I found a Sony EX-555 which was described as working on and off. Hoping that a new belt might make it play again I bought it and got a belt and a service manual. Replaced the belt and re-assembled it and cleaned tape path and rollers with IPA. It sounds great but it seems to prefer playing the A side, sometimes just reversing play direction on it's own and then eating tape by pulling it into the capstan/roller. I can't see tape moving, just whether the wheels turn, thanks to the tiny window. So I can't really tell what's happening until I open it up and find a mangled Maxell XLIIS! The pinch rollers cleaned up easily and look soft and pliable. Not sure what to check next...
Usually a common problem I see when Walkmans eat tape is that the take-up reel is not functioning properly. Let's try to isolate the problem. Remove the lid from the head assembly and run a thin (90-100 min) sacrificial tape while holding the head assembly in place (so it's playing normally with the front lid off). Observe which pinch roller eats the tape, and when it does so, if the take-up reel on that side is turning properly. If you see the reel stop turning for any reason (which can cause the optical sensor to auto reverse), take note and cut power. Remove the board until you can see the mechanism, and look out for cracked gears, broken clutch assembly. try turning the reel pulley by hand and see if it turns the reels smoothly. The take up reel needs to be turning slightly faster to take up any slack past the capstan, and any excess take-up reel speed is controlled by the clutch assembly, which allows for slip. If you rule out the reel mechanism, look for any signs of tape skew as well (use a tape with a transparent shell). Sometimes a broken tape guide or other misaligned head block component can cause skew.
Bub- thanks for the advice! Before taking the lid off I was observing mechanism action (as much as I could see anyway) and I did notice that one hub would stop moving shortly before the auto-reversal. Unfortunately I have a new problem. There is no response when I push buttons, as though there is no power. I tried replacing the battery with no luck. I'm about ready to toss this thing in the garbage! PS- I just noticed this was accidentally posted in boomboxes...it should be in walkman forum instead.
Check the tape detect switch, usually on the opposite side of the heads. Use a multimeter and see if power is going to the main board.
Thanks again Bub, I checked the tape detect leaf switch. I can see it is getting actuated when tape is inserted. Not sure why but the buttons aren't responsive. After some fiddling it did start to play but I couldn't stop it with the controls. So I just let it play and observed the tape path as best as I could. The tape path seems fine to me. It finally stopped playing when I turned the deck over for a look at the other side. After more fiddling and experimentation with different ways to hold the tape head assembly while pressing the buttons. An extra hand would be nice right now.
