Gridcase 1520 CMOS Battery Replacement

Time to look at a Gridcase 1520 portable computer. Not the one that had the power supply failure; this is the cheaper model with the LCD screen instead of the gas plasma display. When it turns on it complains that the real-time clock has stopped and the CMOS configuration is invalid. Time to open it up and replace the CMOS battery!

Getting the hardware together

I relied heavily on a scanned copy of the Gridcase 1500 Disassembly/Reassembly instructions that were uploaded to the (now-defunct) "RuGrid Laptop" Yahoo group. The images in that document are a little low-resolution but hopefully the pictures in this post will help you out.

Also be aware that there are at least two different revisions of the Gridcase 1520 main board: one which has a soldered lithium battery and an MC146818AP RTC chip, and one which has a Dallas 1278A RTC with embedded lithium cell. This post is about the former type; if you have one of the latter then you're out of luck since the Dallas RTC module is difficult to remove and hard to source a replacement for.

Taking the hardware apart

Rear cover — Pop two the plastic covers from the rear of the case and remove the two screws underneath (in red). The top-rear case cover will slip forwards and lift off.

Screen — Unlatch the screen. Do NOT attempt to rotate the screen up with the rear cover removed or you risk snapping the hinge guide. Instead lift it straight up and place it face up to the left of the keyboard on a soft surface.

Keyboard surround — Use a flat-bladed screwdriver to pop the keyboard bezel out it's clips (in red). At this point you should be able to see the lithium CMOS battery above and right of the keyboard. If you don't then you have the Dallas RTC board variant.

Keyboard — On each side of the keyboard, remove the screw holding the keyboard tab and then the two holding in the screen latch receptacle. Remove the latch receptacles and place to one side.

Keyboard connector — Lift the keyboard up from the bottom and push the two ribbon cables off their connectors.

Video board — The video board is next: remove the four screws (in red) and gently pull the board up off it's connectors (underside, outlined in green).

Video board ground wire — As you lift the video board up, make sure to remove it's grounding wire which attaches to the outer battery compartment screw (in red).

Internal modem — If you have the optional internal modem fitted, remove it from beside the battery compartment by lifting it straight up. There are no screws holding it in.

Battery compartment — Remove the second battery compartment screw from between the two disk drive cables (in red) and lift the battery compartment up from it's front end to unplug it from the main board (in green),

Battery eject mechanism — Remove the two plastic pieces and spring that make up the battery eject mechanism (in red). The lower piece pushes out the back of the case.

Backpanel connectors — Unplug the three flex cables from in front of the drive assembly. Push the locking levers in, not out, to release the plug (in green).

Remove the two screws (in red) holding the DC converter and lift it up and out.

Disk drive assembly — Remove the three screws holding the disk drive assembly (in red). Also remove the lower-right screw (in blue) which is longer than the others and keep it separate.

Main board screws — Remove the five screws on the lower part of the main board.

Main board power — Unplug the two connectors at the rear of the main board (in green) and unscrew the final two screws with the grounding straps.

You can now lift the main board out and access both sides to remove/replace the CMOS battery.

Replacing the battery

The CMOS battery is a 1/2 AA size 3.6V lithium. I found those with leads soldered to them quite expensive, so instead I got a regular 1/2 AA lithium and a cheap through-hole battery holder. This seemed like a really good idea until I reassembled everything and found the holder with battery was ~2mm too tall for the keyboard bezel and screen to close properly. I ended up having to sand down the bottom of the battery holder to make it fit :-(

Original batry, removed — After removing the original CMOS battery.

New battery and holder — The new battery in it's holder.

Reassembly

Reassembly is the reverse of disassembly. Remember that you took it apart; you can put it back together again. By all means, do not use a hammer.

Watch out for the one longer screw on the drive assembler: it goes in the lower-right.
When replacing the top-rear cover, drop it into place making sure the display cables are tucked into their hinge recess. Insert the two rear screws and tighten while applying plenty of pressure to the display hinges: the top-rear case has small tabs that need to be pulled by the screws into the hinge moulding.

Main board pictures

Some bonus pictures of the main board: