Editing IBM RS/6000 Maintenance Guide (section)

== NVRAM / RTC Battery ==

The RS/6000 family uses '''Dallas Semiconductor TimeKeeper''' modules on the planar to hold real-time clock, system NVRAM and boot configuration. The internal lithium cell fails after 10–20 years, producing:

* Lost boot list (SMS boots from CD instead of disk after every power-cycle).
* Clock at epoch (1 Jan 1970 or similar).
* Lost machine serial number / model code (rare but possible if the part holds the IPL ROS / VPD).
* Solid LED panel halt at NVRAM tests (typically '''200''' / '''202''' / '''203''' on the LED panel — see [[IBM RS/6000 Troubleshooting Guide]]).

Common Dallas modules in the family include:

* '''DS1287 / DS1287A''' — 24-pin DIP, used on early MCA 7012 / 7013 planars (same family as PS/2 50/70/80).
* '''DS1385 / DS1387''' — DS1385 + integrated battery/crystal in an encapsulated module.
* '''DS1644''' — non-volatile TimeKeeping RAM.
* '''DS1742W''' — 32-pin nonvolatile timekeeping RAM, 5 V or 3 V variants.
* '''DS1746 / DS1746P''' — 128 KB × 8 NVSRAM + RTC, Y2K-compliant.

Replacement options:

# Direct replacement with a fresh-date Dallas/Maxim part (NOS or refurbished). DS12887+, DS1387 with cell replaced, DS1746P+.
# Modern drop-in board replacements such as the '''Glitch Works GW-1742-1''' (DS1742 substitute), '''GW-1387-1''' (DS1387 maintainable repair board) and '''Necroware nwX287''' (DS12887 replacement using a CR1225 + modern SRAM + RTC chip).<ref>https://www.tindie.com/products/glitchwrks/glitch-works-gw-1742-1-dallas-ds1742-replacement/</ref><ref>https://users.glitchwrks.com/~glitch/2017/07/27/ds1387-rebuild</ref>
# DIY: cut the Dallas plastic case open, find the internal cell, replace with an external CR2032 holder. Electrically valid but messy.

Replacement procedure:

# Power off; discharge PSU bulk capacitor.
# Identify the Dallas DIP on the planar — typically near the RTC crystal or near the boot ROM.
# Desolder with solder wick at no more than 350 °C. Limit each cycle to 5–7 seconds — RS/6000 planars are no more forgiving of repeated heating than PS/2 planars.
# Fit a socket (recommended) before fitting the replacement Dallas / Glitch Works / Necroware module.
# Power on; enter SMS (F1 or F4); re-enter boot list, IP / SLIP config, date/time.

After replacement, run '''SMS → Utilities → Update System Vital Product Data''' to write the machine serial back into NVRAM if the previous module had lost it.