LEVEL 1 DIAGNOSTICS ERROR RETURNSDETAIL CODE 70DMA failed addressing test. Evaluate the EXPand OBS DATA fields to determine if the addressfailed along an eight bit address path. If thelower address bus (bits 0 - 7 ) has been alteredthen suspect line driver U32 (U75). Foralterations of the high address bus (bits 8 -15) suspect address latch U12 (U 126). If DetailCode 70 is returned and the EXP and OBS datafields match then suspect U 11.CPU CONTROLLER ERROR TEST (VLSI DEVICE)Format of code:CONTROL :05:ww Date TimeEXP DATA: xx, OBS DATA: yyww = Detail codexx = Expected data from portyy = Observed data from portDETAIL code:11 Port failed read/write test to PIOcontrol register (Port B).Repair Procedure 17The system PIO uses port B for the following controlfunctions: control the speaker on the Main ProcessorBoard, enable RAM parity , read the sense switches,and keyboard control.Because port B is used to control several differentdevices, the diagnostics test for those devicesshould return an error if there is a failure on oneof its control lines. Run RAM PARITY TEST andKEYBOARD TEST using the diagnostics. To test thespeaker depress any printing character key on thekeyboard and hold. When the end of line is reachedthe speaker will click repeatedly until the key isreleased. The speaker should emit a constant tone.Intermittent failure is indicated by a random breakin the tone. All of these tests should be runrepeatedly to check for intermittent component5-50
