On 9/3/25 02:24, Rob Jarratt via cctalk wrote:
One other thing…
With it powered on and measuring voltage at the outputs but not at the
plugs, wiggle the plugs a bit and see if there wierdness with them.
plugs and connectors go bad often and it doesn’t seem obvious that they do
but saves a lot of time just by checking them now.
Sent from my iPhone
On Aug 31, 2025, at 13:34, Wayne S <[email protected]> wrote:
Ps if you didn’t get continuity for a moment in one direction then the cap is
open. If you get continuity in both directions then it’s shorted. Hope this
helps.
Sent from my iPhone
On Aug 31, 2025, at 13:28, Wayne S <[email protected]> wrote:
Rob, replace c21 because of the bulge. If you want to check an electrolytic
cap with a ohmmeter ,(kinda hard with a digital one), connect the meter
across the ends. You should get either infinite resistance or a momentary
reading of zero going back down to infinite resistance as the cap charges.
Then reverse the leads and it should be infinite from the start.
On an old analog meter with a dial, you can quickly tell by see the needle
deflect full scale in one direction then settle back down to infinite. I keep an
old meter around just for this purpose.
Replacing those caps seems to have fixed the issue, need to do a bit more
testing. However I am unsure about some spikes on the +5V output when I try to
check the ripple.
This is the scope trace:
https://rjarratt.wordpress.com/wp-content/uploads/2025/09/5v-output-ripple-after-replacing-caps.png
Does that look reasonable or should I try to work out where these spikes are
coming from? I replaced C21 and C35.
Those are not real. They are conducted interference from
the switching supply getting into the scope preamp via the
ground lead.
I have seen this MANY times, ignore it.
Jon
