Sanyo DP42849 Backlight Shutsdown

[martyparish]

Re: Sanyo DP42849 Backlight Shutsdown

@KJINTF sweet! Nothing like a challenge! Please take pics.

[budm]

Re: Sanyo DP42849 Backlight Shutsdown

I believe there are ballast caps inside the panel for each lamp that should be checked.
Similar to this setup: otherwise also check the 4 ballast caps by the output of the inverter transformer.
http://s807.beta.photobucket.com/use...49858344048522

Since the inverter transformer is driven by half bridge circuits, check the coupling cap C312, C313 which are under the heatsink of the MOSFETs that drive the transformer.
I remember that thread, the person gave up on me.

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

budm

Thanks for the suggestions
I checked the caps by the transformer - no signs of failure
Additionally as stated earlier I substituted the lamps with an external lamp
Check my earlier post on the secondary winding resistance

Waiting on approval from the customer before I attempt the transformer rebuild
I have had about 70% success rate rebuilding transformers - most of the time the transformers that have internal thermal protection / fuses and a few times with shorted coils

[budm]

Re: Sanyo DP42849 Backlight Shutsdown

Do you have ringer for testing the transformer?

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

Hi again

No (ringer) I sure wish I did - always some missing test equipment even after over $20k or more into the stuff

Got any suggestions on how I can kludge one together????????????

[martyparish]

Re: Sanyo DP42849 Backlight Shutsdown

I thought ringers weren't very effective on secondary of step up transformers? (not saying it's so, just heard it was the case)

[tom66]

Re: Sanyo DP42849 Backlight Shutsdown

They work on CRT flybacks well, and those big transformers are doing a similar thing (but with 3-4 kV output instead of 20~50kV.) So I can't see what would stop it working on a transformer like that. As far as building your own, you can use a pulse gen (with low impedance) and a scope. Simply count the rings on the falling or rising edge.

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

tom66

Thanks for the suggestion on a ringer
Just talked to the customer - he wants to buy a new board
Bought one off EBay where they want the core back
Looks like I will not be attempting a rebuild on the transformer afterall
I was looking forward to it - O well there will be another in the near future

[selldoor]

Re: Sanyo DP42849 Backlight Shutsdown

Perhaps you can measure the resistances on all the pin combinations on the new one? and post them for future reference

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

Not sure what just happened - posted a response and it's not there

selldoor,

That's a great idea - Thanks for thinking of it - Good to see others are helpful
Will do when I get the new part - should be by march 10th or thereabouts

[ztu165]

Re: Sanyo DP42849 Backlight Shutsdown

I'm willing to mail my transformer to anyone willing to take the challenge of rebuilding it for me. Anyone?

[jazpa]

Re: Sanyo DP42849 Backlight Shutsdown

have a sanyo dp42849 tv and i check my voltage and all the only thing i have is the 5 v and when i turn it on in a dark room it doesnt blink on for a sec but i can see the picture with a flashlight so i jump out the 5 v to the bl-on and still have nothing

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

Hi guys

I measured a known good transformer
Good measurements
Pins 5 <> 10 - 114 OHms
Pins 9 <> 6 - 66 Ohms

My defective transformer had the following measurements
Pins 5 <> 10 - 399 Ohms
Pins 9 <> 6 - 66 Ohms

New part works great

[ztu165]

Re: Sanyo DP42849 Backlight Shutsdown

Hi guys

I measured a known good transformer
Good measurements
Pins 5 <> 10 - 114 OHms
Pins 9 <> 6 - 66 Ohms

My defective transformer had the following measurements
Pins 5 <> 10 - 399 Ohms
Pins 9 <> 6 - 66 Ohms

New part works great

Based off your finding, I checked my transformer and I found:
Pins 5<>10 - 693 Ohms
Pins 9<>6 - 65.5 Ohms
This means my transformer is no longer good am I right?

[KJINTF]

Re: Sanyo DP42849 Backlight Shutsdown

That would be my guess...
Not sure what else you checked or your exact symptoms

[ztu165]

Re: Sanyo DP42849 Backlight Shutsdown

That would be my guess...
Not sure what else you checked or your exact symptoms

Symptoms are like everyone else's. TV starts up with backlights coming on for a few seconds and then turns off, but audio can still be heard.

[Ray Gianelli]

Re: Sanyo DP42849 Backlight Shutsdown

Well, looks like I've joined the no backlight club on this model of Sanyo with the DPS-260LP power supply board.

I found 2 of what I initially thought were SMD transistors that look bad. But these devices are labeled as diodes on the PC board. They have A.7 stamped in the top, with the number 5 sideways on the end.

Any idea what these are? Pic attached.

Thanks in advance, Ray

[Ray Gianelli]

Re: Sanyo DP42849 Backlight Shutsdown

Well, I replaced several electrolytics around the inverter section with low ESR caps. Checked each one of the old ones with a Peak Electronics ESR meter, they all looked good. But after reassembly the set wouldn't even power on anymore. Thought I'd installed a cap backwards, but that shouldn't have prevented it from powering up, and after checking they were all installed correctly. I had more pressing repairs pending, so I put it aside.

Cleaning the garage this week and decided to put the set back on the bench. Right away I found one of the connectors on the main board was partially unseated. Pushed it in, and now everything works.

One or more of the electrolytics must have been bad, even though they all looked good. I believe this is the most common failure in these inverter circuits.