My Samsung DVD&VCR Combo not powering! What to start with?

[mpdsite]

Hi Guys, I am trying to fix my dvd & vcr combo which does not power up. I've opened the top, checked internal fuse (ok) and now I am scratching my head not knowing what to test first.
I know some components can not be tested on board and I've only got DMM to test with.
Please help! Thanks!
It's Samsung DVD-VR325

 

[Nigel Goodwin]

It's almost certainly an electrolytic in the PSU - you need a scope to check for excessive ripple on the secondary outputs of the PSU. If I recall correctly it's either a 1000uF or 2200uF that commonly fails.

 

[mpdsite]

Thanks for advice I do not have a scope can I remove capacitor and test it capacitance with multimeter?

 

[Nigel Goodwin]

Thanks for advice I do not have a scope can I remove capacitor and test it capacitance with multimeter?

Probably not, you need an ESR meter to test it - the only reason I mentioned a scope was that while ESR meters work in-circuit, on this particular capacitor and circuit they don't, but a scope always does.

 

[mpdsite]

I have taken the electrolytic out and tested it. The electrolytic it self is 400v 100uF and on capacitance meter it showed 93.3uF.
Do you think that this one should be fine?
And why does the tin on my dvd board non want to melt have I got the wrong iron. Its 30-50 watt adjustable. Its really difficult to de-solder stuff from this board.
Thanks

 

[Chippie]

You need a bigger iron that cansupply the heat quicker to melt the local joint rather than heating the plate...

The cap value sounds about right..(its within tolerance..)

Check the voltages on the outputs of the psu...

 

[Nigel Goodwin]

I have taken the electrolytic out and tested it. The electrolytic it self is 400v 100uF and on capacitance meter it showed 93.3uF.
Do you think that this one should be fine?

That one is fine - as it's not the one you should be testing

That's on the primary, it's the secondary ones which give problems - and as I said, it's either 1000uF or 2200uF, not only 100uF - and they will almost certainly check within spec on a capacitance range.

 

[mpdsite]

Thanks for all your help.
-Regarding the Iron: do you mean I should get a more powerful solder iron or just a bigger tip.
-You are saying that if I check electrolytics they would probably show capacitance within tolerance but may still be bad ones.
What tests could I do with my Multimeter or what could I use to do some tests.
Thanks a lot.

 

[Nigel Goodwin]

Thanks for all your help.
-Regarding the Iron: do you mean I should get a more powerful solder iron or just a bigger tip.
-You are saying that if I check electrolytics they would probably show capacitance within tolerance but may still be bad ones.

Yes they most probably would - the main cause of failure is high ESR, and this still leaves it reading pretty well the correct capacitance.

What tests could I do with my Multimeter or what could I use to do some tests.
Thanks a lot.

You can't really - there's only a couple of that size capacitor - just change them. Make sure you use high quality 105 degree capacitors, and low-ESR ones if you can.

 

[Chippie]

-Regarding the Iron: do you mean I should get a more powerful solder iron or just a bigger tip.

More power....100 watts should be enough....

 

[mpdsite]

I've replaced those 2 electrolytics 1000uF and 2200uF with exactly same ones and it's still not powering. I also checked rectifying diodes all 4 showed to be good (I removed one pin of each diode for testing and soldered back in afterwards) What would you advise me to should check next. Thanks for helping

 

[Nigel Goodwin]

Check voltages in the primary of the PSU - bear in mind these are full mains and non-isolated - you need to measure from the negative connection in the primary side. However, I'm a bit worried about your experience in doing this!.

 

[mpdsite]

You're absolutely right I've never measured high voltage. It would be great if you could tell me which components to measure and where exactly place probes. I have basic knowledge about testing HOT components so any tips would great.
I am sure I'm not going to touch anything unless I'm confident about it. Thanks

 

[Nigel Goodwin]

You're absolutely right I've never measured high voltage. It would be great if you could tell me which components to measure and where exactly place probes. I have basic knowledge about testing HOT components so any tips would great.
I am sure I'm not going to touch anything unless I'm confident about it. Thanks

Sorry, but I don't have a circuit for it.

 

[Chippie]

Any update on this? Is the front display on/lit at all?

A couple of fotos of the power supply would help..

If there are any small capacity electrolytics on the primary side, it wouldnt hurt to change them...

Are there any indications of what voltages are on the outgoing side of the power supply? Maybe worth checking to see what's present and what is not, there should at least be a standby supply...

 

[mpdsite]

There is nothing on display no action what so ever .I will explain very simply what I did. There is 248-251V (240V mains) from the fuse all the way to rectifying diodes and after that 124V. Then after transformer there is about 11.5V. When I tested diode and some other components near to the display it showed something about 0.1V (was I supposed to hold the black probe to cold ground when testing secondary side?) I know I must sound very unprofessional but 7 days ago I didn't know what resistor was.
I will try to stick couple of photos in. Thanks a lot again.

 

[Chippie]

Something is wrong....after the bridge you should have around 300volts.......

Could be you are measuring wrong...

What have you got at the main capacitor connected to the diodes?


~Please~ Do be careful when checking in this area...it is at very high voltage at least you could blow a fuse..worst case you could injure yourself...do be careful!!

 

[mpdsite]

Right... I'm touching Black probe to mains -
and the red probe to + on for example capacitor filter 400V 100uF
It shows 126V
same with red probe on cathode on rectifying diodes it this time shows only 136V
capacitor conected to diodes is like rectangular and it shows 250V

 

[mpdsite]

Is it the right way of testing voltage?
Thanks

 

[Chippie]

What have you got when measuring directly across the 100mfd cap?

Should be around 300-340vdc...