Dead RF31 DSSI Disk.. final Question..

Holm Tiffe holm at
Wed May 13 01:13:27 CDT 2015

Jarratt RMA wrote:

> I can really sympathise with you on the PSU front. I tried to repair one of
> these, but it was designed in such a way that it was really hard to get at
> the caps to remove them for testing. My problem was that even when I did
> get to the big Sprague one I couldn't desolder it, presumably there was a
> large track/plane taking all the heat away.

I haven't even tried to desolder this rectangular Sprague 6800µ/20V cap,
since in most cases bad caps in a PSU aren't the big ones, but the small.
I've leaved the entire input section with the big HV Filter Caps alone, if
one of them fails you can easily see that.
Same thing at the output caps, and the big rectangular Sprague is one.

You can desolder such thing using a Hot Air gun (SMD soldering) helping
the soldering iron to heat things up.

I would change thios cap if the PSU would still misbehave after repair,
but it works flawlessly.

But the cause for my rant where two other caps. On one of the two power
Modules" in the PSU sitting two 330µF Caps near thogether but one couldn't
reach the bottom of the PCB since the big power Transistors sitting below
the PCB iscrewed on to a heat sink and are soldered to the PCB from bottom.
There is not enough space around the Transistor Pads on the top of the
PCB to desolder them properly, so you can't dismount the Transistors and
can't dismount the heat sink at all which preventy you to change parts.
That's the thing that I call a design failure. Bad, idiotic.

> In the end I gave that PSU away
> (along with another working one) to someone who is much better than me.
> Although I don't know if he has fixed it yet.
> Regards
> Rob

I do such things all day long, reparing industrial electronics for



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