Mag LT916s Model 900p 19" LCD dropping like flies

[tollfree]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Would it be an option: cutting of the cable's male connector, then strip and solder its 32 wires to the board where the female board's connector pins are originally. Is it possible, do you think?

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

I have a MAG 900P LT916S and the LED simply flashes. My 12Volt line is dead. Traced back from the KIA7812. The input side of that show nothing. Is there are diagram for the LT912 900P board? What can I check next - what is supposed to feed voltage into the this 7812 regulator ?

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

I pulled out the ZD002 (I think its for the 5V line) and restested. The 12V line looks good! I put ZD back in and now the 5V line is like 2Volts +/- change. I am thinking the zener is bad. I put a 7805 regulator in place of the zener (its what I had lying around). And the voltage is still LOW. So I suspect perhaps a regulator on the logic board now...

BTW - the exact original and current symptom is no power on. Only green led flash every second. You can hear it trying to start. I believe a power surge is the cause of this monitor failure. Maybe someone here has some tips ? thanks!

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

I pulled out the ZD002 (I think its for the 5V line) and restested. The 12V line looks good! I put ZD back in and now the 5V line is like 2Volts +/- change. I am thinking the zener is bad. I put a 7805 regulator in place of the zener (its what I had lying around). And the voltage is still LOW. So I suspect perhaps a regulator on the logic board now...

BTW - the exact original and current symptom is no power on. Only green led flash every second. You can hear it trying to start. I believe a power surge is the cause of this monitor failure. Maybe someone here has some tips ? thanks!

Break the problem down into two parts: Separate the signal board from the power supply / inverter, but leave the CCFLs plugged into the inverter. Plug the power cord into the power supply /inverter and into an outlet. Measure the output voltages.

If they are bad the problem is on the power supply / inverter board. If the voltage are are good identify the backlight control line and use a pair of AA batteries in series to pull it high. Do the backlights come on? If so, the power supply / inverter is working properly and the problem is with the signal card. If the backlights flash on briefly, or if they do not come on there is a problem with the inverter section.

PlainBill

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Bill, Thanks for the feedback. I measured V w/o the signal board and 12V line is 11.8 and the 5V line is 4.8 (seems acceptable?) I then hooked the signal board and measured the 5V line and it is 1.2V so it seem the signal board has an issue. There is a 3.3V regulator on there. maybe that is low resistance. I will do the BL test next and report back. I preume by putting 3V on the BL pin that causes the BL to turn on? (essentially a logic high binary 1?)
If the signal board is bad, has anyone here fixed those? The signal board says 200-100-M713 REV:S3 - the regulator onboard is AIC1084-18CE with the center pin not connected. So that makes it a 1.8V 5Ampere regulator if I understand the datasheet correctly. The datasheet says that pin 1 is GND, PIN2 is VOUT and PIN3 is VIN. PIN2 looks like it is no longer soldered to the board? These are not fusable leads are they ??? I measure like 500-800ohms from pin1-2 and 2-3. Accorgind to this the VOUT is no longr connected. That would certainly cause a problem. Hmm. I will measure the volt on VOUT and see if it is 1.8V. I doubt it. Since the 5V line drops to 1.2V when the signal board is connected...
I measured the volt on vout which is not only PIN2 but the heat since tab! That is why it is not connected! Sorry about that... it is less than 1Volt... I think I will remove that after a successful BL test and see if the 5V line goes back to normal. Then see if there is a way to test that regulator.

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

OK I tried the AA battery on the BL line and no luck. I guess the inverter is bad? I tried with and without the logic board connected. What is the best way to check the inverter? The voltages drop like a piece of lead when the singnal board is hooked up. I do not have another monotor to swap or test the inverter board.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Sorry if your ears were burning, I was calling you a fool for ignoring my directions. Then I realized my directions were incomplete.

Here's a quick rundown of the diagnostic steps.

1. Apply power to the power supply / inverter. If the power comes up normally the SMPS is good. We also know that there isn't a short in the inverter loading down the power supply. (A few months ago we had a 'tough dog' problem with a non-starting SMPs that turned out to be a bad transistor in the inverter).

2. With the power supply working, drive the inverter control line high. The CCFLs should come on at full brightness. If they don't, measure the voltages out of the supply. (Yeah, this is the step I failed to tell you about). Most inverters use drivers in a 'totem pole' configuration. (One driver pulls the primary high, then it is turned off and the second driver pulls the primary low). Since both drivers are turned off when the inverter is off, it won't overload the power supply UNTIL the inverter is turned on.

3. With power off, plug in the signal card, then apply power to the SMPS. Of the power supply / inverter passed steps 1 and 2, but won't power up, this indicates the problem is the signal card.

Verifying the power supply is working in step 2 is necessary because the signal card remembers the state it was in when it lost power, and will return to that state when power is applied. If the monitor was operating when a driver shorted (and caused the power supply to shut down), the signal card will turn the inverter on when it sees power.

PlainBill

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Thanks again. I was wonderin why my ears were buring! LOL. OK so let me make sure I got you straight. The "drive the inverter control line high" means to use the 3V batterys on the BL line? Correct ? The +3V goes to BL and the -3V just goes to ground, correct? This is my first monitor project, as you might have guessed. Never worked on an SMPS before.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Thanks again. I was wonderin why my ears were buring! LOL. OK so let me make sure I got you straight. The "drive the inverter control line high" means to use the 3V batterys on the BL line? Correct ? The +3V goes to BL and the -3V just goes to ground, correct? This is my first monitor project, as you might have guessed. Never worked on an SMPS before.

Quick background information. The inverter section of most monitors accepts 12 volts (this varies with the design) from the power supply, and two signals that are sourced on the Signal board, and passed through the power supply. One is brightness (often abbreviated BRI) and On/Off (often marked BL_ON, No/OFF, N/F). The signal board turns on the backlights by raising the BL_ON line to about 3 volts (the exact voltage isn't critical).

By hooking the - lead of a 3 volt supply (2 AA cells in series) to Gnd and the + lead to the BL_ON line with AC connected to the power supply you should be able to turn on the inverter. (It is possible that you can accomplish this by hooking the BL_ON to the 5 volt output of the supply, but I wouldn't recommend it).

If you try this and the backlights come on bright, the power supply is almost certainly OK. If on the other hand, the output voltage of the supply collapses to less than 4.5 volts, you have either a bad power supply or a bad inverter.

PlainBill

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Bill,
I was wondering. Should the DC voltages look essentially pure on a scope ? Since this is a SMPS if I see any AC waveform then my filter caps are crap. Correct? I know there should be ripple in the millivolt range and that is acceptable but any larger then say 2-3 volts or more AC on the 5V or the 12V lines is a problem? Thanks for all your help so far. It is fun learning about these LCD monitors.

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Bill,
I was wondering. Should the DC voltages look essentially pure on a scope ? Since this is a SMPS if I see any AC waveform then my filter caps are crap. Correct? I know there should be ripple in the millivolt range and that is acceptable but any larger then say 2-3 volts or more AC on the 5V or the 12V lines is a problem? Thanks for all your help so far. It is fun learning about these LCD monitors.

Ripple in the millivolt range is OK. I'd question the caps if ripple was as high as .1 volt. Usually if any cap shows signs of failure I'll replace the complete set. Playing games of 'is it too bad to use this way?' does not lead to good customer relationships.

PlainBill

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

I found the schematic for the 860-ALZ-M713W-F board. It does not list hardly any voltages! I am getting +168V on C001. The waveform for pretty much all of the voltages are like a sawtooth. I can hear a distinctive buzz or click from something on the power board. The peak of the waveform coincides with the click. The 5V line shows a sharp rise and gradual falling slope. On 250us scale I see two peaks. So based on your prior post, I guess I have a power supply problem. I checked voltages on the NCP1203D6 and VCC varies from 6.5-8.2 volts. Pin1 = .6V, Pin2= 3.8V, Pin3 and 4 are 0 volts. PIN8(HV) varies from 90-150V. TheQ001 2SK2645 shows 300-500V on PIN2 and zero on PINS 1 and 3. So, does this make sense to anyone? I am still trying to figure this one out... Maybe these symptoms sound familiar to someone?

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

I found the schematic for the 860-ALZ-M713W-F board. It does not list hardly any voltages! I am getting +168V on C001. The waveform for pretty much all of the voltages are like a sawtooth. I can hear a distinctive buzz or click from something on the power board. The peak of the waveform coincides with the click. The 5V line shows a sharp rise and gradual falling slope. On 250us scale I see two peaks. So based on your prior post, I guess I have a power supply problem. I checked voltages on the NCP1203D6 and VCC varies from 6.5-8.2 volts. Pin1 = .6V, Pin2= 3.8V, Pin3 and 4 are 0 volts. PIN8(HV) varies from 90-150V. TheQ001 2SK2645 shows 300-500V on PIN2 and zero on PINS 1 and 3. So, does this make sense to anyone? I am still trying to figure this one out... Maybe these symptoms sound familiar to someone?

The waveform on the 5V line and on Vcc are significant. There are several possible causes. I'd also suggest you look up the NCP1203D6 datasheet, it has a schematic of a typical application.

1. Bad cap on pin 6. This monitor is notorious for this cap failing.
2. Excessive load on either 5V or 12V line
3. Bad (open) diode on tertiary winding (used to provide Vcc after startup).
4. Shorted 5V or 12V diode
5. Bad main filter cap.

Whenever I hear the ticking sound I replace every electrolytic cap on the board with the exception of the large (100 uF, 450 volt) one. Ordering from Digikey (if you are in the USA) the full set will cost about $10, including shipping.

PlainBill

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Bill, Thanks for the tip. I pulled C006 the 47uf and temorarily put in a 16V one (was 25V) and the voltages all went to normal. The LED went to solid green and then to standby! I will next test to see if any other problems. And I think I will order that pack of caps. I will report back on status!

[tester272001]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Bill, Just to confirm the error was that capacitor. Monitor looks fine now! One more saved from the landfill, for now. Thanks to eveyone on here for great help and replies! Next I will order that cap kit!

[bfrencillo]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

MAG 900P

i also have the same problem 2 secs. shutdown... by replacing the 2 caps rated 100uf 25v (c10) and (c11), the problem solved....

thanks for the very informative feeds here....

god bless....

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

MAG 900P

i also have the same problem 2 secs. shutdown... by replacing the 2 caps rated 100uf 25v (c10) and (c11), the problem solved....

thanks for the very informative feeds here....

god bless....

Since that was a bad capacitor, shouldn't that be Faraday Bless?

PlainBill

[catherder]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

MAG LT916s 900P Inverter Mirage Electronics AD-1700 Rev:F 200-000-170DTL1 VERSION:A
Sticker: 860-AB0190DTL1-A AD-190DTL1 J22-001 A 5083725

One by one these are dying. The symptom is that it powers off 2 seconds after turning on. The first I played with the inverter long enough and swapped enough parts to break it completely. Pictured is the second. In circuit ESR testing shows 0.03 ohms with the two Fuhjyyu 470uf 25v output parallel cap pairs and 0.05 ohms with the two single Fuhjyyu output caps. I've pulled and tested the xunda 100uf 400v input cap and its 0.75 ohm ESR looks good too. 100uf caps C10 & C11 are 0.00 ohms so are unmeasurable in circuit and the remaining caps test with good ESR.

The 3rd dead Mag LT916s has been delivered and is working but like the others the runtime will get shorter and shorter until it gets to 2 seconds where it can't be used any more. I haven't even opened it up.

Playing with the first inverter I found that the boards will shut down if you pull too much current, and those sparks and corona effects sure are nifty. One problem might be that aging lamps have increased their current draw and this board doesn't have enough headroom. Unfortunately it's not worth buying new lamps just to find out the old lamps are fine. Turning down the intensity may alleviate this problem for a while but that's hard when the runtime is 2 seconds.

I've also fixed a PC power supply by replacing all of it's bad brand good caps with good brand good caps. That might mean that there are things that go wrong with caps that push marginal circuits out of spec that our meters can't test. Unfortunately I have no 100uf 400v caps and not nearly enough 470uf 25v caps on hand to do 3 monitors only to find out that the Fuhjyyu caps aren't bad yet.

I wouldn't mind a replacement inverter board but since these Mirage units seem defective a replacement would need to be beefed up before I'd trust it. No one sells this inverter yet.

Replacement LCD screens similar to this HannStarr HSD190ME12-A00 LCD are getting dumpster prices so selling the screen isn't an option.

http://forum.electronicwerkstatt.de/...1_bz0_bs0.html
http://www.elektroda.pl/rtvforum/topic746362.html
http://www.google.com/search?hl=en&q...=Google+Search
http://www.google.com/search?hl=en&q...ay&btnG=Search

The input is regulated by an 8 pin chip IC201 203D6 PSDI and the HV inverter has a 16 pin chip IC1 TL494C and two large transistors U1 & U2 D444 (2SD444). The schematic at elektroda.pl looks nice but it doesn't match up with what I see.

BLON and BRI go directly into the inverter section. Perhaps I could defeat the cutoff circuit by cutting the BLON trace and hardwire it to something, assuming the BLON trace does something other than shut off the monitor during power save. The inverter probably has its own safety circuit independent of BLON.

Fortunately we have some sun so my pictures don't suck. The pulled solder pad near the 8 pin chip is to the 100uf cap. I haven't soldered it back in yet.

Hi Severach,
I have the same board and have replaced the six 470uf and the one smaller 220uf near them. I don't have test equipment and would like some advice on the next items to replace.
Symptoms are the screen goes blank after a few seconds and if switched off and on again it comes back for a second. When I replaced the one 220uf it seemed to fix the problem, but then failed again after a few days. Thats when I replaced the 470uf's.
I've read all the threads, but with no conclusions. Perhaps you have one to share.
Regards, cathherder

[PlainBill]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Hi Severach,
I have the same board and have replaced the six 470uf and the one smaller 220uf near them. I don't have test equipment and would like some advice on the next items to replace.
Symptoms are the screen goes blank after a few seconds and if switched off and on again it comes back for a second. When I replaced the one 220uf it seemed to fix the problem, but then failed again after a few days. Thats when I replaced the 470uf's.
I've read all the threads, but with no conclusions. Perhaps you have one to share.
Regards, cathherder

Boy, catherder, you do have a difficult job!

The symptoms are referred to as 'Two seconds to black'. Possible causes include bad capacitors, bad transformers, bad CCFLs, bad CCFL wiring, and a problem in the sense circuitry.

To cover some of the bases, have you replaced ALL of the electrolytic caps? There are a couple that you did not mention that MIGHT be causing this problem.

Next, what brand and series of caps did you use? They must be low ESR caps, I prefer Panasonic FM FR, or FC series; other brands such as Rubycon and National Chemicon also have series that are as good or better.

One other possibility is an aging CCFL. To perform this test, turn the monitor on after it's been off for at least an hour. Does the display have a pinkish tinge for a few seconds when it first comes on?

PlainBill

[jetadm123]

Re: Mag LT916s Model 900p 19" LCD dropping like flies

Hi Severach,
I have the same board and have replaced the six 470uf and the one smaller 220uf near them. I don't have test equipment and would like some advice on the next items to replace.
Symptoms are the screen goes blank after a few seconds and if switched off and on again it comes back for a second. When I replaced the one 220uf it seemed to fix the problem, but then failed again after a few days. Thats when I replaced the 470uf's.
I've read all the threads, but with no conclusions. Perhaps you have one to share.
Regards, cathherder

Other than the items PlainBill suggested, you'll need at least a digital multimeter to perform additional testing. Replacing parts without performing any testing can be both time consuming and a waste of money.