Is logarithmic scale in power BI possible?

Try using a Start value of 0.1

I had struggled with a similar issue - I had set up a combo chart (line + stacked column) with a log scale and it worked fine... but when I made some unrelated changes to some of my measures, the scale changed back to linear!

When I checked the Format panel, the Y-axis option for Scale type no longer showed "Log". Instead, it had a yellow triangle, with the tooltip message: "Can't apply log scale - The axis changed to a linear to accommodate both negative and positive values. To use a log scale, remove one set". 

NOTE: I am confident my measure values did NOT have any negative values - I used a table visual to manually inspect the data. Then I even wrapped my measure in an IF statement to check if the measure value is < 0 and, if so, set the measure value to 0.  But I still got the same error message.

Based on the advice in this forum, I tried entering a non-zero value in the start value, but unfortunately that did not work.

However, if I changed the Start field to a value *between* 0 and 1 (I started with 0.1) then it worked! The Log scale was magically back.

I then discovered that by changing the Start value (0.01, 0.001, etc.) I could change how "steep" the log axis values changed.

I did an extensive web search about this issue, but this forum was the closest I found to a solution.

Hopefully this modified workaround works for others.

EDITED: to add my current version: 2.59.5135.421 64-bit (June 2018). I don't know if this workaround will work in other versions.