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marcel.hirsch
Joined: 10 Mar 2008
Posts: 3
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 17 Mar 2008 19:43 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Hello,
I increase R28 from 680 Ohm to 1KOhm, because of the Information from wulw.
He change R28 and C15 and the TFT ist running.
I think, that R18 is to limit the current through die Diode.
Now, i can't meassure, because me measurement is dead.
Can you give me a tip, how I can repair die TFT, that it run over 15 seconds?
I'm happy about any answer.
Thanks
Marcel
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w_m0zart
Joined: 21 Aug 2005
Posts: 16
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| 18 Mar 2008 21:15 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Marcel, from your postings, it looks like you are not having a lot of knowledge of electronics. If that is the case, it's hard for me to explain to you how the circuit exactly works, in order for you to understand it. Besides I feel you are wasting my and that of others their time. From the things you experimented with, it looks more like you did some random testing, instead of first understanding the circuit structured. Also in your case, working measuring equipment is a must if you want to 'get your hands dirty'. How can someone understand what is going on, if you can't measure anything? How should the community know then what's your problem?
Anyway, from the schematic, I see comparator U1C and U1D, which play the essential role in measuring lamp current. Initially, when Q12 is triggered via a positive puls across C26, Q3, Q4b and Q4a will be triggered as well. With this, the comparator LM339 itself will be powered and being able to compare voltages. The voltages of the 'Measure lamp current' circuit (see at the bottom of the schematic) are compared against a voltage which is offered at the negative input, pin 8 and 10 of U1C and U1D. Via R10, zener D4 regulates the voltage at 6.2 V, which is divided with R17 and R18, which gives a voltage of: 6.2*(100k/(100k+270k))=6.2*10/37=62/37=1.7V. For the comparators in order to remain powered, it makes sense, the output of U1C and U1D, pin 13 and 14 must remain 'high' (open collector output!). With that R34 will guarantee through Q13 that this condition will stay. However, as soon as the output of U1C and U1D becomes low, the comparators will be switched of, via Q13 and Q3.
The 'Measure lamp current' circuit should provide a voltage on the comparator positive input to be at least MORE than the previously calculated 1.8 volt. You can see at R30, I wrote 0.27v, which must be incorrect. It means that the voltage at the anode of D12a should be 0.27v+0.7v. Since 0.97v (+input)<1.8v (-input), comparators U1C and U1D will shut down themselves via Q13.
The 'Measure lamp current' circuit has only one importance, that is to protect the transformer of building up high voltage, when lamps are open. In that situation, the voltage across R30, R29, R.. and R.. (I did not draw that part of the schematic, as it is identical to that of CN5 and CN4) will get lower, because the lamps are contributing LESS to the voltage across R28, R25, etc.
One thing for sure is that the voltage across R28 etc. should be higher than 1.7v (Due to D12a/b and D11b,D9b). With that the voltage across R30, R29, R.. and R.. will raise as well. Basically the voltage across R28, R25 etc. can be measured as well at the positive inputs of the comparator. So if you measure in lamp 'warm condition' 1.7v or less across R28, R25, R.. and R.., or pins 9 and 11 of the comparators, you know the problem has to do with either the CCFL's or as well something with the royer-oscillator.
Unfortunately I can't supply you with accurate measurements which voltages you should expect in normal 'warm' operation. I've seen that other users here mentioned 1.55 volt at pin 8 and 10 of U1C/D, which is a bit different than the 1.7v I mentioned. I've read at a lot of sources, what lamp currents can be expected. Some sources mention 4 mA. If these CCFL lamps are also in this inverter, the voltage across R28, R25, etc. will be roughly 2.5v.
Regards, Marc
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marcel.hirsch
Joined: 10 Mar 2008
Posts: 3
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| 20 Mar 2008 22:09 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Hi Marc,
thanks for your very good posting. It's very good. Now I decrease R18, so the voltage to compare ist lower than 0,97V which is at the diode.
The monitor run and doesn't shut down, but the backlights glimmer. Can you explain why?
Is there anything dead?
Regrads Marcel
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SeleniumRectifier
Joined: 25 Mar 2008
Posts: 1
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| 25 Mar 2008 4:51 Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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| My first post & I wanted to say THANKS for the info in this thread. My LCD1830 died and when I got it apart, I figured it had to be the inverter board (screen completely dark). Did a google on the board part number, ended up here, touched up the solder on those 4 resistors and ... ta da !! It works again. Thanks.
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ccfl2led
Joined: 31 Mar 2008
Posts: 9
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| 31 Mar 2008 19:57 can't find R11-R14 from the inverter schematic |
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Why can't I find those Rs from the inverter schema?
I got similar problem on Acer AL1914bm LCD monitor. Changed the four ccfls. Still has the same problem. Monitor come on for one or two seconds then gone. Power light always green.
Can't find the schematic for AL1914bm any where 
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w_m0zart
Joined: 21 Aug 2005
Posts: 16
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| 02 Apr 2008 12:06 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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| These resistors are part of the royer-oscillator, and can be found between Q8 and Q9, marked as R1112. To enable larger power dissipation, for each branch, two resistors of 270 Ohm each are connected in series. You are right it's not drawn in the schematic, but if you understand how the circuit works, I'd say it is not that hard to find them though.
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Jobob
Joined: 06 Apr 2008
Posts: 2
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| 06 Apr 2008 21:49 nec 1712 lcd monitor schematic |
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| Hi all I was having trouble with a nec 1712 lcd monitor it stays on for about half a second then the backlight turns off and I was wandering if any one had the schematics so I could try and fix.
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Mikem09
Joined: 09 May 2007
Posts: 1
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| 11 Apr 2008 22:49 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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| Does anyone know the value of F1 on the inverter board. I have Q8 and Q9 blown plus F1 and I can't find the value of it.
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sraaf
Joined: 28 Apr 2008
Posts: 1
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| 05 May 2008 4:25 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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I had the same issue with my NEC 1830 monitor working for 2 to 10 seconds (green light on) and then blinking off (green light still on). Don't know if these values will help others - but here's what worked for me: I swapped R18 with a 4.7K resistor, and I swapped C16 with a 1000uf cap (the higher the value, the less flickering you get). This has kept the U1C and U1D comparator from switching off. (Just re-flowing the solder joints on R11 thru R14 and the other caps mentioned in previous posts didn't work for me.)
Good luck!
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freshcafe
Joined: 28 Apr 2008
Posts: 1
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| 06 May 2008 11:17 Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Good morrow to all,
Please can someone specify what Voltage the F2-F5 1.25A Fuses are? I know of an electronics manufacturer I would approach instead of buying F4 and F5 on a reel of 5000. Maybe as I worked there once they might spare them or order them for me. They look like 0402 1.25A but that's as far as I got.
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popescus
Joined: 05 Jun 2008
Posts: 1
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| 07 Jun 2008 22:42 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Similar to mrzilza's post reply above I found on the invertor board HIU-319C all fuses F2, F3, F4 and F4 broken and transistors Q5 and/or Q6 shorted emitter to collector. This board drives 4 lamps but it hosts 8 ferrite trafos, with every second trafo connected in parallel to the previous one. Each trafo pair is driven by a pair of two FMMT619 transistors. Moreover, it seems that all these switchers are somehow syncronised by means of secondary windings in the transformes.
I guess that if Q5, Q6 gone short-circuit then the oscillation of all other transistor pairs where stopped and this is the reason why all fuses blow up.
Has somebody a diagram for this invertor board? Or maybe had the same problem? I would proceed simple by replacing Q5/Q6 and the fuses ... but prior experince may help to avoid further pitfalls.
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eSoul_dot_net
Joined: 14 Jul 2008
Posts: 1
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| 14 Jul 2008 21:50 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Hi all
I have the NEC LCD1830 lcd backlight shutdown problem with green power led staying on and I stumbled upon this thread which is very informative thank you 
But I'm no electronic tech and weary to buy a new inverter board incase that wouldn't fix the problem. One thing though happened last evening as I opened the monitor to get familiar with the inside. I disconnected the inverter board to further inspect it visualy, didn't seem to have bad soldering in eye sight, though when I re-assembled the monitor together, to my surprise it worked and displayed throughout the bootup up to the XP welcome screen then finaly to shut down as expected.
What could that mean?
Thanks
P.S. all connections have been checked internaly and Monitor To PC incase something was loose, but no, everything shown to be tight.
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chriru1
Joined: 02 Jul 2008
Posts: 2
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| 19 Jul 2008 13:48 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Hello, thanks very much for the previous posts,
I have a NEC 2010x with the same backlight-turns-off-after-a-minute-problem.
I tried to compare & understand the inverter-board-circuit ,but
it's a little bit different!
Has someone any schematics or tips for this LCD-type NEC 2010x
Multisync, please then post it!
Bye & good luck!!
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chriru1
Joined: 02 Jul 2008
Posts: 2
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| 27 Jul 2008 1:07 Re: Schematics from NEC LCD1830 inverter: ALPS UHP061104 |
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Hello again, here is the solution for the backlight flickering of the NEC 2010x MultiSync LCD-monitor:
On the power-board there is a relay (black rectangular box located just a few cm from the AC 220V input jack, with the number G3M-203P-xxx on it)
Now go ahead, switch on the monitor and when the lights go out give it a short sharp snip with a screwdriver's end, for example.
If the light comes back be happy- you have found the solution!
Greetings & good weldings!!
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