FANUCA20B-3300-008516 MB DRAM Memory Module – Plug-In CPU Daughter Board for i-Series CNC and Robot Controls

Product Description

What this part is

This is a FANUC A20B-3300-0085 16 MB DRAM module — a compact plug-in memory daughter card that seats on the main CPU printed circuit board inside a FANUC i-series CNC or FANUC robot control rack. It supplies the processor’s volatile working DRAM. It is not the CPU board itself, and it is not the battery-backed SRAM or FROM that holds your part programs, parameters and ladder — those live elsewhere on the control. Confusing the two is the classic buying mistake on Fanuc memory: replacing this card does not restore lost programs, and it does not erase them either.

Decoding the order code

A20B — FANUC’s prefix for printed circuit boards and plug-in board assemblies. (For contrast, A86L- is FANUC’s bought-in component prefix, not a PCB prefix — worth knowing when reading a parts list.)
-3300 — the board family this memory card belongs to, the i-series / robot CPU board group.
-0085 — the specific card: the 16 MB DRAM capacity variant. Its siblings -0084 and -0086 are the same physical card at other DRAM capacities, which is exactly why the last four digits must match your parts list rather than the family number.
/03B — the edition or revision suffix stamped on the board, as in A20B-3300-0085/03B. Editions are usually backward compatible within a capacity, but note yours before ordering.

Correcting the source data

Two numbers that have travelled with this listing are not part numbers. A20B-3900-0085 does not exist — FANUC has never used an A20B-3900 prefix, and it appears to be a transcription slip from A20B-3300. And 00E0E46DA03C is a hexadecimal MAC address from the unit’s own label, not an orderable designation; it identifies this individual card, so do not search on it and do not quote it to a supplier.

What this means in practice

DRAM faults on a Fanuc control present as intermittent system alarms, watchdog resets and boot failures rather than a clean dead machine, so a spare memory card is a cheap way to isolate a suspect CPU board: swap the DRAM first, and if the fault stays you have proved the fault is on the main board. Because the card is small and static-sensitive, it is also one of the few Fanuc spares that is genuinely economical to keep on the shelf.

Quantity and configuration

One memory card ships. No CPU main board, no rack, no backplane, no mounting standoffs or screws, no battery and no documentation are included. The card is a daughter board — it does nothing on its own and has no standalone connector to the outside world.

Installation and setup notes

Power down and lock out the control, then wait for the supply capacitors to discharge before opening the CPU rack. Ground yourself: this card is bare DRAM with no conformal coating, and a static hit shows up weeks later as a random alarm rather than an immediate failure. Note the orientation and the standoff positions before removing the old card, seat the replacement squarely so all pins engage together, and re-torque the standoffs finger-tight — a card sitting proud on one corner is the most common cause of a control that boots intermittently after a memory swap. After power-up, run the control’s memory diagnostic before returning the machine to production.

Interchange guidance

Searched as A20B-3300-0085, A20B33000085, A20B 3300 0085, A20B-3300-0085/03B and A20B-3300-0085 16MB DRAM. Reported fitted on FANUC i-series CNC controls and on FANUC robot controllers including the S-430i, M-6i, M-16i, M-440iH, M-770i and A-520i families. A20B-3300-0084 and A20B-3300-0086 are the same card at different DRAM capacities — carried as cross-references because they share the footprint and the search intent, but the capacity differs and the control expects the capacity its parameters were set for. The CPU main boards this card commonly sits on include A16B-3200-0330 and A17B-3300-0200, which are useful search terms if you are working from a board photograph rather than a parts list. FANUC supports this generation through repair-exchange, so surplus is the practical source.