Sanyo - CE32LC81-B (17PW20v2 PSU)

[tmcw]

Have this LCD TV with an intermittent, blue light, not-starting issue.

There were a couple of episodes where the non starting was attributed to a stuck power/standby button on the side of the TV, but I believe this is not the problem now.

This morning, I managed to get the TV to start after a couple of goes with the standby button on the remote, so decided to do some voltage tests on the powerboard whilst the panel was on.

Across the main cap, I'm getting 390V DC, which from what I've read should be ok.

Here are the voltages on the 4 main connectors off the powerboard, not sure of the numbering, but if the board is orientated with the connectors on the bottom, Pin 1 is on the left. Any connector with a very low +/- 0-20mV voltage is shown with a (mV).

PL801
1-3 NC
4 24.44V
5 24.44V
6 (mV)
7 (mV)
8-10 NC

PL802
1-5 24.44V
6-9 (mV)
10 6.8V
11 1.013V
12 3.116V

PL803
1 3.113V
2 1.014V
3 3.73V
4 (mV)
5 2.589V
6 56.7mV
7 34.8V
8 12.21V
9-10 (mV)

PL805
1 NC (4.97V)
2-3 4.97V
4-6 3.37V
7-10 (mV)
11-12 3.37V
13 5.02V

Now, I've looked at the schematic (for 17PW20 rev 00), and except for the pin 5 on PL803 (I get 2.589, schematic has no voltage specified), the voltages look to be ok.

When I first got the TV (it was being thrown away), it also had startup issues, but at the time, I found that unplugging the connectors, and replugging them seemed to help, for a while.

Physically, no signs of of bulging capacitors. I've included a photo of the small board where the power comes in, as I noticed a thermistor there and some evidence of heat, though I've seen similar before on PCBs with no issues.

Any suggestions for further tests, or suspect components to home in on based on the above?

EDIT: Trying to upload photos, but hitting internal server error messages, will try later if anyone thinks the photos would help.

[selldoor]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Maybe a startup cap problem - small perhaps 50v one in the primary section.
Picture of your board might help. Have you tried reducing the size of the pics or posting one at a time.

[Moreno83]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

The readings look ok to me.

Are there any 2200 caps on the ps? Try to replace those first and see if the tv will start normal.

[tom66]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Most likely it's the 15n caps near the main transformer - these can fail intermittently, causing the set to fail to start. Very common on 17PW15,16,20.

[tmcw]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Thanks for the replies.

Tried uploading again, but same server error (500), reduced file size to 75% (1.15MB to 600kb), and tried one at a time, but it still wouldn't upload.

Not sure which is the startup cap. There is a 10uF/63V (C881) and two 33uF/50V (C840 and C801).

Only one 2200uF on the board, looks ok. Why would that be a target for replacement?

I've read about the 15n's on several other threads, so will get a couple of replacements. Any point in removing them now and testing them?

[tmcw]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

I pulled off the two 15n's, and they are both reading about 11nF.

Is that enough to cause the issues I'm seeing?

[tom66]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Yea. They need to measure within 10%. 13.5nF-16.5nF or the circuit can be destabilised. Also, as the caps warm up or cool down, they can fail intermittently O/C.

[tmcw]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Cheers for that. I'll have a couple of replacements later in the week, and will report back.

Interesting about failing and heat, they're sandwiched between a heatsink and massive transformer, and the casing of each a little brown (originally blue), and looks like the heat impact is from the outside, not the inside.

Given that the voltages seem to be otherwise good, is there any point in changing any of the other capacitors? And if yes, capacitors related to which generated voltages? Which voltage circuits are more likely to be problematic possibly at a later stage?

[tom66]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

I usually up-rate the caps from 630V to 1kV minimum, 1.25kV preferred, the original voltage rating is too low, leading to premature failure.

[Trevtron]

Re: Sanyo - CE32LC81-B (17PW20v2 PSU)

Hi all, first 'tech' post here. I see from numerous threads that these 15nF's seem to be a very common cause of failure in the 17PWxxx PSU's. Is there a critical difference between the original polypropylene ones and, say polyester?
My case is an old Proline branded 26" set someone gave me to play with. It trips as soon as the backlight kicks in, but runs OK when the backlight is powered from an external power source. I had an identical situation with an 'Oki' 32" set a few years ago.