Benq G2255 doesn't power on - amber power light when plugged in - part 2

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok, it's been running fairly well and I have been monitoring the heat on the boards without the cover back on, and noticed that it seems to heat up to 28/29 C.

So I installed a video card fan inside the assembly and now it's keeping it cool. I have fully assembled it now and have been testing it for over an hour and all is good.

I'll leave it on for a while and see how things go, but I think this time it's good.

Thank you to everyone and especially Will62 for helping me out in this great project!

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok, upon reading some of the other threads on 2 seconds to black, I saw one that suggested to resolder the transformer pins and the ccfl connectors (Will had mentionned that too).

So I rechecked everything and redid all solder joints including the high voltage capacitors (even the Frankenstein one that Will showed me how to make) and retested again, and voilà, everything works!

The screen comes on and stays on, and it's asking for an input. I left it on for approximately 10 minutes (as I was suspicious) checking the temperature of the TSUM and the 5V to 3.3V regulator, and all looks well.

So I'm going to leave it to that and wait for Will62 to logon and see if he thinks I should do anything else before reassembling and testing.

It's pretty amazing that it works, but I am somewhat suspicious because this is the 3rd TSUM it had fried the first two.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

I believe I have found the power and inverter board schematics for my monitor, at least they look very close. Posting it here for reference.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

So I checked the TSUM soldering again and found 1 bridge which I removed. Now the green light does not come on, only when I press the power button. So I connected everything keeping a close eye on the TSUM and the voltage regulator (temperature)...everything seems to work perfect, except that now I get the 2 seconds to black symptom. Tried it a few times, maybe 5 and yes when I power on the green light comes on, the CFL'S light up but after about 2-3 seconds everything goes dark.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

OK, so did this:

1. Jump 3.3V and ground to the main.
2. Jump 5V
3. Connect keypad

If you get here w/o any problems, check what the led is doing at power up and if the main is putting out the ps_on and dimming signals.

4. Connect lvds cable

Before the last step, check the ps_on, dim, and pwr_saving pins on the power supply. Any unexpected voltages?

All voltages look fine, however the green light comes on on the keypad. The 3.3V line is pulling approx. 6.3 milliamps, the TSUM is not heating up, neither is the regulator, but the green light is on. I stopped there before connecting the power supply to the main board. I have the fuse (800ma) on the 3.3V line.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

So I ended up checking everything (or almost) on the power supply board and nothing looks bad, so I thought maybe when I soldered the 61-33 regulator, I might have put too much heat.

So I installed a 1.5a regulator and tested the power supply board with only the cfl's connected. Nice clean 5V and 3.3V. So I'm off to test the power on sequence that Will62 wrote in a prior post. I'll be back for an update.......

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Just finished checking the voltages on the power supply, and the 5V line looks very good, even under the oscilloscope. So I'm thinking, maybe it changes when there is a load, but yesterday when I was checking and it blew the 3.3v regulator, I had no load??

I'm thinking of connecting a 10W 10ohm resistor on the the 5v line, which I think would draw 2 amps, and then check how it behaves? Is this a good idea or will I fry something else? Tks.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

I am posting a photo of my board for easier reference, as part 1 of this thread has been a while! Please bear in mind that these are the original photos from the start, and that all caps including the big one were changed for either Nichicon or Rubycon caps, except the C703 (25V 220uf) which is a Panasonic.

I think we are back to the root cause for the 2 threads (part 1 and part 2) and that the 5V line seems to be causing something that fried the 6133 regulator to cook. Initially (at the beginning) the 3.3V line was fine but the TSUM on the main board had fried probably for the same reason?

Any thoughts anyone?

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok, so checked my voltages on the power supply, at first I had a nice 5.02V on the 5V line and 2.87V, moving to 3.22V and after about 5 -6 seconds it jumped to 4.9V on the 3.3V line!!

Checked again, 4.9V on the 3.3V line, so I disconnected everything and checked the mosfet and guess what, it was showing .1 ohm between the 5V side to the 3.3V side. So the power supply is cooking that regulator. I still have 1, 1amp left and 2 1.5amps plus the other formats. But I won't budge until I hear from Will.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

I'll start by checking my voltages on the power supply and go from there.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok Will, the TSUM came in yesterday and I have started to solder it. Unfortunately, some of the pads are starting to lift from the board, but I think I didn't break any of them, except for one that i had to solder over the pin!?!

Still checking it out and doing some final touches before I call it a go for testing. BTW, I should mention that when I ordered the TSUM's the store that had them on AliExpress also had the other board that looks exactly like mine but not the same model. I ordered it at the same time (thinking that if my board goes bad, I'll have a backup just switching the flash and eeproms. It hasn't arrived yet, it was not with the TSUM's so we'll see.

I'll try and get this board working with the 800ma fuses and checking amps like you suggested within the next few days. I presume the fuses is on the 3.3v line or is it on both the 3.3v and 5V? I'll keep you posted. Tks.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

That resistor will load about 330mA. You could try it, but that's probably less than half of what the main will draw, so it won't tell you much. You could just wait until the TSUM arrives.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Hi Will,

Just to keep you posted. I got the parts to repair the power supply. Have changed the regulator and am ready to test. Should I test it under load, say 10W 10 ohms resistor that I have?

Still waiting for the TSUM ..........got the fuses 800ma..so in check!

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Yes, current is measured with meter in series. You might also get a few 700-800mA fuses. If a 1A regulator is on the PS, then the main is probably spec'd to draw a few hundred mA's below that. It would be nice to have the fuse blow before the TSUM gets fried.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok, Will if I understand this well, the the meter is in circuit i.e. the 3.3v goes through it to make the measurement?

Also, I do have 2 extra meters, so I'll be monitoring voltages as we go along. That little oscilloscope that I bought has a meter function as well...pretty accurate too.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

OK. Cut 3.3V line from PS. Move red meter probe to 10A socket. Set meter to DC amps.
PS 3.3V line to fuse to red probe. Black probe to line going to main. If you don't have any extra meters, you may want to pick a cheap one so that you can monitor at least one of the voltages as well.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Ok Will, I think that is an excellent idea. Could you just explain how I would hook up the meter? Between the fuse and line?

Also, I will certainly monitor the temperature on that mosfet as I test it next time. I read that the more current, the more they heat up. I think I am going to get some TO-220 regulators and maybe put a heatsink on it with a small fan in the monitor. Anyhow, I'll test different things.

Thanks for hanging on in there with me Will, I feel so confident with you in the driver's seat!

Ordered all the parts and have to wait a few weeks before coming back on. I'll keep you posted as they come in.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

You could go up to 1.5A on the regulator. If the esr on the capacitor is good, I wouldn't bother with changing it. If any doubts, remove it from circuit.

At this point, you might consider temporarily cutting the 3.3V line and connecting a 1A fuse and a meter to monitor current draw as you go through the stepped connection process.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Hi Will,

Yes it was measured with the PS disconnected. The regulator on the 3.3V is cooked too, but not the 3.3V to 1.8V.

I wonder if the PS regulator could be at the source of this i.e. maybe the main board draws more current because of age and it spikes over 1A and the regulator shorts? Do you think I should try a 1.5A regulator....I have another TSUM coming in and will order a few more.

As for the diodes on the main, they are fine.......

Also, I noticed on one of the boards selling in China, the electrolytic capacitor that is closest to the TSUM was changed .....could those caps be a problem. I had checked them and they were fine, but you never know.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in - part 2

Well, that's bad news. It does sound like a thermal issue, but it will be difficult to track down now that the TSUM is gone. Was the low ohms to ground on the 3.3V rail measured with the PS disconnected? Just want to make sure the 3.3V regulator is not causing the problem.