There seams to be some confusion on if or when to recap your older Boogie's. First off I am only talking about the power supply filter electrolytic caps. Lets start with my first MK3 I got it about 4 years ago, it had sum hum, so it was do for a check up. I have 3 or 4 ways of checking caps, first I have a curve tracer adapter on my Tektronix 468 & 465 so I can test in circuit components. If that shows a flaw I desolder one end of the cap and us a capacitance test. Results the 4 220uF 300v on the ps3c board were all bad the 3 B C D caps one was out of spec and not holding a charge for as long as a new one, thats another test method, out of circuit I charge and time how long it holds the charge. So I changed all 7 caps and amp was happy and without hum. So never changing caps is wrong! But changing every 10 years without reason is also wrong. Solution is to test them if your amp has to much HUM or if it's been idle for more than 2 years or more, yes Idleness is the cap killer also higher than nominal voltage.There is one more reason to change caps if you have to remove the main board on the Mark series especially, then you might as well replace the other hard to get at caps. PS.. I am an Electrical Engineer don't try this at home 450 volts can kill.