Doublesight DS-240WB turns off after 5sec-5min

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

Ok, I had 24v when I checked the power brick. I seem to have 23.5 to that point when the monitor is on. When it goes off I have 24v again. I am not using a digital multimeter so the measurements may not be as exact as they would be otherwise.

That's to be expected the wires drop a bit of voltage when current flows through them.

I am guessing monitor uses a 24V brick?

It seems power is there.

The problem might be with the inverter so the next step is to verify if it is operating. Are there any labels near the power connector for the inverter which might indicate a brightness or enable signal?

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

The monitor does use a 24v brick. I do not see any labels indicating anything that makes sense to me on the board. I took some more pics. Maybe you can see something I am not seeing. There is nothing on the back side of the board.

I was thinking, would it be possible to measure voltage on one of the two wire plugins that go to the individual backlights (I assume)? Would narrow it down to the inverter board if I am thinking about this right.

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

Well, I have an ESR meter ordered so hopefully I can check the caps on the inverter board when it gets here. Other than that I am again at a loss. From what googling I have done you can't buy this board anywhere.

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

The inverter outputs are about 1000V at several kilohertz. Most multimeters can be damaged by this, so don't try and probe there. Anyway, we know the voltages are dropping out, because the bulbs are extinguishing - testing the output wouldn't really tell you anything.

If you can get hold of a digital meter, that would be great. An analogue meter is not really accurate enough for this.

Check the voltage at the three highlighted pins. Note the voltage while working and when the monitor fails. Check relative to the case (black on case, red on one of the highlighted pins.)

If there's a significant change in the pin voltages, something on the monitor's main board is turning off the inverter. It could be something like a sleep timer (perhaps a corrupted user setting in the internal memory), or a fault with the main controller.

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

Acquired a digital multimeter and tested those 3 points. Looking at the picture from left to right:

Point 1 - 0.09 while running, 0.07 when it stops displaying
Point 2 - Nothing? Doesn't change when it stops displaying.
Point 3 - 4.67 while running, 4.66 when it stops displaying

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

Acquired a digital multimeter and tested those 3 points. Looking at the picture from left to right:

Point 1 - 0.09 while running, 0.07 when it stops displaying
Point 2 - Nothing? Doesn't change when it stops displaying.
Point 3 - 4.67 while running, 4.66 when it stops displaying

This confirms the problem is with the inverter. There is a big chip on the inverter board. What is the part # on this device? It might be possible to see if there is a fault output. My theory is one of the transformers is dodgy, or one of the CCFLs is. With these inverters if just one bulb is faulty the entire lot will be shut down. The thing is, the problem usually manifests itself after a couple of seconds, not minutes.

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

The largest chip on the inverter board isn't exactly large so I am not sure this is it but the numbers on it are BIT3105 and below that F387KG. The inverter board itself is part number DS-1224WK.

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

There is a fault output on pin 6. Unfortunately, the board does not have the required pull-up resistor. It may be possible to use the ohms mode on your meter to check the open collector drive, but we'll try that later.

Pin 4 has another useful test voltage. If the voltage is less than 300mV a faulty bulb has been detected.

However, pin 4 is in an awkward position, so while the TV is off, check the resistance between these two points.

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

1323? Does that sound right? Spacing is sooo tight hard to make sure I am only touching that single spot on the chip.

[thepenguin99]

Re: Doublesight DS-240WB turns off after 5sec-5min

Got a chance to stick an ESR meter on the caps today. They seem ok as far as the readouts on the meter go.

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

1323? Does that sound right? Spacing is sooo tight hard to make sure I am only touching that single spot on the chip.

That seems too high. Don't worry about damaging anything while it is off; if the probe is in the wrong place you could get an incorrect reading but it won't damage anything. Give me a moment to think and I'll come back.

[tom66]

Re: Doublesight DS-240WB turns off after 5sec-5min

Okay, check the resistance of this pad relative to case while the monitor is working, and when it fails. Use the 2000 ohm range.

I don't expect that those caps will be a problem. The ESR on those is not critical as they are not part of a power supply control loop.