defective PS section of DVD reader

[ammagamma]

Hello guys,

I detected a problem on the SHARP DV-SV92. It cannot be switched on and the stdby led was always switched off. I supposed it was a power supply issue, so I opened the chassis and found the stdby switching TNY267PN destroyed. It was even on the PCB but the package was destroyed and the PCB near this component was clearly darker that the original PCB colour. Then I replaced the stdby switching with a new one and the DVD reader got working, but the cap C34 was red hot! I cannot keep my finger on the top of the cap for more than a second! I disassemble the CAP and this is what I found:




Now, there is another cap with the same characteristics and both are part of the power supply section of the dvd reader. Do you suggest to replace even the other cap?

Is the cap the problem of stby switching damage? ThePCBA pictures, both component and circuit side





Many thanks for your help.

BR, Francesco.

[shovenose]

Re: defective PS section of DVD reader

I don'tt seem to see any images. We ask taht you use the Manage Attachments feature here on the board as image hosting, instead of embedding images from outside hosts.
If you did use the attachments please try again

[ammagamma]

Re: defective PS section of DVD reader

I made a mistake in the attachment manager, now u can see the photos.

Thanks, BR, Francesco

[Rulycat]

Re: defective PS section of DVD reader

CapXon. A very bad brand of cap. Looks like it could be the problem. I see a Teapo eyeing me from the bottom left, 3rd image. I suggest you replace all bad brands on that board, except maybe the 200/400v main cap. The reason the cap gets hot is because it is essentially now a resistor as it has dried up.

What's the cap series please?

[retiredcaps]

Re: defective PS section of DVD reader

Replace all Capxon brand electrolytic caps. They have a terrible reputation and reliability here. Use something like Panasonic FR or FM low ESR series in the power supply.

[Agent24]

Re: defective PS section of DVD reader

If the cap is getting very hot and the transistor was destroyed, probably the capacitor is very bad and killed it. But you would have to trace the circuit to see if that was the truly the case.

Either way, if the thing does work now, I think you can safely re-cap and get rid of all those CapXon and other rubbish and you'd probably be be OK, unless anything else is damaged.

Check the datasheets from CapXon etc vs potential replacements to make sure you get ESR and Ripple current rating correct. (As a general rule for the replacements, ESR should be same or lower (but not excessively), RCR same or higher than originals.)


Your photos are nice and clear, which is nice, but in fact they do seem to show up some possible issues with your soldering - I can't say all solder on the new transistor looks nice and shiny, though it may just be a trick of the light.

[ammagamma]

Re: defective PS section of DVD reader

CapXon. A very bad brand of cap. Looks like it could be the problem. I see a Teapo eyeing me from the bottom left, 3rd image. I suggest you replace all bad brands on that board, except maybe the 200/400v main cap. The reason the cap gets hot is because it is essentially now a resistor as it has dried up.

What's the cap series please?

Hi, thanks for reply. The series is "GS", C546, 85°C. I attached the datasheet, I hope it is the correct one.

The damaged capxon cap is just 400V.

BR, Francesco

[ammagamma]

Re: defective PS section of DVD reader

If the cap is getting very hot and the transistor was destroyed, probably the capacitor is very bad and killed it. But you would have to trace the circuit to see if that was the truly the case.

Either way, if the thing does work now, I think you can safely re-cap and get rid of all those CapXon and other rubbish and you'd probably be be OK, unless anything else is damaged.

Check the datasheets from CapXon etc vs potential replacements to make sure you get ESR and Ripple current rating correct. (As a general rule for the replacements, ESR should be same or lower (but not excessively), RCR same or higher than originals.)


Your photos are nice and clear, which is nice, but in fact they do seem to show up some possible issues with your soldering - I can't say all solder on the new transistor looks nice and shiny, though it may just be a trick of the light.

Hello, thanks for reply.

regarding the soldering stuff, you're right, but it doesn't seem to be a cold soldering. The solderings are shiny enough despite of the photos, but the tin has poor quality and there are some "dark" point and for sure the solder tool is quite cheap!. However, I will try to improve the soldering.

Then, it seems that the C33 and C34, that is the red hot cap, are in parallel and by my POV they are voltage balancing cap.

I have just attached the cap datasheet, but there is nothing concerning the ESR and RCR parameters, could you helo me to find a good cap for replacement? On the cap body there are the following indications:

GS85°C
C546 VENT
4.7uF 400V

Thanks a lot again, BR, Francesco

[PCBONEZ]

Re: defective PS section of DVD reader

The high voltage caps are usually general purpose [GP] caps and aren't low ESR.
They won't have an ESR spec.
When you need to replace those get caps that have the same or more Ripple Current in the spec sheet.
-
You also have to check that the new and old state the Ripple at the same frequency.
[The one you posted states Ripple at 120Hz. It's in a note under the data table.]
If it's not the same usually there is a conversion factor somewhere in the data sheet to adjust for different frequencies.
Usually doesn't come up, but it does sometimes so need to watch out for it.
-
Low ESR caps usually use 100kHz for the Ripple and ESR.
-
If you end up comparing the Ripple of one done at 120Hz to one done at 100kHz the numbers will be WAY off.
.
.

[Agent24]

Re: defective PS section of DVD reader

regarding the soldering stuff, you're right, but it doesn't seem to be a cold soldering. The solderings are shiny enough despite of the photos, but the tin has poor quality and there are some "dark" point and for sure the solder tool is quite cheap!. However, I will try to improve the soldering.

Dark patches might just be burnt flux. If the solder is cheap, it's likely the flux is poor quality rather than the tin.

As long as your soldering iron is powerful enough and has a clean tip it shouldn't matter how cheap it is really. The cheap ones work, they just may not last very long.

For a basic fixed-temperature iron I would say 25 watts is a good choice. 10-15 watts or less is just too low, and anything 40 watts and higher is overkill for a simple single layer board. (This only applies to fixed-temp irons. Variable temperature irons can have no limit on power, as they always regulate to correct temperature anyway. High wattage fixed irons like 60 watts just get far too hot for general PCB use - but can be good for removing large heatsinks and that sort of thing)

This video might also be of some use to you: http://www.youtube.com/watch?v=I_NU2ruzyc4

[ammagamma]

Re: defective PS section of DVD reader

The high voltage caps are usually general purpose [GP] caps and aren't low ESR.
They won't have an ESR spec.
When you need to replace those get caps that have the same or more Ripple Current in the spec sheet.
-
You also have to check that the new and old state the Ripple at the same frequency.
[The one you posted states Ripple at 120Hz. It's in a note under the data table.]
If it's not the same usually there is a conversion factor somewhere in the data sheet to adjust for different frequencies.
Usually doesn't come up, but it does sometimes so need to watch out for it.
-
Low ESR caps usually use 100kHz for the Ripple and ESR.
-
If you end up comparing the Ripple of one done at 120Hz to one done at 100kHz the numbers will be WAY off.
.
.

Hello and thanks for reply, very useful!

Sorry for my poor knowledge, but in the datasheet I am not able to find the ripple current. My cap is 16x10 mm (LxD), but I do not understand what WV means in the table, could you please help me? It seems that this is the last parameter I miss.

BR, Francesco

[ammagamma]

Re: defective PS section of DVD reader

Dark patches might just be burnt flux. If the solder is cheap, it's likely the flux is poor quality rather than the tin.

As long as your soldering iron is powerful enough and has a clean tip it shouldn't matter how cheap it is really. The cheap ones work, they just may not last very long.

For a basic fixed-temperature iron I would say 25 watts is a good choice. 10-15 watts or less is just too low, and anything 40 watts and higher is overkill for a simple single layer board. (This only applies to fixed-temp irons. Variable temperature irons can have no limit on power, as they always regulate to correct temperature anyway. High wattage fixed irons like 60 watts just get far too hot for general PCB use - but can be good for removing large heatsinks and that sort of thing)

This video might also be of some use to you: http://www.youtube.com/watch?v=I_NU2ruzyc4

Hella Agent24, your explanation was crystal clear! I will follow your suggestion and the video you linked ;-)

BR, Francesco

[Agent24]

Re: defective PS section of DVD reader

Hello and thanks for reply, very useful!

Sorry for my poor knowledge, but in the datasheet I am not able to find the ripple current. My cap is 16x10 mm (LxD), but I do not understand what WV means in the table, could you please help me? It seems that this is the last parameter I miss.

BR, Francesco

As PCBONEZ said, that particular series is general purpose and GP capacitors don't usually specify ESR.

This is because in a circuit application where a GP capacitor is properly used, ESR doesn't really matter.


WV means 'Working Voltage' and is the highest voltage the capacitor can be used at. Typically though, a circuit will use a capacitor rated higher than the expected voltage in the circuit.

For example: In a circuit that runs on 12v, you would usually use a 16v capacitor or maybe higher, but not a 12v one.

This is in contrast to 'SV' or 'Surge Voltage' which is the highest voltage the capacitor can withstand momentarily.

[PCBONEZ]

Re: defective PS section of DVD reader

Like this.

[Evil Lurker]

Re: defective PS section of DVD reader

Is this your soldering job after the repair?

https://www.badcaps.net/forum/attach...1&d=1320961028

If so its absolutely horrid and could possibly be causing problems. Looks like one of the pins in the top left joint isn't even attached! Definately cold.

I see flux residue on there, my guess is it looks like you had a dirty tip when you tried to solder it.

[ammagamma]

Re: defective PS section of DVD reader

Is this your soldering job after the repair?

https://www.badcaps.net/forum/attach...1&d=1320961028

If so its absolutely horrid and could possibly be causing problems. Looks like one of the pins in the top left joint isn't even attached! Definately cold.

I see flux residue on there, my guess is it looks like you had a dirty tip when you tried to solder it.

Hello Evil, thanks for reply.

For sure, I can do a better soldering, but it seems that I used a too high watt iron, 40 W, and a tin provided with flux. This flux probably has been burned by too high temperature coming from the iron or it is a poor quality flux so that what you can see are not "voids" or not completely soldered joint, but burned flux. This is likely what you define "dirty tip"

In any case, I shall solder again the IC with a new iron, 30 W, and a new tin.

Many thanks again, BR, Francesco.

[ammagamma]

Re: defective PS section of DVD reader

Like this.

Ok, now it's clear. Also I cannot understand the measurement unit. It was reported "F" but it seems to me too high capacity...

So, 70 mA rms @ 85 °C and 120 Hz.

Many thanks for your help.

BR, Francesco

[Agent24]

Re: defective PS section of DVD reader

No, it is not F (Farad) it is uF (Micro-Farad) - it does actually show this in the datasheet.
(often written on forums etc as uF for convenience)

I would go for a 105°C capacitor as a replacement, they typically last longer.

So for that specific capacitor (C34) - you'll want a replacement that can handle 70mA ripple (or more) at 120Hz and which is of decent quality. You should as well replace both C34 and C33 at the same time.

[ammagamma]

Re: defective PS section of DVD reader

No, it is not F (Farad) it is uF (Micro-Farad) - it does actually show this in the datasheet.
(often written on forums etc as uF for convenience)

I would go for a 105°C capacitor as a replacement, they typically last longer.

So for that specific capacitor (C34) - you'll want a replacement that can handle 70mA ripple (or more) at 120Hz and which is of decent quality. You should as well replace both C34 and C33 at the same time.

Ok, noted!

Thanks a lot, I will purchase 2 caps with these parameters and a 30W iron (I did not find a 25W with low cost), trying to improve the soldering ;-)

BR, Francesco

[ammagamma]

Re: defective PS section of DVD reader

I found Nippon Chemi-Con cap, attached datasheet. Could it be right? I did not find a cap with 105 °C with the same specs.

My only doubt is that the ripple current is 71 mA instead of 70 mA, I think that 1 mA difference is insignificant, but I want to be sure.

Thanks again, BR, Francesco.