26 December 2014

Contents

1. Machine does not power on
2. Incorrect high-function display operation on Professional Graphics Controller

Problem Log

Machine does not power on

When the machine is switched on, nothing happens. The power indicator may flicker briefly, or the power supply fan may twitch slightly. No other sign of life is apparent.

There is a short circuit, causing the power supply to shut down.

C45 on the 68X3756 Fixed Disk/Floppy Diskette Adapter has failed. Component is a 22µF 15V axial tantalum capacitor. Replace.

After replacing C45, C46 immediately failed, producing the same symptoms. It is the same part as C45; it is probably best to replace both if either have failed.

Incorrect high-function display operation on Professional Graphics Controller

When starting a program which uses the high-function display mode of the Professional Graphics Controller (PGC), the screen is drawn incorrectly or not at all. The program may crash, hang, or exit unexpectedly. All emulated CGA display modes operate correctly. Running diagnostics on the PGC produces an error (3909 or 3906) and the advice to replace the PGC.

The PGC communications RAM has failed. The part is an RCA CDM6116AE3 at U42 on the processor (base) card. Replace. An equivalent 6116-type 2Kx8 150ns CMOS SRAM may be substituted.

The display adapter must be completely disassembled to access the failed part.