If you have an Onkyo Integra tuner that has memory problems, the culprit is most likely a supercapacitor that Onkyo used to provide power for preset memory when unit is unplugged. My newly acquired tuner was diagnosed with such condition. Capacitor replacement is fairly simple procedure as you just have to observe the polarity. Other than that, just get an exact replacement. In case of my tuner, the T-4087, it was a 0.047F 5.5V supercap (C409 on schematic). If you download service manual for your tuner, it should state which capacitor (or sometimes battery) is responsible for maintaining preset memory.
As always, I take picture of the component to be replaced. It is the big flat blue capacitor.
Here is the old one vs the new one. I was actually surprised that the replacement is actually slightly bigger. Usually, it is the other way around when it comes to capacitors.
Supercapacitor was replaced and tuner’s memory is as good as new.