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

[will62]

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

For the diode lift/removal, try ~350c. Go a little higher if solder is not melting quickly. Adding flux and fresh solder helps a lot. Practice on your old parts boards first. Watch the video below. We're going to have to get back to that diode pretty soon.

https://www.youtube.com/watch?v=LADgxZgyJ04

[will62]

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

Before attempting the diode lift, check your other boards for same size diodes, and give me the markings on them. In the mean time, I'd like to rule out connector problems. Going to need you to take some resistance readings. With lamp connectors plugged in, back probe each wire and take resistance to the points in the pic. Just give me color and resistance. If you don't have back probe tips, put an alligator clip on a pin or needle. Follow the wire in from the back of the connector until you hit the metal barrel.

[rddube]

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

Hi Will,

I'm a little nervous about removing the diode or lifting the top pin, because last time I worked on a diode I guess my iron was too hot, so I killed it. Do you have any advice on how I should heat it (like not more than XX degrees)? I checked my inventory of used parts (motherboards, pcb boards, etc.) and didn't find another A1 diode, so this is the only one I have. If I kill it, I could get some from Digikey, but any advice you can give me on how to work it would be welcome! Tks!

[will62]

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

You're going to have to lift the top pin, or take the diode out of circuit. In diode mode, reverse biased (red to either of the bottom pins) meter should read OL.

[rddube]

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

These are the readings I get on D801.

[will62]

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

The attached is a pin-out on that diode. Please check it. If not 100% sure on checking, watch a video on checking a diode.

[will62]

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

Replying to your question about R802:
C805 and R802 go to pin 7. That is your enable pin. C805 is to remove ripple from the signal, and R802 is pulling the pin low to keep the chip off until it receives a sufficient voltage from your main board. We know the chip is running, so R802 is not a problem.

[rddube]

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

Pairing of :

R842-R838
R843-R839
R841-R837

read the same value.

Also, is D801 marked "A1"? Yes it is marked A1.

[will62]

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

Something quick to check... R838, R839 & R837 are used in the current detection circuit on cn801. R842, R843 & R841 are for the cn802 circuit. The pairings below should be very near each other on resistance check:
R842-R838
R843-R839
R841-R837

Also, is D801 marked "A1"?

[rddube]

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

Will, just in case (it might have no bearing) but R802 is a 304 resistor which is 300K ohms, and I get 25K ohms across it?

Ok, for resoldering the 2 pin and removing jumpers. I will also resolder every through hole component from the transformer pin 7 to CN801, including CN801.

Thanks again for your incredible support and knowledge!

[will62]

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

OK, the chip is shutting down due to an over-current reading on the connector 801 circuit. I haven't had a chance to go over the updated under lighted pic yet. It may be sometime tomorrow before I have a chance to get back to you. In the mean time, cold solder joints are sometimes hard to see. You might start at transformer secondary pin 7 and resolder every through-hole component from there down to and around cn801 (including cn801).

We know where the problem is now, so you can resolder pins and remove jumpers.

[rddube]

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

The lights come on and stay on with the 2-3 jumper (pin 2 lifted) and the 1-16 removed and pin 16 resoldered. What do we have to check?

[will62]

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

Well, that shot my over-voltage theory to heck. Now, we need to confirm if it is an over-current problem. You'll have to resolder pin 16 and remove 1-16 jumper. Re-lift pin 2 and replace 2-3 jumper. If light comes on now, we have a current problem. If not, we have a problem with a common component between voltage and current monitoring.

[rddube]

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

ok, with jumper 2 to 3 off, pin 2 soldered down, the lights turn on for a few seconds (2 seconds) and turn off.

[will62]

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

Yes, leave jumper on 16 & 1. Once we narrow it down, I'll try to explain what I think is happening.

[rddube]

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

Inverting connectors, both lights come on and stay on.

I am trying to see how this relates to the connector 801 circuit...can you trace it on the photo for me to understand?

Tks Will, you are a genius!!

Will have to remove the board to do the second test (i.e. resolder pin 2 and remove jumper between 2&3 (I presume I leave the jumper on 1 and 16?). Will get back to you in a few minutes.

[will62]

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

Now try inverting the connectors. Light still come on? If not, we have a lamp or connector problem. If yes, we have a connector 801 circuit problem.

I think that it is an over voltage reading on pin 16. Resolder pin 2 and remove jumper between 2&3. Try powering up again. If lights come on, we don't have a current monitoring problem. We can focus on the components that are used to measure the voltages.

[rddube]

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

Ok, Will, did the first test Lift Pin 16 jumper from pin 1 to lifted pin 16. Lift pin 2, jumper from pin 3 to lifted pin 2. Removed jumper on pin 5, put power and the lights come on and stay on.

I had the lights plugged the inverted way, as I wanted to have the power board upside down so as to not touch my jumpers. So the problem would be connector 801?

[will62]

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

Yes, the diagram of the MP10091ES that I put the voltages on, came from a Philips SM, maybe the same one you attached above. Problem is that we don't have the datasheet for the chip. Parameters could be different, so waves on pins 16, 1, 2 & 3 could also look different.

This is going to be tedious, but I think that it is necessary to move forward. Let's lift 2 pins at a time, so we can narrow down the connector that the problem is coming from. But, when you lift a pin, the chip is not going to be happy with no input, so you'll have to use a jumper to "borrow" the input from the other pin. The OV1(p16) and LI1(p2) go to connector 801. The OV2 and LI2 go to connector 802. So, to start:

Lift pin 16, jumper from pin 1 to lifted pin 16.
Lift pin 2, jumper from pin 3 to lifted pin 2. (jumper can be solder bridge on 2&3)

Now you have voltage and current monitoring from connector 801 removed. Remove the pin 5 jumper and power up. Do lights come on? If not, resolder pins, and lift pins 1 and 3 (jumpers stay, and they need to go to lifted pin, not it's pad). Power up again, any change?

Thanks for the pic, really clears some things up.

[rddube]

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

Ok, here is a photo of the whole board with lights shining under it.