Understanding TV Check in FANUC CNC Controllers: A Comprehensive Technical Guide
Introduction
One of the most commonly misunderstood parameters in FANUC CNC controllers is the TV Check (Tape Vertical Check), often causing frustration when operators and technicians encounter the infamous “TV Parity Alarm” or “SR1591 TV ERROR”. Despite being a legacy feature from the era of punched paper tape systems, TV Check remains embedded in modern FANUC controllers like the 0i-TF, 0i-MF, and other contemporary models. This technical blog provides a deep dive into what TV Check actually does, why it exists, when it matters, and how to troubleshoot related issues effectively.
What is TV Check?
Historical Context
To understand TV Check, we must first acknowledge its historical origins. Before the advent of Direct Numerical Control (DNC) and modern data transfer protocols, CNC programs were stored on and transmitted via punched paper tape. Each character in a G-code program was represented by a series of holes punched vertically across the paper tape hence the term “Tape Vertical.”
The TV Check was an error-detection mechanism designed to verify data integrity during tape reading operations. Specifically, it ensured that each block (line) of the CNC program contained an even number of characters. This simple parity check could detect transmission errors and corrupted data blocks, which was critical when working with mechanical tape readers.
Technical Definition
In modern FANUC controllers, TV Check is a block-level parity check that verifies whether the total number of characters in each program block is even. The system counts every character in a block including letters, numbers, signs, spaces, and special characters and generates an alarm if the count is odd.
How it works:
- Each block (line) of a G-code program must contain an even number of characters
- If a block has an odd number of characters and TV Check is enabled, FANUC alarm 002 (TV Parity Alarm) is generated
- The alarm prevents the program from being read into the controller’s memory until the issue is resolved
Example:
- Valid block: G00G90X.5000 = 12 characters (EVEN)
- Invalid block: G00G90X-.5000 = 13 characters (ODD)
Understanding TV Check Parameters
Parameter Location and Structure
TV Check settings in FANUC controllers are controlled through *Parameter #0000, specifically bit 0 (TVC bit). The parameter location may vary slightly depending on the controller series:
For FANUC 0i Series (0i-TC, 0i-MC, 0i-TF, 0i-MF):
- Parameter #0000 – Bit 0: TVC (TV Check)
- 0 = TV Check disabled (NOT performed)
- 1 = TV Check enabled (Performed)
Step-by-step procedure to reset TV Check error in FANUC 0i Series:
- Set the controller to MDI mode (Manual Data Input)
- Press the EMERGENCY STOP button or keep it in IDLE state
- Press the OFFSET/SETTING key (or SYSTEM key depending on controller version)
- Navigate to PARAMETER or SYSTEM PARAMETER screen
- Go To Parameter #0000
- Identify Bit 0 (TVC) – currently showing as 1.
- Press PARAMETER WRITE = 1 or enable parameter editing mode (PWE)
- Change the TVC bit value to 0.
- Press INPUT to confirm the change
- Exit the parameter screen and verify the new setting takes effect
Important Note: Some controllers automatically update parameters in memory, while others require you to explicitly enable Parameter Write mode first. If you cannot modify the parameter directly, look for a PWE (Parameter Write Enable) setting that must be activated first.
Alarm SR1591 – TV Error
Alarm Description: “An error was detected during single-block TV error.”
This is a variant of the TV parity alarm found in more recent FANUC controllers, particularly the Fanuc 15i and newer models.
Why TV Check Creates Problems in Modern DNC Operations
The Core Issue
TV Check was designed for punched paper tape operations, where data integrity during mechanical reading was critical. However, in today’s manufacturing environment, programs are transferred via:
- RS-232 serial connections with error checking at the protocol level
- Ethernet/Network connections (on newer controllers with connectivity options)
- USB interfaces with built-in data verification
- Direct memory editing through control panel interfaces
All of these modern transfer methods employ their own error-checking mechanisms, making the legacy TV Check function redundant and problematic.
Why It Causes Unexpected Problems
Scenario 1: Manually Edited Programs
When a technician manually edits a program (either directly on the controller or off-line), they rarely consider character count parity. A simple edit adding a space or changing a parameter can alter the character count from even to odd, triggering the TV alarm unexpectedly.
Scenario 2: Post-Processor Generated Programs
Post-processors (software that converts CAM output to G-code) may not automatically adjust program blocks to maintain even character counts. If the post-processor doesn’t include this logic, programs generated from CAM software will frequently fail TV Check verification.
Scenario 3: DNC Software Transfer Issues
Legacy DNC (Distributed Numerical Control) software must add padding characters (typically spaces) to blocks with odd character counts to comply with TV Check requirements. If the DNC software doesn’t perform this padding automatically, or if padding is disabled, TV alarm 002 appears during program download.
When TV Check Should Be Enabled vs. Disabled
TV Check Should Be DISABLED (Set to 0) When:
- Using modern DNC software “ Electronic program transfer eliminates the need for tape-era error checking
- Transferring programs via RS-232 or Ethernet “ Modern protocols have superior error detection built-in.
- Manually editing programs “ Maintaining even character counts in every block is impractical and unnecessary
- Loading programs from external computers “ USB and network transfers don’t require tape parity verification
- Working with post-processor generated code “ CAM-generated programs rarely comply with character count requirements
- Using modern industrial networks “ PROFINET, EtherNet/IP, and other modern protocols make tape verification obsolete
TV Check Should Be ENABLED (Set to 1) When:
- Reading actual punched paper tape “ If your machine still uses this legacy medium
- Operating in isolated/legacy environments “ Some older facilities still rely on tape-based systems
- Using legacy DNC software with tape format “ Some very old transfer protocols required this for compatibility
- Maintaining strict ISO compliance “ In specialized manufacturing environments where tape format compliance is mandated
In practical terms: For 99% of modern CNC shops using contemporary FANUC controllers and electronic program transfer methods, TV Check should be disabled (set to 0).
TV Check vs. TH Check
It’s crucial not to confuse TV Check with TH Check (Tape Horizontal Check):
| Feature | TV Check | TH Check |
|---|---|---|
| Full Name | Tape Vertical Check | Tape Horizontal Check |
| What it checks | Block character count parity | Individual character bit parity |
| Checks for | Odd/even character count | Correct parity bits in each character |
| Legacy purpose | Detects punched holes vertically across tape | Detects correct punch patterns horizontally in tape |
| When it occurs | During block reading | During character reading |
| Typical alarm | Alarm 002 | Alarm with “TH” in name |
| Modern relevance | Obsolete for DNC | Obsolete for DNC |
| Default setting | Usually disabled | Usually disabled |
Both checks can typically be disabled for modern electronic data transfer without any negative consequences.
Real-World Scenarios and Solutions
Scenario 1: Machine Reports TV Alarm
This scenario occurs in new machine when the machine operator enable the Parameter Write enable button in offset window and by mistake he also enable the TV check bit (Making TV check bit from o to 1)
Scenario 2: New Machine Reports TV Alarm Immediately
Situation: Fresh FANUC 0i-TF installation; technician tries to download first program and gets Alarm 002.
Solution: Verify whether TV Check was enabled during factory configuration (common in some regions). Disable it immediately per the steps outlined in this blog. This is likely a parameter set during shipping configuration that needs adjustment for modern DNC use.
Prevention: Always review and adjust legacy parameters during commissioning, even if they appear to be working initially.
Scenario 3: Intermittent TV Alarms During Long Program Downloads
Situation: Large programs (1000+ blocks) occasionally trigger TV alarm mid-download, but smaller programs work fine.
Solution: This suggests buffer timing issues rather than a fundamental TV Check problem. However, the simplest solution is to disable TV Check entirely. If it must remain enabled, consider upgrading DNC software or adding delay parameters to slow down transmission rates.
Prevention: Standardize on modern DNC software that doesn’t rely on tape-era features.
Scenario 4: Works on One Machine, Fails on Another
Situation: Same program downloads successfully to one FANUC 0i-TF but fails on another identical machine with Alarm 002.
Solution: The machines have different TV Check parameter settings. Standardize all machines in your facility by setting Parameter #0000 bit 0 = 0 on all controllers.
Prevention: Create a standard machine parameter configuration document and apply it during setup of all new equipment.
Conclusion
TV Check is a legacy feature from the punched paper tape era that serves no practical purpose in modern CNC manufacturing. While it remains in contemporary FANUC controllers for backward compatibility, modern machine shops should disable TV Check (set Parameter #0000 bit 0 = 0) as part of their standard machine commissioning procedure.
The occasional “Alarm 002 TV Parity Alarm” that catches technicians by surprise is almost always caused by this outdated feature being enabled when it shouldn’t be. Understanding what TV Check does and when to disable it prevents unnecessary troubleshooting and improves overall operational efficiency.
For maintenance technicians, remembering this simple rule “TV Check relates to punched paper tape; if you’re not using punched paper tape, disable TV Check will solve the vast majority of TV Check “related issues in your facility.
Modern FANUC controllers prioritize reliability and ease of use over legacy compatibility in most default configurations, but vigilance is required to ensure that outdated parameters are properly configured for your specific operational environment.
Author’s Note: This article reflects current best practices in CNC machine operation. TV Check understanding is particularly valuable for technicians working with FANUC 0i-TC, 0i-MC, 0i-TF, 0i-MF and other contemporary models. As CNC technology evolves, legacy features like TV Check continue to exist for compatibility but represent technical debt that modern facilities can safely eliminate through proper parameter configuration.
Disclaimer: The blogs shared on CNC machines are created purely for *educational purposes*. Their intent is to help readers understand CNC controls, alarms, diagnostics, and general troubleshooting methods. We strictly avoid any copyright violations, and all explanations are written only for learning and knowledge-sharing. These blogs should not be considered as official repair or service manuals. For detailed instructions, critical repairs, or advanced troubleshooting, it is always necessary to contact and work under the guidance of the respective *machine manufacturer* or *CNC controller support team*. The content provided is focused only on *diagnosis and awareness*. We do not take responsibility for any kind of damage, error, or malfunction that may occur if someone directly applies the information shared here without proper technical supervision
