Couple days ago powered on my Tek 577 D1 and found ripple on the display curves.
https://groups.io/g/TekScopes/photo/255563/1?p=Created,,,100,2,0,0

Later I found a leaking electrolytic capacitor C124 on the A2 collector supply circuit board.
https://groups.io/g/TekScopes/photo/255563/3?p=Created,,,100,2,0,0

Now I got a clean display after replacing it.
https://groups.io/g/TekScopes/photo/255563/2?p=Created,,,100,2,0,0
https://groups.io/g/TekScopes/photo/255563/4?p=Created,,,100,2,0,0

C124:
10uf 475 DC(VDC?) Sprague 43D100F475GJ4

Replaced by:
10uf 450Vdc Epcos B43697 LL