1. Customer agrees to pay deposit of 100
When the deposit is initially entered, the following accounting entry is created:
Dr. Receivables (Deposit) 100
                                Cr. Unearned revenue 100

2. Goods of 40 is sold to customer and thus an invoice of 40 is created and applied to deposit of 100.
These accounting entries are created:
Dr. Receivables (Invoice) 40
                               Cr. Revenue 40
Dr. Unearned Revenue 40
                               Cr. Receivables (Invoice) 40
Net effect is:
Dr. Receivables (Deposit) 100
                               Cr. Unearned Revenue 60
                               Cr. Revenue 40

3. Customer sends Payment of 100 against the deposit
This accounting entry is created:
Dr. Cash 100
                               Cr. Receivables (Deposit) 100
Net effect is:
Dr. Cash 100
                               Cr. Unearned Revenue 60
                               Cr. Revenue 40