Is a speeding ticket valid if the officer refuses to show you the actual radar-gun readout?

I've received TWO speeding tickets from this SAME African American officer in three months. Both times, he claims to have clocked me going 5-10mph over the limit. However, upon asking him to show me the speed-gun, he claimed both times that he "reset" radar gun or that it automatically resets itself and therefore couldn't show me the actual readout. Both times, I couldn't have been going that fast and this guy just seems so shady. Are these tickets valid? What's the police officer's requirement for confirming speed when writing a ticket. I fought the first ticket in court and it was thrown out but I'm afraid that continued appearances will make ME look like the scumbag. How can I argue this one?