if the original value of the asset is 689.68 but only 114.91 has been depretiated. What would be the entry at the time of sale of the asset for 650.00? Would it be this:

Acc. Dep 114.91
?? 114.91

Asset 574.77
gain on sale 75.23
Cash 650.00

Should I credit dep. Exp. Account for the 114.91?

You're almost there, DrDrea. Note that the "Asset" account should be credited for the original cost of the asset. Remember that you need to zero out that account in recording the sale, and that account should have the asset's original cost in it, just before the sale.

Adjust your entry accordingly, and you've eliminated the need for that mystery "plug" entry. Good luck,

Debit Disposal 574.77
Debit Acc. Dep 114.91
Credit Asset 689.68

Debit Cash 650.00
Credit Gain on disposal 75.23
Credit Disposal 574.70