[sdiy] TX802 Power Supply failure (replacing 3W with 5W resistor)‏

[Gil W.]

Thanks a lot !

I managed to find an 2SC3752 which supposed to be ok?
http://www.alldatasheet.com/datasheet-pdf/pdf/38890/SANYO/2SC3752.html

so, 5W is fine ? and 1N4148 - just try it ? or is there any better match for the 1SS84 ?

Thanks !



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On Tue, 3/11/14, rburnett at richieburnett.co.uk <rburnett at richieburnett.co.uk> wrote:

 Subject: Re: [sdiy] TX802 Power Supply failure (replacing 3W with 5W resistor)‏
 To: "Gil W." <gil_we at yahoo.com>
 Cc: synth-diy at dropmix.xs4all.nl
 Date: Tuesday, March 11, 2014, 3:58 PM
 
 > It's actually a 2SC3559 (800v),
 now replaced with BUT11A:
 > 
 > http://pdf1.alldatasheet.com/datasheet-pdf/view/268894/ISC/2SC3559.html
 > http://www.classiccmp.org/rtellason/transdata/but11.pdf
 
 You're proposing to replace an 800V switch with a 450V
 one.  This may not have sufficient Vce rating.
 
 > Original diode is 1SS84:
 > http://pdf1.alldatasheet.com/datasheet-pdf/view/230245/HITACHI/1SS84.html
 > 
 > I think I was wrong and it's not D2 but D5 actually.
 > 
 > Are these two replacements good at these places ?
 
 It depends what voltages they'll experience in practice.
 
 > Still no idea why all those failed in the first place.
 
 Check every other semiconductor in the SMPS for s/c or o/c.
 
 > I do see some
 > greenish acid on some components' leads
 > so there might be a leaking cap somewhere.
 
 In which case replace any suspect electrolytics too. 
 (Electrolytic capacitors in flyback converters have a hard
 life with very-high pulsed currents and often run quite hot
 so don't last very long!)
 
 > As for R1, I guess 3W is critical for it to burn (fuse)
 out on failure ?
 
 If Q1 goes s/c there will be plenty of energy available to
 fuse a 5W resistor or a 3W resistor.  Just don't jumper
 it with a piece of wire, or you'll probably find the PCB
 trace underneath will fuse instead!
 
 -Richie,