Sanyo DP42848 sound but no picture

[ChrisInVT]

I've repaired three TVs in the past year by myself by replacing the bulging/leaking capacitors, but this one seems to be a bit beyond that.

I have a Sanyo DP42848 TV that I purchased for $50 because the display does not power on. This is a backlight or inverter problem from what I can tell. It turns on, you have sound, everything works but you can only see the picture with a flashlight. The inverter PCBs are getting 24v from the power PCB. I've checked the fuses on the inverter boards and they are good.

I've read a few threads concerning this model TV here on the forums, and most are turning on for a couple seconds, then going out or turning off - mine does not do this. It turns on and stays on for as long as you'd like - you just don't get the CCFLs turning on.

I work at an electronics manufacturing facility, so testing the PCBs down to a component-level shouldn't be an issue. My knowledge and tools are limited, but what I don't understand, and what tools I don't have in my arsenal I could have one of my Electrical Engineering friends help me with (I'm just the I.T. guy).

When talking with my EE friend, we originally suspected the horrible solder joints on the inverter boards to be the cause of the backlighting problem. We cleaned up all the joints real good and touched up a few bad ones but the backlights still didn't fire up.

I have tested the inverter transformers (per https://www.badcaps.net/forum/attach...4&d=1350660859) and on the master and slave, the outboard is open while the inboard is not.

I've attached photos of the boards to this post, both with the flash on and off (flash washed out some parts, but without the flash the focus is fuzzy)

[vinceroger69]

Re: Sanyo DP42848 sound but no picture

dont know if you have read this post but some good testing tips in it
https://www.badcaps.net/forum/showth...=Sanyo+DP42848

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

Yeah, I've gone through a bunch but not all. The ones I've read everyone experienced a couple seconds, then black. This one doesn't do that.

[vinceroger69]

Re: Sanyo DP42848 sound but no picture

Yeah, I've gone through a bunch but not all. The ones I've read everyone experienced a couple seconds, then black. This one doesn't do that.

post 23 and 24 may help in the link i posted have you got the service manual?
http://www.tgohome.com/ServiceManual...&Search=Submit

[budm]

Re: Sanyo DP42848 sound but no picture

Will backlights come on if K8L connector is removed?

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

I forgot to list my ohm readings across the inverter board transformers, tested on 20k setting.

Primary PCB:
Inboard transformer testing to pin 10:
1: open
2-7: 8.88
8: .02

Inboard transformer testing to pin 9:
1 & 8: open
2-7: 8.85
8: .02

Outboard transformer testing to pin 9 & 10:
1: open
2-7: 8.88
8: .02 to pin 10. Open to pin 9


Secondary PCB:
Inboard transformer testing to pin 9 & 10:
1: open
2-7: 9.49
8: .02

Outboard transformer testing to pin 9 & 10:
1: open
2-7: 9.50
8: .02 to pin 10. Open to pin 9

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

post 23 and 24 may help in the link i posted have you got the service manual?
http://www.tgohome.com/ServiceManual...&Search=Submit

I checked those posts regarding the K8L connector, I do have the service manual from that link.

Will backlights come on if K8L connector is removed?

No, they don't.

[budm]

Re: Sanyo DP42848 sound but no picture

OK, so we have check the Inverter circuits and may have to check the lamp per that thread.

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

From what I've read, everyone that's experienced the 2-seconds then black issue has had burnt bulbs, and disconnecting K8L keeps the backlights on (K8L is the error sensing circuit I think I read?).

The backlight on this never powers on at all, even when K8L is disconnected. What should I see coming out of the inverter boards? I'm sure we have meters here capable of high voltage.

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

Alright guys, I got it! On the main inverter board, look at the power in socket. Directly below it is an SMD fuse that I missed, which showed no continuity (I was testing the large fuses next to the connector, which were good).

24v on the input, 0.00 on the output. I grabbed a scrap piece of CAT5, stripped a single wire to make a jumper and powered on the TV. With the fuse jumped, the backlights power on and stay on. I'm going to see if we have on of those fuses in stock, or if I can solder a different style (same rating) in it's place. I don't want to "hotwire" it by shorting the two terminals, because fuses blow for a reason.

Tomorrow I'm going to test the load on the fuse and see what amperage is going across the two terminals. It's labeled F1 on the PCB and I've attached a picture of it's location.

Best part is there's uniform light across the screen, and the TV stays on with K8L plugged in.

[budm]

Re: Sanyo DP42848 sound but no picture

I have seen that type of black fuse failed a lot for no reason. I use PICO II through hole fuse for replacement, that fuse is for supplying B+ to the PWM IC. It should be around 1A fuse. You can set your meter to DC AMP Mode and put the probes on each pad of the fuse to measure the current draw, then double up that reading.

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

Yeah, I already did that. It spikes about 50mA when powered on and stays about 5mA when running. I don't have the exact numbers in front of me.

[ChrisInVT]

Re: Sanyo DP42848 sound but no picture

It looks like my biggest problem now is finding where all the screws to this thing are. It seems that the package of screws to hold the case together and the base to the case have come up missing. Lovely.

[CDGraves]

Re: Sanyo DP42848 sound but no picture

I had a bad Sanyo DP42848. Picture on for 2 seconds and then black.
I wasted my time and money trying inverters. No fix.
I discovered it was bad backlights. Reading various forums, this seems to be a very common problem with this TV.
I disconnected the 2 ribbon cables from the T connector board to the control boards that ran the glass panel and removed the boards and glass panel. I left everything else intact. That way I could turn on the TV and observe the backlights.
I had 3 bad backlights. The originals backlights are 950 mm long and 3.3 mm wide. The ends are covered in conductive silver coating.
I could not find an exact replacement. The closest I could find was 950 mm long x 3.0 mm wide bulbs with wires at the end. I purchased these from http://www.ccflwarehouse.com for $25 each. Part number CC30950. I bent the wire ends back and soldered them to the metal sockets. When the 3 bad lights were replaced the Television came on and stayed on. So far so good.
There are 12 ribbon cables from the control boards to the glass. Unfortunately I damaged one of those cables and ruined the TV. These cables are glued on to the boards and they are pealed off very easily. I made several attempts to glue it back on and on my last attempt, I accidentally cracked the screen. The moral of the story is, if you must remove the glass, be super careful, otherwise you will turn a fixable problem into a non-fixable problem.

[mrbudders]

Re: Sanyo DP42848 sound but no picture

24v on the input, 0.00 on the output.

Hello long time reader first time poster. When I test the F1 fuse I get 24v one way, when i turn the probes I get -24 v. this means that it is good correct? if this in't correct where is the "output" you mention?
I am new to this but have a general grasp on it.
]
Also, i can see image with flashlight. I am having same issue as OP. No pic whatsoever (except with flashlight) and have sound. Same model

[Aldrich67]

Re: Sanyo DP42848 sound but no picture

Any suggestions to the following problem would be highly appreciated.

When I turn on the TV, the backlights comes on and shut off but the TV green light stays on. Unplugging hte K8L connection on main board and turn on the TV, the backlights turn on and then off but the TV still stays on.

When the backlight are on briefly, looking at the front of the TV, I do see couple of dim darker horizonatal sections. Is it the imfamouse brokrn CCFL bulbs?

[johnboy1313]

Re: Sanyo DP42848 sound but no picture

Sounds like it. Check out post #26 in this thread.

https://www.badcaps.net/forum/showth...t=24040&page=2

[Neelix]

Re: Sanyo DP42848 sound but no picture

Hello long time reader first time poster. When I test the F1 fuse I get 24v one way, when i turn the probes I get -24 v. this means that it is good correct? if this in't correct where is the "output" you mention?
I am new to this but have a general grasp on it.
]
Also, i can see image with flashlight. I am having same issue as OP. No pic whatsoever (except with flashlight) and have sound. Same model

The "output" that ChrisInVT mentions is the other end of the fuse. The voltage at both ends of the fuse needs to be measured

[Newbie62]

Re: Sanyo DP42848 sound but no picture

I checked those posts regarding the K8L connector, I do have the service manual from that link.



No, they don't.

Where is the K8L Connector, I don't see it.

[budm]

Re: Sanyo DP42848 sound but no picture

See that small white connector on the main board with 2 wires (blk and wht)?
https://www.badcaps.net/forum/attach...0&d=1362680597