Vizio 26" LCD VA26L Inverter Problem

[DakotaKid]

I have a Vizio VA26L that will turn on but there is no backlight. I did the flashlight test in a dark room and can see the picture/menu being displayed but there is no backlight. The power on (white Vizio logo) and off (orange logo) works as it should. Voltages out of the power supply are 11.8V on the 12V, 23.3 on the 24V when turned on. The inverter board is getting 23.3V. However, it appears that the surface mount 1A/76V fuse labeled "20" (see red circle) is blown because I don't get continuity across it. Should I check it a different way? I was considering soldering in a new fuse and seeing if it blows again. The power supply was full of Capxion caps but none appeared bulging or failed. I did, however replace all except the 450V 150uF big cap on the power supply board in case some had failed without visible signs. Is there anything else I should test or check before trying the new fuse?

There are 4 caps of unknown origin and size (label side is glued down to board) but none appear bulging. Should I replace these? It looks as if someone might have reflowed them at some point but I do not know for sure.

Board markings: VIT70063.50 rev 3, 27-D023043, I260B1-5UA-L201C

Thanks in advance.
DK

[jetadm123]

Re: Vizio 26" LCD VA26L Inverter Problem

I have a Vizio VA26L that will turn on but there is no backlight. I did the flashlight test in a dark room and can see the picture/menu being displayed but there is no backlight. The power on (white Vizio logo) and off (orange logo) works as it should. Voltages out of the power supply are 11.8V on the 12V, 23.3 on the 24V when turned on. The inverter board is getting 23.3V. However, it appears that the surface mount 1A/76V fuse labeled "20" (see red circle) is blown because I don't get continuity across it. Should I check it a different way? I was considering soldering in a new fuse and seeing if it blows again. The power supply was full of Capxion caps but none appeared bulging or failed. I did, however replace all except the 450V 150uF big cap on the power supply board in case some had failed without visible signs. Is there anything else I should test or check before trying the new fuse?

There are 4 caps of unknown origin and size (label side is glued down to board) but none appear bulging. Should I replace these? It looks as if someone might have reflowed them at some point but I do not know for sure.

Board markings: VIT70063.50 rev 3, 27-D023043, I260B1-5UA-L201C

Thanks in advance.
DK

I suggest you check the two mosfets (looks like Q18? and Q20?) to the left of the blown fuse for shorts. Also, a cap can look fine, but still be bad.

[tom66]

Re: Vizio 26" LCD VA26L Inverter Problem

Test the resistance from the case of the TV to both ends of the fuse. If you get a reading of nearly 0 on one end, a MOSFET is probably failed somewhere on the board.

[DakotaKid]

Re: Vizio 26" LCD VA26L Inverter Problem

Checked all 4 mosfets Q19, Q20, Q28, Q29. Q19 and Q28 are P4404EDG and Q20 and Q29 are P2504BDG. the P4404's measured about 10Kohm across the pins, the P2504's were about 1600Kohm across the pins.

The side of F20 closest to the edge of the board measured 60Kohms to chassis gnd and the other side was infinity to chassis gnd. The 7A/160V fuse to the left of Q19 tested good at 0 ohms across.

Thanks.

[retiredcaps]

Re: Vizio 26" LCD VA26L Inverter Problem

There are 4 caps of unknown origin and size (label side is glued down to board) but none appear bulging.

Those might be Nichicon low ESR HV caps? Do they have a "X" vent and a plastic bottom (bung)?

See this for a reference.

http://www.ebay.ca/itm/290658691589

If they are Nichicon, they are good caps. The Capxon, on the other hand, are terrible quality and might warrant a complete replace on sight judgement.

[jetadm123]

Re: Vizio 26" LCD VA26L Inverter Problem

Checked all 4 mosfets Q19, Q20, Q28, Q29. Q19 and Q28 are P4404EDG and Q20 and Q29 are P2504BDG. the P4404's measured about 10Kohm across the pins, the P2504's were about 1600Kohm across the pins.

The side of F20 closest to the edge of the board measured 60Kohms to chassis gnd and the other side was infinity to chassis gnd. The 7A/160V fuse to the left of Q19 tested good at 0 ohms across.

Thanks.

Did you check only across two pins for each mosfet?

Ideally, you should check the following combinations:

S-G
G-D
S-D

[DakotaKid]

Re: Vizio 26" LCD VA26L Inverter Problem

Great call retired. Yes, they have the X vent and plastic bung. I peeled one up and they are indeed nichicon, 270uF 35V.

[tom66]

Re: Vizio 26" LCD VA26L Inverter Problem

It looks like you don't have any obvious shorts.

The fuses used on these boards can occasionally blow, even without apparent cause, simply due to thermal stress and metal fatigue (internal to the device.) So it may be sufficient to simply replace the fuse. If it blows again, then you need to locate the failed component, or replace the entire inverter (your choice.)

[DakotaKid]

Re: Vizio 26" LCD VA26L Inverter Problem

Q19: S-G infinity, G-D 1500 kohm, S-D 150 kohm
Q20: S-G 10 kohm, G-D 1400 kohm, S-D infinity
Q28: S-G infinity. G-D 1600 kohm, S-D 160 kohm
Q29: S-G 10 kohm, G-D 1400 kohm, S-D 1300 kohm

The 1300-1500 numbers seemed to continue to build and my meter goes to infinity and flashes 1000 when it hits 2000 kohm. All of the readings over 1300 would probably have gone to infinity if I had waited.

I guess I should go ahead and try the fuse? The fuse is marked "20" on top and the board says 1A/76V, not sure what the "20" signifies. Is this the right fuse?
http://search.digikey.com/us/en/prod...77-1-ND/615050

Thanks.
DK

[tom66]

Re: Vizio 26" LCD VA26L Inverter Problem

Are you sure it's only 1A? A TV like this is probably going to use a 3 or 4A fuse.

[DakotaKid]

Re: Vizio 26" LCD VA26L Inverter Problem

I am going by what is on the board when I determined it to be 1A. Here is the pic of that fuse.

Thanks.

edit: I found this thread using google which didn't show up when I searched badcaps for my problem. Looks like PlainBill recommended the same fuse that I came up with on digikey. I wish there was some followup from RichR on whether he found or fixed his problem because it seems nearly identical to mine in the short thread from November.
https://www.badcaps.net/forum/showthread.php?t=17214

I have some 1A automotive fuses around the house, would there be any harm in soldering in a fuse holder with those to test this while I wait for the nano fuses to arrive?

[tom66]

Re: Vizio 26" LCD VA26L Inverter Problem

There would be no harm in using an automotive fuse. It will be difficult to solder to those tiny pads though, but it might be best if you leave the failed fuse in parallel as a mount for soldering your wires to. An automotive fuse is typically 32V rated, and the highest voltage these boards use is typically 24V.

[DakotaKid]

Re: Vizio 26" LCD VA26L Inverter Problem

Replaced the fuse and all is good. I think the power supply may have been the root of the problem. I replaced all of the Capxon caps on it with the Panasonic caps, replaced the 1A fuse on the inverter board and it is working great.

Thanks for the help.

[tom66]

Re: Vizio 26" LCD VA26L Inverter Problem

A bad power supply could blow the fuse, I suppose, if the ripple current was very high through the caps, but it would have to be very high and it would most likely pop the caps before the fuse. These fuses tend to blow on T-cons and main boards too, seemingly without cause.