YM:S7 Diagnostic

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1 Diagnostic Buffer

If you have any OB Alarm of PROFIBUS fault, check the Diagnostic Buffer first to get more details.

The PLC Stop reason will be also explained there.

File:S7 Diagnostic Buffer start.jpg

• Click on Diagnostic Buffer

File:S7 Diagnostic Buffer Contents.jpg

• Check the PLC Time and Date Settings to validate the time stamps. It is in the same screen if you click on Time System

File:S7 Diagnostic Buffer PLC Time and Date.jpg

2 OB Fault/Messages

OB No	Start Event	Cause	Remedy
OB1	End of startup or end of OB1, Free cycle
OB10 - OB17	Time-of-day interrupt 0-7, No default time specified
OB20 - OB23	Time-delay interrupt 0-3, No default time specified
OB30	Cyclic interrupt 0 (default interval: 5 s)
OB31	Cyclic interrupt 1 (default interval: 2 s)
OB32	Cyclic interrupt 2 (default interval: 1 s)
OB33	Cyclic interrupt 3 (default interval: 500 ms)
OB34	Cyclic interrupt 4 (default interval: 200 ms)
OB35	Cyclic interrupt 5 (default interval: 100 ms)
OB36	Cyclic interrupt 6 (default interval: 50 ms)
OB37	Cyclic interrupt 7 (default interval: 20 ms)
OB38	Cyclic interrupt 8 (default interval: 10 ms)
OB40 - OB47	Hardware interrupt 0 - 7
OB55	Status interrupt 2 DPV1 interrupts
OB56	Update interrupt 2
OB57	Manufacturer specific interrupt 2
OB60	SFC35 "MP_ALM" call 25 Multicomputing
OB61 - OB64	Synchronous Cycle Interrupt 1-4
OB65	Technology synchronization
OB70	I/O redundancy error (only in H CPUs)
OB72	CPU redundancy error (only in H CPUs)
OB73	Communication redundancy error OB (only in H CPUs)
OB80	Time error	Asynchronous error
OB81	Power supply fault
OB82	Diagnostic interrupt	Diagnostic of modules (e.g. Safety) failed	* if it's a safety module, check for short circuit on the In/Outputs * if safety module, check in HardwareConfig -> Module Properties -> Parameters -> Channel x,x -> Discrepancy time (ms), this should adapted to the hardware (e.g. switch with 2 seperate contactor, maybe cannot close in 10ms)
OB83	Insert/remove module interrupt	Module was removed	* check that the module is pluged in a right way
OB84	CPU hardware fault
OB85	Program error
OB86	Failure of an expansion rack, DP mastersystem or station for distributed I/Os
OB87	Communication error
OB88	Processing interrupt
OB90	Warm or cold restart or delete a block being executed in OB90 or load an OB90 on the CPU or terminate OB90
OB100	Warm restart	Startup	Normal for S7-300
OB101	Hot restart	Startup
OB102	Cold restart	Startup	Possible for S7-400
OB121	Programming error		FAULT!! * Program want to read from a unkown address (on the plc)
OB122	I/O access error	Module or Node not online	* Check Hardwareconfig * Check Profibus Connector/Cabel *

3 OB 121 Programming Error Quickfix

On a OB121 Error open the plc "module information" -diagnostic buffer.

3.1 OB121 Diagnostic with plc stop

In case you cannot find the fault and it is possible to STOP the plc then

• bring the plc to run
• go to "Blocks"
• go online
• delete the OB 121 (The plc will go to stop immediatly)
• open "module information"
• in the tabulator "Stacks" you can find where the OB121 were created.

3.2 OB121 Diagnostic without FC number

In case you have like this:

Area length error when writing
Instance DB, double-word access Access address: 996
Requested OB: Programming error OB (OB121)
Priority class: 1
Internal error, Incoming event

Find the highest number of "Access address" (e.g. here 996) Add +36 (header-offset) (996 + 36 = 1032), search for an DB (offline) which length is near the 1032.
The cause is, that variables was added in an instance DB, but was not downloaded to the plc. The "Access address" is the address of the variable which is not declared in the online DB. There is "double-word", maybe the variable is a "real".

4 PLC LED Diagnostic 319F-3 PN/DP

LED	Description	Cause	Remedy
SF	Summery Fault	Fault present
MAINT	Maintance Required	Wrong adjustment of the profinet configuration	* Check if a sinamics CU is double assigned (See Sinamics Commissioning -> Troubleshooting)
DC5V	?	?
FRCE	Force	Force is active	If not needed delete force
RUN	Plc Program Run	Normal status
STOP	Plc Program Stop	* Mode Switch is in "STOP" postion * Program stopped because of program fault
BF1	Bus Fault 1	Profibus Fault	check Profibus Mastersystem connected to X1
BF2	Bus Fault 2	Profibus Fault	check Profibus Mastersystem connected to X2
BF3	Bus Fault 2	?Profinet Fault	Check in the Hardware config the profinet slaves

5 PLC LED Diagnostic 416F-3 PN/DP

WOK/EEA: I do not have a 416 on my table right now but this type should also be considered here in this tables, and it will be for sure different from a 319 type

LED	Description	Cause	Remedy
SF	Summery Fault	Fault present
?	?	?	?
DC5V	?	?
FRCE	Force	Force is active	If not needed delete force
RUN	Plc Program Run	Normal status
STOP	Plc Program Stop	* Mode Switch is in "STOP" postion * Program stopped because of program fault
?ExtF?	?	?	?
?BF1?	Bus Fault 1	Profibus Fault	?
?BF2?	Bus Fault 2	Profibus Fault	?
?BF3?	Bus Fault 2	?Profinet Fault	Check in the Hardware config the profinet slaves

6 Monitor/Modify Variables

To check IO's and internal variables open the "Monitor/Modify Variables" Table.

File:S7 steuernVar1.jpg

Enter the address of the variable you like to monitor. Click on the "glasses" to establish an online connection to the PLC.

File:S7 steuernVar2.jpg