How to convert *DEDUCTIBLE* IRA to Roth

I have an old IRA funded with pretax dollars (from 20 years ago).  I would like to convert some of it to a Roth.  I was told that the backdoor Roth process can accomplish this, but every suggestion only relates to new NON-DEDUCTIBLE  IRA contributions which are immediately converted to a Roth.  My situation is different since I am starting with IRA funds which are pre-tax dollars. 

 

When I try to follow the "non-deductible IRA to Roth" instructions, I always wind up with an excess contribution penalty. I know that I will have to pay basic income tax on my IRA withdrawal, but I am not expecting the excess penalty.

 

I have been trying to figure this out and in the process, I have created 10 different returns and in each one, I try to adjust my Roth contribution answers in some tiny way to try to find the magic combination, but no luck. Always, I get the 6% penalty for excess contribution.   I felt sure that it is possible to convert a deductible IRA to a Roth without penalty, but I can't figure out how.  I also can't find a TT community answer for this exact situation.

 

As a little background, yes, I entered the Roth conversion in the "deductions & credits" section of TT first, and THEN I entered the 1099-R information in the "Wages and income" section. 

 

Does anyone have any suggestions?