Resources referenced:
Sharp GF-777 Disassembly Instructions Manual
I found no detail information on how to replace the pinch rollers, so I will write about that so you can use this as a reference to replace your GF-777’s pinch roller.
This is my Sharp GF-777. This model is considered “the holy grail of all boomboxes”. My unit has loose belts and friction wheel belts, and both pinch roller were very slippery as well. So I went to 闲鱼 (Chinese online second hand market app which is also friendly to personal and casual sellers of other stuff including brand new items) and bought new belts and pinch roller.
The main goal of this restoration is to repair all tape functionalities, and perform a thorough cleaning on the exterior parts.
Still using my trusty pillows to cushion the machine.
Steps to Replace Pinch Roller
This operation is performed on the FRONT side of the tape mechanism block. This operation does not interfere with replacing belts, and can be performed either before or after replacing belts.
Follow the service manual or the PDF by Bobby Jenkins all the way until you have taken out the tape mechanism block.
On the front side, for each deck, remove 4 screws holding the keys assembly. Cut any offending zip ties, redo them after reassembling.
Slightly rotate the keys assembly towards the front of machine, then slide the keys assembly down to remove.
Now you can access the pinch roller assembly. Undo 1 small spring on the pinch roller assembly pivot point.
Remove the circlip using specialized tool or a very small flat screwdriver by prying away from the pin. Be carful that the circlip may fly out, so put your other hand around it, do not lose it. Also remove and collect the washer under the circlip.
Pinch roller assembly should be free now.
Remove pinch roller assembly, punch out pinch roller shaft(pin).
Images showing pinch roller removed and new pinch roller (generic one, works fine).
Put in new pinch roller, insert pin back. On a vise, clamp a small metal cylinder to put against the pinch roller shaft hole. Carefully hammer in the pin from bottom.
Now you have successfully replaced the pinch roller. Reassemble the front of the tape mechanism block in reverse order. Note that it may take some effort and jiggling to reinstall the keys assembly.
Replace Belts and Friction Wheel Belts
This part is pretty straightforward and well documented in the PDF file by Bobby Jenkins which I have linked on the top of the page. Here are some photos from my take.