Rdu -
In my experience, TEK power supplies are one of the things that fail with some frequency.
My strategy is to have a (at least one) spare power supply. It should be relatively easy to find a "sare 7704 supply. Unfortunately, the 7704 supply is different from the 7904 (you other scope if it ever comes home) so you may need two kinds. I made sure my scopes all use the same supply and I have more than one back up.
Cheers!
Bruce
Quoting Radu Bogdan Dicher <vondicher@...>:
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I think I'm done with the repair. See
/g/TekScopes/album?id=282665.
What leaked (mainly?) was C3016, but C3017 was also suspect, so I replaced
both. Though I'd never run this with dissimilar caps even if one may be OK.
There was a huge mess to clean - these large caps have quite a load of goo
to spill!.. - and I used successive applications of pure alcohol and
ammonia with different types of swabs and pads (ammonia being the more
effective treatment). Some of the leaking electrolyte even triggered
arching through the board (documented in the pictures). I removed the
artifacts of that by essentially digging in there with some of my
"soldering/desoldering" tools I have until I reached unaffected PCB
material.
I've sparingly and locally applied a bit of contact cleaner on the caps
traces to make sure my contraption of the "screw top" caps makes perfect
contact in a compromised situation.
Fully back into operation now. I also have some added confidence in how
long this will be trouble-free not only because of the age of the caps
(brand new), the added capacitance (not enough to be a problem), but mostly
the rated max voltage. Also, 105C caps, which never hurts.
Radu.
On Sun, Dec 25, 2022 at 11:03 AM Radu Bogdan Dicher via groups.io
<vondicher@...> wrote:
I've placed an order for some screw terminal caps, but I do have some
United Chemicon KMZs (680uF/450V) at hand that may work. I'd need to
jerry-rig then in there, which doesn't seem too difficult.
But I wonder what I should be looking for with caps in this application as
minimum safe ratings. I assume the SMPS application with its direct line
exposure and such subjects these to some hefty abuse. For instance, my
particular KMZs are rated up to 2.25A ripple at 105C/120Hz.
Any thoughts and recommendations would be appreciated.
On Sat, Dec 24, 2022, 11:05 AM Radu Bogdan Dicher via groups.io
<vondicher@...> wrote:
I think the green/white wire goes to L3236, the 5V lights supply
On Sat, Dec 24, 2022, 8:48 AM Radu Bogdan Dicher via groups.io
<vondicher@...> wrote:
Hi all,
And Happy Holidays to all celebrating!
I've woken up the morning of Christmas Eve to a nice surprise - smoke,
noises, smell, etc. Upon pulling out the power supply, I see that the main
caps (computer grade Sprague caps) have failed and made a big mess inside
the unit. Things have been leaking so bad this morning, I had to take it
apart very quickly, and scrambled to wash off any of the goo and
electrolyte. Luckily, I think this all almost happen in front of my eyes,
so not much of this stuff has stayed very long on the board, but there's
some more serious damage on the board and traces just below the caps.
Some requests for input:
- what have you found best for cleaning this up? I used various
sizes cotton swabs to cosmetic pads and alcohol (not single malt... ;))
- suggestions on caps replacements? I haven't started looking, but I
do have some faves to search (Nebraska Surplus, etc.).
- When scrambling to extract the caps without leaking too much in
too many places I've detached a very short wire (white/green?). I really
hate it when the design includes short sighted decisions like this - where
a wire is too short to open up access by unfolding a board while all other
wires are long enough, WTH? Would anyone know offhand where this attaches?
I know this is a very long shot.
- Does anyone have a spare, "known good," PS and is willing to
depart with it?
Thank you all.
Radu.
