Troubleshooting Siemens 65421/97D Timer Relay on Graziano Sag 12

Overview: Graziano Sag 12 Siemens Electrical Cabinet

The Graziano Sag 12 is an Italian precision toolroom lathe produced with two distinct electrical control philosophies: a Loral/Sag original Italian relay logic cabinet and a Siemens-designed control cabinet. Units that left Italian production through certain North American resellers or that were specified for U.S. laboratory installations shipped with a Siemens electrical enclosure. These cabinets are functionally equivalent to the Italian design but use Siemens timers, contactors, and rectifier assemblies, and they were installed on machines originally built with single-speed main drive motors (single-winding induction motor paired with a Graziano gearbox) rather than the more common two-speed Dahlander-wound motor.

The Siemens cabinet is built around a control transformer with two isolated secondaries, a diode bridge that produces DC power for electromagnetic transmission clutches, a Siemens pneumatic-style time delay relay (catalog designation 65421/97D), a small pilot relay labeled 49V9, an oil pressure switch integrated into the gearbox, and a speed selector drum switch with discrete positions corresponding to mechanical feed and spindle speed selections. Restorers frequently encounter units that have sat unpowered for 15-30 years. The troubleshooting patterns below assume a Siemens-cabinet Sag 12 that has been stored on a pallet, may have missing components, and is being commissioned for the first time or being returned to service after long storage.

Control Transformer and DC Power Architecture

The Siemens cabinet uses a multi-secondary control transformer as the central power source. The unit has two distinct secondaries that serve entirely different load families:

The 32 VAC secondary feeds a discrete diode bridge mounted inside the cabinet. Under load the rectified DC bus typically sits between 38 and 42 VDC; the no-load value of approximately 45 VDC is the value cited in legacy documentation. All six transmission clutch coils draw from this same DC bus. Because the coils are inductive, the diode bridge itself is exposed to the back-EMF generated when a coil is de-energized; the bridge must be rated for the inductive switching load and must include snubbing or must rely on the inherent clamp of a full-wave bridge to freewheel the inductive energy through the DC bus capacitance.

On long-stored machines, the diode bridge is a frequent failure point. Restorers commonly find that the original bridge has been replaced with a generic automotive-style or industrial three-phase bridge that may have insufficient current rating for the clutch surge currents. Verify that any replacement bridge is rated for at least the steady-state DC load plus a 2-3x surge margin during transmission shifting.

Siemens 65421/97D Time Delay Relay: Function and Wiring

The Siemens 65421/97D is a pneumatic-style on-delay timer (dashpot / air bellows construction) with two normally closed (NC) timed contacts. It is the functional heart of the cabinet's protection and soft-starting logic. The two NC contacts perform distinct roles that are easy to confuse during troubleshooting because they appear to do similar things electrically (both close at rest and open after the timing interval).

Contact A: Ballast Resistor Bypass (Coil Surge Function)

The first NC contact of the 65421/97D is wired in parallel with a ballast resistor bank in series with the transmission coil supply rail. The ballast resistors limit steady-state current to the energized clutch coil to reduce heat dissipation and power consumption once the coil has pulled in.

However, solenoid-actuated clutches require substantially more current to pull in (close the initial air gap and overcome the return spring) than they require to hold. The 65421/97D's NC contact closes the relay's coil circuit at startup with the ballast resistors shorted out, applying full DC bus voltage to the selected transmission coil. Once the dashpot times out (typically 1-3 seconds), the contact opens and inserts the ballast resistor bank into the coil circuit, dropping the steady-state current to the holding value.

Contact B: Oil Pressure Switch Bypass

The second NC contact of the 65421/97D is wired in parallel with the oil pressure switch (OPS) contacts. The OPS is a normally-open pressure switch mounted on the gearbox that closes once lubrication oil pressure exceeds its setpoint. If the OPS opens (drops out) while the machine is running, the main drive motor contactor is dropped out via a holding circuit, stopping the spindle.

The reason for the bypass contact is straightforward: at the instant the main motor is started, the gear pump is not yet spinning fast enough to develop line pressure, so the OPS is open. Without the bypass, the motor would refuse to start. The 65421/97D's second NC contact provides a 1-3 second window during which the OPS is electrically ignored, allowing oil pressure to build. After timeout, the bypass opens and the OPS takes over its protective role.

Transmission Coil Load Profile

The Sag 12 Siemens cabinet controls six discrete electromagnetic clutches, all sourced from the same 45 VDC bus. Their functions are:

• 4 speed selection coils: One for each discrete speed selected by the drum switch (e.g., on a unit configured for 125 / 200 / 320 / 500 / 800 / 1250 RPM, the drum switch has 6 positions, but only 4 coils route through the selector logic depending on gearbox configuration).
• 1 forward coil: Engages forward rotation through the gearbox.
• 1 reverse coil: Engages reverse rotation through the gearbox.

Coil resistance values reported from field measurements are in the 3.5 - 4.5 ohm range per coil at room temperature. A reading substantially below this (e.g., 0.5 - 1.5 ohms) indicates a shorted turn; a reading above 10 ohms indicates an open or high-resistance joint. A specific failure pattern observed on restored units is the 1250 RPM coil developing a partial short that draws enough current to blow the 10 A fuse on the DC clutch bridge during selection. Disconnecting the defective coil's wire from the drum switch is a viable field workaround but leaves that speed position non-functional.

The 49V9 Pilot Relay

The 49V9 is a small 24 VAC pilot relay mounted on the speed control board. Its role is to interface the low-current drum switch contacts to the higher-current DC clutch bus. The relay's coil is fed from the 24 VAC bus; its contacts switch the 45 VDC clutch supply under command of the selector logic.

On long-stored units, the 49V9 commonly fails due to oxidized contacts or dried-out coil varnish. Field reports describe contact welding (relay will not drop out) and contact erosion (high resistance, insufficient coil current). A field bypass technique that has been used successfully is to insert a small insulating wedge (e.g., a sliver of plastic) into the relay's armature pivot to hold the contacts in the closed position. This is acceptable for short-term commissioning work but must be replaced before returning the machine to production use. A direct equivalent from the Siemens 3TH or 3RT contactor families of the same era is generally pin- and function-compatible with minor wiring adaptations.

Identifying the "Missing Component on the Lower Left"

A common visual question on stored Siemens-cabinet Sag 12 lathes is: what was originally mounted at the lower-left of the cabinet interior? Multiple field photos from restored units show that this position is occupied by the diode bridge rectifier assembly (the same component that converts 32 VAC to ~45 VDC) on some builds, and by a secondary relay or auxiliary contact block on others. Restorers who compare their cabinet to a known-working unit typically find the missing component is one of the following:

1. The diode bridge itself, if the cabinet has been retrofitted with an external bridge mounted elsewhere.
2. An auxiliary contactor or relay that interlocks the spindle direction with the coolant pump or chuck guard interlock.
3. A line filter or suppressor capacitor across the DC bus.

Cross-reference the actual wiring present in the cabinet against the schematic for the build. The "single-speed with brake" schematic differs from the "two-speed" schematic in the interlock wiring for the 49V9 circuit and in the contactor count.

Brake Function: Dual-Clutch Engagement

The Sag 12 Siemens single-speed cabinet does not use a separate electromagnetic brake. Spindle braking is achieved by energizing two transmission clutches simultaneously: one selects a mechanical condition that opposes rotation (typically the reverse clutch combined with the active speed-selection clutch), and the resulting counter-torque brings the spindle to a rapid stop. A pushbutton on the selector switch is the user interface for the brake function.

Commissioning Procedure: First Power-Up After Long Storage

1. Visual inspection: Document missing components before applying power. Photograph the cabinet interior. Compare to a known-good Siemens Sag 12 schematic.
2. Insulation test: Megger the transformer secondaries to ground at 500 V. Expect readings > 10 megohms on a healthy unit. Below 1 megohm indicates moisture ingress; bake the transformer or replace.
3. Transformer no-load test: Apply primary power with secondaries disconnected. Measure 24 VAC on secondary 1 and 32 VAC on secondary 2 (allow ±10%). Verify no hum or visible arcing.
4. Rectifier test: With secondary 2 loaded only by a dummy resistor (e.g., a 10 ohm 50 W resistor), measure DC bus voltage. Expect 38 - 45 VDC depending on load.
5. Timer substitute test: If the 65421/97D is suspect, jumper Contact A (ballast bypass) closed and Contact B (OPS bypass) closed. The machine should start and run. If clutches fail to engage, the bypass is incorrect; revert and troubleshoot the timer.
6. OPS functional test: With the machine running, manually depress the OPS plunger (simulating low oil pressure). The main contactor should drop out within 1 second. If it does not, the OPS contacts or the OPS circuit is faulty.
7. Coil resistance sweep: With power off, disconnect each transmission coil wire from the drum switch. Measure each coil's resistance. Replace any reading outside 3.5 - 5.0 ohms.
8. Speed-by-speed engagement test: With the gearbox in neutral and oil pressure confirmed, energize each speed position one at a time. Listen for the clutch click and feel for the spindle to drive through the selected gear.
9. Brake test: With the spindle running at low speed, press the brake pushbutton. The spindle should stop within 1 - 2 seconds. If the 10 A fuse blows, the dual-coil current draw is excessive; check for shorted coils.

Troubleshooting Matrix

Bypass Operation: Risks and Limits

Two bypass techniques are common on commissioning benches and should be understood before being deployed in production:

Bypass 1 - 49V9 contacts held closed with an insulating wedge: Functionally replaces a failed pilot relay. The risk is loss of the protective drop-out function: if an OPS event occurs, the 49V9 will not de-energize the clutch bus because its contacts are mechanically held. Use only for short-duration testing.

Bypass 2 - 65421/97D Contact A shorted across the ballast resistor: Functionally delivers full pull-in current continuously. The risk is coil overheating: a clutch coil rated for 1 A hold current may see 3 A continuous draw, with a proportional I²R heating increase. The coil insulation life will be reduced from decades to hours-to-days depending on duty cycle. Use only for a few shift hours of commissioning work.

Neither bypass is a substitute for repair. Both can be left in place temporarily to bring the machine up for inspection of mechanical systems, but the timer and relay must be replaced before any production run.

Known Failure Patterns on Long-Stored Units

• Diode bridge degraded: 25 years of thermal cycling and oxidation can degrade the bridge's internal solder joints. Symptoms are reduced DC bus voltage under load and audible buzzing from the transformer under clutch selection. Replace with a bridge of equal or higher current rating.
• Timer dashpot leak: The 65421/97D uses a pneumatic bellows for timing. Bellows that have sat compressed for decades may not extend properly. The symptom is timing that is either instant or never. The bellows can sometimes be massaged back to function by manually actuating the timer several times before installation.
• Coil insulation breakdown: Long-term storage in humid environments can wick moisture into the coil varnish. Megger each coil to ground before first energization.
• OPS plunger seizure: The OPS plunger can corrode in place. Free it up and verify free travel before relying on the OPS for protection.
• Drum switch contact erosion: The selector drum switch is the highest-cycle component in the cabinet. Oxidation on the contacts presents as high resistance and voltage drop across the switch. Clean with contact cleaner or replace the switch.

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