HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

[bvamunds]

Hi, I've read all the threads about the F1703, but still haven't solved my issue, so am looking for advice.
I re-soldered the induction coils, suggested in a couple of threads for this particular monitor. There are no bulging capacitors present. Foubnd schematic service manual at
The voltage outputs on the connector (CN102) from power/inverter board to main board are:
Pin 1 4.49 until LED goes yellow then 0 (on/off lead)
Pin 2 2.24 (DIM)
Pin 3 5.16 (+A5V)
Pin 4 5.16 (+5V)
Pin 5 0.00 (GND)
Pin 6 3.32 (+3.3v)
Pin 7 3.32 (+A3.3V)
Pin 8 0.00 (GND)
Pin 9 1.8 (+1.8V)
Pin 10 0.00 (GND)
Pin 11 13.73 (+12v)
Pin 12 0.0 (NC)
Pin 13 0.00 (GND)
Pin 14 0.0 (NC)
appear to be within tolerance for 1.8v, 3.3v, and 5V.

The symptom is that if I turn on the monitor, the blue LED is lit and a "WARNING, check cable" window flashes up for a second or two then disappears, if I then plug in the VGA cable, the desktop background will also flash for a two seconds and then disappear. If I unplug and plug in the VGA cable it will again appear for a second or two and then disappear. If I don't plug in the VGA cable and simply watch the panel, a dim light shadow of the "WARNING" message starts to wander the screen ( the wandering is normal effect that I see with a F1503 that I also own). The power LED stays blue in both cases. I've also fully disassembled the screen to verify there isn't a CCFL solder point broken, suggested in a YouTube issue for black screen timeouts. I've downloaded the available HP F1703 Service manual with schematics of both boards. The power/inverter board appears to be the same, but my main board layout seems to be a later version than the service manual.

My question is this, is this still a capacitor issue, or should I start with the transistors of the Highvoltage circuit to see if that is the issue? Where is the circuit or sense circuit that keeps the inverter on for the back light CCFL's? Clearly something is telling the CCFL's to turnoff.

I have a True RMS meter that can also measure capacitors. I've been working on this for last night and today and seem stumped, so thought I'd ask for help and direction. Thanks in advance. Best Regards, BrianA_MN

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Sorry I meant to upload the photos with the first post, here they are of the power/inverter board and the video control board. I also will do more posts following the guide for 2 seconds to black as best I can.
Best Regards, BrianA_MN

[Agent24]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Unless your meter can check capacitor ESR then it is not much help here. ESR is what you really need to test to see if the capacitors are bad or not.

That said, the purple ones are all HERMEI brand which are known to be garbage. I myself have had dead ones in LCD monitors but they did not look blown or even bulging. So, it might be worth it to replace them anyway if you do not have an ESR meter.

Also, it seems this monitor uses an external PSU? So that could have bad capacitors in it also. Did you check it or at least swap with a known good or new one?

[stj]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

those transistors that drive the ccfl transformers are known to be a problem.
if you meter each matching pair i bet you find they arent equal.

if they are gone, replace all 4 with something more powerfull and with a lower on-resistance.
along with the 2 blue polyester caps between them.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Thanks for the suggestions. Yes the purple caps are Hermei, the black two say "TL" and the polyester ones are PMG. The external power supply is good and provides a solid 15VDC.

Here is an interesting issue, the HP linked document for this monitor has the parts listed per board. The only thing is the inverter board model listed is IDPC7425A1 and the board in this monitor is IDPC7426A1, and the caps seem to be slightly different. For example the two large polyester caps are listed as .22uF-250V, but the ones on this board are .15JuF-250V, so which should I use? The board doesn't appear to have been previously repaired.

I'll check the transistors and caps. My RMS DMM meter only checks capacitance, but I'll look into ESR and determine if I can also measure it with one of the other settings, like Freq. The DMM also measures diodes, which I think I can use to verify the transistors emitter to base is working correctly (is that right?). If not what resistance should there be for B-E, E-C, C-B? These are 2SC5706-P-E Transistors.
Why should the polyester caps be replaced?

[stj]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

the transistors should be checked on the diode setting, if they are bad use something better.
maybe a load of 13006's out of old pc psu's - those are not going to fail!!!

the polyester caps can breakdown internally and cause the transistors to heat up.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Do I need to test the caps and transistors out of circuit? I'm asking because I'm getting the same reading on all four transistors. These little guys are NPN type according to the schematic, they measure B(+)->C(-)= .178; B(+)->E(-)= .506, C(+)-.E(-)=.507. Each one matches exactly in measurement. The emitter lead goes to power ground. Base and Collector both go to separate loops of the high voltage transformer coil. The Base leads each act as one end of the loop, but there are two parallel 2K resistors off the Base which goes to the center tap of C's loop. This all being on the low side of the CCFL transformers. The polyester caps are on the Collectors transformer loop ends.

If I need to test everything out of circuit, then I'll pull out my soldering iron and re-test, but with all readings matching I'm not sure if that is needed? Advice for a novice is appreciated.

[budm]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

When you inspect the lamps, are the lamps's end blackened?
To properly test the devices, you need to test them off the board. The inverter transformer drive circuit is just a simple Royer Oscillator circuit. The transistors are very low Vsat type, I use 2SC5707 for this kind of repair if they are bad.
You should also use two test lamps to verify for sure if you have circuit problem or lamps problem.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

budm, no the CCFL's were clean and had little discoloration at then ends. I pulled them primarily to inspect for a cold soldering joint, but they were solid connections. Thanks for the advice and alternate part number. Do I need to test them disconnected even though they measure equally in circuit?

[budm]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

You need to remove them off the board and test them. You also should check the inverter transformer secondary side winding resistance and compare the readings between the two transformers.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

budm -> thanks for the instructions. I'll also checkout your signature tutorials to better understand circuits. I have a HP F1503 monitor, are its internal similar enough to test the CCFL's or even temp swap to this F1703 logic? Thanks

I also have a Dac-19M009 that has died (no power) but will start separate thread for it. As a teenager I use to enjoy hobby projects like these, then life with college, married, kids and my hobby became software and voice/data networking. Now I'm retired and would like to refresh my knowledge enough to do some part time repairs on boards. Hoping this forum will be a great re-training start.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Finally got back to this. I ordered replacement .15uF polycaps, and 2sc5707 transistors to replace the 2sc5706 from Digikey (great folks to work with and fast shipping). Put them in the circuit last night. Unforunately I'm getting the same results, ie 1 seconds to black.

BTW, the old caps tested at 150.02 nF each. All four of the old sc5706 read "35Meg ohms when measured B(+) to C(-) and E(-) but "OL" or infinite in all other matchings, does that mean they are good or bad?

The original problem persist, so I'm dealing with a different issue than these parts.... I've tested the CCFL's one at a time and each will light for a second, so there isn't a burnt out lamp. I've also the four lamps all connected to another inverter board with four outputs, they all stay on without trouble for extended period of time. (The other inverter is for a Dell 1908fp which has a bad CCFL which I need to replace, it starts in pink state and causes blinking until it turns off and the whole backlight circuit shuts down).
For this inverter board where is the voltage sense circuit, ie is this a ASIC issue?
Should I still replace the other capacitors on the board? (high target ones?)
Do I need to check diodes or zener diodes?
Could this still be a transformer issue?

Since this seems to be related to the inverter board, I'm not sure if it is transformer issue (the individual bulbs will light for a two seconds before being timed out) or the sense circuit? Is the next step to replace all the other caps? Or is there a place to focus on rather than the caps?

As always I appreciate advice on how to proceed.

[Agent24]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

BTW, the old caps tested at 150.02 nF each. All four of the old sc5706 read "35Meg ohms when measured B(+) to C(-) and E(-) but "OL" or infinite in all other matchings, does that mean they are good or bad?

They sound OK. It is unlikely that all would have failed exactly the same. When all parts check out much the same, it is far more likely they are all OK. (Except if they all went shorted, then you are likely to see pretty much identical readings too. But 35MOhm is not shorted). You can see how to do a basic test of BJT transistors here: http://www.allaboutcircuits.com/text...ransistor-bjt/ to understand what the readings are. It is sometimes better to use diode test mode if your meter has the ability.

Those basic tests will show you if a transistor is open or shorted. More advanced tests are required to find if they are leaky or have low gain etc.

The original problem persist, so I'm dealing with a different issue than these parts.... I've tested the CCFL's one at a time and each will light for a second, so there isn't a burnt out lamp.

That doesn't prove anything, actually. Faulty lamps can usually still work to some extent, but they only light momentarily before the inverter controller senses an under or over-current condition and then shuts down. Also, inverters can only be tested with all lamps connected at once, as any one of them being unplugged will trip the protection when it senses some lamps are not drawing current (because they are not plugged in).

To test the lamps one at at time you'd need an inverter that does not have protection, and will drive the lamps if they are bad or not. In that case, they may light up pink (end of life) or flicker, or run very dim etc, then you would know they are bad.

You can test unknown lamps on a good inverter one at a time, as long as you populate the unused lamp outputs with known good lamps. That way you know any shutdown will have been caused by the 1 unknown lamp you connected.

I've also the four lamps all connected to another inverter board with four outputs, they all stay on without trouble for extended period of time. (The other inverter is for a Dell 1908fp which has a bad CCFL which I need to replace, it starts in pink state and causes blinking until it turns off and the whole backlight circuit shuts down).

That is a much better test. If all those lamps work well on a known working inverter, then you know the lamps are OK.

For this inverter board where is the voltage sense circuit, ie is this a ASIC issue?
Should I still replace the other capacitors on the board? (high target ones?)
Do I need to check diodes or zener diodes?
Could this still be a transformer issue?

The inverter sensing it done in the inverter controller IC. This will be the FP5451 IC, U201.

The Hermei capacitors could be the issue, if they've gone bad without visible signs (happens quite often). But it would make sense to check the transformers and buck MOSFETs and diodes etc first.

Check the transformer secondary windings (these are pin 7 and 9 according to schematic (Page 24)) and compare the two. If they have significantly different resistances, one is probably faulty.

I would check the Q203\Q204, all the diodes. Maybe even the small BJT transistors that drive the MOSFETs are bad. Check them all.

Since you have two inverter circuits, you can easily compare readings on parts between each one. Just compare the components that are in the same point on each circuit. In-circuit testing is usually a bad idea because you can get false readings from other components in parallel, but when you have two or more circuits that are the same, it doesn't matter. Where the readings are close together, you know both are probably OK. If one is quite different to the other, one of them is probably bad.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Finally back to fixing this monitor. In the meantime I've been fixing the Westinghouse and Dell 1908FPc which had bad main supply capacitor and bad CCFL respectively. To review what has been done so far, CCFL's have tested good with a different known good inverter. The transistors and poly caps feeding the transformers have been replaced. The transformers ohm out equally on the secondaries.

I haven't been able to test the sense circuit yet, because the test points are on the bottom of the board. I'm not sure if I can run the inverter board without the digitizer board attached (dont' want to blow something else while testing. So my question is, can I only test the power/inverter board separated from the digitizer board?

The monitor's manual (see post #1) suggest a test procedures on page 32 for U201, but I don't have oscillascope, so can't read square wave present. Is there another test, volltage sensing that would emulate the square wave?

Thanks, BrianA_MN

[Agent24]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Yes, you should be able to run the inverter by itself just fine. You may however need to give it a power up signal for it to do anything. A 1K resistor between 5v rail and the ON/OFF pin on the inverter should power it up. Don't do this while it's connected to the mainboard though!

I still don't see if you have replaced the Hermei capacitors yet? As I said before - these can go bad without looking bad at all, and they are one of the first things I would check\replace.

I also notice in your first post that you said:

If I don't plug in the VGA cable and simply watch the panel, a dim light shadow of the "WARNING" message starts to wander the screen ( the wandering is normal effect that I see with a F1503 that I also own). The power LED stays blue in both cases.

This suggests to me that that mainboard is working (driving the panel with the cable unplugged warning message) but that the inverter is just not running the backlights for some reason.

The inverter may not be getting the ON\OFF control signal from the mainboard, you could watch that signal while powering up the monitor and seeing what it does after the lamps go off but when the warning message is still on the screen.

But definitely look into replacing those Hermei capacitors if you have not already!

The monitor's manual (see post #1) suggest a test procedures on page 32 for U201, but I don't have oscillascope, so can't read square wave present. Is there another test, volltage sensing that would emulate the square wave?

If you have a frequency counter you could check for the correct frequency of the wave (assuming you know what it should be)

You could also just use the voltmeter, but it won't tell you much, except if the signal is completely missing and you just measure 0v. If it measures some voltage, it tells you there is some voltage (DC or a square wave) but nothing about it, so you really need an oscilloscope if you want to be sure that you have 1) Correct waveshape, 2) correct frequency 3) correct voltage, 4) correct duty cycle, etc etc.

[bvamunds]

[SOLVED] Re: HP f1703 Monitor Blackoutafter 2 seconds

Tonight I decided to diagnose the problem a little more in depth. With schematic in hand I sought to trace the power from input through to CCFL's. The input voltage from the PSU was 15 VDC rather than the 12 VDC rating on the PSU. Now, an early suggestion in this thread was to check the external PSU for proper voltage and stability. At that time I checked voltage and found 13.8 VDC and thought OK this is strong but typical of PSU's rated for 12 VDC. I didn't check that the amperage output matched the label on back of monitor. As we all know power is a measure of both voltage and amperage, and a circuit with heavy loads, like CCFLs, require the correct voltage and amperage. Tonight I noticed that the PSU amperage rating was only 750mA, but in checking the monitors back label it called for 12VDC with 3.5 Amps! I found a replacement external PSU with proper voltage and amperage rating and the problem I was experiencing is now gone. SO.... I'm not sure if the initial issue was a failing PSU, or loose inductor connections or the transistors and caps in the high voltage output. I suspect the re-soldering of the inductor cores and replacing the transistors all helped refresh the unit, but the major problem may have been the external PSU amperage power output failing. So those nasty little early checks like verifying the power source is correct are important details to include in every diagnosis. Thanks to everyone who helped me, and reminding me to not skip a step simply because I "think" the power isn't a problem. This is now the third monitor the wonderful helpers on this forum have helped me SOLVE. Next another Dell 1907FP with 3 seconds to black. Last Dell was bad CCFL, glad I ordered an extra bulb set!

[budm]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Thanks for the follow-up, so you did not use the original power supply to begin with.
I guess we should have asked if the original supply is being used or not first.

[bvamunds]

Re: HP f1703 Monitor Blackoutafter 2 seconds, but reappears with each insert of VGA

Thanks again budm for your advice.