Re: 7704A power supply fail (big leak of the main caps)
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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 <vondicher= [email protected]> 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 <vondicher= [email protected]> 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 <vondicher= [email protected]> 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.?
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