Units that are locking up. And if it is not due to the HD being a Maxtor 340mbi with abort off. Problem may lie with IC35 and/or IC54.
To test: format HD - record onto HD - play - rewind - stop - ff - ect.. play - mess with jog/shuttle wheel - does it lock up? Apply heat to IC35 & IC54 does unit lock up? If so then one or both of these chips are bad and BOTH must be updated.

Part #s : IC35 - #EI414969J $22.55 list $18.40 dealer cost
IC54 - #EI419187J " "





info from Dave @ Akai service