TTPR No Output: Field Troubleshooting Steps-Technical Articles-KULUN Electric

Bottom line first: a TTPR power controller with a valid setpoint but no output usually has a wiring or setting issue. Check five things in order: RUN LED, signal type versus SW2, closed-loop mode, G-K gate leads and load circuit.

This field guide covers the TTPR three-phase SCR power controller from Sichuan Kulun Electric Co., Ltd., rated AC 260-440 V and 25-3000 A on the main circuit. It is written for electricians and maintenance staff. Full power output at any setpoint has its own section below.

KULUN TTPR three-phase SCR power controller

What should you confirm before troubleshooting?

The AC 220 V ±10% control supply is connected.
The three-phase main supply is connected.
Any fault shown on the display is written down.

The TTPR protects against phase loss, overcurrent, load break, load imbalance, SCR overtemperature and frequency fault. A protection trip also results in no output.

In what order should you check a TTPR with no output?

Check that the RUN LED lights.
Match the signal type to SW2.
Confirm the closed-loop mode and load size.
With power off, test the G-K gate leads.
With power off, check the load circuit and fuses.

Step 1: Does the RUN LED light when SW1 is closed to GND?

SW1 is the run/stop input and takes a dry contact. When SW1 is closed to GND, the main board signals the display board. The green RUN LED then lights.

From Kulun field service experience, a lit RUN LED means the three-phase trigger board is able to work.

Where should you look if the RUN LED stays off?

SW1 and GND wires are secure.
The external run contact actually closes.
The control supply is present.

Step 2: Does the signal type match SW2?

What do SW2 open and SW2 closed select?

SW2 open to GND: 4-20 mA or 0-20 mA setpoint on AI1, 200 Ω input impedance.
SW2 closed to GND: 0-5 V setpoint on AI2, ≥100 kΩ input impedance.
GND: signal common.

Signal type, input terminal and SW2 state must all agree.

Which wiring mistakes are common on site?

On new installations, the setpoint wire is not properly connected between SW2 and GND.
The setpoint source was changed to communication, while the site still feeds a current signal into AI1.

Either mistake leaves the controller with no output.

Step 3: Why does constant-current mode give full voltage on a small load?

The TTPR supports constant-voltage, constant-current and constant-power closed-loop control.

Symptom: in constant-current mode with a small test load, the output goes straight to full voltage.

Cause: the measured current is too low, so the trigger board drives full voltage. From Kulun field service experience, full-voltage output in this situation is normal.

Action: reconnect the real load, then judge whether the output is controllable. Never force a no-load test on a model that does not allow no-load operation.

Step 4: How do you measure and check the G-K gate leads?

How do you measure G-K resistance?

Switch off the main supply and the control supply.
Test for dead.
Measure the resistance between G and K on each gate lead.
Compare the reading with 10-50 Ω.

From Kulun field service experience, G-K resistance is normally 10-50 Ω. The exact figure varies by manufacturer. A reading well outside that range points to the gate lead or SCR gate on that channel.

Are the gate leads connected to the main board correctly?

Plugs are fully seated.
Each phase sits on its matching socket.
G and K are not reversed.

Kulun repair records include a unit whose G and K wires had been swapped on site.

Step 5: Is the load or main circuit open?

What should you check on the load side?

With power off, continuity from U, V and W to the load.
Burnt-out heating elements.
Loose terminals.

An unloaded output can show a phantom voltage on a meter. That reading does not prove the controller is conducting.

What should you check on the fuses?

TTPR models with "F" in the part number have built-in fast-acting fuses. Check that none has blown. Check that each replacement matches the original rating.

One returned unit had a 125 A fuse fitted in place of the original 160 A. Once one phase fuse blew, the controller could not run.

What if the TTPR gives full power at any setpoint?

Symptom: the TTPR delivers full power whatever the setpoint and cannot be controlled.

In what order should you check?

Rule out constant-current mode on a small load.
Confirm the signal type matches SW2.
Check for a shorted SCR.
Check the trigger circuit for faults.

What has repair work found?

One returned TTPR ran at full power with no setpoint applied. The fuses and SCRs tested normal. The fault was a damaged resistor in the setpoint op-amp circuit on the main board, and replacing the resistor restored normal output.

How can you quick-check a TTPR with no output?

Check	How to check	Normal	If abnormal
Control supply	Measure at L and N	AC 220 V ±10%	Restore the control supply
RUN LED	Close SW1 to GND	Green RUN LED on	Check SW1 wiring
SW2 open	Check AI1 wiring	4-20 mA or 0-20 mA on AI1	Correct wiring or SW2
SW2 closed	Check AI2 wiring	0-5 V on AI2	Correct wiring or SW2
Constant-current mode	Test on the real load	Output adjustable	Full voltage on a small load is normal
G-K resistance	Power off, multimeter	Typically 10-50 Ω	Check gate lead and SCR gate
Gate leads	Check plugs and G/K order	Seated, not reversed	Restore original wiring
Load circuit	Power off, test U/V/W continuity	Circuit continuous	Repair load or terminals
Fast fuses	Check for blown fuse and rating	Intact, original rating	Replace with original rating

FAQ

Q: The RUN LED is on but there is still no output. What next?
A: Check the signal type against SW2, then the G-K gate leads, then the load circuit.

Q: What do SW2 open and SW2 closed select?
A: SW2 open selects 4-20 mA or 0-20 mA on AI1. SW2 closed selects 0-5 V on AI2.

Q: Can G-K resistance be measured with power on?
A: No. Switch off the main and control supplies first.

Q: Full voltage in constant-current mode on a small load. Is the TTPR faulty?
A: No. The measured current is too low, which is normal.

Timeliness note

This article is based on TTPR product documentation and Kulun field service experience as of October 2026. Terminal names and parameter ranges may change between product versions; always follow the manual and wiring diagram supplied with the unit.