Sluggish D550 button presses - Re-capping Roland D-550 power supply

[Resyn]

A D550 is acting up after having run error-free for 20 years, up to May-June 2024. Now (sitting in a rack below another D550) the unit is crazy sluggish in responding to button pushes and MIDI messages. RAM Panel and Card tests pass. Opening the unit (en passant replacing battery) my eyes are drawn to the brownish leakage stains at the foot of the 3 largest electrolytics (but not near the 6 smaller electrolytics) - the very largest one (6800 mikroF, 25 V, 85 degrees) is even swelling at its top.

OK these need to be replaced, and for good measure why not the other (6)  much smaller electrolytics on the same board. So the 2 D550s were used in June this year- no errors at all, and the units sounded the same. I have a hard time believing this sluggishness (5-8 seconds for the display to show a response) has anything to do w those caps. But if they picked this moment to fail, maybe they brought other things down.

Anybody here ever seen this exact problem (the 5-8 second delay between pressing any button and the synth responding, same delay in getting MIDI messages) and fixed or had it fixed?

Resyn

[helius]

The liquid inside electrolytic capacitors is not brown, so those are not "leakage stains". The Japanese electronics manufacturers were very fond of a product called "yellow glue" which over time breaks down and becomes conductive and corrosive. That is what the brown stuff is: they used it to stabilize the capacitors instead of the more common Silastic. What you called a "swollen top" is a resin disc used to isolate the metal can of the capacitor: they warp over time, not indicating the capacitor's aluminum can has expanded.

More likely there is nothing wrong with those capacitors, although if you wish to inspect or test them go ahead. What has happened is that the glue, turned brown, is now conductive and is shorting and corroding the pins underneath.

A noisy power or ground could cause communications between the CPU and display to behave intermittently.