What transformer do I need?

solomon911 · 28th July 2011, 07:09 PM

I was given a broken KEF PSW 2150. When I plugged it in after 30 seconds or so a relay inside of it started clicking on and off constantly. I dug around in it and found the transformer is outputting 39vac yellow to black mid 70s yellow to yellow. I think it should be 50vac per yellow but I'm not sure. Could someone tell me if I am right and what would be the best replacement?

jeronimo2003 · 28th July 2011, 09:17 PM

What is the voltage reading of the 2 large power supply capacitors.
A transformer of 2x39Vac would give you plus and minus 53Vdc. Voltage of the caps is then most likely 63V. A 2x50Vac transformer would give you plus and minus 71Vdc. The caps should then be rated for 80V

kevinkr · 28th July 2011, 09:48 PM

Likely there is something else wrong with this unit that is loading down the power supply. Relay cycling is often an indication of a fault somewhere like a blown output device or power supply problem..(Amongst many other possibilities too numerous for me to think about..

)

solomon911 · 29th July 2011, 12:45 PM

Thanks Jeronimo and Kevin, the capacitors are 63V. As you can probably tell by now I am new to repairing electronics. I have been reading a lot of articles. People are saying the small cap at C52 next to the big cap has been failing and causing this issue. I'm going to test that. I'll let you know what I find.

These are the caps.

I have read a lot of post where people say this cap has been failing.

This is the transformer I thought might be bad.

metalsculptor · 29th July 2011, 11:42 PM

Failure of a transformer is very rare and usually accompanied by smoke or blown fuses. The transformer sounds like it is 37.5V 0 37.5V which will give +/- 50V dc supply rails. As mentioned you should measure the voltage on the filter capacitors which should be close to 50V

28th July 2011, 07:09 PM	#1
solomon911 diyAudio Member Join Date: Jul 2011	What transformer do I need? I was given a broken KEF PSW 2150. When I plugged it in after 30 seconds or so a relay inside of it started clicking on and off constantly. I dug around in it and found the transformer is outputting 39vac yellow to black mid 70s yellow to yellow. I think it should be 50vac per yellow but I'm not sure. Could someone tell me if I am right and what would be the best replacement?

28th July 2011, 09:48 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Likely there is something else wrong with this unit that is loading down the power supply. Relay cycling is often an indication of a fault somewhere like a blown output device or power supply problem..(Amongst many other possibilities too numerous for me to think about.. ) __________________ www.kta-hifi.net

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28th July 2011, 09:17 PM	#2
jeronimo2003 diyAudio Member Join Date: May 2010	What is the voltage reading of the 2 large power supply capacitors. A transformer of 2x39Vac would give you plus and minus 53Vdc. Voltage of the caps is then most likely 63V. A 2x50Vac transformer would give you plus and minus 71Vdc. The caps should then be rated for 80V

29th July 2011, 12:45 PM	#4
solomon911 diyAudio Member Join Date: Jul 2011	Thanks Jeronimo and Kevin, the capacitors are 63V. As you can probably tell by now I am new to repairing electronics. I have been reading a lot of articles. People are saying the small cap at C52 next to the big cap has been failing and causing this issue. I'm going to test that. I'll let you know what I find. These are the caps. I have read a lot of post where people say this cap has been failing. This is the transformer I thought might be bad.

29th July 2011, 11:42 PM	#5
metalsculptor diyAudio Member Join Date: Sep 2010 Location: Melbourne	Failure of a transformer is very rare and usually accompanied by smoke or blown fuses. The transformer sounds like it is 37.5V 0 37.5V which will give +/- 50V dc supply rails. As mentioned you should measure the voltage on the filter capacitors which should be close to 50V

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