TENMA 72-5016 Function Generator

[Ketema]

Hello guys! Hope every one is oky!

Four months ago I purchased a broken TENMA 72-5016 5MHz function generator from Ebay. The advertisement said it doesn't power up and was sold as is. But after looking around inside the instrument a simple fuse replacement brought it back to life. But recently I can't seem to adjust the output frequency beyond multiples of 5 and 7 using the frequency adjustment pot. That is, it can only output 5 to 7Hz on the ones range, 50 to 70Hz on the 10th and 500 to 700Hz on the 100th range and so on.

I changed the Pot but that didn't fix it. What I was hoping from you guys is to share a service manual for it if you do have one as that would greatly simplify finding the fault. By the way, I did search every where in the internet but couldn't locate any manual.

Thanks you for any help you provide in advance!