According to Wikipedia, when Salyut 7's solar-array-pointing system failed in 1985, its batteries were rendered unable to charge, and the station almost immediately went completely dead:
The first order of business was to restore electric power. Two of the eight batteries were destroyed, the rest fully discharged. Dzhanibekov determined that a sensor in the solar array pointing system had failed, preventing the batteries from recharging. A telemetry radio problem prevented the TsUP (mission control center) from detecting the problem. Salyut 7 had quickly run down its batteries, shutting down all its systems and accounting for the break in radio contact. The cosmonauts set about recharging the batteries and used Soyuz T-13 to turn the station in order to point its solar arrays to the sun.
But solar arrays produce power whenever they're illuminated, meaning that, even with inoperable solar-array pointers, Salyut 7 should still have had power at least intermittently, whenever it was outside the Earth's shadow and happened to have one or more solar arrays in sunlight. This should have happened fairly frequently, as Salyut 7 was not frozen (no pun intended) into a single, unchanging orientation; instead, to quote Wikipedia again,
[...] As the crew approached the inert station, they saw that its solar arrays were pointing randomly as it rolled slowly about its long axis. [...]
Thus, the station's rotation should have periodically brought at least some of its solar arrays into sunlight; even if the illuminated arrays were suboptimally oriented for generating electricity from the light absorbed thereby, some power should still have been available, at least momentarily, which should have caused Salyut 7 to intermittently start to wake and send (fragments of) telemetry from time to time.
Instead, Salyut 7 went completely and uninterruptedly dead until Dzhanibekov and Savinykh arrived to repair it.