Advice on LG DVD player blown power supply

[Dannyx]

Re: Advice on LG DVD player blown power supply

Since the chokes are in parallel with the AC lines, can I just feed AC straight to the bridge rectifier ? What would some side effects be ? No EMI filtering as far as I know...again, no expert

[Toasty]

Re: Advice on LG DVD player blown power supply

It's a Sanken SC6700. Again, available from China & eBay. I can't locate a valid datasheet either.

T

[Toasty]

Re: Advice on LG DVD player blown power supply

Chokes are in -series- with power lines. For testing, you can jumper them.

Desolder them. You may find they burned off just at the base pins.

T

[Dannyx]

Re: Advice on LG DVD player blown power supply

Chokes are in -series- with power lines. For testing, you can jumper them.

Desolder them. You may find they burned off just at the base pins.

T

Even if the pins did break off at the base, I wouldn't think of reusing those chokes - not with the state those windings and cores are in....

[jazzie366]

Re: Advice on LG DVD player blown power supply

Even if the pins did break off at the base, I wouldn't think of reusing those chokes - not with the state those windings and cores are in....

Yeah I went on eBay and found that the chokes aren't that expensive. The amperage rating = higher price though. 2A chokes are 2-3$ for 10, however 5A ones are significantly more.

However, those look to be 1A chokes at best. Now, what I would do is replace the rectifier (as was mentioned) just to be safe. Now, considering the PTC didn't blow, I'm gonna guess that there's something further on. The components chosen seem to be rated close to their max, which isn't much.

IMO I'd just check for shorts as it sits. Check all the big places first, I suspect something will be a little obvious. I'd reconnect the traces that burned with wires temporarily and see if you can't find anything.

[stj]

Re: Advice on LG DVD player blown power supply

run it through a lamp bulb

[momaka]

Re: Advice on LG DVD player blown power supply

Even if the pins did break off at the base, I wouldn't think of reusing those chokes - not with the state those windings and cores are in....

Don't worry about the chokes, indeed, as the other have said. Just replace with jumper wire for now until you get the PSU running.

Once you do, you can re-wind the chokes with new wire. Your local hardware store should have some. If not, you can use regular 20-22 AWG wire. No? Want to go for GOTY (Ghetto-Of-The-Year) award? Two parallel strands of telephone/Ethernet wire for each winding will do - just try to keep a straight face when you see your neighbor and he complains that his house phone is no longer working.

But seriously, you CAN rewind input chokes many ways and with no problems.

[Dannyx]

Re: Advice on LG DVD player blown power supply

"Good" news on this project: not really wanting to admit defeat, I'm going to revisit this guy and hopefully find the right components this time. The transistors were not in spec and neither was the fuse....I was still getting used to my new work environment and that took a HUGE toll on my patience and concentration, so I was like "sure whatever-if the guy at the shop said so, it's gonna work" and didn't bother checking with a datasheet first...boom boom...

With regards to the lightbulb test: I DID run the test first, but the supply wasn't connected to the rest of the DVD player. I heard it's not a good idea to load a SMPS when running it through a bulb...don't know how much of that is true and how much is bunk, because someone suggested running the bulb even when attached to the amp and main board to see what happens.

[momaka]

Re: Advice on LG DVD player blown power supply

With regards to the lightbulb test: I DID run the test first, but the supply wasn't connected to the rest of the DVD player. I heard it's not a good idea to load a SMPS when running it through a bulb...don't know how much of that is true and how much is bunk, because someone suggested running the bulb even when attached to the amp and main board to see what happens.

It's fine to try and run everything through the bulb. At worst, the power supply may refuse to work if the device it is powering tries to draw more than approximately 1/3 to 1/4 of the bulbs power rating - i.e., if you are using a 60W bulb, then trying to pull more than 15-20 Watts with the PSU will make the bulb drop too much voltage and the power supply may not be able to cope with the low input voltage, going into under-voltage or PWM-limit protection.

If that happens, you just use a bigger light bulb or two in parallel. Still not enough power? Then replace the bulb with something like a toaster, a hair drier, or anything else with a heating element inside it. A power rating of 400-800 Watts for that will give you approximately 50-200 Watts to play with, depending on how low of an input voltage the PSU can take before it goes into PWM-limit mode.

[Dannyx]

Re: Advice on LG DVD player blown power supply

Another thing I noticed is that the lamp may sometimes "false-trigger" with some power supplies: for instance, I recently wrote a post where I asked for help on choosing some capacitors for a Samsung TV which sustained primary damaged and the caps got blown. I replaced them today, along with other active components which got busted and of course ran the lightbulb test first: the bulb flashed once like it's supposed to do when it takes away the initial inrush current, but after going off once, it came back on brightly and seem to flicker very briefly like every half second or so. I thought "shirt...something's still wrong"....however I checked every goddamn part there was, I couldn't spot anything else so I just said yolo and went straight into the outlet while clenching the nether parts of my body Surprisingly it worked: PFC started up, got steady output...perfect

However, it's not the first time I see it happening: I've had an LG power supply once which did the same thing: a snubber was blown on the thing and took out the PFC transistor - replaced them, ran the lightbulb test, bright light...damn....check the thing all over again, STILL bright bulb...went straight into the mains, no boom - it worked...WTF ?

[Dannyx]

Re: Advice on LG DVD player blown power supply

Also, can't remember what the bulb in my test rig is rated at, though I DO believe it's 60w indeed...TBH I kinda fear the day when it burns out (highly unlikely given the very little work it does) or gets smashed by falling off the shelf or desk and I'll have virtually no easy way of obtaining these good ol' incandescent ones for testing purposes...try doing this with a CFL or LED I imagine it MIGHT work with halogens which are still being produced from what I've seen in stores.

[momaka]

Re: Advice on LG DVD player blown power supply

Another thing I noticed is that the lamp may sometimes "false-trigger" with some power supplies: for instance, I recently wrote a post where I asked for help on choosing some capacitors for a Samsung TV which sustained primary damaged and the caps got blown. I replaced them today, along with other active components which got busted and of course ran the lightbulb test first: the bulb flashed once like it's supposed to do when it takes away the initial inrush current, but after going off once, it came back on brightly and seem to flicker very briefly like every half second or so. I thought "shirt...something's still wrong"....however I checked every goddamn part there was, I couldn't spot anything else so I just said yolo and went straight into the outlet while clenching the nether parts of my body Surprisingly it worked: PFC started up, got steady output...perfect

The bulb flashing (i.e. "false-trigger") is because of the Active PFC circuit in the PSU. To run a PSU with APFC, you need a 100W bulb minimum. And even then, it will flicker quite a bit. Halogen may be better for PSUs with APFC, as halogen bulbs have lower cold resistance.

That said, you can use Halogen bulbs for any testing in place of the oldschool incandescent.

I'm surprised you can't find classic incandescent bulbs in Romania, though. I know the EU banned their import and production, but I bet you some small store still has these as NOS. Or perhaps look in the local flea market. Alternatively, your local "building materials" store (Bauhaus?) may have "decorative" incandescent bulbs. May be a bit more pricey, but hey, at least they are still obtainable.

[Dannyx]

Re: Advice on LG DVD player blown power supply

"China Mall" is the way to go for these old bulbs

What's PFC doing anyway ? I mean, yeah I KNOW that it's boosting the voltage and I know what its components are, how the transistors switch the coil on and off and the diode blocks and "pumps" the caps and whatnot I know what to look for when it's faulty, but what's actually going on there that makes it "tick" - quite litteraly in case of the bulb ?...any good reads/vids on SMPSs ? I have watched many good videos that explain their operation in detail, yet simple enough that an average-Joe like me can still comprehend the theory behind them, since I have no degrees in electronics or anything: I learned everything I know and constantly learn new stuff "my own way", hands-on, possibly plugging something in and having it go bang...you know

[Toasty]

Re: Advice on LG DVD player blown power supply

I disagree with using halogens for testing. Because of the lower cold resistance, too much current can pass, effectively defeating the series bulb's purpose.

They're good for load testing however.

If you find yourself working on this type of equipment more often, another (safer) option is to use a variac in conjunction with an isolation transformer and fuse or 1-2A circuit breaker. There are combo units such as the RCA/VIZ Isotap which have all 3.

That setup plus the series lamp is the way I roll...

T

[Dannyx]

Re: Advice on LG DVD player blown power supply

I do have a variac....it's only a small 3kW one but it should be enough. However the reason I haven't used it for testing SMPSs is the aforementioned reason: some sources say it can cause them to malfunction or even damage them if they're undervolted or ran at limited current (such as through a bulb). Ok, undervolting actually makes sense: there's a sense circuit which detects if the incoming mains is appropriate for running the supply on. 90v seems to be the absolute minimum, though I personally don't see why a SMPS designed to output say 12v couldn't run on as low as 14-something V (don't hate me for this - just asking). Even some datasheets for some PWM ICs describe this sense pin something along these lines: "...in order to protect the supply from damage by attempting to run on incorrect voltage", the so called UVLO I believe (undervoltage lockout to my recollection).

[Toasty]

Re: Advice on LG DVD player blown power supply

Please specify the sources. I've never heard that load of crap before.

Lowest I've had them start to work is ~50-60V. Not loading it mind you, just operational.

3kW! Lucky you!

T

[Dannyx]

Re: Advice on LG DVD player blown power supply

Can't track it down right now (the one that claims it's not a good idea to run a SMPS with a "ballast"), though you're right: the key detail I missed is the load. Under no load, there should be absolutely no reason damage can occur - I can safely say that myself despite not being an expert. Load the output and you can see why limited current might start to pose problems, though even then I'm not sure what would cause damage and in what way - THAT'S actually the scenario I had in mind, since someone suggested powering this home theater WITH the ballast bulb in place.

THISseries is probably the best I've ever watched on SMPSs - taught me a lot. It's a shame he decided to pull the plug on it and discontinued it

[Toasty]

Re: Advice on LG DVD player blown power supply

He did? Last video was just 2 weeks ago...???

[Dannyx]

Re: Advice on LG DVD player blown power supply

He did? Last video was just 2 weeks ago...???

I meant he discontinued the series on SMPS - the channel is still active and despite people asking for more, nothing's come up on that subject.

[momaka]

Re: Advice on LG DVD player blown power supply

What's PFC doing anyway ?

Well, when it comes to AC circuits, there are three types of power: real, reactive, and apparent. Real power is associated with a purely resistive load, whereas reactive is associated with a purely inductive or capacitative load. Apparent power is when you have a combination of real and reactive power. None-APFC SMPSs (and many other AC electrical devices for that matter) fall into that category, with most being slightly capacitative in nature (due to the large input filter caps). The Power Factor (PF) is essentially the piece of information that tells you how much of the power used by a device is real, how much is reactive, and how much is apparent.

PF = real power / apparent power = cos (theta**)
** where the angle "theta" is an angle between real power and apparent power in a right-angle triangle. (Lol, so many variations of the word "angle" in that sentence )

In layman's terms, APFC essentially makes the PSU appear as a resistive load to the power grid. This is good in a way, because the PSU then draws only as much power as it actually uses. A reactive load on the other hand (be it capacitative or inductive) tends to "borrow" and "return" power in continuous cycles. Only a part of this power is used for powering the device. It does NOT make the device more inefficient, but it does put a bigger load on the conductor lines of your house and the power grid.

That said, APFC does actually make your PSU more inefficient, as it is another power supply in itself - namely a boost-converter circuit. And as with any power conversion, you will always have some losses.

So in short, APFC can help the power grid but it does hurt the efficiency of your devices a little bit. You also end up paying a slightly higher electric bill, as the electric company only bills you for the real power you use (and APFC essentially "eliminates" reactive power at the expense of adding a few more Watts of power dissipation in your PSU - hence the slightly higher inefficiency).

I disagree with using halogens for testing. Because of the lower cold resistance, too much current can pass, effectively defeating the series bulb's purpose.

Not exactly.

While true that a halogen will allow a much higher surge current when cold, this can only last for a split-second of a moment before its resistance rises to safer current-limiting levels. Not to mention that the surge current usually isn't that much higher than the surge current from a large bulk cap charging up. So in reality, it won't make that much of a difference. At the absolute worst, you may blow up a weak transistor in an SPMS. But it will still save your fuse, bridge rectifier, and NTC inrush limiter.

Thus using a halogen is still 100's of miles better than using nothing.

If anything, a variac by itself is useless if you don't have current limiting, because you can still draw a ton of current even at low voltages if there is a hard short somewhere. Now a variac with a halogen lamp - that will easily do the trick just fine. The slow starting of the voltage with the variac will allow the halogen lamp to warm up so that nothing will get damaged.

That said, I like my simple method of just using a bigger series load, like a toaster or hair dryer.