Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

[James Mandapati]

Symptoms:
The LCD TV was dead from October. However in between this period when we randomly tried switching on the TV it worked and continued to work normally till it was switched off and the next attempt you try switching on, it would not. The last time it worked was on 22 Dec 2013

Tests:
1) Checked power across the power terminal and its normal 250 v AC
2) Checked Voltage across the filter capacitor (big one) and its 345 v DC

BTW i measure voltage across the terminals say for measuring the voltage on the capacitor i placed the black lead on the capacitor -ve and the read lead on the capacitor +ve

I understand from the forum that the first thing is to check 5VSTB but not sure where the red and black probes need to be paced

Observation:
All the electrolytic capacitor look good without bulges. (Power supply snapshot attached) and i do not see/smell any burnt components

[James Mandapati]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Is it Ok if we remove all the connectors on the right side (see the power supply image)and troubleshoot?

[tom66]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

For now leave connectors in -- later can try without them. Check 5VSTB by touching against the outer sheaf of a 5VSTB pin with the red probe, and the black probe against the chassis. Set meter to 20V DC or volts DC autorange, whichever is available, and observe result.

[James Mandapati]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Hello Tom,

I should connect red probe to pin 9 (From attachment 2) and iam not clear on the chassis part Could you suggest any point on the power supply attachment? like the area where the screw fits

Other thoughts, in attachment2 are pin numbers 4,7,14 not ground? if so can i connect the black probe here?

[tom66]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Chassis: the metal frame of the TV, back of LCD panel, the wall mount bracket mount points, etc. Yes you can also use a grounding point but that is a lot more difficult to do.

[James Mandapati]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Checked 24VA, 5VA, 12V, 5VSTB and all of them read 0 volts

checked the voltages on all electrolytic capacitors (between the black colored heat sink and the connectors) by placing the red probe on the top of the capacitor and the voltages where les than a volt.

I read in this forum that 345 VDC on the mains filter capacitor is on the lower side. Any other points to look at?

[budm]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Up load good clear pictures of the bottom side of the board, we should work on getting the 5VSTBY circuit working first. There are 2 electrolytic caps by the T602 that should be checked, you can try heating it with hairdryer first to see if the 5VSTBY will start up.

[James Mandapati]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Hello budm,

Uploaded pictures of the bottom side of the board which are not very clear.The schematic is available at
http://elektrotanya.com/sanyo_lcd-32.../download.html

on page 64

I do not have a hairdryer nor a capacitance meter to measure capacitance

However i did the following voltage checks (across the 2 electrolytic caps by T602)

1) power terminal - 240 v AC
2) input AC Voltage to the bridge rectifier - 240 v AC
3) output DC Voltage at bridge rectifier - 340 v DC (steady)
4) Voltage at filter capacitor - 340 v DC (steady)
5) capacitor c1601 47mf/35v - 7.8 V DC
6) capacitor c1607 47mf/50v - 0.1 V DC (or might be zero too)

[selldoor]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Maybe just me or the picture but is Q602 ok - looks cracked?



EDIT Moving down the heatsink the component at the other end doesnt look great either but hard to tell for the dust.

[James Mandapati]

Re: Sanyo LCD 42CA9S No Lights(R,B,G) & No Standby Power

Maybe just me or the picture but is Q602 ok - looks cracked?

Q602 is good no cracks


EDIT Moving down the heatsink the component at the other end doesnt look great either but hard to tell for the dust.

This is also good no cracks

Do the 2 voltage readings of the startup capacitors @ T602 mentioned by budm give any clue?
1) capacitor c1601 47mf/35v - 7.8 V DC
2) capacitor c1607 47mf/50v - 0.1 V DC (or might be zero too)

With No Lights(R,B,G) & No Standby Power, is the steady 340 V DC at bridge rectifier and filter capacitor the right voltage?