Warwick Sweet25.1 Power Stage repair

Alexander Baev · 21st March 2012, 07:12 PM

Hi.

I have Warwick Sweet25.1 combo with burned output stage. Exactly transistors Q27 and Q30 (the schematic is attached). I replaced them, turned the amp on via the electric bulb (it’s a good method to start the amp for the first time after power section repair). I measured idle current through R113-R116 resistor and set it around 70mA. I put some music from CD player to input. Everything was ok. Then I connected power supply cord directly (without the electric bulb). After that the amp was working for about 5 minutes, than there was not very loud click in a speaker and again Q27 and Q30 were dead. And F1 fuse was burned too. When I soldered Q27 and Q30 out the amp was still working ok but without them.

I tried this twice

Does anyone have any suggestions how to fix this?

http://www.warwick.de/media/manuals/...SWEET_25.1.pdf

jaycee · 21st March 2012, 11:09 PM

Are you sure the replacement devices were genuine?

Alexander Baev · 22nd March 2012, 11:00 AM

Quote:

Originally Posted by jaycee

Are you sure the replacement devices were genuine?

I’m not sure that they are genuine. The marking on the top of the package was correspondent. I also checked voltage drops across BE, BC, CE – they were fine. (Before the installation) How can I check new one transistors that they are genuine?

jaycee · 22nd March 2012, 09:55 PM

cut the top off the blown ones and take a look to be sure

21st March 2012, 07:12 PM	#1
Alexander Baev diyAudio Member Join Date: Jan 2012	Warwick Sweet25.1 Power Stage repair Hi. I have Warwick Sweet25.1 combo with burned output stage. Exactly transistors Q27 and Q30 (the schematic is attached). I replaced them, turned the amp on via the electric bulb (it’s a good method to start the amp for the first time after power section repair). I measured idle current through R113-R116 resistor and set it around 70mA. I put some music from CD player to input. Everything was ok. Then I connected power supply cord directly (without the electric bulb). After that the amp was working for about 5 minutes, than there was not very loud click in a speaker and again Q27 and Q30 were dead. And F1 fuse was burned too. When I soldered Q27 and Q30 out the amp was still working ok but without them. I tried this twice Does anyone have any suggestions how to fix this? http://www.warwick.de/media/manuals/...SWEET_25.1.pdf

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21st March 2012, 11:09 PM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Are you sure the replacement devices were genuine?

22nd March 2012, 09:55 PM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	cut the top off the blown ones and take a look to be sure