/fail fault monitoring, but now it's on both LI1 and LI2.

Question:
How do we get back to where we were? What all changed between when you ran the tests? Was it putting the original mosfet back in? Is a subtle change on the primary side, kicking us over the fault threshold? Which goes back to why did the lamps light up for 10 seconds (w/o anything jumped) when you put the under rated mosfet (AF) in? Did it in fact blow?

If we can't get consistent test results, we're never going to be able to rule anything in or out as the problem. You can put the diode tab back down, but please don't change anything else until you confirm or modify what was said above.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Doing tests with pin 5 jumped, both lamps on bright, right?

We're looking for about 12Vpp.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

ok, with diode tab lifted, at the setting of 1V X 1 multiplier, I get 1.57V vpp for R837 and 1.73V vpp for R841.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

At the setting of 1V X 1 multiplier, I get 1.45V vpp for R837 and 1.65V vpp for R841. I'll try now with the diode tab lifted and report back in a few minutes.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Left side, closest to diode, of R837 and R841. If you do not get a sine wave of ~12V peak to peak, try lifting top tab of diode.


On the scope:
OK, your multiplier and volts/div combine on screen. My multi is on the probe. You're still getting a low Vpp.
Yeah, I realize that you are using a 200kHz scope to look at 70kHz waves. Enough bandwidth to see that a signal
is there, but not enough to zero in on anything.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

The pics today are on 2 voltage scales (says in the lower left of the screen). Also, notice that the voltage readings are in white font...when I was probing between r837, r839 and r841, r843, the voltage readings were in red and didn't seem to register? Might be my scope, this thing is not precise.

Also today's pics were taken at the chip pin, whereas the other pics were taken at the output of the diode which was my closest point near a component.

Just to make sure I am doing it right, when you say to probe between r837 and r 839, I suppose you mean the left side of R839 or the left side of r837?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

That's exactly what I had in mind for Frankie II, but hold off, you may not need it. Your pics of waves taken today, show that the diode is doing what I expected. Compare today's pic Vmins with an older pic that had me concerned about the diode. I wrote on the screen what the Vmins were on the older pic. Also Note the difference in Vpp. Today, you're barely clearing 1V, whereas before you had ~12V. Are you using different multiplier settings on the scope? If you are actually near 1V, that Vpp is right at the threshold for open lamp fault. (from 1009 datasheet: LI1 and LI2 Inputs...-5.8V to +5.8V, typical circuit on datasheet not using clipping diode)

Try probing at the voltage divider as mentioned in an earlier post. No need for pics, just give me the voltage readings on the scope.

Added: Voltage readings at dividers?

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, so I probed between R837,R839 and then between R841,R843 and am getting pretty much the same waves. If you want I can upload pictures.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

In the meantime I took some more readings with the oscilloscope, this time I used my needle probes and was at the pin itself. Here they are.

For Frankentein 2, is this what you had in mind?

Will wait for your comments on the oscilloscope readings before building Frankie!

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I was thinking that the one marked B6 was a BAT54. The BAT54 comes in 4 flavors. The "cw" is a single diode package. I believe the B6 is dual common anode, which is what we need. It is under-valued and might blow at power on, but I was wanting to check it. If you can't find the B6, I see Frankenstein II coming on. The HSB2838 has perfect ratings, but is a dual common cathode. Can you figure out how to use 2 of those with pieces of a resistor leg to make a dual common anode that will solder to D801's pad?

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hi Will,

Ok, thank you so much for clearing that up. While reading your post, I realized that I had ordered some switching diodes from China a few years ago while trying to fix an Asus motherboard. So I searched my "motherboard" junk box and found some Bat54cw-7, L2n7002ltig, hsb2838, hsm2838c and some other marked 3IA that I can't remember the technical number, but I believe the bat54cw-7 could maybe do the job?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

We need an ultra fast switching diode. Regulars won't work. I believe the B6 was one of the ones you listed the other day. If it's what I think it is, it's the only one that is close to what we need for D801. I know you checked D801, but we need to rule it out.

(added explanation)
The way D801 is set in the circuit, it should be clipping most of the negative portion of the wave (see pic 1). D801 is a dual, both signals (pin 2,3) are going through it. That's why I asked you if the negative swings on pin 2 were a fluke, or happening all the time. The chip has an open lamp detector and it is triggered by either LI1(p2) or LI2(p3) pulling down an internal signal (see pic 2). I hope that explains why I'm concerned about the negative swings on the signals.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Oops, Will I think you lost me there. I googled 1n4148 diode and they are those little orange diodes ...i have lots on scrap boards. We need 2, so where would we put them? I can't seen to find the B6 diode? Please elaborate or guide me....I have lots of all kinds of standard diodes like the black ones in the photo.