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

Richie Burnett rburnett at richieburnett.co.uk
Fri Mar 14 09:56:01 CET 2014


If you've got a couple of decent laboratory bench power supplies, I would set them to provide the appropriate voltages and use them to feed the TX-802. It should run all day long functioning correctly and you can read off the current drawn on each rail. Then you can pick a suitably rated replacement power supply arrangement to fit the shed load of space that Colin mentioned. You can also watch for any abnormal operation when the Tx-802 electronics warms up, or when you make it do a particular thing. This should put your mind at rest as to whether an intermittent fault exists on the main board.

-Richie,


Sent from my Xperia SP on O2

"Gil W." <gil_we at yahoo.com> wrote:

>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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