GV42LFDTV10a - no power

[ahickman]

My father was given a 42 Visio by a neighbor. They cut it on and heard a "pop". Opened up the case and looked the power supply over. 156 VDC at the main cap but no 5VDC STBY. Flipped over the power supply and noticed the blown 16 pin chip on the primary side. I believe this is the PWM chip? ShopJimmy of course sells the replacement PS for $50, but I would like to take a stab at repairing the PS. Anyone seen a Delta PS like this with similar issues?

[Jasgriff]

Re: GV42LFDTV10a - no power

That blown chip will have blown other components at the same time. I can see that at least a couple of SMD resistors are blown just underneath the IC.

[budm]

Re: GV42LFDTV10a - no power

Check Q601, Q602 in the picture for shorts also.

[retiredcaps]

Re: GV42LFDTV10a - no power

Are you sure the TV part number isn't GV42LFHDTV10a? It matters if you trying to find a service manual so you can determine the pwm chip.

[ahickman]

Re: GV42LFDTV10a - no power

You are correct, it is a GV42LFHDTV10A. Thank you for noticing.

[ahickman]

Re: GV42LFDTV10a - no power

Just received the replacement powersuppy and need suggestions on how to safeguard the investment during power-up. I am visiting my father in AZ and don't have my isolated variable transformer which would allow me to slowly bring it up to supply voltage while keeping an eye on the input current. Can anyone suggest an alternative method of powering up the set safely? Household light bulb in place of the AC fuse? Plug in one component at a time?

[retiredcaps]

Re: GV42LFDTV10a - no power

Household light bulb in place of the AC fuse?

I haven't done the above myself, but it is a long standing trick that I know budm, PlainBill, etc all use.

More details at

http://www.repairfaq.org/sam/smpsfaq.htm#smpstslbt

budm has pictures too. Let me look for them.

edit: Found it.

https://www.badcaps.net/forum/showpo...3&postcount=12

[ahickman]

Re: GV42LFDTV10a - no power

Thanks, that is exactly what I was thinking. Just didn't find it in my first few searches.

[budm]

Re: GV42LFDTV10a - no power

Just plug the TV in to that box but do not turn it on, if the light (150w) comes up bright and then dim down then there is no shorts, BUT, since NOT all circuits will be on yet until yu hit the power switch on the TV. this is for initial test only, then you need to put in 300watts bulb (since your 42" TV uses a lot of power) in place before turning on the TV otherwise the 150w bulb will ligth up and not gives enough voltage for the TV to run.

[ahickman]

Re: GV42LFDTV10a - no power

Budm, just want to make sure I understand the kinematics on this. By putting the filament/bulb in series, it acts as both a fuse and a visual indicator? How exactly does it protect the components downstream?

[tom66]

Re: GV42LFDTV10a - no power

Budm, just want to make sure I understand the kinematics on this. By putting the filament/bulb in series, it acts as both a fuse and a visual indicator? How exactly does it protect the components downstream?

A 150W bulb will only draw ~1.5Arms from a 115V socket, so it will limit any short circuit current. Maybe try with a lower wattage bulb first? Even a 20-30W? But I use a variac and ammeter if I were doing this, so I don't know enough about this trick...

[budm]

Re: GV42LFDTV10a - no power

It limits the current and voltage, lets say that it has shorted bridge rectifier, most voltage will be drop across the lamp, and very little on the shorted load (shorted rectifier). The lamp also function as an indicator at the same time, but it is not a fuse.
Anothe example, the bridge is shorted out due to the MOSFET is shorted, so you replace the fuse and the bridge but you did not check the MOSFET, you power it up, you blow up you new fuse an bridge again just to find out that you have bad MOSFET also. But if you use the lamp after the bridge and tghe fuse were replaced, the lamp would have stay lit brightly telling you that you still have shorts circuits still, and you will still have good bridge and fuse.

[ahickman]

Re: GV42LFDTV10a - no power

We found a local ham radio operator down the road that was kind enough to lend us a variac. Only problem is that it does not have an amp meter. He provided me with a 1 ohm power resistor which I can place in-line on the hot leg and measure the voltage across the resistor. Anyone advise against this method of measuring the rising current as I turn up the variable transformer?

[tom66]

Re: GV42LFDTV10a - no power

We found a local ham radio operator down the road that was kind enough to lend us a variac. Only problem is that it does not have an amp meter. He provided me with a 1 ohm power resistor which I can place in-line on the hot leg and measure the voltage across the resistor. Anyone advise against this method of measuring the rising current as I turn up the variable transformer?

Seems fine. Use AC volts; one volt AC will mean one amp AC. A short circuit will show itself on low currents and variac will often buzz. (Careful not to leave it too long with shorted load, could burn out winding.)

Oh and of course the obligatory - you'll be working with hot stuff so be careful!

[Sparky277480]

Re: GV42LFDTV10a - no power

My father was given a 42 Visio by a neighbor. They cut it on and heard a "pop". Opened up the case and looked the power supply over. 156 VDC at the main cap but no 5VDC STBY. Flipped over the power supply and noticed the blown 16 pin chip on the primary side. I believe this is the PWM chip? ShopJimmy of course sells the replacement PS for $50, but I would like to take a stab at repairing the PS. Anyone seen a Delta PS like this with similar issues?

Amazing! If I didn't know better I would have thought you took a picture of my power supply from a vizio VS42LFHDTV power supply part number 0500-0507-0331 DPS-283BP A REV S0

I purchased a power supply from shopjimmy.com for $49.00 and free two day shipping during the month of April.

I too would like to find out where I could get that ic chip. the replacement boards chip had no identification on it. To the person that said that it looks as if some resistors had been blown , are you going by the discoloring of the resistor?

Also the locations Q601 and Q602 what exactly are they (sorry for my ignorance) and would I test them for a short to ground or continuity across certain pins. I would love to have a backup power supply for my TV (which is working perfectly with the replacement board BTW) Thanks in advance for any help.

[ahickman]

Re: GV42LFDTV10a - no power

Thanks to all. The replacement PS from ShopJimmy worked well. We were able to scavenge the variac and used a DVM inline to watch for spikes in the current draw while powering up slowly. Always a little intimidating when it is not your own stuff you are working with. The set did not seem to have any other issues and drew a nice picture.

Sparky, regarding the suspect resistors, I measure each one alongside of the devoured chip and then compared them with the new powersupply. About 5 resistors were damaged. Several were much higher in value and others were almost shorts. Regardless of their varying values, they all had bubbling on the top side when looked at closely under a magnifying glass.

[Sparky277480]

Re: GV42LFDTV10a - no power

Thanks to all. The replacement PS from ShopJimmy worked well. We were able to scavenge the variac and used a DVM inline to watch for spikes in the current draw while powering up slowly. Always a little intimidating when it is not your own stuff you are working with. The set did not seem to have any other issues and drew a nice picture.

Sparky, regarding the suspect resistors, I measure each one alongside of the devoured chip and then compared them with the new powersupply. About 5 resistors were damaged. Several were much higher in value and others were almost shorts. Regardless of their varying values, they all had bubbling on the top side when looked at closely under a magnifying glass.

ahickman, thanks for the reply. Maybe it would be too much trouble to repair this power supply if it is more than just ic chip I would have tried that no problem but more than that is probably beyond my skill level at this time I have a basic grasp of ohms law and ac theory but testing in circuit gets tricky the more I read about it. Removing and testing and replacing would be tedious at best.

Right now I am limited to replacing bad caps and specific components and taking readings with my meter with specific values to be expected. I must say though that badcaps.net forum seems to be the most active and helpful so far.