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!...
sjfehr
Member
Last Activity: 12-04-2014, 05:33 PM
Joined: 10-18-2012
Location: Chesapeake, VA
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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.
...Leave a comment:
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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, lolLast edited by sjfehr; 12-01-2012, 06:26 AM.Leave a comment:
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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: [url]http://www.discount-merchant.com/1107770-DP42848-p/1107770.htm[/url]
What kind...Last edited by sjfehr; 11-30-2012, 09:56 PM.Leave a comment:
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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*
...Last edited by sjfehr; 11-03-2012, 05:11 PM.Leave a comment:
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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....Leave a comment:
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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...Last edited by sjfehr; 10-27-2012, 08:16 PM.Leave a comment:
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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.Last edited by sjfehr; 10-27-2012, 07:58 PM.Leave a comment:
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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...Leave a comment:
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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?Leave a comment:
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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.Leave a comment:
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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....Leave a comment:
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Re: Sanyo DP42848 42" LCD TV: sound, but no picture
Ah, that should have been obvious. IC800 is on the mainboard and was the first troubleshooting step in the service manual, btw.
I'm getting 24VDC on several pins on the invetrer boards, and 2.2-3.2VDC on several other pins, and 0V on the rest. Unfortunately, I have no way of knowing which pin is BL_ON.Leave a comment:
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Re: Sanyo DP42848 42" LCD TV: sound, but no picture
What is BL_ON? I'm getting 5V on IC800 pin18, and 5V on connector K8B pin 1, both of which indicate the inverters should be on.Leave a comment:
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Re: Sanyo DP42848 42" LCD TV: sound, but no picture
Well, it's gone black again. Same as before, though this time it shows a few seconds of video before going dark. Sound continues to play. What should I check next?Leave a comment:
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Re: Sanyo DP42848 42" LCD TV: sound, but no picture
Yeah, I counted the transformer windings and looked at the insulation, and figured it was operating somewhere in the 200-300V range. So, set my meter to 600V and... well... didn't give me useful data, but appears to still be working. Even if the voltage isn't that high, the frequency is likely well outside the range of this meter.Leave a comment:
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Re: Sanyo DP42848 42" LCD TV: sound, but no picture
Update: just reinstalled the 2nd inverter board without the cage to try to measure the output to the backlighting. And the damned TV just started working again! Crossing my fingers and hoping it was just a loose connector and the troubleshooting process corrected it. Also hoping I didn't fry my meter, as there was quite a bit of sparking and wierd things on the display...
Odd, though, that the symptoms persisted through playing with the PSU, mainboard and 1st inverter. And started working when I reinstalled the...Last edited by sjfehr; 10-19-2012, 10:10 AM.Leave a comment:
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Sanyo DP42848 42" LCD TV: sound, but no picture
Yesterday, out of the blue, our 42" Sanyo DP42848 LCD stopped working. No lighting strikes or anything, it just stopped working properly. It's out of warranty.
When turned on, we see a black screen with the blue "HDMI1" input notification in the corner: the screen appears to be uniformly lit, so it sure looks like the LCD and backlighting are all working properly. A few seconds later, at the point where it would normally start showing video, the backlights turn off and sound comes on. If I shine a light in, it looks like the LCD is showing video, but it has no lighting....Last edited by sjfehr; 10-19-2012, 09:38 AM. -
Re: New Members - please post your introductions here
Hi, I'm an electrical engineer from Virginia, and my TV is broken: I'd much rather replace a couple $1 components than buy a new $500 TV. I don't normally get into component level repair, and suck at soldering, but I do enjoy a good challenge. Unfortunately, I'm having a bit of trouble figuring out just exactly which components failed. Not quite as straightforward when I lost 3 motherboards at work about 10 years ago to counterfeit capacitors, mobos which the idiot contractors kept replacing with boards well known to have bad...Leave a comment:
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