door will not open unless I hold down the opener button, all-o-matic RS

[manutd20]

I have an older garage door opener, an all-o-matic RS model. A few days ago an issue came up where the door will not open without me holding the button down to open it. If I press the button, the door only opens up a few inches and then stops. Once the door is completely up, I can press the button just once to close it...no need to hold it down the whole time. Same thing with the remote ( allister delta 3 ). There are no safety sensors on the door. Any ideas how I could fix this issue ? Does anyone know where I could find an instruction manual for this old opener ?

Thanks

[TJR]

It might be a relay going bad, but not 100% sure. Anyway if you need to replace any parts in the opener you will have a hard time finding them if any.
Before you spend too much time and money, think about a new opener. All-O-Matic +20 years it have done a good job.
Also check your spring/s, close the door and disconnect it from the opener and open/close the door by hand. You should be able to do so without major effort.