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mrtweaver
Joined: 06 Jun 2009 Posts: 6
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Posted: Sat Jun 06, 2009 1:05 am Post subject: IBM thinkvision 9205-HB2 power problems |
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I have a 9205-HB2 that is having power problems and I need help. The power problems are in the high voltage side that control the CCFL lamps. The problem is as such, turn unit on, unit powers up, splash screen is shown, then regular screen is shown, then after a very short period of time 10 sec or less, the lamps turn off for some reason. I know this because I can shine a bright light on the screen and see the picture is there but with out illumination you can not see things. I have taken my meter and checked and sure enough you get the high voltage to the lamps during turn on, then just like that it turns off and there is no voltage present to the lamps. Any help greatly apprecaited. thank you. |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Sat Jun 06, 2009 3:10 am Post subject: |
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As usual check for puffed lytics on Power and Inverter boards. A bad bulb (unplug ALL and try plugging in one-at-a-time) or bad solder joints can also cause. |
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mrtweaver
Joined: 06 Jun 2009 Posts: 6
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Posted: Mon Jun 08, 2009 5:18 pm Post subject: |
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I have gone over the board looking for the usual, damaged transistors, damaged diodes, resistors out of spec, etc.. I have not been able to find anything concrete as of yet. I can tell you that the problem seems to be around the invertor section of the power supply.
What they have is an IC and from what I have been able to find out it is called a push/pull or full bridge driver. This IC drives two mosfets which in turn then go to a step up transformer and then out to the load or in this case the CCFL bulbs.
Now what I have gone thru so far is the fact that something is turning off the signal to the mosfets. I am now sure where it is getting turned off at being as I do not have a set of scematics for this board. I can say with certainty that you can see the clock signal come out of the IC, you can see it drive the mosfets and you can see the signal come out of the transoformer. So what drives the IC? That I do not know. What could tell it to turn off the power to the lamps, again I do not know. I can tell you what I see and what I know and I am right now making my own schematic but it would be helpful if someone already had it.
Anything else I can look at to troubleshoot this power board???
jts1957 wrote: | As usual check for puffed lytics on Power and Inverter boards. A bad bulb (unplug ALL and try plugging in one-at-a-time) or bad solder joints can also cause. | |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Mon Jun 08, 2009 8:24 pm Post subject: |
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For sake of argument, let's say that there are 4 lamps (2 at top and 2 at bottom of the panel. Let's say one has become weak (or broke). The inverter drive IC has ways of monitoring for ANY unbalanced condition, and WILL turn off the output signal. That's why I mentioned looking for each bulb to light independently by plugging in one at a time. |
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mrtweaver
Joined: 06 Jun 2009 Posts: 6
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Posted: Mon Jun 08, 2009 11:58 pm Post subject: |
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Ok lets say that there are 4 lamps, although since it is a smaller screen and there are only 2 wires to each end I am only assuming that there is one on each end. Anyway here is my list of questions:
1. If I unplug one set are you saying it will still work?
2. What if I unplug both sets?
3. I have tried it with one then the other then both and I still get the same results. So my next question is what is the voltage of the lamps? This way I can test the lamps using an independant power supply.
4. I did notice when i first took the monitor apart that the one set of lamps the plug was shorted to the frame of the monitor I dont know if that would damage any of the components. Would it?
jts1957 wrote: | For sake of argument, let's say that there are 4 lamps (2 at top and 2 at bottom of the panel. Let's say one has become weak (or broke). The inverter drive IC has ways of monitoring for ANY unbalanced condition, and WILL turn off the output signal. That's why I mentioned looking for each bulb to light independently by plugging in one at a time. | |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Tue Jun 09, 2009 12:51 am Post subject: |
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You hadn't mentioned size or number of lamps/wires, so I used what I've observed to be a very common "across the board" (an average) scenario.
"Two wires to each end" infers 2 lamps.
1. If I unplug one set are you saying it will still work?
No. It will let you tell if a bulb is working. If possible to observe bulb itself, it should be a "White" light (Not "Pink").
2. What if I unplug both sets?
Obviously with both unplugged, No light can light.
3. I have tried it with one then the other then both and I still get the same results. So my next question is what is the voltage of the lamps? This way I can test the lamps using an independant power supply.
See an example): http://www.microsemi.com/micnotes/1401.pdf
Yes, I know it's not the IC driver for your application, but still much theory transfers.
4. I did notice when i first took the monitor apart that the one set of lamps the plug was shorted to the frame of the monitor I dont know if that would damage any of the components. Would it?
Possibly. |
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mrtweaver
Joined: 06 Jun 2009 Posts: 6
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Posted: Tue Jun 09, 2009 12:29 pm Post subject: |
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First off I do not know the size of the lamps. The size of the wires is pink wire size 20, white wire size 22 maybe even 24. It is a 15inch screen. As for number one I do realize if I unplug the lamp it will not light, that is just common sence. Maybe I should have formulated the question more like:
If I unplug one set of lamps and leave the other set pluged in will the set plugged in still work? ( I asked this because you mentioned there is circuitry that monitors the load and since the load has changed then that would mean it would still shut off, that is if I understood what you were saying about the load monitoring circuit) SO this is why I asked if it would still work the lamps that would remain connected.
As for the IC I think I found out whom made the IC but have not heard from the company as yet, most likely because I gave them our company email and our email server when up in a blaze of glory. It is still down.
I will read over the literature you attached and see what I can find out. Hopefully all bulbs are the same voltage. All I can say for certain right now is:
1. Turn power on to monitor, you get the splash screen then for a short period you get the normal data then the lamps turn off.
2. The IC has two signals that come out and trigger two mosfets. The two mosfets are fed into a transformer.
3. When power is first applied the IC sends out pulses to the mosfets, which makes a simulated AC wave form which is then amplified and filtered thru the transformer and some caps.
4. I think I found the maker of the IC and am trying to get a datasheet, I have googled and everything else and can not find any other data on this device which is why I am hopping the company I contacted is the correct one.
5. The signal is being switched off at the IC.
I think that is about everything for now. Have a great day.
jts1957 wrote: | You hadn't mentioned size or number of lamps/wires, so I used what I've observed to be a very common "across the board" (an average) scenario.
"Two wires to each end" infers 2 lamps.
1. If I unplug one set are you saying it will still work?
No. It will let you tell if a bulb is working. If possible to observe bulb itself, it should be a "White" light (Not "Pink").
2. What if I unplug both sets?
Obviously with both unplugged, No light can light.
3. I have tried it with one then the other then both and I still get the same results. So my next question is what is the voltage of the lamps? This way I can test the lamps using an independant power supply.
See an example): http://www.microsemi.com/micnotes/1401.pdf
Yes, I know it's not the IC driver for your application, but still much theory transfers.
4. I did notice when i first took the monitor apart that the one set of lamps the plug was shorted to the frame of the monitor I dont know if that would damage any of the components. Would it?
Possibly. | |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Tue Jun 09, 2009 12:54 pm Post subject: |
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Just to be absolutely clear: The Monitor will NOT "work" with any bulbs / plugs unplugged.
I'm just saying if there is one bad or broken bulb, and you connect the bulbs to inverter one-at-a-time, you can easily tell which bulb is defective. Good ones will light "white" for a moment and then shut off, bad ones will either not light at all, light "pink" or you can sometimes hear / see them arcing. |
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