Sharp LC-32D40U Negative picture unless the contrast is almost 0

[MikeRWK]

This only affects the picture but not the tv menus. Selecting any of the default picture settings gives a negative picture but turning the contrast down to 5 'fixes' it but then the tv is too dim which is hard to tell in the pictures.

This tv has a main board, scaler board, and a tcon.

I tore it down so I could probe the tcon which is nicely labelled. I've also included a pic of it.Here are the voltages I got:

VGH 32V
VGL -6V
GAM1 14.6V
GAM18 185mV
VLS 14.67V
3V 3.01V
RESET 2.95V
TCLK 0V
SCC_VDD 2.99V
D_VCC 2.99V
VCC+5V 4.9V
D_VDD 2.98V
VCOM3 6.58V
VCOM2 6.57V
CS2 6.57V
SDRAM_VDD 2.99V
PLL_VDD 2.99V
RSDS_VDD 2.98V
STHF 0V
D_VDD_F 2.98V
LVDS_VDD 2.99V
D_VDD_B 2.99V
VCOM1 6.57V
CS1 6.57V
1COM+ 6.41V
SDRAM_CLK 1.46V
RAMCLK 1.44V
STHB 0V

[R_J]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Check all the gama voltages 1~18. The fault is likely the AS15-f
gam1=
gam2=
gam3=
etc.
gam18=

the voltages should be linear: something like 1,2,3,4,5,6,7,8,9,10 etc. and not 1,2,8,9,5,6,7

[MikeRWK]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Check all the gama voltages 1~18. The fault is likely the AS15-f
gam1=
gam2=
gam3=
etc.
gam18=

the voltages should be linear: something like 1,2,3,4,5,6,7,8,9,10 etc. and not 1,2,8,9,5,6,7

Here are the voltages, I couldn't find points GAM8 or GAM11.
GAM1 14.58V
GAM2 14.22V
GAM3 12.08V
GAM4 11.27V
GAM5 10.65V
GAM6 10.21V
GAM7 10.05V
GAM8 --
GAM9 8.25V
GAM10 7.16V
GAM11 --
GAM12 5.18
GAM13 5.07
GAM14 4.79V
GAM15 9.37V
GAM16 3.45V
GAM17 0.65V
GAM18 0.18V

[nomoresonys]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Yep, bad, 8, 11, 15, need new gamma chip or tcon board.

[MikeRWK]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Yep, bad, 8, 11, 15, need new gamma chip or tcon board.

I meant I can't find physical pads for 8 and 11 but i think you're right

[nomoresonys]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Voltage on 15 should be between the voltage of 14 and 16, like around 4 volts or so.

[MikeRWK]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

Voltage on 15 should be between the voltage of 14 and 16, like around 4 volts or so.

Looks like i'll be ordering a new ic

[R_J]

Re: Sharp LC-32D40U Negative picture unless the contrast is almost 0

I think the pc board numbering is wrong, I believe there should be 15 (14+1) test points