18 September 2016

Contents

1. Disk Expansion XBUS module emits smoke, expires
2. No display, keyboard status lights flicker continuously or stay on solid
3. External 36v DC power supply module emits smoke

Problem Log

Disk Expansion XBUS module emits smoke, expires

When powering on the Series 386+, the secondary Disk Expansion module (P/N HX-020 AB) emits smoke and fails to come ready. CTOS does not load.

Replace capacitor C60 on Miniscribe 6085 main logic board. The silkscreen is under the component; it is near transistor Q17. Component is 4.7µF 20% axial tantalum.

Adjacent inductor L2 consumed during failure of C60. Replace—component is 1/2W 82µH, 10%.

No display, keyboard status lights flicker continuously or stay on solid

After being stored for some time, the Series 386+ will power on, but not self-test or load the operating system. The status lights on the keyboard flicker continuously, or stay on solid. Nothing appears on the display.

Disassemble processor module (CP-003 AB) and reseat all boards and all socketed components.

Module is showing minor corrosion on interior metal surfaces. Electronics appear mostly fine—for now.

External 36v DC power supply module emits smoke

After the system is powered on for some time, the external bulk power supply emits smoke. The system appears to continue operating before the plug is pulled from the wall outlet.

C3 has failed. Replace it. Component is 0.22µF 250V film capacitor, with 25mm lead spacing and X safety rating. PCB will accept several lead spacings at C3, down to 10mm.

C4 may be replaced prophylactically. Component is 0.11µF 250V film capacitor, with 18mm lead spacing and X safety rating.