Philips BDL3231

[medbor]

I recently got a trashed LCD panel from work and it was broken (surprise!)
It does turn on, then it chirps and turns off, restarts again and so on (about once per second).
So i took it apart expecting bad caps, and this is what i found:
1. 1200uF 35V 105C CapXon x2
2. 2200uF 16V 105C CapXon x1
3. 680uF 35V 105C Capxon x2
that was obviously bulging and broken.
I have "replaced" them with some scrap i found, but it still chirps and won't stay on for more than half a second. With "replaced" i mean:
1. 1000uF 35V 85C Nichicon + 220uF 35V 85C Nichicon x2
2. 2200uF 35V 85C Nichicon x1
3. 680uF 35V 105C Elna x2
The Nichicons i found in a trashed Sony CRT TV (so they might be old), but the Elna Caps where unused.

It is very hard to photograph this perticular tv, the main power supply is decent to reach, but the lcd power board is located under the motherboard and i just don't have it in me to take it apart again right now.

Is there anything simple i might have overlooked or should i just take it apart once more?
The power led seems constant, and also the display driver, so it might be the cffl perhaps (or its power)?

[retiredcaps]

Re: Philips BDL3231

Is there anything simple i might have overlooked or should i just take it apart once more?

1) Reusing old caps is a bad idea. Unless you measure the capacitance and ESR, you have no idea if the replacement caps are working.

2) Using 85C caps is also a bad idea when the originals were 105C.

3) Capxon makes terrible quality caps. We generally recommend replace on sight regardless if they are bloated or not.

4) Smaller caps usually never bloat when they go bad and play an important part of the SMPS startup process. This could be your chirping sound every second.

5) The power LED being on probably means that 5V standby is present. Now the main board is instructing the power supply to start.

--- standard answer, regulars may skip this part ---

https://www.badcaps.net/forum/showpo...84&postcount=3

[medbor]

Re: Philips BDL3231

I realise that reusing caps is not at all recommended, but i don't like spending money if i don't know it it will help. Should i replace all caps everywhere i go by your approach?
Also i don't think digikey distibutes to sweden, i have elfa.se though, they seem to have a lot of caps.

Some pictures after my initial atempts.
Do you need pictures of the main board aswell?

[medbor]

Re: Philips BDL3231

found two badly burned diodes on the primary side, is this a bad or common thing?

[tom66]

Re: Philips BDL3231

Those are the clamp diodes for the SMPS. They get hot, so it's not entirely a surprise they show up as burnt. It would probably blow the fuse if they went short circuit, but there's the possibility the power supply is current limiting on the primary side because of this - I've ran this through my head a few times and it seems plausible.

To test:
- unplug TV from mains
- leave for 5 minutes for bulk caps to discharge (HIGH VOLTAGE!)
- use the diode test mode on your meter (looks like -|<-)
- note the reading when the probes aren't touching anything ("OL" or "1") - this is the open circuit reading
- place red lead on one end (doesn't matter which), black on other, note reading
- reverse leads, note reading
- test the other, although we expect the same reading as they are most likely in parallel

We are expecting around 500 one way, and open circuit the other way.

[retiredcaps]

Re: Philips BDL3231

Should i replace all caps everywhere i go by your approach?

It is up to you. If you are not going to replace caps, then start doing your voltage measurements.

[Mr Bill]

Re: Philips BDL3231

Those 2 diodes that are burned was causing my cousins 37" Philips to chirp after we replaced the bad caps. The one actually had a small pin hole in it and was emitting a small puff of smoke.

[medbor]

Re: Philips BDL3231

Those 2 diodes that are burned was causing my cousins 37" Philips to chirp after we replaced the bad caps. The one actually had a small pin hole in it and was emitting a small puff of smoke.

What happened next? everything ok?

The diodes in question are actually connected in series, but are they broken?

If i did recap the whole PSU and Inverterboard, what are my chances that the tv will function fine? until i saw the diodes i thought it would work with just the caps, but now i wonder what more could have gone bad...

i have the schematic if you are interested... page 17



The inverter board is not in there, but there is no visible damage at all except for the popped caps from the pictures above (purple ones). And as you probably have seen already the caps i replaced these with where Jamicon not Elma as i previously wrote.

[medbor]

Re: Philips BDL3231

It is up to you. If you are not going to replace caps, then start doing your voltage measurements.

Of course i'm going to replace caps, i just hoped my original efforts was enough.
Do you mean replacing all the small caps on the main baord too or just in the psu+inverterboard? There are about 50 caps on the main board...

[retiredcaps]

Re: Philips BDL3231

Of course i'm going to replace caps, i just hoped my original efforts was enough.
Do you mean replacing all the small caps on the main baord too or just in the psu+inverterboard? There are about 50 caps on the main board...

Normally, just the power board for most situations as they undergo the most stress. Some TV manufacturers do have problems with caps on the inverter board as well. Obviously, there is NO guarantee that replacing the caps with new low ESR will work.

Since you found a schematic, you should take some voltage readings to see where the problem is.

I would check

a) for stable 5V standby power
b) for steady power at main board (probably 5V)
c) IC904 pin 1 (VCC)

[Mr Bill]

Re: Philips BDL3231

What happened next? everything ok?

The diodes in question are actually connected in series, but are they broken?

You'd have to determine if they're broken with your multimeter. In my case we went to radio shack and bought a general purpose diode (2 pack), soldered them in and the tv fired to life. Then we ordered the correct diodes from digikey and the tv has been working solid for a couple months now.