Dear Student:
In writing minutes (of a meeting, I presume), you are reporting what was discussed during the meeting. So in some of your examples, you can use present tense when speaking of ongoing activities when that present-tense verbiage is embedded in a statement using past tense. Or you can just use present tense throughout, such as "Mary/Jane/Sally reports that sales are increasing (have increased, will increase, etc.). The determining factor is the style used in your organization; you can either follow the style used in previous minutes or discuss how you want to change that style with those above you.
Example 1. The team is checking on the machine. (Should it be: The team was checking on the machine)?. You could say: Nancy (or whoever is stating this information during the meeting) reported/stated/said [choose one] that the team is checking on the [operational status of the] machine [and will report back at a later date]. {or something to that effect}
Example 2. Checks on the system are being done. (Should it be: Checks on the system was being done). This is a restatement of the sentence above and the same answer applies--i.e., Nancy reported that checks on the [operational status of the] machine are being done. Please note that "checks" is a plural subject, so the verb must be plural (not "was").
Example 3. When something is not certain. Example : - If there is sufficient data to support the efficiency of the new system... (Should it be: If there was sufficient data to support the efficiency of the new system...). You need to complete the rest of the sentence and rewrite it to know what tense to use. Are you saying that "John reported that if sufficient data are generated that support the efficiency of the new system, then [more funding will be committed to the project]"? {or something to that effect?}. You are stating a conditional and therefore usually you should use "were."
Best regards,
Louise
English/ESOL tutor