Returning MIN Row_Number() SQL - sql

Question

This is probably the clunkiest query I have ever made. I have to use a read-only account so I can't use temp tables or anything to make this easier. The goal is to return the MIN(RowNum) when sumPiecesScrapped = maxSum. I have tried adding the entire query into another subquery trying to return the MIN(RowNum) however, it is one-to-many that is tied to the primary key JobNo and when I tie it to JobNo and StepNo it gives me the same result as the one below.
SELECT
JobNo,
StepNo,
sumPiecesScrapped,
maxSum,
CASE
WHEN sumPiecesScrapped = maxSum THEN ROW_NUMBER() OVER(PARTITION BY JobNo ORDER BY JobNo, StepNo)
ELSE 0
END AS RowNum
FROM
(
SELECT
JobNo,
StepNo,
sumPiecesScrapped
FROM
(
SELECT
JobNo,
StepNo,
SUM(PiecesScrapped) as sumPiecesScrapped
FROM
(
SELECT
JobNo,
StepNo,
PiecesFinished,
PiecesScrapped
FROM TimeTicketDet
) tt2
GROUP BY JobNo, StepNo
) tt3
GROUP BY JobNo, StepNo, sumPiecesScrapped
) tt4
LEFT JOIN
(
SELECT
JobNo as tt5JobNo,
MAX(PiecesScrapped) as maxSum
FROM
(
SELECT
JobNo,
PiecesScrapped
FROM TimeTicketDet
) tt5
GROUP BY JobNo
) tt5
ON tt5.tt5JobNo = tt4.JobNo
WHERE tt4.JobNo = '12345'
Result:
+-------+--------+-------------------+--------+--------+
| JobNo | StepNo | sumPiecesScrapped | maxSum | RowNum |
+-------+--------+-------------------+--------+--------+
| 12345 | 10 | 0 | 5 | 0 |
| 12345 | 20 | 1 | 5 | 0 |
| 12345 | 30 | 5 | 5 | 3 |
| 12345 | 40 | 5 | 5 | 4 |
| 12345 | 60 | 5 | 5 | 5 |
| 12345 | 70 | 5 | 5 | 6 |
+-------+--------+-------------------+--------+--------+
Desired Result:
+-------+--------+-------------------+--------+--------+
| JobNo | StepNo | sumPiecesScrapped | maxSum | RowNum |
+-------+--------+-------------------+--------+--------+
| 12345 | 10 | 0 | 5 | 0 |
| 12345 | 20 | 1 | 5 | 0 |
| 12345 | 30 | 5 | 5 | 3 |
| 12345 | 40 | 5 | 5 | 3 |
| 12345 | 60 | 5 | 5 | 3 |
| 12345 | 70 | 5 | 5 | 3 |
+-------+--------+-------------------+--------+--------+
Other Possible Result:
+-------+--------+-------------------+--------+-----------+
| JobNo | StepNo | sumPiecesScrapped | maxSum | RowNum |
+-------+--------+-------------------+--------+-----------+
| 12345 | 10 | 0 | 5 | 0 |
| 12345 | 20 | 1 | 5 | 0 |
| 12345 | 30 | 5 | 5 | Something |
| 12345 | 40 | 5 | 5 | 0 |
| 12345 | 60 | 5 | 5 | 0 |
| 12345 | 70 | 5 | 5 | 0 |
+-------+--------+-------------------+--------+-----------+