Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Computer Displays
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 04-14-2008, 01:08 PM   #1
severach
Badcaps Veteran
 
Join Date: Aug 2007
City & State: Michigan
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 982
Default 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.
severach is offline   Reply With Quote
Old 04-14-2008, 03:29 PM   #2
Crasoum
New Member
 
Join Date: Apr 2008
City & State: Near Tyler Texas
Posts: 15
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

I actually fixed on of these by replacing the 6 470 caps and the 219 (220uf ?) cap, first recap job I did, with the exact same symptoms. Running fine 24/7 8 months later.

Tested capacitance on the 470s?
Crasoum is offline   Reply With Quote
Old 04-15-2008, 12:31 PM   #3
severach
Badcaps Veteran
 
Join Date: Aug 2007
City & State: Michigan
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 982
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Quote:
Originally Posted by Crasoum
Tested capacitance on the 470s?
Testing ESR is usually sufficient. I've found that both capacitance and ESR tests are almost equally reliable. ESR has more negative effect on the circuit, can often be tested in circuit, and is detectable sooner.

Score 3 for the good guys! All 3 Mag monitors are working, even the one that a nitwit who shall remain unnamed burned out with too much experimenting and spark fun. Once I saw the pattern the 3rd time I decided it had to be a capacitor problem so I decided to attack. The pattern goes like this:

The original owner gets tired of 2 second shut off, disconnects the monitor, tests it on a few computers, and brings it to me. I plug it in and it works for a few hours. When I come back after it has run for several hours it exhibits the same 2 second shutdown.

The power supply runs continuously whether green or orange led which keeps all the parts heated. Knowing that we can expound:

The original owner runs the monitor continuously until time and heat destroy some caps beyond the tolerance of the circuit. All of their brief testing between computers occurs while the circuits are still hot so they bring it to me after it fails all tests. It is stone cold by the time I test it so it runs for a long time. I leave it at an orange led which lets all the circuits heat up and when I come back it immediately exhibits the 2 second shutoff.

Knowing the problem only happens when the circuit is hot I disassemble the monitor while it is running to keep it at max heat hoping the extra heat would more easily expose the culprit. Turns out this was unnecessary.

Having tested all the other caps in circuit I start with the untestable caps C10 & C11 Xunda TL 100uf 25v. Fresh off the soldering iron they measure 35 ohms. Cooling for a few minutes they rise to around 90 ohms. Watching this happen live on the ESR meter is a great demonstration of the rule that heat reduces ESR. They are a bit hard to test accurately since only a few seconds of body heat is enough to drop 30 ohms so I leave them on the table untouched to maximize ESR.

Failure #1 >99ohm, >99ohm, 57uf, 14uf
Failure #2 >99ohm, 95ohm, 58uf, 47uf
Failure #3 >99ohm, 87ohm, 52uf, 48uf
Monitor #4: 1.2ohm, 1.3ohm, 97uf, 94uf

The capacitance is 50% it's proper value. I've seen far worse caps still operational. Only one of the 6 caps from failed monitors is so far off that the need for replacement is clear. The ESR is 100 times what it is supposed to be on every failed cap. I replaced the caps in Monitor #4 even though they haven't failed yet. My 100uf 25v reclaims have 2 different ESR averages.

Rubycon MH, Taicon VT, Jamicon TK, G-Luxon SM, Lelon LZG: 0.80-1.1ohm
United Chemicon KY: 0.16ohm (from D-Link router)

I chose the highest ESR 5 Rubycon and 3 Taicon.

The burned out board had a bad 3.15A output fuse which I jumpered with a resistor lead wire cut down with a razor to reduce the current capacity. I'll find a fuse eventually. I believe that sparks that size could burn out a 3.15A fuse.

The fuse burned out and not a chip. The board ran with ridiculous ESR. Maybe this Mirage Electronics board ain't as bad as I thought.
severach is offline   Reply With Quote
Old 05-10-2008, 07:01 AM   #4
RMPCTek
New Member
 
Join Date: May 2008
Posts: 1
Talking Re: Mag LT916s Model 900p 19" LCD dropping like flies

Hi! I have a fujitsu scaleoview 19C, at the first months the lcd had to be repaired in the fujitsu authorized repair shop. The same simptoms: after turned on it turned black after a few seconds! Last week it did it again! As it has no warantee any more, i've opened it! First thing i've noticed : The fujitsu repairman left two loose capacitors inside the controller/power supply case(new, no welding marks on the legs of the components)!! Those bastards hehhehehe.. My PSU had six bad 470uF caps and two 100uF 25V also bad caps! I've replaced all bad caps. Now it runs like new....

The thing is: The 100uF caps were 25V bu i've replaced it with 100uF 50V (couldn't find the right ones). Is this gonna be a problem for the future of this unit ? LOL

Thanks from Portugal !!
RMPCTek is offline   Reply With Quote
Old 05-10-2008, 02:09 PM   #5
weirdlookinguy
Badcaps Veteran
 
Join Date: Sep 2007
City & State: San Diego, CA
Posts: 1,611
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

RMPCTek, what brand were the capacitors that failed in the Fujitsu? I always thought Fujitsu made decent stuff but I guess not.
weirdlookinguy is offline   Reply With Quote
Old 05-12-2008, 08:41 AM   #6
Krankshaft
Badcaps Veteran
 
Krankshaft's Avatar
 
Join Date: Jan 2007
City & State: New Jersey, USA
Posts: 2,283
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Quote:
Originally Posted by RMPCTek

The thing is: The 100uF caps were 25V bu i've replaced it with 100uF 50V (couldn't find the right ones). Is this gonna be a problem for the future of this unit ? LOL
Going higher in working voltage is fine all that really matters when replcing caps is their uf rating and type low ESR or general purpose.

I'm surprised the warranty guy even had the brains to change out the caps.

Although not soldering them in was a real dumb move.

Most warranty places I know are just parts replacers and would just replace the entire inverter board and most likely that new board would contain the same crappy caps that the old one did and would fail in time just like the original inverter.

I remember a post I read on another forum about a Toshiba hypermodule that had bad caps. It caused wavy picture on the sets (including mine).

This guy was bragging that he could get a new board (they were discontinued at the time) for around 250 bucks rather then replace the SMT caps at around 20 bucks with shipping.

Little did the parts replacer know that the board he was buying had the same crappy SMT caps that his current board had so eventually he would be in the same boat AGAIN. With his wallet 250 bucks lighter.

I on the other hand replaced the caps and have a permanent repair for much less.
__________________
Elements of the past and the future combining to make something not quite as good as either.

Last edited by Krankshaft; 05-12-2008 at 08:50 AM..
Krankshaft is offline   Reply With Quote
Old 05-12-2008, 10:04 AM   #7
Harvey
Badcaps Veteran
 
Harvey's Avatar
 
Join Date: Apr 2007
Posts: 251
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

...I'm never keen on LCD monitors that have the PSU built in. Relibility seems much higher when the PSU (and most of the heat) is seperate.
Harvey is offline   Reply With Quote
Old 06-16-2008, 11:17 AM   #8
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Boy am I glad I found this thread, I have two of these suckers with the same problem, screen goes blank after 15 minutes of use, unfortunately I don't have the savvy to diagnose what caps are bad and whatnot, would you guys mind telling what caps I should replace? also when getting the replacements are they low ESR or general purpose?

Thanks a lot!
phubar is offline   Reply With Quote
Old 06-16-2008, 04:41 PM   #9
Michaels
New Member
 
Join Date: Jun 2008
Posts: 4
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

http://www.youtube.com/watch?v=AXjww...eature=related

Hey phubar, check that video out. Very helpful to find the ones to replace.

My only problem is I've done this and the monitor still turns off after some use (heated up). I only replaced the 6 large caps though, should I go so far as to replace the small 220uf one that's next to the large ones?
Michaels is offline   Reply With Quote
Old 06-16-2008, 06:11 PM   #10
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Well I don't mean to be cocky by any means but I know how to do that (take it apart, desoldering old capacitors, solder new capacitors), I actually need more info or orientation regarding the required parts, diagnosing or determining the actual problem.

I think I'll just change all the capacitors (6 medium size and the smaller ones) if I don't get any input from this thread.

Is the inverter board in this monitor integrated with the power supply? or is the inverter board the board next to the power supply? I don't remember and don't have the monitor with me right now to check.
phubar is offline   Reply With Quote
Old 06-16-2008, 10:45 PM   #11
Krankshaft
Badcaps Veteran
 
Krankshaft's Avatar
 
Join Date: Jan 2007
City & State: New Jersey, USA
Posts: 2,283
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

If the screen goes blank randomly then it may be a cracked solder joint on the board when the screen goes blank try whacking the monitor if the image returns thats your problem.

However if your inverter board is like the one pictured in this thread then it uses Fujiyuu caps one of the worst cap brands out there.

They attempted to take out two of my Antec power supplies before I replaced them.

As a matter of course I would replace all of the Fukyuu on the secondary side of the supply then continue troubleshooting from there.
Krankshaft is offline   Reply With Quote
Old 06-16-2008, 11:18 PM   #12
severach
Badcaps Veteran
 
Join Date: Aug 2007
City & State: Michigan
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist Tech
Posts: 982
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

The inverter is on the power supply.

I had two tiny inverter caps go and others have had the power supply caps go. There are other things that go wrong too so naming the bad part on your board requires testing. You can test or replace caps willy nilly hoping you catch it. One of the tips that helps narrow down where to look is to watch the power led as the monitor goes off. If the led goes off then the power supply is shutting down. If it says on then the inverter is shutting down.
severach is offline   Reply With Quote
Old 06-17-2008, 08:20 AM   #13
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

KS, the monitor consistently goes blank in around 15 minutes of use.

Good tip on watching the power led, I thought the light would stay on regardless and didn't even pay attention to it but that makes a lot of sense. Is the inverter circuitry clearly defined in the power supply board? (I'm guessing is located in the top part of the board).

How would I test the caps on these things?

would a regular digital multimeter do or do I need some special equipment?

are the caps low esr or standard?

what brand would you guys recommend, nichicon, sanyo, rubycon, nippon? can they be any voltage, like 10v or 16v? or any voltage over 25v?

does the height/size matter 8mm, 6mm, etc?

Thanks a lot guys for all the replies!
phubar is offline   Reply With Quote
Old 06-17-2008, 03:00 PM   #14
Crasoum
New Member
 
Join Date: Apr 2008
City & State: Near Tyler Texas
Posts: 15
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

I got a capacitance meter, you can get one from sears for like $20, a cheapy but it'd work, if it goes off the scale it's better then nothing, but an ESR meter is really the only way to check if they are good, or replace with new.

Caps are low ESR
Don't need to be the same size, but do need to be higher votage or equal, and if they are close to one another be careful about width. It's been a year since I fixed mine and I gave it to a friend for Christmas, Still going strong today.
Crasoum is offline   Reply With Quote
Old 06-17-2008, 03:28 PM   #15
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Well caps are cheap and it seems easy enough (I once replaced the caps in a motherboard, that was a bitch and it didn't work! lol), I see 11 caps 6 470uf, 3 220uf, 2 100uf, might as well replaced them all, because if I have to buy a tool worth $20 that I'll rarely use for anything else, plus the caps (at least $20), plus I'm getting some new soldering tools for about $30, might as well just get a new monitor and forget about the whole thing lol

Thanks again guys, y'll have been tons of help.

BTW: -suggestion- this threat tittle should be edited to include some other mag, aoc, kds and proview LCDs with the same problem and same board so it can be indexed better by search engines as before finding this thread I found tons of websites with people asking about a fix for this monitor with no replies.

I actually just noticed that I found this thread by typing the model number
for the power supply board, but my monitor is a KDS 17", which is also re-branded as proview, kds and aoc, as far as i know, probably re-branded as many other brands.

Last edited by phubar; 06-17-2008 at 03:33 PM..
phubar is offline   Reply With Quote
Old 06-17-2008, 03:35 PM   #16
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Also I just tested the monitor as suggested above and the green light stays on when the monitor goes blank, so it seems the problem is the inverter, would replacing the caps fix it?
phubar is offline   Reply With Quote
Old 06-17-2008, 04:19 PM   #17
Krankshaft
Badcaps Veteran
 
Krankshaft's Avatar
 
Join Date: Jan 2007
City & State: New Jersey, USA
Posts: 2,283
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

It really depends the brand of caps on your board should be replaced on sight their quality is really that horrible.

There are some cap companies whos caps will work fine in some applications and horribly in others but Fujiyuu caps are just plain horrible and that is from experience and a whole bin of them.

If you don't have an ESR meter then that should be the first step if the monitor still exhibits the symptoms further troubleshooting will be required.

Many problems such as this are solved by cap replacement.

It could also be bad CCFL backlights shutting the inverter down as well but we don't go that far until the secondary caps are confirmed as good.

As for the type of cap they are low ESR caps I use Panasonic FCs from Digikey on my inverter recaps.

As for working voltage it ALWAYS has to be either equal to the original caps WV or higher.

The other important factor is size you don't want to install the new caps and not be able to put the cover back on. Diameter and height are what you are looking for here you shouldn't have to worry about lead spacing too much.

Any low ESR cap from Sanyo, Nichicon, Nippon Chemi-con, Rubycon, Samxon, or Panasonic will do just fine.

Last edited by Krankshaft; 06-17-2008 at 04:24 PM..
Krankshaft is offline   Reply With Quote
Old 06-17-2008, 08:18 PM   #18
Michaels
New Member
 
Join Date: Jun 2008
Posts: 4
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Well darn.

I just replaced the 220uf one I had as well, along with the other 6 caps.

220uf:
here

and the 470's: here

Now, for the purpose of keeping a the LT916s it should be fine right? Mine's still shutting off. If it's left "cold" for even 30 minutes or so it will stay on longer - but only about 10 seconds compared to 2 so it's obviously heat related?

Anyone have any ideas, because I'm out of them now

I'm about to just replace all the capacitors I can, including the ones on the slightly smaller board that is separate from the board with the 6 470's but wanted an opinion from you guys first
Michaels is offline   Reply With Quote
Old 06-17-2008, 09:01 PM   #19
Krankshaft
Badcaps Veteran
 
Krankshaft's Avatar
 
Join Date: Jan 2007
City & State: New Jersey, USA
Posts: 2,283
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Definately check the backlights remove them from the LCD panel and inspect them.

Backlights nearing the end of their useful life can shut the inverter down.
Krankshaft is offline   Reply With Quote
Old 06-17-2008, 10:33 PM   #20
phubar
New Member
 
Join Date: Jun 2008
Posts: 8
Default Re: Mag LT916s Model 900p 19" LCD dropping like flies

Quote:
Originally Posted by Michaels
Well darn.

I just replaced the 220uf one I had as well, along with the other 6 caps.

220uf:
here

and the 470's: here

Now, for the purpose of keeping a the LT916s it should be fine right? Mine's still shutting off. If it's left "cold" for even 30 minutes or so it will stay on longer - but only about 10 seconds compared to 2 so it's obviously heat related?

Anyone have any ideas, because I'm out of them now

I'm about to just replace all the capacitors I can, including the ones on the slightly smaller board that is separate from the board with the 6 470's but wanted an opinion from you guys first
Michael, RMPCTek in the third post said that he had to replace the 100uf caps, I would replace those first and see if that fixes your problem.

I think I'll try to get an ESR for cheap, ebay maybe.

Thanks a lot guys this thread only keeps getting better and better for the noobs like me.
phubar is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 03:44 AM.
Did you find this forum helpful?