[rescue] Sun Voyager: a) great story b) repair question c) looking for a new home

[John Hudak]

In general, the obvious place to replace electrolytics is in the power
supplies. My rule of thumb is to replace them with the same or slightly
higher capacity, and higher working voltage by at least 10%.   The PS are
usually switch mode power supplies (SMPS). If you are doing an overhaul, my
suggestion is to replace ALL the electrolytics.
Do not choose replacements based on capacity and WVDC alone.  You need to
consider the ESR (Equivalent Series Resistance).  Electrolytics are usually
used as filtering devices in SMPS.  SMPS operate anywhere from ~35KHz to
60kHz and above. The capacitor ripple current in a typical power supply is
a combination of ripple currents at various frequencies. The rms value of
the ripple current determines the heating of the capacitor. The heating can
reduce its life expectancy. Without going into a lot of the calculations
for design, suffice to say that getting a low ESR replacement cap is
advisable.  Usually suppliers will have a column in their selection guide
that will note 'low ESR'.  Things get a little confusing because mfg don't
always specify ESR values the same way.  The most common way is: Low ESR
down to [mN) @ 20B:C / 100kHz].  Typical values for aluminum electrolytics
are in the range of 15-25.  This can vary by the technology (aluminum vs
polymer aluminum etc).  Best to look at the mfg spec sheet and their
product line details.

In addition, tantalum caps are in SMPS and should be replaced as well.
tantalum caps usually always fail shorted, they tend to grow whiskers which
causes the failure.  Given where they are used in SMPS, a short can take
out diodes and transistors.  Replacing them is cheap insurance.
Modern tantalums are better for longevity than ones of 20-30 years ago, so
I'd replace the tantalums with the same type.  I'd stay with the same
capacity rating, and bump the voltage up a bit.  In most cases, if in a
pinch, tantalums can be replaced with electrolytics.  Tantalums are
basically electrolytics - their main characteristic is low leakage, hence
they are used in analog ckts such a sample and holds. They have excellent
long term stability which is why they find use in SMPS.

One last thing, a lot of MOVs in the input line side.  These tend to fail
short, causing a direct short across the incoming AC line.  They usually
then explode and have a real foul smell.  I'd recommend replacing them as
well.
Have fun.
J




On Wed, Nov 3, 2021 at 1:36 PM Dan Moisa <dmoisa at gmail.com> wrote:

> I'd love some hints for successful recapping. I have 2 voyagers bought as
> "for parts"/broken and one had the cap issue. I thought I did it right, but
> now the screen is solid black. I tried the adjustments at the bottom and
> nothing worked. I'm about to try swapping in a off-the-shelf vga LCD with a
> converter running off the original signal sent to LCD. some small research
> on the LCD connector from the service manual kinda indicates I have 8 bit
> per color RGB and h/v syncs so I can use a simple VGA chip.
>
> The other voyager has a few problems - boot tests fail at probing the cg6 -
> if I take it out the system boots, but more worrisome, if left plugged in
> there's some power supply issue causing it to randomly turn on and off
> after 22 hours.
>
> Are the LSI chips interchangeable, for same LSIxxxx identifier, between the
> voyager cg6 and a standalone sbus cg6? I'm tempted to buy some card and try
> swapping chips.
>
> Thanks,
> Dan.
>
> On Wed, Nov 3, 2021, 10:25 Toby Thain <toby at telegraphics.com.au> wrote:
>
> > On 2021-11-03 1:01 p.m., Doug McIntyre wrote:
> > >> Question: is there an obvious cause for LCD failures / are there easy
> > ways to
> > >> troubleshoot/repair this? The repair guide says: just replace the LCD.
> > That
> > >> will be hard..
> > >
> > > LCD panels especially succumb to the same drying out of electrolytic
> > > capacitors that plague the industry.
> > >
> > > I am 3 for 4 in fixing LCD panels by replacing the obviously blown
> >
> > I see better than 90% success by recapping (I've probably fixed 20 or 30
> > - another one this week).
> >
> > Stop and think about that level of pointless waste...
> >
> > --Toby
> >
> > > electrolytic capacitors on the control or power board inside the LCD
> > > panel.  Just look for any bulging cans, especially on the vent end, as
> > > they are designed to vent out the magic smoke.
> > > _______________________________________________
> > > rescue list - http://www.sunhelp.org/mailman/listinfo/rescue
> > _______________________________________________
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