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Central Surplus Bearing Finder
A faster way to search our bearing inventory Today we’re launching the Central Surplus Bearing
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1 in stock
4 MB FROM (flash ROM) plug-in memory module for Fanuc Series 16i / 18i / 21i CNC main boards. Holds CNC system software, PMC ladder and macros. Internal board-mounted module, not a front-slot removable card. One module.
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| MFR / Brand | FANUC |
|---|---|
| Model | A20B 3900 0074 |
| Base Number | A20B-3900 |
|---|---|
| Industry Terms | FROM module, flash ROM module, CNC memory module, F-ROM board, program memory module, memory card |
| Application Types | CNC control repair, machine tool retrofit, Fanuc i-series spares |
| Controller Platform | Fanuc Series 16i / 18i / 21i |
| Mpn Variants | A20B-3900-0074; A20B39000074; A20B 3900 0074; A20B-3900-0074/01A |
| Manufacturer Status | Legacy / discontinued, surplus and refurbished supply only |
| Compatible With Replaces | Fanuc Series 16i / 18i / 21i CNC main CPU boards |
| Part Number | A20B-3900-0074 |
| Mounting Type | Internal plug-in module on main board |
A Fanuc A20B-3900-0074 — a 4 MB FROM (flash ROM) memory module that plugs into a connector on the main CPU board of a Fanuc Series 16i / 18i / 21i CNC. It is the non-volatile store for the CNC system software, the PMC ladder program, macro executors and option software; the contents are copied into system DRAM at power-up for execution.
A20B — Fanuc printed-circuit-board / module product class.
3900 — the i-series plug-in memory module family (FROM and SRAM modules share this block).
0074 — the 4 MB FROM specification within that family.
Boards are commonly stamped with a revision suffix such as /01A; the revision does not change the memory capacity or fit.
Type: FROM (flash ROM) plug-in memory module.
Capacity: 4 MB (4 M).
Function: CNC system software, PMC ladder and macro storage — non-volatile.
Host boards: Fanuc Series 16i, 18i, 21i main CPU boards.
Mounting: internal connector on the main board.
Weight: approx. 2.0 oz.
Origin: Japan (Fanuc nameplate).
FROM is flash, so it retains its contents with no battery. That is the practical difference from the SRAM modules in the same A20B-3900 block, which hold part programs and parameters and do depend on the CNC backup battery. If you are chasing lost parameters or an SRAM battery alarm, this module is not the fix. This is an internal plug-in memory module, not a removable PCMCIA-style front-slot memory card.
Module only. No main CPU board, no CNC rack, no SRAM module, no battery, no memory card or card adapter, no CNC or PMC software, no ladder program, no cables and no documentation.
Sold as one module.
A20B-3900-0074 and A20B39000074 are the same part. Other numbers in the A20B-3900 block are different capacities or different memory technology — a 0075 or 0304 is not a substitute for a 4 MB FROM, and the SRAM modules in the block are a different function entirely. Note that A03B and A20B are Fanuc’s own numbering schemes, and the A86L prefix seen on other Fanuc-branded parts marks bought-in components; none of those are GE Fanuc IC-series numbers.
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A faster way to search our bearing inventory Today we’re launching the Central Surplus Bearing
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Our team can locate, cross-reference, and source all parts.
Our team can locate, cross-reference, and source all parts.
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