The M48T02 timekeeper chip is found in many vintage computers from the late 1980s and early 1990s, including Sun SPARCstations, SGI workstations, and various other systems. These chips combine a real-time clock, NVRAM, and a lithium battery in a single package. The problem is that the battery is sealed inside the chip and eventually dies, taking the clock and stored settings with it.
You can buy replacement M48T02 chips, but they’re becoming harder to find and increasingly expensive. Worse, any new chip you install will eventually suffer the same fate. A better solution is to modify the existing chip to use an external coin cell battery that can be easily replaced.
Why Modify Instead of Replace?
Replacement M48T02 chips (70ns or 150ns versions) can still be purchased, but there are good reasons to consider the modification approach:
- Cost: New chips are expensive; CR2032 batteries are cheap
- Longevity: External batteries are easily replaced when they die
- Sustainability: Keeps the original chip in service
- Frequency: These chips fail roughly every decade, faster in machines that aren’t powered on regularly
Tools and Materials
- Dremel or rotary tool with a grinding/cutting wheel
- Multimeter
- Soldering iron and solder
- CR2032 coin cell holder with wire leads
- Hot glue gun (optional, for securing the battery holder)
- Safety glasses
A Note on Different Chips
The procedure described here is specific to the M48T02. Other timekeeper chips in the M48T family (M48T08, M48T12, M48T59, etc.) have similar internal construction but may have the battery located in a different position or oriented differently. Before grinding into any chip, do some research—check the datasheet, search online, or ask an AI about your specific part number. A few minutes of research beats grinding into the wrong end of the chip.
The Modification Process
Step 1: Remove the Chip
Power down the system and remove the M48T02 from its socket. These are typically in DIP-24 packages and should pull straight out. Note the orientation before removal.
Step 2: Grind Down the End
Flip the chip over so you’re looking at the bottom (the side with the pins). The battery is located at the end of the chip opposite pin 1. Using a Dremel with a grinding wheel, carefully remove the potting material from this end.
Work slowly and keep the tool moving to avoid overheating. You’re grinding through epoxy potting compound, which will produce fine black dust. Wear safety glasses and work in a ventilated area.
Step 3: Expose the Battery Contacts
Continue grinding until you see two shiny metal contacts emerge. These are the positive and negative terminals of the internal battery. Stop grinding as soon as both contacts are clearly visible and accessible.
If your chip still has some battery life remaining, use a multimeter to identify which contact is positive and which is negative. The positive terminal should read around 3V relative to ground. In the photo above, you can see the orientation with multimeter probes on the contacts.
If the battery is completely dead, there’s an alternative approach: check the chip datasheet for the ground pin (pin 12 on the M48T02), then use your multimeter’s continuity mode to test from each exposed contact to that pin. The negative battery terminal will have continuity to ground, while the positive terminal will not.
Step 4: Prepare the Battery Holder
CR2032 coin cell holders with pre-attached wire leads are readily available from electronics suppliers, eBay, or Amazon. Tin the ends of the wires with solder.
Also tin the exposed battery contacts on the chip. A small amount of solder on each pad will make the final connection easier.
Step 5: Solder the Connections
Touch the tinned wire ends to the tinned pads on the chip and apply heat with your soldering iron. The solder should flow together quickly. Red wire goes to positive, black to negative.
Double-check your polarity before reinstalling. Reversing the battery connection could damage the chip.
Step 6: Mount and Reinstall
You can secure the battery holder to the top of the chip using hot glue, or mount it elsewhere in the case if space is tight. In cramped systems like some SPARCstations, tucking the holder under an expansion board or in an unused drive bay works well.
Insert a fresh CR2032 battery and reinstall the chip in its socket, being careful about orientation.
After the Modification
With Sun workstations, you’ll need to reprogram the IDPROM after replacing or modifying the timekeeper. This includes the machine type, Ethernet address, and serial number. See Resetting IDPROM on Sun Workstations for the complete procedure.
Other systems may have similar post-modification requirements for restoring configuration data stored in the NVRAM portion of the chip.
Applicable Systems
The M48T02 timekeeper is used in many vintage systems:
- Sun SPARCstation IPC, IPX, 1, 1+, 2, SLC, ELC
- Sun SPARCstation 10, 20, LX, Classic, Voyager
- SGI Indigo, Indy, and other early systems
- Various other Unix workstations and industrial equipment
The M48T08 and M48T12 are related chips with larger NVRAM that can be modified using the same technique.