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

Gil W. gil_we at yahoo.com
Tue Mar 11 14:43:56 CET 2014

It's actually a 2SC3559 (800v), now replaced with BUT11A:


Original diode is 1SS84:

I think I was wrong and it's not D2 but D5 actually.

Are these two replacements good at these places ?

Still no idea why all those failed in the first place. I do see some greenish acid on some components' leads
so there might be a leaking cap somewhere.

As for R1, I guess 3W is critical for it to burn (fuse) out on failure ?

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, 2:25 PM
 Something doesn't quite add up
 here.  The schematic shows Q1 as 2SC3359, but this is
 only an 80V rated signal transistor.  The transistor in
 the place of Q1 in an off-line flyback converter will
 usually be a high-power switching transistor rated for at
 least 600V.  D2 in the snubber circuit will be a
 fast-recovery rectifier diode also rated for 600V or
 more.  UF4006 or UF4007 are common here.  If
 either the snubber diode or Q1 have failed s/c then you
 would expect R2 to fuse open.  Also remember that C12
 can store a lethal charge at around 340VDC so avoid
 Switched-mode power supplies can be dangerous and
 notoriously difficult to repair.  Usually the switching
 transistor fails for a reason, so it's worth checking the
 semiconductors on the secondary side for any failures before
 replacing the switch and trying to power it up again. 
 A shorted diode on the output side will often just pop the
 switch on the input side if you try to power it up. 
 Also check the electrolytics for any obvious signs of
 overheating (bulging) and replace with good quality
 (Rubicon) low-ESR of identical voltage, capacitance and
 temperature rating.  (Powering-up from the mains via a
 100W bulb in series can often minimise the fireworks while
 there are still faults to be found!)
 Good luck!  If it was me I think i'd consider
 retro-fitting a whole new SMPSU if you can find one that
 will fit.
 On 2014-03-11 11:36, Gil W. wrote:
 > Hi all! I need some help fixing that TX802, thanks in
 advance !
 > My TX802 wan't powering on, I found that Q1 (2SC3559)
 and D2 (1SS84)
 > were short out (well, I think it was D2 but need to
 check again...)
 > Replaced Q1 with BUT11A (instead of BUT11AF which is
 supposed to be an
 > equivalent) and 1N4148 in place of the 1SS84 (is that
 > Then I found the wirewound resistor between the diode
 bridge (R2) and
 > the big filter cap (C12) was dead. This is a 22ohm/3W.
 I'd like to
 > replace it but the lowest wattage I can find is 5W.
 Would that be fine
 > or is it too much in that place ?
 > Here's the PS diagram:
 > http://www.loscha.com/ybb/Tx802-power-A.gif
 > thanks very much for the help !!
 > _______________________________________________
 > Synth-diy mailing list
 > Synth-diy at dropmix.xs4all.nl
 > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

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