Re: Owon PDS 5022S

On Thu, 15 Aug 2024 13:42:12 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Wed, 14 Aug 2024 20:55:27 -0400, legg <legg@nospam.magma.ca> wrote:
>

On Wed, 14 Aug 2024 14:26:48 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
>

A few years ago, my Owon PDS 5022S oscilloscope failed with a strange
looking display.  See photo at:
<https://photos.app.goo.gl/rYGeaGygSMXHtMCb8>
From what is visible on the display, everything seems to be working
except for the strange display.  Whatever is wrong is probably in
either the color LCD display or the circuitry that drives the display.
Does anyone have a clue what might have failed?  Mostly, I'm trying to
save time fixing it.  (I haven't torn it apart yet).
>
User manual (no schematic or block diagram):
<https://www.saelig.com/downloads/pds5022s.pdf>
Specs:
<https://www.batronix.com/shop/oscilloscopes/digital-oscilloscope-pds5022s.html>

>
Don't be afraid to open it up, just be carefull.

>
I'm fearless and moderately careful.  My problem is that I'm in the
process of purging all the old junk from my house.  When I retired and
closed the office, I had to drag everything from the office to the
house.  The house has been a mess since Sept 2020.  I have quite a bit
of equipment that I know can be fixed if I had the time and bench
space.  For this DSO, the problem is both lack of time and lack of
bench space.  I can't just tear it apart and leave it.  The reason I
asked for clues is to save time monopolizing the workbench and
troubleshooting the problem.  In this case, I've seen literally
hundreds of failed LCD computers displays, but none have ever looked
like the photograph.
>

Could be something simple. I had a TDS210 that was shipped with a
reversed and burst electrolytic. Worked fine for a while before
requiring a simple fix. Display showed first symptoms.

>
The DSO is old enough that a bad electrolytic is a likely problem.  I
couldn't find any information that would help establish the age.  So,
I measure a few voltages.  If that fails, I find where my ESR tester
is hiding and check every electrolytic.
>

The bloom around the LCD display looks physical, to me.

>
There's no evidence of a crack in the display.

The pattern of 'bloom' looks like poisoning from an adhesive
layer.

>

As a battery-powered device, it'll have it's uses.

>
It has an AC charger and power supply built in.  The battery pack is
proprietary.  I plan to use the AC PS for testing and to build a
suitable battery pack when it's fixed.

I crack mine open, replace the cells and add a balance w/test points,
then re-seal. I haven't 'adjusted' the EOC charge voltage yet.
Probably before the refurbed battery sets (always bought 2 with
each scope) are fried. Or a battery disconnect switch.

I use the mains 'off' switch when not in use and plugged in.
Never leave it quiescent and plugged in - that green light is
a fool's reassurance.

>
Incidentally, I used it for about a year before it suddenly quit. It's
only 20MHz bandwidth, but that was good enough for audio.
>

I have a few Owon SDS8202s that are eating their batteries
regularly. I've introduced balancing, internally, but the
charging circuit possibly overvolts the battery chemistry.
Simple is good, but ignoring the float upper limit is just
stupid.

>
That's a much later 200MHz DSO:
<https://www.saelig.com/product/PSBEB100007.htm>

SDS was successor of PDS.

The previous owner of my PDS5022s mentioned that overcharging the
battery was also a problem.  If it used LiIon and there was no BMS, I
would not expect the battery to last very long.  I have a few devices
have no battery protection or balancing.  When possible, I add the
necessary circuitry.  More commonly, I just bring out all the internal
battery connections to a balancing connector and use a radio-control
style external charger.  I have one of these which will charge almost
any battery:
<https://hobbyking.com/en_us/skyrc-imax-b6-v2-60w-6a-1-6s-dc-charger-discharger.html>

Battery management in the SDS is so rudimentary and ignorant of
internal ( ~third party) battery characteristics, that it can't
always manage to under-voltage reliably. One of mine corrupted
it's own firmware recycling on/off on a low battery in the
first few months and went back under warranty.

Software battery gauge is a joke.

Not all LiIon chemistries have the same EOC voltage - I think
the chemistry was changed after they shot the design engineer.
(Ship it!)

RL