Sanyo DP32746 - CCFL testing results - 2 seconds to black

[alecjahn]

First note: DB32746 is different from DP32647
(I have the 746, my father has a 647 that I gave him a while back).

Anyway.

Got this at a thrift store, my brother is in need of a TV about this size. Got to plug it in at the store and when it was 2-seconds-to-black (OSD pops up in the corner before light goes out), I figured it was a safe purchase (and the price wasn't too bad).

So of course, I crack it open and don't find any blown caps. I thought maybe the two main [640?]uf/[250?]v caps on the PSU were bulging, but when I replaced those with some spares sitting around it didn't change anything.

I learn the inverter board has a couple of SM fuses. For the record, getting to the inverter requires some chassis deconstruction, which makes working on this one a huge pain in the rear in comparison to other more modern/streamlined models. Fuses check fine. There's 8 mosfets (but oddly... only 14 transformers/CCFLs? Weird. I didn't care enough to study the layout and figure out why they didn't just do 7 (1 mosfet for 2 transformers/ccfls), but whatever.
Mosfets check fine (none seem shorted? 8-pin, and all drains, D1 and D1 and D2 and D2 are connected on the board so an easy brainless test).

Transformers... I Started doing an impedance test on those but then decided I didn't actually know what I was doing so I stopped.

So I get to the bulbs. I remember I have an old PC case mod mini CCFL thing, runs off of the 12v rail on your standard molex connector on a PC power supply. Cool. I crack that open, separate the bulb from the circuit. First I started connecting the mini-CCFL's *circuit* to the Sanyo's bulbs, one at a time (using a little regulated molex-equipped 5/12v power supply). First I thought it wasn't working, but upon further inspection (with the lights off) the CCFLs inside the Sanyo WERE lighting up on one side but not very bright. I assume the driving board on that POS little toy isn't robust enough to get the larger Sanyo's bulbs to operate correctly.
Well, that didn't tell me too much, except that every bulb appeared to light up the same amount.

Then, I decided to try the reverse. Got the TV all re-plugged, back together, and then used the mini toy CCFL bulb in each spot on the Sanyo's inverter board, one at a time. To my surprise I found a configuration (third blue CCFL line from the bottom) that kept the TV on! Plugged in my PS3 to verify a good picture and all is well!
Except then the TV turned off.
Crap.
So using this sloppy (I'm sure you all will whip my back side when you see the pictures below) setup, the TV will stay on for a little while. 15 seconds or so. Then the backlight shuts off.


http://www.pictureshack.us/thumbs/59982_Sanyo_DP32746_rig-1096.jpg


http://www.pictureshack.us/thumbs/59982_Sanyo_DP32746_rig-1096.jpg
Click the links for giant sized ones if those thumbnails don't cooperate.

So... It appears that I have a bad CCFL in the panel. Right? OR is there the possibility that something else is amok?

I'm still a little weary of this PSU and inverter. There's a couple instances of DP32746 inverters dying on the 'net, though it seems like they normally have shorted mosfets and blown fuses.

[alecjahn]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

Using the test points on the power board, (top left of picture)

24v - 23.8v
5v standby - 5.14v (sorry this one is behind the 8-pin cable)
Then there's two more but they're weird?
6v?-5.47v (very top, to left of leftmost capacitor)
13v?-14.20v (very bottom left)

It's not easy to see in this shot, but the pcb is actually a bit darker around the leftmost heatsink and transformer. Check the auxiliary shot and its pretty apparent.

Also attached is the inverter board. Not a whole lot to see. It's a Logah Rev 5 VIT79002.51/VIT79002.52

[tom66]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

A spare CCFL may not have perfect matching to the panel's bulbs, causing a slight balance fault as the panel warms up, so shutting off after 15 seconds isn't entirely unexpected. I'd say replace that bulb and you should be good to go.

[alecjahn]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

It's certainly a heck of a lot smaller than the ones in the panel, which I think are like ~700mm. I think I'll probably order the new bulb by the end of the day (it's Sunday of course so I have some time to make the decision :P )

[alecjahn]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

Update:

Got two new bulbs in (decided to order two for kicks).

Installed the new bulb fine (scary stuff but totally do-able if you're inclined and take your time).

No dice.

BUT.

That bulb is not lighting up! You can barely tell with the lights off but right where it is located is a slightly darker band across the panel when all black (no signal). So either it's a dud (again, I've got another to try!) or my wiring is really terrible. I know the non-plug side is fine, continuity-wise. I'll have to dig alllll the way in again another day and try swapping the other bulb.

I hope!

[alecjahn]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

I'm at a loss. Same thing with the new bulb, nothing has changed. Tried my toy CCFL connection as outlined in the first post and that still works fine... I checked the connections again and everything looks/checks primo.
Really not sure what else to do other than order a new inverter board and try that... and then I'm getting embarrassingly close to the value of the TV (which isn't much, being a pretty old 720 res Sanyo)...
I suppose saving it from the dumpster is key, but...

[alecjahn]

Re: Sanyo DP32746 - CCFL testing results - 2 seconds to black

After a DOA inverter board from eBay, I did more testing (why didn't I do this before? I mentioned in the first post that I started doing this and totally flaked-out... I feel like a fool!). The transformer on the "dead" bulb's line was reading infinity on the output coil (if that's the correct term). Well. I swapped the allegedly dead coil with another on the same board and though the overall status didn't change the dark spot moved to that new position of the dead coil. Luckily for me the corresponding mosfet appears to check out fine.
A winner is me! Wish I hadn't spent all that money on this thing, a [tv price]+[coil price] is a hell of a lot cheaper than [tv]+[2 CCFLs]+[DOA inverter board]. Crap.
You live, you learn. I certainly learned a lot, which is pretty awesome and maybe priceless.
Thanks for the help everyone. I've said it before and I'll say it again: You're all amazing for taking time out of your day to help people like I, even if it is just a nudge in the right direction to figure something out for ourselves.
Case closed? Maybe?

P.S. But wait, why did my toy CCFL setup work?...