Viewsonic N3250W LCD (dang Chinese garbage) - Videokarma.org TV - Video

radiotvnut · #1 11-02-2009, 03:54 PM

Someone asked me to fix a 2005 32" Viewsonic LCD TV model N3250W. When I first pressed the power button, the green light came on and it started making a pulsing squealing sound like when there's a short. So, I removed a ton of screws and unfastened a bunch of clips just to get the back off. Then, I had to remove a bunch of other screws to get the metal shield off so I could get to the PC boards. Once this was done, the first thing I saw were two swollen 68uf, 450 volt caps. I thought, "good, this should be an easy one". So, I went to the local parts house where they gouged me $8.63/ea. for the caps! I could have probably ordered a half dozen for that price from some place like Mouser; but, you know how it is when you're in a hurry. I installed the caps and it still does the exact same thing. I checked the heatsink mounted semiconductors for shorts; but, could not find any. In this set, the power supply and inverter are on the same board. I'm about ready to put the old caps back in and give the POS back to the owner. And, some people wonder why I have no desire to actually OWN one of these sets. From now on, if someone ask me to look at an LCD or Plasma set, there will be an upfront check out fee charged before I pull the back. I'm real tired of spending my valuable time opening these things just to find out there's nothing I can do with them.

matt_s78mn · #2 11-02-2009, 05:20 PM

My advice would be to replace ALL the electrolytics on the inverter board... There probably aren't all that many total. Even if they don't look swollen or poofed out, get rid of em and put good quality Xicon's in there. I've had to do that a lot with Samsung LCD TVs. They used cheap worthless CapXon brand lytics on their inverter boards.

Quote:

Originally Posted by radiotvnut

Someone asked me to fix a 2005 32" Viewsonic LCD TV model N3250W. When I first pressed the power button, the green light came on and it started making a pulsing squealing sound like when there's a short. So, I removed a ton of screws and unfastened a bunch of clips just to get the back off. Then, I had to remove a bunch of other screws to get the metal shield off so I could get to the PC boards. Once this was done, the first thing I saw were two swollen 68uf, 450 volt caps. I thought, "good, this should be an easy one". So, I went to the local parts house where they gouged me $8.63/ea. for the caps! I could have probably ordered a half dozen for that price from some place like Mouser; but, you know how it is when you're in a hurry. I installed the caps and it still does the exact same thing. I checked the heatsink mounted semiconductors for shorts; but, could not find any. In this set, the power supply and inverter are on the same board. I'm about ready to put the old caps back in and give the POS back to the owner. And, some people wonder why I have no desire to actually OWN one of these sets. From now on, if someone ask me to look at an LCD or Plasma set, there will be an upfront check out fee charged before I pull the back. I'm real tired of spending my valuable time opening these things just to find out there's nothing I can do with them.

MRX37 · #3 11-02-2009, 05:21 PM

I'm glad the Chinese junk I'm trying to fix is fairly easy to work on. Just 10 or so screws that hold the back of the TV on. 4 screws holding the main chassis board in place... only shielding is around the tuner can.

radiotvnut · #4 11-02-2009, 09:14 PM

I replaced more caps - still no change. It squeals constantly if I unplug the backlight cable. When the cable is plugged in, the squealing pulsates. Im about ready to tell the owner to get it off my property. Better yet, he should leave it with me so I can do something creative with it.

zenith2134 · #5 11-02-2009, 11:31 PM

Yeah it'd be fun to get it running and experiment with it somewhere if he gave it to you....which it sounds like he should....

Regarding a set's country of origin: it doesn't matter they're all this bad IMHO at the consumer level...

Findm-Keepm · #6 11-05-2009, 06:41 PM

Most of the LCD sets I've encountered were indeed cap-only repairs. On a few sets, the lamp inverter supplies were defective. Most of the time, it's the power MOSFETs that are bad - look for heatsink mounted devices with a "KXXXX" part number on them. The check them drain-source for a resistance of 5K or less.

From some archived Hitachi literature:

One of the most common failures in the Inverter Supply unit is a shorted FET (Field-Effect Transistor). The procedure outlined below describes a quick test method for determining when a Inverter Supply unit has failed due to a shorted FET. This information is particularly helpful in the following cases:
(a) When a lamp has failed and a new one is being installed; prior to applying AC, it is recommended to check the FET in the Inverter Supply, otherwise a new lamp could fail prematurely.
(b) Any time a Inverter unit is suspected of failure.
Procedure: (See Table 1)
1. Measure the resistance of the FET (positive (+) to drain, negative (-) to source) using a Digital Multimeter .
2. If the resistance is 5K ohms or less, the FET is shorted and the Inverter unit is defective.

If you do find a bad inverter power MOSFET, MAT Electronics is where I've obtained them in the past. If you need a manual, I can't help there, but there are a few manufacturers that post manuals for the public - Polaroid and Dynex are two that have LCD service manuals available.

Cheers,

wa2ise · #7 11-06-2009, 03:53 PM

Quote:

Originally Posted by zenith2134

Regarding a set's country of origin: it doesn't matter they're all this bad IMHO at the consumer level...

As none are "USA" anymore, that's another reason that it doesn't matter...

zenith2134 · #8 11-06-2009, 04:27 PM

Exactly, wa2ise. Not to mention that the Japanese sets aren't even built there anymore.....sad!