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Old 02-10-2018, 09:21 AM   #1
FitPaul
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Default Philips 170B4 BB/02 flashes on for a split second

I have been trying to fix a Philips/LG 170B4 BB/02 monitor and I need your help. Initially, it just wouldnít stay on with the power light off. I took it apart and changed all the electrolytic caps (some were bulging and some were leaking). Now when I turn on the monitor it flashes the display for a split second before going black. The power light now stays on now.

I found a circuit diagram on the internet but although it's mostly the same, some areas are different. The circuit diagram shows three voltages 3.3, 5 and 12v but on measuring, my monitor only seems to have two (3.8v and 12.7v). Should the 3.8v on my monitor be 5v? There are some markings on the circuit board where components should be but there are none so there has obviously been a design change.

If I hold the screen up to a bright light, I can see the image on the screen so the lcd circuitry seems to be working. I bought a backlight tester and all the back lights light up to the same degree (there are 4). The two output transformers for the four backlights have equal resistance on the primary and secondary coils. There is 12v power at various places on the backlight circuitry.

What should I check next?
Also, how do I attach a pdf to this message. I can't see a way.

Last edited by FitPaul; 02-10-2018 at 10:11 AM..
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Old 02-10-2018, 10:56 AM   #2
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Pictures and circuit diagram I found attached.

Just found out how to attach a file
Attached Images
File Type: jpg 20180210_155840.jpg (605.7 KB, 16 views)
File Type: jpg 20180210_155917.jpg (429.5 KB, 8 views)
Attached Files
File Type: pdf Power ciruit diagram.pdf (860.5 KB, 4 views)

Last edited by FitPaul; 02-10-2018 at 10:59 AM..
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Old 02-10-2018, 11:11 AM   #3
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Default Re: Philips 170B4 BB/02 flashes on for a split second

JPG shows where I measured voltages
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File Type: jpg 20180210_155917.jpg (427.6 KB, 5 views)
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Old 02-10-2018, 07:21 PM   #4
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Take voltage measurements at the cable connector that connects the power board to the main board. You should have 3.3V, 5V and 12V there. If not, we need to find out which one you don't have.

All caps you replaced have been installed correctly? What kind of caps are they and were you able to test them before installing them?
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Old 02-10-2018, 08:33 PM   #5
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Default Re: Philips 170B4 BB/02 flashes on for a split second

some of the schematics only show +12 volts (pin7) and +3.3 volts (pin 1-2) on the plug to the scaler board
Backlight control seems to be pin 12, check and see what voltage you have there, I suspect it is ok and the problem is in the backlight inverter section, or maybe one bad ccfl

Last edited by R_J; 02-10-2018 at 08:41 PM..
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Old 02-10-2018, 08:43 PM   #6
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Default Re: Philips 170B4 BB/02 flashes on for a split second

"suspect it is ok and the problem is in the backlight inverter section, or maybe one bad ccfl" +1
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Old 02-11-2018, 05:08 AM   #7
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Thanks for your message. Like I said, the circuit diagram I found is not 100% correct for this monitor. I don't have IC7001 or any of the circuitry around it. The caps were all new electrolytics but I didn't check them before I installed them. I will check again that installed them the right way.
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Old 02-11-2018, 05:16 AM   #8
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Default Re: Philips 170B4 BB/02 flashes on for a split second

I do have 12v on pin 7 and 3.3v on pin 1-2. Pin 4-5 have 0v and don't seem to be physically connected to anything. So presumably I only have 3.3 and 12v. Pin 12 gives 3.3v. I checked all the ccfls with an inverter I bought on ebay and they all light up with the same intensity.
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Old 02-11-2018, 05:46 AM   #9
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Default Re: Philips 170B4 BB/02 flashes on for a split second

To be sure you should now check the inverter with different lamps.
Ccfls may work but draining too much power.
Look carefully at the corners of the screen if the light is different, pinkysh or fluctuating. That indicates wear of the lamp.

In the inverter section check the winding resistance of the two transformers and reflow all the solder points in the case some are cracked.
Post a photo of the other side of the board.

Last edited by Dumah Brazorf; 02-11-2018 at 05:57 AM..
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Old 02-11-2018, 06:14 AM   #10
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Here's the service manual for you rmonitor. Are those photos of your actual board or some you found with google?

Also, I think you should have 5V on pin 10 and 11. When you say you have 3.3V on pin 1 & 2 I think you are looking at the connector backwards, that should be pins 13 & 14.

Last edited by rddube; 02-11-2018 at 06:51 AM..
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Old 02-11-2018, 10:37 AM   #11
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Default Re: Philips 170B4 BB/02 flashes on for a split second

this one might be closer to your board, but still no schematic of the inverter section.
Here is a picture of the bottom of a 3138 103 5768.5 board for reference
Attached Images
File Type: jpg 3138_103_5768_5.jpg (1.58 MB, 4 views)
Attached Files
File Type: pdf philips_170s4_monitor_power_board.pdf (1.08 MB, 7 views)

Last edited by R_J; 02-11-2018 at 10:43 AM..
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Old 02-12-2018, 04:54 AM   #12
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Thank you all for your advice and suggestions.
Rddube, The circuit diagram RJ has posted looks like mine. It shows 3.3v on pins 1&2 and 12v on pin 7. There is no 5v. The pictures I posted earlier are of my actual board.

Dumah Brazorf: As far as I can tell, all four ccfls look the same when they light up. I got this tester on ebay.

http://www.ebay.co.uk/itm/132427753417

The winding resistance of the two inverter transformers is the same. I reheated the solder points on the pins of the transformers as you suggested. I donít understand why if there are two inverter circuits for four ccfls, why donít they work independently. If there is a faulty ccfl and I unplug it why doesnít the other come on.

RJ: Yes the photo you posted looks like my board as and the circuit diagram looks correct. Now that the voltages check out I guess the problem must be with the inverters or the ccfls. The ccfls seem to work with my tester so I guess it must be the inverter. Where do I go from here?
Attached Images
File Type: jpg Bottom of board.jpg (765.3 KB, 5 views)
File Type: jpg Bottom view inverter section.jpg (682.5 KB, 4 views)
File Type: jpg Top view inverter section.jpg (586.4 KB, 5 views)
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Old 02-12-2018, 11:08 AM   #13
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Default Re: Philips 170B4 BB/02 flashes on for a split second

The circuit checks the current drawn by the ccfl, if the lamp is unpluged, the circuit detects there is no current, (ie bad lamp) and turns off. the circuit must see a certain amount of current drawn by the lamps for it to stay on.
You could still have a bad ccfl even though that tester lights it.
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Old 02-12-2018, 12:44 PM   #14
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Thank you RJ. Should I put an amp meter in circuit and check all the ccfls again? See if they all draw the same current?
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Old 02-12-2018, 01:55 PM   #15
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Default Re: Philips 170B4 BB/02 flashes on for a split second

That might tell you more information? you would need to meter the current to the inverter not the lamps themselves

Last edited by R_J; 02-12-2018 at 02:37 PM..
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Old 02-12-2018, 02:12 PM   #16
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Ok I'll do that tomorrow and get back to you.
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Old 02-12-2018, 02:25 PM   #17
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Default Re: Philips 170B4 BB/02 flashes on for a split second

you can't measure the current at the lamp connections as it is high frequency and high voltage

Last edited by R_J; 02-12-2018 at 02:27 PM..
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Old 02-12-2018, 08:13 PM   #18
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Default Re: Philips 170B4 BB/02 flashes on for a split second

https://www.badcaps.net/forum/showth...er+testing+cfl
I save lots time troubleshooting the problems.
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Old 02-13-2018, 10:52 AM   #19
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Default Re: Philips 170B4 BB/02 flashes on for a split second

Thanks RJ, budm. I know a new monitor is very cheap these days but I'm frustrated that I can't fix this one. You know what it's like. I've already learned SO much.

I'm now pretty sure the problem is with the inverter.

There are four ccfl lamps in the monitor. I have used a two lamp inverter that I had lying around to test all combinations of the four ccfls, two at a time. Every combination works and draws 0.6amp in the low voltage supply of the inverter. I tried substituting the T5 4watt lamp as shown in budm's example with each of the four ccfls in turn and all work.

The monitor inverter will not work replacing any of the ccfls with the T5 lamp. Can you give any other suggestions?
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