Poofed PS parts

[RC cola]

I have a power amp with some blown parts on a power supply board, a TO-220 and a TO-92 package. I looked at the number on the opposite parts and the TO-220 package has an f with a 209 then A940. I did a search and found a Fairchild part KSA940 noted as a vertical deflection output transistor. It lists the complementary part as a KSC2027, this is the part I think is the burnt one I have.

The TO-92 package is a 2N5551 thats connected to what Im thinking to be the KSC2027.

Am on the right track here? The output of this power supply board is 100 volt.

[Enzo]

Japanese part numbers for bipolar transistors start with "2S" and then the rest of the number.  The 2S is understood and not printed on most parts.  SO an A940 is a 2SA940.  And a C2027 would be a 2SC2027.  SOme factories make an equivalent, so the numbers are similar.  If i recall correctly, the K series parts first came out from Korean companies like Samsung.  ANyway KSC2027 would be the same thing as 2SC2027.

IN old NTSC TV sets, the vertical sweep was at 60Hz, and the voltage and current transistor ratings in use made them also usually suitable for audio use.

A list of part numbers tells us nothing of the circuit.  If you could mention the make and model of the amp, we might look up the schematic, and that would not only specify the parts, but also what they were doing.  That would allow us to suggest good substitutes if necessary.

[RC cola]

I called and e mailed the company and was told they do not release schematics to customers. Its Nady, I dont have the model number handy at the moment.

[Enzo]

Oh, sorry to hear that.  I have bumped into Nady before.  Not only do they not release schematics, they do not have a service network, they expect their stuff to be sent to them for repair.  LAst time I enquired they had some absurd flat rate.  A little wireless unit we had was going to cost more to repair than purchase of a new one.

[RC cola]

This amp is very heavy, I dont want to ship it to California. I figure I cant kill it any more than the death its had so far.

I followed the board trace and these parts are in the 100volt rail.

One of the two 2N5551 transistors exploded and the TO-220 case next to it had a lead blown out and the case damaged where no info was visible.

[Enzo]

No, not suggesting you send it off to them, I was just griping about Nady.

Is it a stereo amp?  If so, you should have a good channel left to compare parts content, and even voltage readings.

[RC cola]

I fully understand griping about Nady! Its been a while since I first cracked it open and I have the board on my shop desk and the cover is on the amp right now. This single board looks like it supplies both channels. Each channel are on separate boards. I can post a pic of the board if you want to see it.

[joecool85]

I fully understand griping about Nady! Its been a while since I first cracked it open and I have the board on my shop desk and the cover is on the amp right now. This single board looks like it supplies both channels. Each channel are on separate boards. I can post a pic of the board if you want to see it.

Pics always help, please post them :-)

[RC cola]

Here are pics of the board. The bridge rectifiers are mounted on the trace side of the board.

In the second pic you see on the right side where the poofed parts were.

[RC cola]

I think this board is a product of Shenzhen Uniwisdom Technologies out of China. UWTech I think is the product name of audio gear.

[RC cola]

I got the chance to plunder on this board this evening. I found a shorted zener diode that connects to the blown 2n5551 transistor. Its a 1N4752A.