Mars 4 reached Mars on 10 February 1974. Due to use of helium in preflight tests of the computer chips, which resulted in degradation of the chips during the voyage to Mars, the retro-rockets never fired to slow the craft into Mars orbit. Mars 4 flew by the planet at a range of 2,200 km. It returned one swath of pictures and some radio occultation data. More details Mars probe intended to enter Martian orbit and comprehensively photograph Mars.
Parameters are for Mars orbit.
Mars 5 reached Mars on 12 February 1974 and was inserted into a 1760 km x 32,586 km orbit. Due to computer chip failures the orbiter operated only a few days and returned atmospheric data and images of a small portion of the Martian southern hemisphere. More details Mars probe intended to make a soft landing on Mars. Total fueled launch mass of the lander and orbital bus was 3260 kg. It reached Mars on 12 March 1974, separated from the bus, and entered the atmosphere, where a parachute opened, slowing the descent.