245BW, can't find problem. No 24 or 6.3V, standby is good.

[WiseguyTom]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

I had the same problem with my syncmaster 245B (which has a BN44-00195A power supply).
Blue light came on but no image on the screen.

I was able to fix it and want to share my experiences.

At first, the problem was intermittent.
Sometimes an image was displayed and then suddenly it went black again.
Hitting the back or side of the screen a few times, often brought back the image.
But I had to hit it harder and harder to get the image back and after a few weeks I deciced to have a look inside.
After visual inspection I saw nothing special, no bad capacitors or resistors.
Also the fact that hitting it often/sometimes brought back the image made me believe it's not caused by an electronic component but by something else.
But what? A bad or loose transformer was my first guess.

I took out a DVM and started measuring on the stand-alone power board.
Standby 5.2V was ok. Connected it to the Pwr-On line to activate the other output voltages.
Nada, no 24V.

Then I started bending the PCB, pulling up one side while holding down the middle.
Don't do this with you bare hands or you'll get electrocuted!
All of a sudden, the 24V appeared!

Then I stumbled on this blog:
http://blog.whitesites.com/How-to-Fi...97265_blog.htm

Here they mention soldering joins that went bad.
So I re-soldered all big end medium joints and that did the trick.

So get your soldering iron out guys!

Cheers,
Tom

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Ok. I keep working. I've got all 24V and 5.3V now. I thought I swapped the zeners in 24V-to-5.3V section but I didn't. Anyway this part is now fixed.
I still need to find out why this power supply randomly making my "trick bulb" to light.
With video board connected test bulb always comes on. When I use 2k resistor the bulb comes on only sometimes. I really don't even want to think that the logic board is fried. I prefer to think it is because of the load.

Could it be because I used some Panasonic EB which are not low esr caps?
How do I diagnose that? Please help.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Yes of course.

[selldoor]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Budm is your best bet but can you put up a picture of the whole of the bottom of the board- cant see one and as the OP posted off site they have disappeared

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

It doesn't look good. I've got more than one issue.
I removed solder from pins 12 and 14 of ICM801 - MC33067. With logic board connected test bulb is coming on randomly. But when I use 2k resistor and I start the power supply board with it the test bulb never comes on.
I don't think the video board is bad as I have short circuit behind the J830 jumper (on the picture). When I reconnect the jumper I can see sparks and board dies.
I need your help guys.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

I've just connected everything together and unfortunately it's not working. Test bulb comes on and after 2s is pulsing quickly.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

It is good old style 100W incandescent bulb which is now banned in bloody EU. Fortunately I found some on eBay

[selldoor]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Can I just check - the bulb in your bulb trick device is a filament bulb? not a powersaver cfl or led. What wattage?

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Hi selldoor
Not I didn't. I'll try after work. But that in my opinion doesn't explain such a randomness.

[selldoor]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Have you tried with the ccfls connected - with them not connected may shut down as
being faulty?

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

When I say the bulb i refer to "in series bulb trick" bulb. Inverter is not even connected so I didn't mean ccfl. LED is the led on the front panel.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

I had 24V jumper lifted. When I soldered it back on the 24V gone. Now I need to switch off/on many times more to get the bulb come off, and event then I have no 24V.

[selldoor]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Whilst you are saying what you are seeing I am not so it would help if you could
differentiate between bulbs? May be just me

That is please say "Dim Light test Bulb" "Power led" or "ccfl" as against "bulb"

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Then the bulb comes on and pulsing the 24V slowly coming down, 1V every 2s.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Ok that's weird one. When I let it cool down for a few minutes, after first power up the bulb comes on, then power off and on and the bulb only flash once and stays off and I have the 24V!
Unfortunately only until next power off/on. Then the bulb comes and stays on until I let the system cool down again.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Yes. It's brand new and it's 22nF 630V.

[budm]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Did you check that red rectangular cap next the 24V transformer? I believe it is 18nF 630V it is one of the commonly fail cap, verify that it is still 0.18uF.

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Hello
I finally received all replacement parts. I also used the lamp in series trick. Looks like it saved me a lots of trouble.
When I switch power on bulb comes on then after 2-3 seconds starts pulsing at almost full brightness. When I touch on/off button led comes down as well as the bulb. Stand-by is working, that for sure
I've no idea what's wrong. Could it be MC33067 (ICM801)?

[Yaaman]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

Yes I read about lamp trick, I'll try it. The heatsink is missing because 24V jumper I lifted was underneath.
I am away from my pc so I don't know the zener values but I've got schematic and I go by it.
Every part I order now is always more than I need so I have a spare.
First FETs I ordered were exacly the same but now I'm thinking to get replacement as per Fairchild Semicon the original are not being made.

[Toasty]

Re: 245BW, can't find problem. No 24 or 6.3V, standby is good.

With no load and it blew, I'd be looking carefully at prior work.

In the future, use the "lamp-in-series" trick to prevent these types of surprises:

https://www.badcaps.net/forum/showpo...2&postcount=23

Make sure to use a real incandescent lamp, not any other type (no CFL or LED).

-----

Don't need those white caps. I re-read your list, and now with the pics, I saw you already replaced the mains cap with a KXG.

Assume you have the missing heatsink. ( Why is it off? )

What zener values did you choose? DZT852 and...? (just to be sure)
How did you determine?

Order more than 1 of the 100Ω. Usually a strip of 5 or 10 is minimum...?

Same with the 0.22Ω a couple-three won't hurt.

Check QT851. ( 1P type )

Both FETs, correct? Did you do ~exact~ replacements in the first go or subs?

Double check RB801S, the other power resistor.


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