In June, four other West Midlands officers charged in connection with the case were cleared at Leicester Crown Court after Deputy High Court Judge Sir Douglas Brown ruled police station CCTV evidence unsafe.
Previously, the jury considered recordings from a camera in the custody suite at Thornhill Road station at the time Mr Powell was taken in.
Pc Lee Howard, Pc Andrew Edwards, Pc Luke Gill and Sergeant David Williams were all charged with misconduct in a public office for allegedly failing to deal with Mr Powell's condition. They denied the charges.
Directing the jury to acquit the men, the judge told them: "I will say very little about that except that it's almost entirely based on consideration of the audio tape and the various inter-pretations of it.
"And I have ruled that the tape is in such a condition and the interpretations put in the transcript are so lacking in reliability, that you will not be troubled with them and they will be taken from you.
"Equally, and as far as the defendants are concerned probably more importantly, in relation to counts... involving Lee Howard, Andrew Edwards, Luke Gill and David Williams, their cases should be withdrawn from your consideration."
The same charges were dropped against Pc Hackett and the judge directed the withdrawal of one of the charges faced by Acting Sgt Wilson and Insp Guest.
Allegations the two senior officers failed to ensure Mr Powell was taken to hospital were struck off.