Sharp Aquos LC-46E77UN inverter testing

[JFarm]

I picked this TV out of a trash pile. When I plug it in I can hear the relay on the power supply “click” almost immediately, and then 7 seconds later there is another “click” and the power/OPC LEDs start to flash: two pulses on the power LED, one on the OPC LED. I didn't notice any sign of life from the backlight, but more on that below.....

The service manual () says this is a “DET_10V error: UR10V or A9V is not applied”, but after checking several voltages I believe the power unit is tripping off due to an overload as soon as the backlight tries to come on; this kills the UR13V lines to the main board, which causes the error.

To test this theory I unplugged the master inverter and jumpered the STB and ERR pins together to prevent the main board from sensing a lamp error: in this configuration the power unit does not trip off. This arrangement also gave me time to confirm with a flashlight that there is an image on the screen.

I then re-connected the master inverter board but disconnected the slave inverter board. In this configuration the power unit also stays alive, and this was also the first time I had noticed any of the backlights briefly flickering on. After re-connecting the slave inverter and with the room darkened I could finally see that the backlights have actually been briefly lighting up all along, but it is much dimmer and has a much shorter duration than with the master inverter alone.

I have tried to troubleshoot the inverter boards using information from old threads, but I haven't made much progress. For example, I tried measuring the resistance of the secondaries on the transformers (as shown in post #29 in https://www.badcaps.net/forum/showthread.php?t=52087), but I get an open-circuit on all 10 transformers on the master. Could they all have failed? On the slave board I read 0-ohms on all of them, but as you can see from the close-up photo this is to be expected because they are joined by a trace (the red lines mark the legs of the transformer). The part number on the transformers is 2874029300; I haven't been able to find any information on them, other than places that want to sell me a new one.

If anyone has any ideas on how I might proceed, I would appreciate any suggestions.

[R_J]

Re: Sharp Aquos LC-46E77UN inverter testing

Check the resistance between that secondary pin and one of the pins on what would be the primary side. The resistance should be around 900Ω more ore less

[JFarm]

Re: Sharp Aquos LC-46E77UN inverter testing

On the master I have these measurements:
1361, 1362, 1371, 1375, 1369, 1376, 1370, 1372, 1378, 1369

On the slave I have these:
1368, 1364, 1371, 1379, 1374, 1376, 1366, 1384

The lowest is 1361 and the highest is 1384; that doesn't seem too bad?

[R_J]

Re: Sharp Aquos LC-46E77UN inverter testing

It could be that the inverters/transformers are ok and there is a bad or broken ccfl. I believe there is a way to force the backlights on using the front buttons, I will look.
with unit unplugged, hold down CH_DOWN and VOL_UP and plug in the tv

[JFarm]

Re: Sharp Aquos LC-46E77UN inverter testing

That’s interesting.... When I power it up with CH_DOWN and VOL_UP, the behavior is mostly the same: after 7 seconds the backlights do that brief, dim flash, and all of the ‘higher’ voltages from the power unit drop to zero (UR13V to the master board, the 12V and 60V lines to the inverter, and the 12V line to the LCD unit). The difference I see is that the PS_ON from the master board stays high (2.9V) and there is no second “click” from the power unit relay..... I guess in this mode the master board ignores any of the usual errors and doesn’t drop the PS_ON signal?

You got me thinking about the CCFLs so I tried another test: I connected the inverter boards as normal, but lifted them so that none of the bulbs were connected. There is no backlight flash, of course, but the behavior is otherwise the same as before: with the slave board present the 60V line drops to 0V after 7 seconds, but with the master board alone it stays up. In fact, it rises a little bit: from 60.1V within the 7-second window, rising to 61.1V after.

I’m still leaves me suspicious of the slave inverter, given how its presence always seems to kill the power unit, with or without any bulbs in the system.

[Anooc7]

Re: Sharp Aquos LC-46E77UN inverter testing

It could be that the inverters/transformers are ok and there is a bad or broken ccfl. I believe there is a way to force the backlights on using the front buttons, I will look.
with unit unplugged, hold down CH_DOWN and VOL_UP and plug in the tv

I know its an older post but it solved my tv (LC-46E77UN)'s problem - pwr led 3 times opc once flashing issue! Thanks and Cheers !