Interior of the old Saia PCD2.M120 automation controller with expansion modules

p.kaczmarek2 987 3

TL;DR

Opens the Saia PCD2.M120 base unit of an old Saia programmable controller, including the enclosure, main board, I/O bus, cover, LEDs, display and PGU connector.
The motherboard sits above the I/O bus as a separate PCB, with side connectors, DIP memory sockets, and a mode-change jumper.
Key parts include the Xilinx XC9572, MC68340 processor, V3022 clock chip, DS75176 RS485 transceiver, and an L4972A-based power section.
The unit is over 20 years old, the copy shows broken plastic spacers, and the display is missing, so restoration remains uncertain.

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Post #1
21878284 06 Apr 2026 11:26

Some time ago I presented the interior of the Saia PCD2.C100 extension cassette , today I would like to show its main module, the PCD2.M120 base unit. The PCD2.M120 consists of an enclosure, inside of which is the main board and the bus for the I/O modules, and a cover with LEDs, display and PGU (programming) connector. The connectors for the expansion cards are located on the side:

The motherboard sits above the bus as a separate PCB. Immediately striking are the markings and the battery for keeping time. There is no display on my copy.

Photo from the other side; you can see the DIP pin sockets on the memory bones along with the jumper for changing the mode.

Additional connectors on both sides of the motherboard:

The way the motherboard is connected with the bus on the bottom:

Module with 7580 DS75176 - RS485 transceiver:

There are further RS485 line control chips nearby - DS14C89 and DS14C88. In addition we have circuits HC30, 74HC14, HC74, 74HC03, LM339D, perhaps from bus control.

An interesting component is the TICOMEL visible in the photo - the model is obscured, but you can see an example online - SD-17-0.63-500 0.63A 500UH. This is simply a coil. That whole circuit there is a power section based on an inverter on the L4972A.

After the power section we have the region with the main ICs. There are the Xilinx XC9572 (CPLD), MC68340 (processor with DMA, also of age, 1994) and V3022 (clock chip - you can see the oscillator next to it).

Let's remove the motherboard now. My copy must have been dropped by someone because there are broken plastic spacers:

Four I/O modules can be placed on each side of the bus.

I can still show them in a few pictures, but in general I have already discussed these modules: Interior of the Saia PCD2.C100 expansion cassette from the PCD2 programmable controller

In summary, this was over 20 years old industrial equipment. In this section I have shown the base unit, the expansion card was shown separately . Perhaps the copy shown here could be made to work, although I don't know about the display. For now, let's treat the whole thing as a curiosity - in modern times, it's getting harder and harder to find this kind of controller design, separate logic chips, separate memory bones, still in DIP sockets.... and I am not even mentioning their parameters.
Have you worked with this type of Saia controller? When did you last see them used in practice, in what applications? How do you assess their design and reliability?

Attachments:

PCD1_PCD2_Hardware_Manual_26-737_E.pdf (10.59 MB) You must be logged in to download this attachment.

pcd-2.pdf (2.92 MB) You must be logged in to download this attachment.

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#2 21878307 06 Apr 2026 12:05

jerry1960 jerry1960

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Post #2
21878307 06 Apr 2026 12:05

We still have two of these controllers in operation at our site, you could say for 30 years without failure.
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#3 21878529 06 Apr 2026 16:54

Kris52 Kris52

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Post #3
21878529 06 Apr 2026 16:54

A certain industrial robot for receiving parts from the injection moulding machine was also fitted. From what I've heard it still works today. I still have one such working controller without external modules on the shelf.
#4 21878605 06 Apr 2026 18:45

DJ MHz DJ MHz

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Post #4
21878605 06 Apr 2026 18:45

Also three conveyor belts in the works. Circa 2003 I think something assembled
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Interior of the old Saia PCD2.M120 automation controller with expansion modules

FAQ

TL;DR: The Saia PCD2.M120 base unit exposes 4 I/O slots per side and users report "30 years without failure." This FAQ helps repairers, PLC collectors, and maintenance staff identify the motherboard, bus, power, and expansion layout of an old Saia controller before inspection or revival. [#21878307]

Why it matters: Old Saia PCD2 controllers still appear in working machinery, so a clear internal map reduces damage during service and speeds fault triage.

Item	PCD2.M120 base unit	PCD2.C100 expansion cassette
Main role	Main module with motherboard and I/O bus	Expansion cassette for extra cards
Internal focus shown in thread	CPU board, power section, RTC battery, bus connectors	Expansion-card area discussed separately
Module capacity stated	4 I/O modules on each bus side	Not quantified in this thread
User context	Base unit teardown	Separate earlier teardown

Key insight: The thread shows a classic modular PLC design: a separate motherboard above a side-access I/O bus, plus discrete logic, socketed memory, and field-proven longevity well past 20 years.

Quick Facts

The motherboard sits above the I/O bus as a separate PCB, and the expansion-card connectors are placed on the side of the enclosure. [#21878284]
The bus accepts 4 I/O modules per side, giving 8 positions total in the photographed base unit layout. [#21878284]
The communications area includes a DS75176 RS485 transceiver plus nearby DS14C89 and DS14C88 line-control chips. [#21878284]
The power section includes a TICOMEL SD-17-0.63-500 coil rated 0.63 A and 500 uH, built around an L4972A inverter-based circuit. [#21878284]
The main logic area contains a Xilinx XC9572, an MC68340 marked as a 1994-era processor with DMA, and a V3022 clock chip beside its oscillator. [#21878284]

What is inside the old Saia PCD2.M120 automation controller base unit, and how is its motherboard connected to the I/O bus?

The base unit contains an enclosure, a main board, the bus for I/O modules, and a front cover with LEDs, display area, and PGU connector. The motherboard sits above the bus as a separate PCB and plugs down into the lower bus section through board-to-board connectors. The photos also show markings, a timekeeping battery, memory in DIP sockets, and a mode-change jumper. [#21878284]

How many I/O modules can the Saia PCD2.M120 handle on each side of the bus, and how are the expansion connectors arranged?

The PCD2.M120 handles 4 I/O modules on each side of the bus. That gives 8 module positions across both sides of the internal bus frame. The post also states that the connectors for the expansion cards are located on the side of the unit, which matches the modular side-access layout shown in the photos. [#21878284]

What is the role of the DS75176, DS14C89, and DS14C88 chips in the Saia PCD2.M120 controller?

They serve the controller's serial line interface and line-control area. The thread explicitly identifies the DS75176 as an RS485 transceiver and places the DS14C89 and DS14C88 nearby as additional RS485 line-control chips. That positions these parts around field communications or bus signaling rather than the main CPU core. [#21878284]

What is the TICOMEL SD-17-0.63-500 coil, and what does it do in the L4972A-based power section of this controller?

The TICOMEL SD-17-0.63-500 is a coil used in the controller's power section. The post gives its marking as 0.63 A and 500 uH and states that the surrounding circuit is a power stage based on an inverter on the L4972A. In practical terms, it belongs to the onboard power-conversion section, not the logic or I/O interface area. [#21878284]

How do the Xilinx XC9572 CPLD, MC68340 processor, and V3022 clock chip work together in the Saia PCD2.M120?

They form the main logic set of the controller. The thread places the Xilinx XC9572 CPLD, MC68340 processor with DMA, and V3022 clock chip together in the main IC region, with the oscillator visible next to the V3022. That means the board combines programmable logic, a central processor, and a dedicated clock source on one motherboard. [#21878284]

What is the PGU connector in a Saia controller, and what is it used for during programming or service?

The PGU connector is the controller's programming connector. The post names it directly on the front cover alongside the LEDs and display area, so its intended service role is programming access rather than expansion I/O. The thread does not provide a pinout, cable type, or software tool, only that the connector is present on the cover. [#21878284]

What is a CPLD such as the Xilinx XC9572, and why was it used in older industrial automation hardware?

"CPLD" is a programmable logic device that implements fixed board-level control functions, with predictable hardware behavior and non-CPU timing. In this controller, the Xilinx XC9572 appears in the main IC area beside the MC68340 and V3022, which shows it was part of the core logic design used in this older industrial platform. [#21878284]

How do you safely remove the motherboard from a Saia PCD2.M120 without damaging the bus connectors or plastic spacers?

Remove it slowly and support the board evenly, because the thread shows broken internal plastic spacers on a dropped unit. 1. Open the enclosure and inspect spacers, connectors, and cracks first. 2. Lift the motherboard evenly from the bus, avoiding side loading. 3. Stop if the board binds at the board-to-bus connectors. This matters because the motherboard is mounted above the bus and plugs into it as a separate PCB. [#21878284]

Why would a Saia PCD2.M120 have no display fitted, and how can you diagnose whether the display section is missing or faulty?

A unit may simply be missing the display, because the author states, "There is no display on my copy." Diagnose it by checking whether the front cover only has an empty display area, whether connector hardware for a display is present, and whether the rest of the board still shows normal internal parts such as the battery, CPU area, and front-panel LEDs. The thread does not confirm an electronic display fault. [#21878284]

What does the battery in the Saia PCD2.M120 maintain, and what problems appear when the timekeeping battery is dead?

The battery maintains timekeeping. The post explicitly calls it a battery for keeping time and also identifies a V3022 clock chip and nearby oscillator on the motherboard. If that battery is dead, the clock function is the first feature to suspect. The thread does not describe secondary symptoms such as memory loss, so the safe thread-based conclusion is loss of maintained time. [#21878284]

How reliable are old Saia PCD2 controllers in real industrial use, and what kinds of applications were they still running in after 20 to 30 years?

They appear highly durable in the examples given. One site still had 2 controllers operating after 30 years without failure. Another report says a controller in an industrial robot for taking parts from an injection moulding machine still worked, and a third report mentions 3 conveyor belts still using them. Those examples show long service life in real factory automation. [#21878307]

Where were Saia PCD2.M120 controllers commonly used in practice, such as conveyor belts, industrial robots, or injection moulding machine handling systems?

The thread places them in conveyor systems and in robot handling around injection moulding machines. One reply reports 3 conveyor belts still in operation, and another describes an industrial robot that picked parts from an injection moulding machine. A separate reply also says 2 units remained active on one site, confirming practical industrial deployment rather than laboratory use. [#21878605]

How does the Saia PCD2.M120 base unit compare with the PCD2.C100 expansion cassette in function and internal design?

The PCD2.M120 is the base unit, while the PCD2.C100 is the expansion cassette shown separately in the linked earlier teardown. In this thread, the M120 includes the main motherboard, front cover, battery, processor area, and internal I/O bus. The author says the expansion card or cassette was discussed elsewhere, so this post focuses on the controller core rather than the add-on enclosure. [#21878284]

What should you check first when trying to revive a dropped or physically damaged Saia PCD2.M120 controller with broken internal spacers?

Check the mechanical damage first. The author says the unit must have been dropped because the internal plastic spacers were broken. Start with the spacer mounts, the motherboard seating, and the board-to-bus connector alignment. Then inspect the side expansion connectors and front cover area. A mechanically shifted board can create connection faults even when the chips and power section still look intact. [#21878284]

What are the typical failure points, spare-part availability issues, and repair options for a 20-plus-year-old Saia PCD2 automation controller?

The thread points to mechanical damage, missing display parts, and age as the main service concerns. The shown unit has broken spacers, no display on that copy, and is described as over 20 years old. Repair options in the thread are limited to inspection and possible revival, because the author says the unit might be made to work but is unsure about the display. It is presented mainly as a technical curiosity from an older design era. [#21878284]