Sluggish D550 button presses - Re-capping Roland D-550 power supply - Page 1
Forum section: electronics / repair

author: Resyn
author_rank: Newbie
timestamp: September 07, 2024, 03:33:17 pm
content: 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

author: helius
author_rank: Super Contributor
timestamp: September 07, 2024, 04:02:02 pm
content: 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 thebrown stuffis: 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.

author: Resyn
author_rank: Newbie
timestamp: February 25, 2025, 10:05:36 pm
content: Helius,Thanks for the support - and: I'm slow on a good day...If I understand you correctly, even if the capacitance might be tested to be correct, the brownish stuff might be impacting matters electrically ("...the glue, turned brown, is now conductive and is shorting and corroding the pins...") - is it self-evident they need replacing? Please correct me if I've misunderstood.There is an exception to the many-seconds-long delay (not always exactly the same, but always at least 8 seconds and as much as 16) for a button press to get a response (as seen on the screen), which is when using the up or down arrow to monitor a patch/sound: that only takes 2-3 seconds. It also takes 2-3 seconds for the audio to die out after releasing that up or down arrow.So: turning on the D550 one sees it boots correctly, but extremely slowly. Once it loads, that patch can be heard after a 2-3 second press on the up or down arrow key. Changing a patch can take up to about 16 seconds, but more usually closer to 10 sec.I like the sounds the D550 can make, and while I've replaced simple things in other gear, like whole power supplies, and only rarely caps, so I'm an electronics amateur. But there is something about the way this D550 is acting that I would expect hasn't only happened this single time over nearly 40 years, and thus I would think it should be recognizable. Much seems to work correctly (the D550 boots, LCD-screen is fine, patches can be loaded, they can be listened-to) but there's this total weirdness with the time-factor in every button press. All the apparent weirdness involves button presses, and though all types of button presses take too long, they take different amounts of too long, so behavior that should be instantaneous (choosing a patch, which now takes several seconds, listening to a patch, which when hitting an up or down arrow button should be instantaneous but now takes 2-3 seconds before sound comes - and 2-3 seconds to die out when the button is released. Some time-bandit at work somewhere...My guess is that an EE familiar with the electronics/logic of the D550 would suspect a particular IC.Which could it be?Anyone?ResynPS for completeness: just did a quick test of the faulty unit's MIDI-response. Chords for example can be played, but the D550 responds to key presses on the MIDI controller I used (QuNexus) just as slowly as the up or down arrow buttons on the D550, ie from playing a chord it takes 2-3 seconds for sound to be heard, and once released, the sound continues for another 2-3 seconds before ending.

author: helius
author_rank: Super Contributor
timestamp: March 25, 2025, 09:58:21 pm
content: There is possibly a constant stream of interrupts that is slowing down the MCU processing keys and events. On a lot of these instruments, both the MIDI and keyboard input pass through the same UARTs as the front panel buttons, so if there is (for example) a button that is constantly repeating, then there will not be enough processor cycles to service keys or MIDI notes. The buttons are read by a key matrix decoder. The frequency and voltage levels of each row and column of the key matrix need to be checked.I don't have a D550, but the MT-32 is sort-of similar, I think. I can take some oscillograms of the front panel if it would help you test if your unit has the right voltage levels.

author: benj38
author_rank: Frequent Contributor
timestamp: March 27, 2025, 06:32:21 pm
content: Quote from: Resyn on February 25, 2025, 10:05:36 pmNo, the capacitors most likely do not need replacing since the glue and the potential corrosion are external. Simply remove the capacitors, clean their bottom part and the pins from any corrosion and glue residues, then clean the PCB from the glue residue, and reinstall the capacitors.You may want to take the opportunity to test the capacitors when they are out of the circuit for capacitance and ESR if you have the equipment. Also, consider using a non-acid curing silicone to mechanically support the capacitors (which was the original purpose of that deteriorated glue).