Sanyo DP42848 42" LCD TV: sound, but no picture

[budm]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

I think you should remove the transformer then you can see how the wires are attached to the pins.

[f67bird]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

In my experience: If I get a Sharp or Sanyo lcd that has backlights shutting off after 2 seconds, I check the inverter...and if that seems ok, I go ahead and take the panel apart to check the ccfls.
Many Sharps and Sanyos seem to be set to what I call "roman candle mode"- the backlights are all the way up.
They wont last too long like that.
When I repair any lcd, I try to make sure the backlights are set down to about 2/3 brightness or lower so the ccfls have a chance to last as long as the rest of the tv.

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

There are several slits cut in the board; it's not a feature I'm used to seeing in PCBs. There's a screw hole next to it that I left off white troubleshooting (I used the two grounded screws.)

I did a brute force attack on the 2nd inverter board. There were no resistances in the 2000 Ohm range. Number of .2Ohm and open. Odd measurements and measurements inconsistent between inboard and outboard transformers:

Inboard Transformer Pin 3-7: open
Outboard Transformer Pin 3-7: 170kOhm*

Inboard Transformer Pin 6-7: open
Outboard Transformer Pin 6-7: 156kOhm*

Inboard Transformer Pin 6-9: open
Outboard Transformer Pin 6-9: 172kOhm*

Inboard Transformer Pin 7-9: 24.6Ohm
Outboard Transformer Pin 7-9: 24.6Ohm

Inboard Transformer Pin 9-10: 10.7Ohm
Outboard Transformer Pin 9-10: open

Inboard Transformer Pin 7-9: 24.6Ohm
Outboard Transformer Pin 7-9: open

Inboard Transformer Pin 7-G: 10.7Ohm
Outboard Transformer Pin 7-G: 10.7Ohm

Inboard Transformer Pin 9-G: 35.2Ohm
Outboard Transformer Pin 9-G: 35.2Ohm

Inboard Transformer Pin 10-G: 35.3Ohm
Outboard Transformer Pin 10-G: open


All other pins open to ground at 200kOhm range. I did verify the open readings were not bad probe points by testing at two different points on the solder joints to verify continuity.

* these 3 readings would slowly change, either increasing or decreasing a few kOhm per second until stabilizing at the numbers recorded. I suspect these readings are reflecting resistance through other components on the board, and not the transformer coils. I tested a few diodes with inconsistent results, too; a number had identical resistance in both directions, but it was impossible to isolate them, and without a wiring diagram, impossible to know what they should read.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

I still find those readings a bit confusing.

Try the "brute force" method and list the results of all possible combinations. Some will be 0.2 ohms, others will be open loop, but there should be a combination that shows around 2000 ohms.

You might want to clean off all that flux residue. Use cotton swab with isopropyl alcohol.

On T2, pin 10, there looks like a hole in the board?

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

There are 8 pins on the primary side, but only 6 are connected, the first and last pins are unconnected stubs; what I've been calling pin 8 may actually be pin 7, if that makes more sense.

There may not actually be any direct connectivity between pins 9 & 7; the path likely goes 9-10-7, as the inboard transformer has just 0.1 Ohms resistance between pins 9-10, while the outboard transformer is open. All transformers read 25Ohm between pins 10-7.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

the outboard transformer had open circuits between pins 8 & 9 while the inboard had 25 Ohms between 8 & 9.

Hmm, somehow this doesn't make sense. Show me a picture of your multimeter measuring pins 8 and 9 and the reading of 25 ohms.

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

I was assuming the two large triple pins on the side with the secondary windings (pins 9 & 10) were S1/S2, but the diagrams on lcdparts.net showed a different arrangement, so I sketched out the readings I got. Both boards had identical measurements on the two respective transformers- on each board, the outboard transformer had open circuits between pins 8 & 9 while the inboard had 25 Ohms between 8 & 9. Of course, the inboard transformers had continuity with nil resistance between pins 9 & 10, so it could be a red herring.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Sorry, I actually tested the transformer secondary resistance with every scale up to 20M, including 20k- nothing, all read open.

Are all the secondaries testing open or just one? If it is just one, then you found the problem.

What pins are you calling secondary?

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Sorry, I actually tested the transformer secondary resistance with every scale up to 20M, including 20k- nothing, all read open.

Edit: oops, didn't see your post on the top of this page. Lemme do a few more checks; I assumed the two large terminals were S1/S2, but they might not have been.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

All 4 inverter transformers have identical part#s, written in two rows:

T51.0165.211 e5

This page here

http://lcdparts.net/T.aspx

shows similar, but not identical transformers. For testing purposes, let's choose this one for identifying the primary and secondary pins.

http://lcdparts.net/TransformerDetai...ProductID=3619

What is the resistance between pins S1 and S2? Note in the above link the expected resistance is around 2K. So if you are using 2K ohms on your multimeter and the reading is 2050 ohms, your multimeter will show out of range. That is why I asked you to use 20K.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

the transformer closest to the center of the board is reading 0.2 Ohms across the secondary, and the other transformer reads open on both 200Ohm and 2kOhm scales.

As I mentioned in post #17, use the 20K (twenty thousand) scale and retest. 2K (two thousand) may be too low.

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Thanks, retiredcaps! That 2-seconds to black page is great, too. Didn't think to check the FAQs on the computer display forum.

I double-checked the transformer secondaries. Found the same thing on both inverter boards: the transformer closest to the center of the board is reading 0.2 Ohms across the secondary, and the other transformer reads open on both 200Ohm and 2kOhm scales. I filed down into good solder to ensure resin wasn't fouling the measurements; the solder joints appear good.

All 4 inverter transformers have identical part#s, written in two rows:

T51.0165.211 e5
0815 709 S

Ring a bell for manufacturer/source? No obvious manufacturerer information on it.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

What is the part number of the inverter transformer?

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

I measured 0.2Ohms on the LV side of each transformer between 3-4, & 4-5, but open circuits between 2-3 and 6-7.

You should be getting a reading on the secondary side and not open circuit. If you have a manual range multimeter, you might have to set it to 20K ohms as some secondaries will reading > 2K ohms.

[retiredcaps]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

2 seconds to black can be

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Any final advice/things to check or board to replace before I give up and buy a new TV?

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Yes, but the interval is shorter now; the backlights come on for only about 1 second before going out.

[budm]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

BL_SW is the backlights on signal and it looks OK, >3VDC. It looks like the inverter boards are getting all the correct signals and power.
So right now do you still get the backlikgts to be on for seconds then the backlights turn off?

[sjfehr]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

The fuses near the connector on both inverter boards look good. I was able to identify and test two likely pins: BL_SW=3.3V and BL_ADJ=3.3V.

[budm]

Re: Sanyo DP42848 42" LCD TV: sound, but no picture

Can I see good clear pictures of the master and the slave inverter board around the connector?
Check that black surface mounted fuse close to the connector that looks like a SMD resistor to see if it shows open. Check all fuses of both boards.