hey.
my friend gave me a video to fix. I found the problem at its power supply.
I found a short circuit diode 3SM16.
does someone know where can I get datasheet of it diode (3SM16)?

note:
on the diode is written 3SM16 with line above 16, if it is meter.

thanks a head.

 

You are sure it is a diode? What package is it in? 3SM16 doesnt sound like a diode part number (is it really old equipment?)

Point #1] Unless someone has your datasheet on this part number, you will probably end up guessing at a replacement.. Telling us about what part of the power supply it is in and package size and your guess on the V & I operating requirements will help users recommend something for you.


If you plan on fixing it...

Point #2] Do you have a reasonable hypothesis as to why this part went bad? What assurance do you have that when you put in a replacement that the exact same fault wont happen again perhaps even worse damage second time around?

 

the diode is D206.
I think it is the damaged component becase it is look like a diode and when I check it with DMM it measured me 0 ohm on both directoins.

I don't have any assurace that it won't happen again, how should I check it?
It is my first time I am trying to fix something like this. if u have tips for me it is good, give me them please.

does it's PCB help you? I don't have a circuit.

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well that is a diode for sure.
do a google on CMK 77X

 

Yes, it's a rectifier diode. The chances of finding an identical one, or identifying this one, are probably very slim. As a service engineer who repairs VCR's I would replace it with one I had to hand.

It's a fairly substantial rectifier, and (as it's a switchmode PSU) it will be a fast recovery type - I would suggest looking for a fast recovery rectifer rated about 5A. I'd probably use a BY299 - because I've got them in stock!. If you've got a choice of a number of rectifiers, pick the fastest one, the faster they are the cooler they run!.

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thats some nice photography by the way(close up)..
what did you use ?

 

It seems to be an old Shindengen part number, and if so, it would make it a 3 amp, 250nS fast recovery diode. I would seriously suspect the capacitor it is feeding, I think it's C208 ( ? ) the large electrolytic that is connected to the diodes trace on the PCB. I bet that cap has developed high ESR or has become leaky, overloading the diode. Electrolytics tend to go bad after awhile, and it is common for them to destroy a feeding diode when they do.

Without an ESR meter, it would impossible to tell if the capacitor is bad or not. I would just replace it. For the diode, if you have access to either ECG or NTE replacement parts, it could be replaced with ECG or NTE #580 or regular parts such as a MR852 or a BYW95B

There appears to be some heat damage to the PCB, so check all the solder joints too.

 

And when you put your new diode back in, be sure to clean up the bottom side of the board where you removed the original.

 

i agree , in the last photo the upper pad to the diode seems to be missing ,or it is just the angle of the photo that makes it look like that.
but it appears to be bare PCB in that spot

 

what is ESR, ECG and NTE?
and how can old capacitor damage a diode or else component?

 

What is on the capacitors?
Who needs it?

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Sorry, I got carried away with there. ESR is Equivalent Series Resistance. This is a value of resistance that is the internal resistance of the capacitor. Think of it as the value in Ohms the capacitor would be if it were replaced by a resistor. This value is normally very low, but if it starts to become higher, as a capacitor goes bad, it changes the performance of the capacitor, limiting its ability to filter variations in the voltage applied to it.

If an electrolytic capacitor is leaky, this means that more current than should is able to flow through it from one terminal to the other, and if one terminal is grounded, then the capacitor acts as a load on the circuit. This is not what we want in a power supply filter. If the capacitor adds significant load to the circuit, more than what the diode can handle, it will damage the diode.

NTE and ECG are companies that sell replacement parts for the repair industry. They stock a selection of parts that suit a wide range of devices. For example, they will stock a part like your diode, but in a 600 Volt rating and list it in their catalog a a suitable replacement for the the same type of diode with a 100, 200, 400, and 600 volt rating.

NTE website: http://www.nteinc.com/

the capacitors have a glue on them to hold them in place and provide som mechanical support. The large ones on the right are the ones that I suspect are damaged.

 

I don't know where can I get BY299 diode. Can I replace it with 1N5404 diode?
and how can I be sure that this diode wouldn't damadge again?

 

No, you can't use 1N5404, it's far too slow - you MUST use a fast recovery diode, a normal rectifer will simply fail again very quickly.

As suggested by 'zevon8' it's probably a good idea to change the electrolytics on the output of the rectifier.

__________________
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what diodes can I take excapt the BY299 one?
there is any site that I can give parameters I need and it will show me the components name that have it's parameters?