When you are ready to perform an action that you want to trace, activate the VTAM buffer trace for the Mainframe Access ACB. You do this using a z/OS Modify command to VTAM. In this example the VTAM JCL procedure name is VTAM. The name may be different on your z/OS system. The only other thing you may want to change is the ID= parameter so that it specifies the name of your Mainframe Access VTAM ACB.
F VTAM,TRACE,TYPE=BUF,ID=MFM62ACB,AMOUNT=FULL
IST097I MODIFY ACCEPTED
IST1515I BUFFER TRACE ACTIVE
IST1144I TRACE INITIATED FOR DDINET1.MFM62ACB 316
IST1045I NODE TYPE = APPL
IST314I END
GTF should now be up and running and VTAM should be creating TYPE=BUF trace records for any activity associated with MFM62ACB. If someone has previously started a TYPE=BUF trace for another VTAM resource and did not bother to stop the trace, these records may also appear in the trace data set and complicate the analysis of what you are tracing.