Dead Darfon inverter in 37" Hitachi L37VP01

[PowerAmpFreak]

Hello!
As subjectline says. The Darfon inverter recieve +24V from PSU. After 4 seconds the PSU goes back into standby.
I think this is due to inverter doesn't output "Inverter OK" signal.
All SMD fuses OK. Measured across all transformers. No probs found.
What next?

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

These inverters don't have an inverter OK signal, as far as I remember. The PSU may go into standby if it is bad. Pretty typical of these 17PWxx power supplies to go bad, cheap Vestel junk. Also could be main board.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

I fixed the "Normal stuff" on the PSU, the 15nF caps and so on. No help.
Also tried another PSU, same problem.
Main board could be the problem eventually.
One thing that points to inverter is that it recieve +24V for a few seconds but still does not generate any high voltage.
Am not sure about the "BL ON" signal but will look deeper into this.

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

If 24V drops out, check 12V, 5V too. And check the PSON signal from main board.
Single inverter? Or master-slave?

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Tom, you're right. This inverter does not have a "INV OK" signal. It has just PWM and BL ON and a DIM pin which is not connected.
I can see that BL ON is jumping from +3V3 to 0V directly after startup. For some reason, the mainboard is shutting down the inverter.
Oh well, I begin to get used to those corrupted mainboards!!

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

90% of these bad older Vestel main boards are just eeprom issues - the eeprom is often socketed so you can remove it and put in a blank one (of same size.) Set will usually boot with wrong LCD panel settings (bad colour typically) so go into Menu 4725 to change LCD panel model and reset everything to correct values after doing this.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Aha. Great info. Is "MENU 4725" the service menu magic code?

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Yes. The normal user menu should pop up then press 4-7-2-5. In some cases 4-7-2-5 needs to be pressed then Menu but that is rare, on only older sets.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Got a new EEPROM in and set turns on backlight and the screen looks OK the second the backlight is on. Then the backlight shuts off (It looks like Backlight on signal from mainboard stays on) so there are perhaps a failure in the inverter aswell?
I don't know if those inverters are sensitive to bad grounding of the shield plate, like I've seen in some Toshibas?

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Install all screws but usually they can operate without metal cover.
Check transformer resistance, common fault on DARFON board.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

All transformers measures equal, spot on.
All screws installed.
Another PSU tried.
No improvement.

Could it be a chance that lamps are bad? Is it safe to unplug on HV connector at a time? Or does it also sense "open circuit" ?

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

It will also sense open circuit.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

I don't think I've ever come across a bad lamp. How big chance is this really?
Could it be worth trying a new inverter?

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

A high resolution photo of inverter board may help in locating the faulty lamp by means of testing the feedback voltage.

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

AHA! Found it. When I had removed the inverter to take some high resolution photos, I noticed two of the pins in the HV sockets (two of them) had been slightly bent so it didn't have contact with the connector. When pulled it up, the inverter stays on!
GREAT and THANKS A LOT TOM!

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

Fantastic!

[PowerAmpFreak]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

And this showed that inverter has protection for open circuit loads aswell, just as you told.

[tom66]

Re: Dead Darfon inverter in 37" Hitachi L37VP01

All inverters do. In fact that is basically all they check.

When a bulb fails, 99.9% of the time it fails open, which means it failed to ignite and is not loading down the inverter output. When this happens, output of transformer climbs to 3~4x nominal output which risks arcing and damage to transformer leading to smoke and fire. That is what the 2 sec to black circuit aims to prevent.