bad capacitor

[davidvincent]

Hi I am new to posting on here my name is David from Wigan Lancashire in England.

I am trying to fix a psu on a Baird x37dtv I have replaced the start up caps as they were bulging so now the tv will switch on so a victory there.

The screen now flashes on and off, using info from one of the members on here I have been testing the big Cap 150uf 400v when warmed up with a hair dryer the tv works perfect except for a slight hum on sound.
My question is should the big cap hold the 400v for quite a while after switch off as I have tested the voltage while working and its just over 400 volts once warmed up, before using the hairdryer its only getting to 332 volts, 10 mins after switch off and its showing no voltage is this capacitor buggered shouldn't it still be charged up

Thanks in advance for any advice

DV

[davidvincent]

Re: bad capacitor

I have isolated the capacitor by cutting pieces of plastic and surrounded the cap so the heat goes on to the cap and not surrounding components and the tv starts to work after 30 seconds with the hairdryer I think it is defo this cap so I will order a new one

DV

[ReeceyBurger123]

Re: bad capacitor

Ok it sounds like the pfc is failing what psu is in the tv (model number) and does the cap look physically failed ?

[davidvincent]

Re: bad capacitor

Hi thanks for your response

the cap looks fine, the psu is AD301M24-4N1

There is a thread on here were he had the same fault and heated the cap up and it worked he replaced the cap and it was the same, now like I posted I used some plastic and surrounded the cap and heated it up and bingo I had it on for 2 hours then switch it off for 5 mins and to get it back on you have to heat it up again

regards

David

[ReeceyBurger123]

Re: bad capacitor

Try replacing the cap with a higher value like 180uf 400-450v.

[davidvincent]

Re: bad capacitor

Would this make any difference

[SteveNielsen]

Re: bad capacitor

What adjascent components may be heating up during the test?

[davidvincent]

Re: bad capacitor

I will upload a picture

[davidvincent]

Re: bad capacitor

You can see the components near the Cap from this photo

[ReeceyBurger123]

Re: bad capacitor

Would this make any difference

I usally replace 150uf with 180uf on sets that are worth something it basically gives cleaner voltage to the switchers.

[ReeceyBurger123]

Re: bad capacitor

I dont think its the cap what voltage does the cap measure when the set is on ?

[davidvincent]

Re: bad capacitor

around 330 -340 volts at my latest test

[davidvincent]

Re: bad capacitor

the cap goes down to nothing within a few mins when not plugged in

[davidvincent]

Re: bad capacitor

I just done another test on the cap
Cold no power ie not plugged in 0 volts
Plugged in not switched on 350 volts
Turned on screen flashing 340 volts
Use hairdryer on Cap until screen stops flashing (steady backlight) 325 volts

[ReeceyBurger123]

Re: bad capacitor

Interesting, sounds like something els but replace the cap first to rule that out.

[davidvincent]

Re: bad capacitor

ok I will get back once I have the replacement I will order one off ebay

thanks for your help

DV

[ReeceyBurger123]

Re: bad capacitor

ok I will get back once I have the replacement I will order one off ebay

thanks for your help

DV

Your welcome, keep us updated

[davidvincent]

Re: bad capacitor

Hi after looking at it again and taking into account all that you guys have said I am now of the belief that the 400v cap is not at fault.

I have really isolated the 400v well using cardboard and plastic and blew warm air above it and the tv started to work, so above it is a diode (that is ok) and a ceramic cap so I put a tube on the ceramic cap and blew warm air the tv did not change.

So above the Ceramic cap there is another diode that seems ok. two small transistor's 1 big transistor TIP31C and 4 very suspect small electrolytic caps 3 @ 47uf 25v and 1 @100uf 25v I have put a tube over the caps I seem to get a reaction from the 100uf cap when I blow warm air on it I am now waiting for the tv to cool down and repeat the tests a few more times

BTW the electrolytic caps are samxon which are known to be pretty bad caps

At last I maybe getting somewhere

I will post again later with results

DV

[kc8adu]

Re: bad capacitor

just shotgun all those samxons.
that series/color are known bad.
nice to track it down to a single troublemaker but in the long term those all need replacement.

[davidvincent]

Re: bad capacitor

Yes Agreed the low voltage side is full of them I changed 2 of the samxon start up caps they had blown their tops well on their way anyway.

I am going to change out the 100uf first and if I get the tv working ok I will give the option to my friend (its his tv) to do a full cap change to rubycon caps