Stevie Mambor was held on remand for more than 18 months after he was accused of paying a 15-year-old girl cash and cannabis for sex.

But an ACT Supreme Court jury this month found the 58-year-old man not guilty of having sexual intercourse with the girl.

Instead it convicted him of intentionally possessing child pornography - an image that found on his phone depicting him engaging in a sex act with the teen.

The trial hinged on whether Mambor knew the girl was just 15 when they had intercourse.

She told the jury she had initially lied, telling Mambor she was 18, but said he had kept up their sexual relationship after she had told him the truth.

Mambor, however, said he broke off the relationship with the girl as soon as he learned the truth when he discovered her ID in her bag.

Police arrived at Mambor's Allawah Court flat in April last year armed with a search warrant.

They found Mambor, the alleged victim and another girl at the flat.

A subsequent search of his phone revealed the offending image.

Mambor was arrested and remained at the Alexander Maconochie Centre until the end of his trial this month.

At the time of his arrest Mambor was subject to a good-behaviour order, having pleaded guilty to committing an act of indecency in the presence of another 15-year-old five years earlier.

In April 2010 Chief Justice Terence Higgins sentenced Mambor to six months, wholly suspended, largely due to his poor health.

He admitted supplying the girl cannabis and wine until she passed out, and touching the inside of her thigh as she dozed.

But the girl would later tell police she had lied about her age, telling him she was 16.

An initial, more serious charge was subsequently amended and there was no longer any allegation he was aware of her real age.

Justice John Burns, when sentencing Mambor for the child pornography offence on Wednesday, cancelled the good behaviour order from 2010 and activated the jail sentence.

But because Mambor had been behind bars from April last year he was considered to have already served his time.

The court also heard Mambor had a heart condition and had suffered two heart attacks while he was on remand.

Justice Burns took into account the fact the image was not published in any way, the girl willingly took part and Mambor had the photo in his possession for just a few days.

He convicted Mambor and imposed a 12-month good behaviour order with conditions to take part in counselling and programs to address his cannabis use.