[sdiy] << FIXED >> TX802 Power Supply failure

[Barry Klein]

I've recently begun to utilize a new short-finding tool - a handheld FLIR camera.
It has been great in finding shorted ceramic caps on motherboard-size boards.
True, not too many have the cash to obtain one or know someone that has one - but they will become more plentiful as I think <$300 units will soon be available.

Barry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Gil W.
Sent: Thursday, March 13, 2014 6:22 PM
To: rburnett at richieburnett.co.uk
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] << FIXED >> TX802 Power Supply failure

Ok so it seems my report was made too soon :/

It didn't take more than 15 minutes for the TX802 to finally become unstable.
When it does, the voltages starts to drop and the PS gets really hot (no, I didn't touch it...)

Obviously there's something which has caused it to fail at the first place which I still haven't figured out...
But what can this be ? All elect. caps and regulators are now fresh...

I'm starting to want to go the linear path :/ Is it likely that something outside of the PS circuit taking it down ?










--------------------------------------------
On Fri, 3/14/14, rburnett at richieburnett.co.uk <rburnett at richieburnett.co.uk> wrote:

 Subject: Re: [sdiy] << FIXED >> TX802 Power Supply failure
 To: "Gil W." <gil_we at yahoo.com>
 Cc: synth-diy at dropmix.xs4all.nl
 Date: Friday, March 14, 2014, 1:39 AM
 
 Well done!  If the outputs are
 the correct voltages and relatively ripple-free, and nothing  is getting excessively hot (touched after completely  removing power!) then it sounds like it's good to go.
 
 Q2 may have been fine when you checked it the first time,  then got damaged when you unsuccessfully tried to power up  the partially repaired supply.  This sort of thing is  quite common with SMPS's.
 
 -Richie,
 
 
 On 2014-03-13 23:19, Gil W. wrote:
 > I somehow missed Q2 it appears. Was shorted as well,  for some reason I  > was sure it tested fine. Also found that  > the PCB trace going out from one of it leads was not  leading and  > needed a jumper :/  >  > Overall I replaced:
 >
 > The optocoupler
 > Q1 with 2SC3752
 > Q2 with same as original
 > D5 (1SS84) with UF4007
 > All electrolytes with fresh ones
 >
 > Boots just fine now, could get nice +5, +15 and -15  calibrating the trimpot.
 >
 > Thanks everybody for the help, very much appreciated !
 >
 >
 >
 >
 > --------------------------------------------
 > On Thu, 3/13/14, Gil W. <gil_we at yahoo.com>
 wrote:
 >
 >  Subject: Re: [sdiy] TX802 Power Supply failure  (replacing 3W with 5W resistor)‏  >  To: synth-diy at dropmix.xs4all.nl  >  Date: Thursday, March 13, 2014, 11:14 AM  >  >  Hi.
 >
 >  So I replaced D5 with UF4007, Q1 with 2SC3572  (equivalent to  >  original 2SC3559), the 7915 and 7815 with fresh  ones, and  >  the PC817 optocoupler. Also put a new 22ohm/5W  instead of  >  the dead R1. I powered up and nothing... can't  get the final  >  +15/-15/+5 volts.
 >
 >  The two other fast 1SS84 diodes has some marks of  greenish  >  acid on the leads. Could this have taken D5 out  in the first  >  place ? The do not short, however. These are D2  and D6..
 >  Could Q1 take out the T1 transformer while  shorting ? I also  >  think about recapping it. Do you think there's a  point  >  insisting to fix this ? couldn't find other bad  components  >  so far (well, checked only diodes and  transistors).
 >
 >  I think I have a Polysix powersupply board laying  around.
 >  Will it do the job ? IIRC it should make
 +15/-15/+5/-5
 >  volts...
 >
 >  Thanks again !
 >
 >
 >
 >  --------------------------------------------
 >  On Tue, 3/11/14, Colin f <colin at colinfraser.com>  >  wrote:
 >
 >   Subject: Re: [sdiy] TX802 Power Supply  failure (replacing  >  3W with 5W resistor)‏  >   To: synth-diy at dropmix.xs4all.nl  >   Date: Tuesday, March 11, 2014, 4:14  PM  >  >  >   > 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.
 >
 >   There is a metric shedload of room.
 >   My TX802 supply died.
 >   I replaced it with a 5V SMPS line lump  and a simple linear  >   supply for the 15  >   volt rails.
 >   Much simpler than messing with that  nasty looking  >  switcher.
 >   By the time it had died a fair area of  the PSU PCB had  >   blackened, so even if  >   I had identified the component(s) at  fault, it might need  >  a  >   new PCB.
 >
 >   Cheers,
 >   Colin f
 >
 >
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