Mitsubishi M800/M80 communication diagnosis: why Selfdia counters do not equal current faults

A communication-error record in Selfdia does not establish that errors are occurring now. Different numbers in similar fields do not establish a faulty monitor either. First identify what each field measures, when its observation window starts and whether power was cycled or records cleared between screenshots. Otherwise, old evidence can be mistaken for a new fault and a consecutive-error maximum for a cumulative total.

Scope: read the evidence without creating a fault

This article uses the Mitsubishi M800/M80/E80 Series Maintenance Manual IB-1501273-L, revision L, August 2023, §4.5.1, printed pages 94–97. It concerns Selfdia under Diagn, not M70, M800V/M80V, C80 or machine-builder diagnostic pages. Verify the installed series, software version, displayed fields and machine documentation first.

Interpret existing records or authorized read-only observations only. Do not clear counters, restart to “check zero,” connect or disconnect cables, or move axes to reproduce a problem. Selfdia H/W state is common to part systems, while Operation state depends on the part system. Seeing the same hardware record after changing part systems does not itself represent another occurrence.

Servo Num and Acc: separate windows and error types

Page 95 defines Servo comm err Num1 as occurrences of Y51 receive-frame-number error xx04 since power-on, with Acc1 the cumulative count for that type. Num2 counts Y51 data-ID error xx03 since power-on, while Acc2 is its cumulative count. Servo clear clears both cumulative error counters.

Num1 and Acc1 therefore describe the same error type over different windows; Num1 and Num2 describe different types. Do not transcribe merely “communication errors = a number,” or add Num1 to Acc1 as a total: their coverage can overlap. Clearing history affects the cumulative baseline, so it cannot automatically be treated as a lifetime count since manufacture.

RIO: read location, consecutive maximum and retention together

On the same page, RIO channel/station1 identifies the channel/station of continuous errors since power-on. RIO retry count max 1 gives the maximum value of continuous errors since power-on, not a sum of every communication error. RIO channel/station 2 and RIO retry count max 2 retain their records through power-off. RIO clear can reset the retained channel/station to 0/0 and its count to 0.

The channel/station helps locate the communication segment to investigate, but map it to actual equipment using the machine's topology and station assignments. A station number is not automatically an axis number. An unchanged max 1 establishes only that the recorded maximum did not rise; shorter runs of errors may still have occurred. A nonzero retained value alone does not establish a present connection fault. These fields are not used here to infer retry periods, outage duration or failure probability.

Hypothetical comparison: an increment is not a maximum

This is a teaching example, not machine test data. Values are neither alarm thresholds nor acceptable limits. Assume both records come from the same applicable controller during one power-on session, without clearing, reset or gaps in the record:

Field	Record A	Record B	Supported finding
Servo comm err Num1	2	5	Three additional xx04 occurrences recorded in this window
Servo comm err Acc1	12	15	Cumulative increase of three agrees with that change
Servo comm err Num2	0	0	No increase observed for xx03
RIO retry count max 1	4	4	Maximum unchanged; zero new errors cannot be claimed

Report “xx04 records increased by three; physical cause undetermined,” not “the cable failed three times.” The cumulative increase does not represent three further independent faults. If A and B span a power cycle or clearing operation, this difference analysis is no longer valid; separate the observation windows. Conflicting changes call for checking transcription, error type, controller identity and clearing/power-on times, not guessing missing history.

Turn readings into useful maintenance evidence

1. Save complete screenshots, timestamps, controller model and software version together with the actual alarm text and suffix. Record known power-on, clearing and maintenance times. Mark unknown information as unknown.
2. Keep Num1, Acc1, Num2 and Acc2 separate. For RIO, preserve both channel/station pairs with their respective counts and identify the equipment segment each station represents.
3. If all you have is a historical nonzero value without comparable windows, retain it as evidence of a past discrepancy, not a finding of ongoing errors. With a comparable increase, correlate alarms and machine states at the same time to narrow the investigation.
4. Counters alone cannot distinguish connector contact, cable, interference, power-supply or unit faults. Qualified personnel must plan physical checks using the machine and relevant drive/I/O manuals; one number does not justify a replacement decision.

Stop conditions and reference

The clear menus on pages 96–97 change the evidence. Clearing is not a repair and must not precede preservation of records. If a clearing confirmation is entered accidentally, stop further input and follow the machine builder's procedure; do not confirm just to see the result. Handle unexpected motion or active alarms under the machine's safety procedure. Cabinet, cable and connector work requires the specified power isolation and residual-energy verification. These counters do not establish safe isolation.

Mitsubishi M800/M80/E80 Series Maintenance Manual IB-1501273-L, revision L, August 2023, §4.5.1: printed page 94 covers screen and part-system scope; page 95 defines communication fields; pages 96–97 cover clear menus. Field definitions follow the manufacturer. The hypothetical calculation, comparison conditions and evidence reasoning are editorial analysis, without machine testing or a finding about the cause of any particular machine fault.