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

Hi Will, ok tried it on DC, here is what I get:

Pin 6, I get .92V with a sine wave (small amplitude) steady.
Pin 2 & 5, I get .32V straight line no waves steady.
Pin 1, I get .32V but about every 2-3 seconds I get a spike (it's too fast to see the measurement) and it is constant, every 2-3 seconds like a heartbeat. It stays at .32V and only comes high with the spike that lasts a micro second.

[will62]

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

Doesn't sound like good comms between the main ic and the flash. Does pin 1 stay low, or go back to a steady 3+V after several seconds?

[rddube]

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

It stays low, with the spikes every 2-3 seconds....I left it on for about 30 seconds to see if it would come back high, but did not.

[will62]

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

OK, it is accessing the flash, attempting to load the hex code, unable to do so, then staying in a loop trying. If you had a good clock and data in signal, it might be the flash chip with the problem. Doesn't sound like you have either.

At this point, I think we need to try to resolve the low ohms to ground issue with the 3.3V and 1.8V. The 1.8V is the chip's core voltage. It goes nowhere else on the board. The only 2 places the 2 voltages are in close proximity is at the voltage regulator and inside the chip. I would start by removing the U12 regulator. Recheck ohms, if still low, remove filter caps C85,86,87.

If you still have low ohms, I'd be willing to bet that the chip is causing it. It is available on ebay for $7.99.

[rddube]

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

Ok, I'll get to that asap. Just curious however, when you say the chip is causing it, do you mean the big 128 pin chip? Oh boy, if that is it, then I'm in for a real contract to change that chip...I'll definitely need your moral support!

Will get back to you with my findings soon. Tks Will.

[will62]

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

Just watch some videos on drag soldering. If it turns out to be the chip and you order it, you'll have 2-3 weeks to practice before it arrives. Practice on your junk boards. Wick off as much solder as you can from a chip and practice your drag soldering.

If the regulator checks out, do you think that you'd be able to lift single pins on the chip? I don't think I've ever attempted lifting them on fine pitch chip like that. Maybe using the tip of an exacto knife as you heat the pin? There's only 18 power pins, and if you choose wisely, you may only have to lift 1.(LOL)

If you are going to replace it, most people cut all the pins from the chip, then remove each pin from the board.

[rddube]

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

ok, I'm in it for real! Will, what about C530, I also get 80ohms on that one too (haven't started yet on the mosfert and the other caps)?

[will62]

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

All of your filter caps are in parallel. You'll probably read that 85 on all of them.

[rddube]

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

Ok Will, took out the mosfet (still low ohms, so removed C85, C86 and C87 and it's still at 82 ohms on the 3.3V rail and 42-43 on the 1.8V rail.

[will62]

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

I'm thinking that it is the chip. I'll look back over the schematic. In the mean time, please give me the resistance between the 3.3V and 1.8V rails.

[rddube]

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

Hi Will, resistance between 3.3v and 1.8V rails is 118.3 ohms (looks like the sum of each rail?).

[will62]

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

My best guess is that the problem is with the TSUM chip. We can't be for sure that the 40 & 85 ohms to ground is a problem for that chip, but the lack of a good clock and data signal to the flash, points to the chip. I'd be more certain if your scope had higher bandwidth, but that's the best tool you have available to check it with.

Before ordering, you could go back and try different settings on your scope to make sure that clock and data signals are absent. On your scope, signals should look similar to the crystal (but brighter). If you get different results, problem would shift to the flash chip.

[will62]

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

Read the thread below. OP had power rail with 65 ohms to ground. Some thought that indicated a short on the CPU. OP replaced board. The new board also had low ohms to ground, but worked.

The 85/40 on your board may be normal. This gives me pause on jumping to the conclusion that the main chip is bad.

https://www.badcaps.net/forum/showth...t=36494&page=2

[rddube]

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

Yes, you're right. One of the guys in that thread says he baked the board in the oven!!

Ok, so I'll put everything back in place (mosfet and capacitors) and maybe try and do some more tests on the flash. What about the EEprom, is there any way we can check that? It's getting voltage ok.

Would the main chip communicate with the flash if the EEprom was wiped or erased?

[will62]

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

Yes, the eeprom could be checked next. I've included the datasheet below.

Pins to check:

5 - SDA (data)
6 - SCL (clock)
8 - VCC

Here's something I found on a BenQ similar model:

1.) DDC (Display Data Channel) function: We use DDC IC to support DDC2Bi function. DDC data is store in 24C02 (EEPROM). Those data related to LCD monitor specification. PC can read them by “SDA” and “SCL” serial communication for I²C communication for DDC2Bi.

2.) Scalar IC: TSUMU58NWHJ-LF-1 is a total solution graphics processing IC for LCD monitors. It is configured with an integrated triple-ADC/PLL, an integrated DVI receiver, a display processing engine, an integrated micro-controller and output display interface that can support LVDS panel interface format. And it also integrates power management control capability for green-mode requirements and spread-spectrum support for EMI management.

3.) EEPROM: We use 24C16 to store all the adjustable data, user settings and use 24C02 to store D-SUB and DVI EDID data.

4.) Flash ROM : We use 2M bit flash to store the FW hex.

I would think that the led would change from amber once the firmware was loaded from the flash.


Added:
Maybe try freezing the eeprom and flash. Watch about 6:20 in to this video:

https://www.youtube.com/watch?v=kPCisa9BYkk

[rddube]

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

Do you think it could be worthwhile trying to do what I mention in post #4, on board?

As soon, as I get the board back together that small cap is giving me a headache, I can hardly see it, I will try freezin the flash and EEprom and see what that does.

Will report probably tomorrow night. Tks Will!

[will62]

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

On post#4, you're doing this to learn, and that would definitely kick the learning up a notch. I would recommend trying to find a 24c16 on a another board, and experiment with it. I wouldn't erase the eeprom on this board until you are confident that you can get a copy of what is on it. Be aware that only a few Arduino models have a 3.3V signal voltage. Probably not a problem on this eeprom, but it would be for the flash. You might need voltage dividers.

Can you give me the link to where you got the .bin file?

[rddube]

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

Hi Will,

If I remember well, I think I got it here:

http://**************/forum/54-31467-1

I registered and passed the test to be able to download the firmware.

[will62]

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

OK, looks like that's actually the firmware for the flash chip, not the eeprom. Glad you found it. The highest tolerated signal on the flash is about 4.6V. As mentioned above, only a few Arduinos are below that. You need to check the specs on the Uno. Not a deal killer, but would require the voltage dividers.

[rddube]

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

Hi Will,

Redid some testing on the Flash and Eeprom chips.

Flash: pin stays low, like 0 volts all the time. Pins 6, 5, and 2 also don't seem to be much activity almost not change on the line which is at 0 volts (i found out how to zero my oscilloscope). Only pin 8 gives a steady 3.02V.

Eeprom: Pins 5 and 6 have .60V pretty steady. Pin 8 is at 3.02V also.