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, I did find a few 5V to 3.3V regulators but they are SOT-323 instead of SOT-252. Do you think that could do it or will it heat up to much? I could add a small heatsink if you think it could work?

part number FS1117 33GJAD02. On the same board I also have a 1.8V regulator in the same format SOT-252 in case something goes wrong with the one on the main board.

PS - I had found a SOT-252 on a video card but it was so difficult to remove with hot air, I had to crank up the heat to 390 and I either killed it or it was already bad, because I have 0 ohms from input to ground but ok resistance from output to ground.

Question Will: Could the 5V line not be clean and that is causing the issue and also killed the 5V to 3.3V regulator..or am I just being paranoiac ? Also, I got a new hand held oscilloscope AllSun EM125 wich is supposed to be 25mhz, but just starting to know it...but if I can do better checks than with the former one, I'll do them. I'll also be getting tonight a used Leader 1020 oscilloscope that seems to work fine. I'm pretty sure I'll be able to do more tests with that thing!

[will62]

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

I couldn't find anything on the old regulator. Problem is, we don't know the current draw of the 3.3V on the main. If you put an undersized one on, it will not last. You could look at the 5V with one of those scopes. If there's anything on it, you'll see it.

[rddube]

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

Hi Will,

I guess I'm a little stuck - searched for the part number (it is good) and nothing comes up like you mentionned. Tried with the part number from the Philips manual RM2101D0BA and can't find anything either.

A question that I think was already answered is I shouldn't power up the main board without the cfl's connected, right?

I can check with the small oscilloscope the 5V line, but I'm not sure what I am looking for?

How about your idea of connecting a 3.3V battery to the main board with my amp meter in series, would that tell me how much milliamps it's pulling?

[rddube]

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

Here's a larger photo of the chip in case I might have missed something. There seems to be something written over the 61-33.

The first character I'm not sure what it is (looks like a reversed 3) and the other 2 are ll...probably the manufacturer?

I think Will I should check the 5V properly, as it doesn't really show up in the photo but the chip looks charred on the left edge (the edge of the 5V pin).

I got the Leader LS1020 oscilloscope late last night, wow what a mammoth. Not sure how to set it to check voltage, but I'll check on youtube and see if I can find something.

The FS1117 are rated at 1.2 amp, do you think it could be more than that? If yes, then I would need to order some from Digikey, they go up to 5A.

[vinceroger69]

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

user manual for your scope if you dont have it already

[rddube]

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

user manual for your scope if you dont have it already

Thank you Vinceroger69!

[rddube]

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

Ok, checked the 5V line at the regulator pin with the small oscilloscope. Probe on 1X measuring AC. Photos attached.

Unless I'm reading this wrong, I have ripple of approx. 800mv which I think is not good. What could be causing that if it is that much? The caps I installed are Nichicon, so probably not the caps?

Have to fix that before going any further..what do you think Will?


PS - Tried the bigger oscilloscope but wasn't getting consistent results, maybe it needs calibration or cleaning I don't know. What do you think Vinceroger69, do you have this oscilloscope?

[vinceroger69]

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

i have a trio 20 meg analogue scope myself but still getting used to using it so cant really comment, although i have calibrated the probe leads to the scope as per user manual im sure a more experienced member who has used a analogue scope will advise you more, there are also some good analogue scope videos on you tube im just watching a few now myself.

[will62]

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

I believe I've found the regulator. If this is it, it is rated at 1 amp (see pic and datasheet). I would try to verify that ripple on the 5V with one of your other scopes. It looks like ripple with a noise (ringing) component on it. Inductors and capacitors on the circuit would be suspect. Watch this video by Dave @ EEVblog:

https://www.youtube.com/watch?v=Edel3eduRj4

Edit: Is the ripple with the bad regulator in circuit? If so try removing it.

[rddube]

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

Wow you found the datasheet, incredible! You're not only a master in electronics but also an amazing guy! Tks Will.

Ok, so I watched the video, very very interesting. So I set out to do what Dave shows in the video with the Leader oscilloscope, with the chip out but wasn't able to reproduce what Dave was doing (I think my leader osci needs either cleaing or calibration...that will be my next project once I get this monitor going).

Checked the circuit with the mini osci and the 5V line looks good. Checked the chip with my transistor tester and it shows good. I checked the chip with 5V input and it gives me 4.5 volts output out of circuit. I replaced the chip back in circuit and now it gives me 4.5 volts output (instead of 3.3V), so I checked the capacitor and it is 10.02 uf (the datasheet says 10 uf)....so not sure what is going on.

I also tried the FS1117 chip instead and hadn't looked at the pinout, so I fried it. I have another FS1117 or an FS8860 (this time I would connect them the right way if you think I should try those). The FS1117 asks for a 22uf cap at the output, whereas the FS8860 requires a 10uf cap at the output.

So what do you think I should do Will?

[rddube]

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

Ok, so I got the Leader oscilloscope working fine and watching the video, I checked ripple on the 5V line and it is approx. 25 millivolts, so I guess that is not an issue, right?

[rddube]

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

Ok Will. I decided to move on with the power up test using the FS8860 chip. I get a nice 5 volts and 3.3V on the power supply board.

I did the following:

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.

When I apply power (120V), I have all my voltages, including the 1.8V, the chip is not heating up, no leds come on. When I try to power up the monitor with the keypad (without LVDS connected) it does nothing. Nothing happens. My voltages are all ok.

I stopped there waiting for your guidance.

[will62]

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

Thanks Rddube, but no master here, I'm learning just like you. If I knew more, we would wrap these threads in a couple of pages. The 25 millivolts on the 5V line is fine, let's move on to replacing the regulator.

The capacitor in question is for frequency compensation. Although the 1117 shows a 22uF in the diagram, the sheet specs a minimum of 10uF, so no need to change the cap. For good heat dissipation, that top tab needs to lay on the pad. Can't do that unless the tab is ground on the replacement regulator. Check for continuity between the tab and pins 1 & 2. If no resistance to pin 1 (ground), then you can use it. Even then, you would have to use pieces of a resistor lead (or small wire) and solder in jumper wires that cross w/o touching, because the input is pin 3. Let's see what you find.

Edit: posted this before reading your most recent post.

[will62]

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

Power up and check the other pins on the power supply. Do you see any voltages that would damage the main when we connect it (ps_on, dim, pwr_save)? If not, go ahead and remove jumpers and connect power supply with everything else disconnected, feeling for heat on the chip. If stable, move back to connecting keypad.

Reminder, don't connect or disconnect anything with power on.

[rddube]

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

Will! Guess what.....total success!!! Thanks to you! I am writing you with this new monitor that has a Frankenstein cap, has had it's chip legs lifted and jumpered a few times and all the wonderful fun and learning I have done!!

Again, thanks to you - it is picture perfect! Photo attached.

I don't know how to thank you enough, I just hope the board manager TopCat sees this and promotes you to Top Badcaps Master!

Again Will, sincerely, I have never learned so much in electronics repair than with our 2 adventures (part 1 and part 2). I am extremely grateful to you!

Thank you also to all of those that have contributed (Budm, Dumah, Momake, VinceRoger) and a total mega thank you to Will62...from the start, I knew if you would continue to guide me that you would take us to this total success, and you have. I'm completely overwhelmed!

[rddube]

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

Well, well, I might have jumped to conclusions too quickly. Although the screen works fine, after about 15-20 minutes the green power light went out....not responding to any key press. I had to unplug the monitor from the main, restart it and the light came back and stayed on for another 15-20 minutes then off. It might have to do with a factory reset, so I'm going to explore how to do this..otherwise it is working crisp and clear!

[rddube]

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

Update...after trying to get into the factory menu (holding Menu key and powering on), I did see the factory menu for approx 3 seconds, and then the screen went black, and the light became amber with no response to key press. Tried disconnecting the main and reconnecting but then I would get "no input signal" on the monitor, amber light. After a few tries, when I would power up I would still get "no input signal", pressed the enter key and it came up with DVI or DSUB, so I chose DVI. It went back dark, and amber light. The last 3-4 tries it's acting the same problem as in the beginning, amber light comes on and does not respond to keypress. Tried to cycle a few times and same result. Nothing on the screen.

Must be those lower capacity diodes I put in that didn't like 2 keypresses at the same time? Well, tomorrow I am going to reopen it and check the components and the voltages to see where I'm at....almost got there!

[rddube]

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

Well, I guess the TSUM is shot, as I have 2 ohms on the 3.3V line and 168 ohms on the 1.8V line. The 5V line is fine.

Back to square one.....too bad because it worked for about an hour....maybe it is heat related?

[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.

[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.