V7 L27ADS-2E LCD monitor repair - dead

[Jeroni Paul]

The video/control board in this LCD monitor seems dead. It has a TSUM088CDT9-7 video processor and does not react to any button press, does not enable the back light and is not detected when plugged to a computer. It runs off a single 5V supply and contains two voltage regulators, 3,3V and 1,2V that supply the Vcc pad and core respectively. The crystal oscillator seems to be running checked with a short wave radio at 14,31MHz.

I can't find any information on that processor and I am not sure if the 1,2V supply is right. The nearest I could find is a service manual for a LG LM91C chassis with a TSUM088GDT that states 1,8V for the Vcore. I found some other service manuals using other TSUMxxx models and all state 1,8V core voltage. However the 1,2V regulator seems fine, the control input is feed with a resistor divider from the output and it is at 0,6V just like the 3,3V regulator. The resistors are unmarked black SMD resistors so I can't tell if they are the right value but they are not open. Before trying to hack the regulator to 1,8V I would like to be sure this IC it is not supposed to run at 1,2V.

Anyone ever heard of that processor IC?

[Peter X1]

Are you sure its must be 1.2V which seems to me for a LCD monitor
somwhow strange. Whatś the input voltage of the "regulator" ?

I think feeding things with 1.8V, providing doing this with low current,
will not harm things. If you habve a bench power supply, give it a slow
try.


--
Mvg...
Peter

[Jeroni Paul]

Peter X1 wrote:
> Are you sure its must be 1.2V which seems to me for a LCD monitor
> somwhow strange. Whatś the input voltage of the "regulator" ?
>
> I think feeding things with 1.8V, providing doing this with low current,
> will not harm things. If you habve a bench power supply, give it a slow
> try.
>
>
> --
> Mvg...
> Peter

1.2V is the measured voltage, I can't properly measure the voltage setting resistors because the circuit effect. I hacked the resistors to increase the voltage to 1.8V with no difference.

I identified the reset input, it is implemented with a 10uF electrolytic just like the similar manual I pointed and it is fine. I scoped the crystal and it is oscillating with 0.8V amplitude centered around 1.7V, I guess it is fine. So it seems the micro is dead. No attempt to read the flash memory, as soon as the reset goes low both SDA and SCL go and stay low.

I am seeing 15 ohm resistance in the 1.2 / 1.8V line. From my experience this is normal with some processors but maybe with this one indicates an internal short.

[Peter X1]

You could try to scope the voltage which should have no circuit effect.
Powering thingsvia a resistor divider network seems odd to me, perhaps
it act as reference only.

Difficult to investigate without datasheet/reference. Try to find pins
that may do "something" and work your way up or as last resort,
(de/solder skills required & risk to damage) swap the chip.
Before that, I would check the electrolytic conndensators first.


--
Mvg...
Peter