Samsung Home Theatre unit died

stephenfalken

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Hi guys!

Is there anyone with any electrician experience repairing PSUs from appliances such as Blu Ray players?

My beloved Samsung HT-C5550 refused to power up yesterday, and upon looking inside, I saw the internal fuse was fine but part of the PSU board has very small burn marks near some jumper pin connectors. The solder joints appeared bad so I dapped a fresh bit of solder over them to restore connectivity but it hasn't helped and it still sits dead.

ImageUploadedByTapatalk1427112374.065975.jpg

It's possible a capacitor has failed but I have no idea how to find it or where to begin, they all look ok with no bulging or leakage.

I really don't want to have to replace the entire system as it's a really good one and cost about £450 when I got it in 2010. I alsoc can't find any replacement PSU boards online anywhere.

Any help appreciated :)
 

protek

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Are you able to measure the output voltages of the PSU board, and possibly find some reference, what the voltages should be?
 

stephenfalken

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Yeah I have given that a try, the PSU board isn't generating any output at all - the service manual suggests in such an instance to replace the entire PSU. Not much help at all!

Regards
 

Ed.D

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After brightening up the image a bit and looking at that right hand rectangular solder pad it looks like it has gotten so hot it melted the solder away. It would be interesting to know what components are on the other side of the board around that central area in the photo, a rectifier perhaps?
 

stephenfalken

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You are absolutely correct it is a rectifier on the other side. The solder pads are simple jumper wires so it's strange that the part heated up right there and not along the track or something!

I will get a picture of the top side too.
 

Ed.D

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I'm no electronics guy but I once did a repair to a PSU where the rectifier shorted out internally. It controlled the production line PLC at work. If you can de-solder it, it is possible to check with a multi-meter.
 

stephenfalken

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Hmm interesting.

I can easily desolder it, but prefer to let the experts do their stuff, since I myself hate being asked to fix something that an 'amateur expert' has made worse lol

Should each of the rectifier pins be individually isolated? As I already noticed that several of the rectifier pins are connected to each other when testing continuity on stuff!

Thanks so much for your help so far it really is appreciated!
 

stephenfalken

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Oops!!

Seems what I thought was a rectifier is actually a transformer!

Need to brush up on my terminology, it's the heavy yellow block that sits over that part
 

stephenfalken

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ImageUploadedByTapatalk1427118424.505305.jpg
Top side of board

ImageUploadedByTapatalk1427118435.445431.jpg
Wires which have melted solder

ImageUploadedByTapatalk1427118446.841601.jpg
Another view of damaged area
 

demolition

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The transformer usually has one primary winding and one or more secondary windings (depending on how many output voltages is needed). How many pins does it have in total?
On the PCB you can see a line which indicates the safety barrier. The transformer is the bridge between these two sides. One side is connected to mains (two pins usually), the other is the low voltage side (2 or more pins). Using continuity checks, there must be no connection between any pins across that barrier. There must be a connection between the two pins on the primary side as this is a coil. The same goes between pairs on the secondary side. Perhaps some of the printing on the PCB shows what is what.

Unfortunately if the transformer is dead, it can be very hard/impossible to get a replacement since this is usually a custom part which is made specifically for this product. The rectifier on the other hand (black rectangular component with 4 pins) is usually a common part which can be replaced if faulty.
 

stephenfalken

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Thanks for that!

Just checked, there is no continuity between pins of the transformer across the black line. The transformer has a total of 12 pins.

The following shows a continuity test between all the pins. The bottom part below the line is the AC part, then above I am guessing where we get the DC?

attachment.jpg

Thanks
 

demolition

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Both sides are AC, but one is high voltage and the other is low voltage. It does not become DC until after the rectifier which is the black component just north of the big capacitor on your top side picture.

If you do a resistance measurement between the pins, it might be easier to isolate what is what. Include an offset measurement by shorting the pins on the multimeter directly. This value can be subtracted from all measurements.

The discoloration on the solder pads looks like maybe there has been some arcing between them?
 
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