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

[Dumah Brazorf]

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

My experience is that i had to change lamps that look good the few seconds they was working but was worn/burned at the ends.
You can only open that panel, it's not hard but tedious. Changing the cfl desoldering the old and resoldering the new in the manner that fits inside the panel instead is a pain in the arse...

[rddube]

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

Will, I am getting weird results. Still with pin 3 lifted and jumped to pin 2. When CFL's inverted, they come on and turn off after a few seconds. I did the test 3 times, same results.

Swapped the CFL's, first test they wouldn't come on, so I thought maybe I have to wait a little for the chip to reset. Tried it after a few minutes, wouldn't come on. So I checked my jumper and the AC plug and tried it again, and this time they came on, but out after a few seconds. Waited approx. 2 minutes, they came on and out after 2 seconds. Waited about 5 minutes, this time they came on and stayed on. Turned them off, waited another 2-3 minutes, they came on and stayed on.

It's as if the problem is intermittent? What should I do now?

[rddube]

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

My experience is that i had to change lamps that look good the few seconds they was working but was worn/burned at the ends.
You can only open that panel, it's not hard but tedious. Changing the cfl desoldering the old and resoldering the new in the manner that fits inside the panel instead is a pain in the arse...

Hi Dumah,

Tks for the info. I would really like to avoid having to change the lamps, because I don't have any spares and also, there is a problem on the main board that I haven't tackled yet, trying to get the power board to work. If you look at Budm's previous post, he show a way you can test the board with scrap CFL lamps which is pretty neat. I'll have to see what Will thinks (and Budm) before contemplating changing/testing the lamps.

[will62]

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

Move on to pin 2 lifted.

[rddube]

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

Ok, Will. Just to let you know however, I tried it again after about 10 minutes (pin 3 up) and CFL in original slots, and they came on and 2 seconds they were out. Waited about 45 minutes before coming to see if you had replied, so went to the board to move on to pin 2 lifted. Before dismantling it, tried it again, the came on and stayed on!

Ok, moving to pin 2 now.

[rddube]

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

Ok, so resoldered pin 3, lifted pin 2, jumpered to pin 3. CLF in original position. First time I flip the power bar switch, I got a quick flash from the CFL's then black. Waited approximately 1 minute, then when turned on they stayed on.

Swapped the connectors. Exactly the same thing. First time I switched the AC on, got a quick flash from the CFL's then black. Waited approximately 1 minute, turned them on and they stayed on.

[will62]

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

Ok, solder pins back down. Get me that resistance to ground for each pin (2,3).
Let's try extending the time the chip gives before faulting. Remove C803. Measure it's value. Try to find a replacement on another board with ~3 times the value. Remember, if you have to, you can parallel 2 and add their values.

example: If you measure it as 820nf, try to find a replacement in the range of 2.5uf.

After changing cap(s), turn on with and without pin 5 jumped.

[rddube]

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

Ok, resoldered evrything and measure pin 2 and 3 to ground.

Pin 2: 2.403Kohms
Pin 3: 2.406Kohms

Now did partially the other operation to remove C803 and checked the value with my Fluke and transistor tester.

With the Fluke I get: 1.027uf
With the transistor tester I get 1030nf

I guess this is the same thing. As a replacement I found a 2.15uf and a 6.14uf...the 2.15uf is 2X the value and the 6.14uf is 6 times the value. Which one should I use Will?

[rddube]

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

Ok Will, found one that was 2.33uf, so I tried it. Now the lamps turn on for about 5 seconds before going out. Jumpered on C803, they stay on nice and bright.

[will62]

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

OK. We doubled the delay, and it still failed. Do you have any 1N4148 diodes? Would need 2. If not, you're going to need to pull that B6 diode off the other board and check it. Is it a common anode dual? Should test just like the diode D801. If so, go ahead and try it. It's under valued, so it may fail, but we need to rule out the diode.

[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.

[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

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

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

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!

[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.

[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

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

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

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.