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

[will62]

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

I think that is your problem. It is a voltage regulator. Can't read the number on it, but it looks like it has a 33 in it. The pins are marked I/O. See if you have 0 ohms from your 5V line to the input pin, and 0 ohms from your 3.3V line to the output pin. I wonder if your 3.3V to 1.8V regulator on your main board was taken out as well. Do you have a CR2032 battery on an old motherboard that you can use to check it? (or any other 3V power)

[rddube]

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

Ok, so I set out to do the tests...took some time because I prepared myself with some jumpers on the connector to be able to do the step by step.

As I was ready to go, before starting to jump the 3.3V, I checked my voltages on the power supply. Turns out I have 5V but .3V on the 3.3V line.....yak....so I checked the mosfet in the photo....on the bottom pin I have 5V on the top pin, I have .4V.

Probably something happened when I fried the TSUM, I no longer have 3.3V. Do you think it's the mosfet that's gone? I checked the resistance between all pins and I get around 275K ohms, but I only get .4V where I think I should have 3.3V, right?

Ok, so I have to take a step back and fix this before doing the other tests. What do you think Will?

[rddube]

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

Just wanted to make sure that you are not connecting/disconnecting any of the connectors when the power is on. That could cause a voltage spike.

No don't worry Will I learnt my lesson a long time ago. I'll keep you posted.....tks

[will62]

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

Just wanted to make sure that you are not connecting/disconnecting any of the connectors when the power is on. That could cause a voltage spike.

[will62]

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

Good question on the diodes, and I'm not sure about the answer. Not much to the keypad. 5V switched in to the leds, 3.3V to tact switches with a resistor ladder. Nothing there that I can think of that would kill a 6.2V zener. You could check resistance between the signal pins and led pins to ground (disconnected from main).

[rddube]

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

Ok Will, I understand, will get to testing in a few minutes.

I have a question however...why do you think the 3 diodes were killed? Could the keypad be defective? I'm not sure I totally checked it there are a number of pins on the switches ...but I checked all the resistors and they were good.

Let me know if I should check it further before proceeding with the tests. Tks

[will62]

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

Nice work. If you're sure that there are no bridges, we can proceed with a power up sequence. I'll attempt to explain the approach that I was thinking about, and you can let me know what you think.

Rather than just connect everything and power up to see what happens, we need to be able to isolate where the problem comes from if the chip gets fried again. Start with everything disconnected from the main, then connect in the sequence listed below. Before powering up after each connection, press your finger(s) to the top of the TSUM, and with the other hand, be ready to kill the power switch if you feel the chip heating up. Wait a while to make sure everything is stable before powering down, and moving to the next connection.

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?

5. Connect power supply.

[will62]

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

Nice work. If you're sure that there are no bridges, we can proceed with a power up sequence. I'll attempt to explain the approach that I was thinking about, and you can let me know what you think.

Rather than just connect everything and power up to see what happens, we need to be able to isolate where the problem comes from if the chip gets fried again. Start with everything disconnected from the main, then connect in the sequence listed below. Before powering up after each connection, press your finger(s) to the top of the TSUM, and with the other hand, be ready to kill the power switch if you feel the chip heating up. Wait a while to make sure everything is stable before powering down and moving to the next connection.

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?

5. Connect power supply.

[rddube]

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

Looking at the photos, you'd think there is a bridge between pins 12 & 13, but there is no bridge, I rechecked it and with meter and that is fine.

[rddube]

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

Ok, so changed the diodes (and checked them, OK), checked the PWR_Saving Diode (OK), checked the caps near the diodes for resistance (OK), installed the TSUM, checked for bridges and cleaned her up, and all seems fine. Rechecked all diodes and transistors on the main and they all look ok.

Attached are photos of the new chip and the new diodes.

What next Will?

[rddube]

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

Ok Will. For the C2's I have a bunch of them on another scrap board, so I won't have to order them. I'll make sure to check the diode on the Pwr_Saving now.

When I'm all done, I'll definitely let you know before trying anything. Thanks Will!

[will62]

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

You should be fine with a slightly lower rated zener, as long as it's still above Vcc (3.3V). Just make sure the orientation is correct when the new ones go in.
For the capacitors, just check resistance across them. As mentioned before, the three signal lines have pull up resistors on them. The lines should have a low resistance to the 3.3V rail, and a high resistance to ground.

Before ordering the diodes, go ahead and check the diode on the Pwr_Saving circuit of the power supply. I don't think that you ever checked that one. It's probably ok, but let's make sure before you put that order in.

If you have checked all transistors and diodes on the main, the new chip is ready to go in. Once you have it in, cleaned and checked for bridges, let me know. Let's try to come up with a cautious power up sequence to avoid frying this chip.

[rddube]

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

Will, you're right again. I hadn't realized that there is another connector circuit, boy am I learning stuff as we go along.

Thanks Will for sticking in there with me!

Ok, so the ones I have that are bad are UDZ6.2B and the only ones I found that are zener diodes of the same size (the C2) are UDZ5.6B.

As per the attached specs, they are slightly lower rated, so do you think I could try them or is that risky? Should I be better off ordering the exact same thing?

Also, I notice that there is a capacitor on each line - should I check those out of circuit?

Finally, if you think I could try the C2's, do you think I'm good to go and install the other TSUM and test?

Thanks again for your advice.

[will62]

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

Your board is very close to the schematic... ZD6, ZD7, & ZD8.

[rddube]

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

Wow Will, that was like magic! A few questions, the datasheet seems to show SOD-323F type even though they say SOD-323 - the diagram shows the legs coming from the bottom of the diode whereas mine come from the top of the diode which is a true SOD-323. Also, I can't find the E6 marking in the datasheet, it stops at E5. As for the part number on the schematics, don't forget it is close to my board but not exactly the same. They have ZD6, 7 & 8 whereas on my board shows in the legend ZD6 and ZD9? What do you think?

[will62]

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

Attached schematic with part numbers and main board pic with locations. Also the datasheet.

[rddube]

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

I found a bunch of C2 diodes (from a scrap monitor main board) and those are marked on the board ZD also. I tested them and they conduct only in one direction on the board.

[rddube]

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

Hi Will,

Yes that is correct. I think your post crossed my edit of the last post. So they are zener diodes! Can you figure out the legend on that, it doesn't seem to correspond to what is on the board?

[will62]

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

Look at the schematic, the part number is given. They are zener diodes. When you say "they don't give anything in resistance", I take that to mean 0 ohms in both directions... correct? if not shorted, they are non-critical. They are in parallel with capacitors to provide ESD protection. The capacitors may also provide debouncing for the the switches. If they were shorted, they would pull the 3 signal lines to ground. We went over the keypad voltages a few pages back and all was well with it. Read back to where we checked it. You can recheck voltages again if you like. All three signal lines have pull up resistors to 3.3V. When you press the keys, the voltages change. The chip responds to the voltage change.

[rddube]

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

Ok so I removed the bottom one in the photo in the previous post, and in diode mode, both ways it gives nothing. So I guess it is open? Doesn't give anything either in resistance check.

But I am trying to get the datasheet for it, and Will you were right they are standard diodes I think, but I think the marking is E6 instead of 93. When I search for E6 marking (or 93 marking) for SOD323 I get all sorts of results. Don't know what the specs are. I have same size diodes from a scrap video card and they are marked S4...do you think they could be used? I tested the S4, and they conduct .250V one way only.

Also, I uploaded a photo of the diode I removed and circled a legend on the board which seems to correspond to that area, and the coding is ZD....I guess for zener diode?