Obsolescence guides · SIMATIC S7-300 catalogue
SIMATIC S7-300 withdrawn from sale — what now?
Siemens SIMATIC S7-300 · 1995–2023, discontinued
Where the platform stands
Siemens withdrew the S7-300 family from sale in October 2023. Spare parts support continues for a defined period, but new modules are no longer sold through the normal channel and availability through distribution has largely dried up.
Why spares are hard to find
S7-300 is one of the largest installed bases in European manufacturing. Withdrawal did not reduce the demand for spares, it removed the supply — so the secondary market now carries essentially all of it. CPU 315 and CPU 314 variants are the most requested, followed by SM 321 and SM 322 digital I/O.
What actually fails first
From what comes through a repair bench on control gear of this age. Worth reading before you buy a replacement — two of these are cheap fixes that get misdiagnosed as a failed module.
Processors of this era keep the program and retentive data in volatile memory backed by a lithium cell. The cell lasts years, not decades — and when it dies the program goes with it on the next power cycle. Many "dead processor" calls are a flat battery and a lost program. Keep a current backup of the program off the machine; it is the cheapest insurance in the panel.
Electrolytics dry out over 15–25 years, especially in warm panels. The supply does not fail cleanly — it sags under load, which presents as random processor faults and I/O dropouts that look like a software problem. If an old rack is behaving strangely, suspect the supply before the program.
Later S7-300 CPUs hold the program on an MMC rather than battery- backed RAM, which removes the battery problem and adds a different one: the card itself fails, and a CPU without a valid card will not start. Keep a programmed spare card as well as a spare CPU — they are cheap and they are the part nobody has.
The migration route, and what it really costs
S7-1500 with TIA Portal is the successor. Siemens provide program migration tooling, and it does a reasonable job of the logic — but the hardware configuration has to be rebuilt, and **S7-300 signal modules do not fit an S7-1500 rack**. Migration kits exist that reuse the front connectors and therefore the field wiring, which is the single biggest cost saving available and the thing to ask your integrator about first.
The case for keeping it running
Substitutions we would consider within the family
Each of these has conditions attached — read them. None is a blind swap, and we do not offer substitutions for safety-related functions at all.
| 6ES7315-2AG10-0AB0 | 6ES7315-2AH14-0AB0 — needs a configuration change in the plc program |
|---|---|
| 6ES7307-1BA01-0AA0 | 6ES7307-1EA01-0AA0 — fits and runs with no changes |
| 6ES7307-1EA01-0AA0 | 6ES7307-1KA02-0AA0 — fits and runs with no changes |
Spares worth holding
If you are keeping the platform running, these are the items whose failure stops production — hold them rather than waiting to need them.
All 63 SIMATIC S7-300 parts we source →
Need one now?
Request a quote Or sell us your surplus
Forge Horizons is an independent sourcing merchant and not an authorised distributor or agent of Siemens. This page is general guidance from our own sourcing experience, not engineering advice — confirm anything safety-related with the manufacturer or your integrator.