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

[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.

[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

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

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

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

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

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 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.

[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.

[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.

[tomstr]

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

Did you ever fix this tv?

[sjfehr]

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

Did you ever fix this tv?

To be honest, procrastination got the best of me, but I still want to fix it and I definitely appreciate the help! Tore more into it earlier this evening; the CCFLs were a bitch to get to. But I FOUND THE PROBLEM! Well, I found a smoking gun at least; I'm really hoping it's the root cause and not a symptom.

Surprise surprise, a blown cap. (and a burnt out bulb)

Found a replacement interface board for $20 here: http://www.discount-merchant.com/110...-p/1107770.htm
What kind of bulb is this? It measures appx 3x950mm, but I can't find any markings.

[budm]

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

You have badly burnt out ballast cap. Good price for the replacement board. Check http://www.ccflwarehouse.com/ for the replacement lamp.

[johnboy1313]

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

That was exactly the same spot that one of my bulbs went out. New bulbs are ~$25 a piece, not really cost effective to replace them all with new ones. Instead, I called a guy advertising that he buys broken LCDs on Craigslist. He sold me three used ones for $25. A word of caution, those plastic support clips WILL break when you remove the bad bulbs. Be ready to replace them.

[johnboy1313]

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

To be honest, procrastination got the best of me, but I still want to fix it and I definitely appreciate the help! Tore more into it earlier this evening; the CCFLs were a bitch to get to. But I FOUND THE PROBLEM! Well, I found a smoking gun at least; I'm really hoping it's the root cause and not a symptom.

Surprise surprise, a blown cap. (and a burnt out bulb)

Found a replacement interface board for $20 here: http://www.discount-merchant.com/110...-p/1107770.htm
What kind of bulb is this? It measures appx 3x950mm, but I can't find any markings.

You won't find any like that for sale new. You will have to buy the ones like what ccflwearhouse sells and solder them in. 3.4mm X 950mm though I used 940mm and bridged the gap with solder. Check out my profile for pics.

[budm]

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

https://www.badcaps.net/forum/showth...hlight=DP42848

[f67bird]

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

I knew you would find it.
Any time I go to throw out an lcd with a busted screen or
other times I have to strip them to make room...I keep all of the ccfl's
for this situation.

Remember to turn down the backlights.
For most Sanyo tvs its called Energy Saver in the on screen menu- turn it to high...if you want the rest of the ccfls to last.

[sjfehr]

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

Just ordered the parts. And I'm going to turn down the brightness of all my TVs now.

Glad to see you got yours fixed, johnboy! I ordered 950s, but I'm going to have to do the solder trick to build up the diameter of the ends, looks like.

Just hope I can get it all back together, lol

[sjfehr]

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

Parts are in, 950mm bulb was the right size but needed some solder and hot glue. In the process of swapping the bulb & board, I broke another bulb, though: for the stupidest reason, too: I mistakenly leaned on it trying to get better leverage on the broken bulb. I moved the bottom-most bulb up so there won't be a dark band in the middle; I'll have to see if the dark band at the bottom bothers me enough to go through this again. I broke roughly half the little plastic loops, but a little hot glue fixed them.

I was unfortunately rather pessimistic about fixing this TV and didn't documenting disassemble like I should have, so reassembly is proving challenging. No idea what screws go where at this point, but it's coming along. Hopefully I'll have an update in a few hours.

[sjfehr]

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

Got it all back together- comes on for a second with a damaged LCD, and then goes out. Screen isn't visibly cracked when turned off, and I was always being REALLY careful with it during removal and after I got it out, but to no avail. I'm really bummed now, I really thought this was gonna work. I'm just going to part it out on ebay, I guess. Or if any of you who have been so helpful need any of the parts, just let me know, they're yours!