You go in from the front of the machine. You may have to take the case off to get at minor things, but access to the counter and belts is from the front. See page PL 7 in your Service Manual's parts list section, section "F" Brake System.
The front panel of the A77 comes off very easily, just follow the directions in the front part of the service manual (page 6, section 3.2). Put on your thinking cap, move slowly and carefully, and take your time and you'll do just fine. Pull gently, but firmly on the cover panel (front panel) when taking it off. Pull on the upper edge after removing the two screws the manual says to remove. You can see, in the manual, the "retainers" or clips that are going to be holding the front panel on, they are the three black cylinders sticking up from the top of the front of the bare chassis, in the diagram Fig. 3.5-6, on page 7 of the manual. The top of the machine is nearest you in that diagram.
Judging by the exploded parts diagram on page PL 7, it looks like you'll need to take off the front panel, the take-up reel table, and the brake hub below that. So far we're talking about only 4 more screws than just taking off the front cover. And it looks like only two more screws to get the counter off, if you need to. Should be easy work if you take your time and work carefully after studying what you need to do.
Again, and I can't emphasize strongly enough: take your time, study the manual and diagram well, and be careful and thoughtful as you work. You'll be fine.
Be very, VERY careful with the brake band around the brake hub. Lift the hub out very carefully. Don't touch the hub lining or the band with your fingers (finger oils) or anything oily or greasy. Put the hub back in very, VERY carefully to avoid bending or kinking the band. The brake bands are very thin and if distorted can give you no end of headaches.
