Hello there, i recently got my Hands on a minty WM-GX670 which sat for years in drawer somewhere. Beside some minor scuffs it looked like never used much. Head, Pinch Roller and Capstans looked very clean and after giving them a proper cleaning and demagnetized the heads, i tested it. I noticed that the Tape could play but FF and RW wasn't possible, pointing to a worn out Belt. I ordered one from "FixyourAudio", together with fresh Pinch Rollers and after replacing everything and adjusted the speed for the new Belt, i took the unit for another test drive. I put a 90 Min Cassette in and let in play through the whole Tape, so the new belt can adjust itself. The Sound on FWD Playing is very crisp and clear. However, Reverse Playback sounds a little bit muffled with Trebles taking a hit in comparison. Things are worse on the Beginning of the Tape, taking around 1 minute of Playtime for the Levels to get better. I double checked the contact between Pinch Rollers and Capstans and they look OK. I even compared the positions on my WM-EX678 which uses the same exact components, besides missing the Erase Heads and they are identical. It looks like an Azimuth Problem to me, but unfortunately, adjusting it on this unit is impossible. Any thoughts or recommendations for what to look next? Thank you in Advance!
Indeed it does seem to be an azimuth problem, but I wouldn't necessarily suspect a tilted head (especially on those units that don't have adjustemnt screws). I would do the following: try to run the unit with the cassette door removed (and cassette pressed with your fingers) and observe if there is any tape curl occuring at the reverse pinch roller when looking perpendicular to the cassette. The fact that the problem goes away after the first minutes is also indicative of a pinch roller/capstan curling the tape up or down and not a tilted head. It is possible that there is an uneven wear on the capstan (not visible to the naked eye) in a spiral form, that tends to pull the tape up or down. If that is the case, roughening the capstan with ferric chloride usually solves the problem. If you decide to do this, use a cotton swab and immerse it in the solution. Then rotate the capstan (manually from the flywheel below) while rubbing the solution against the capstan until it's no longer shiny. You only need to do the center part that's in contact with the tape. Then you clean the capstan thoroughly of any remaing solution and try again.
@Valentin: Just tried to play a clear Case Tape with the door remove, like you suggested. I couldn't see any curling of the Tape but i noticed, when i was applying more pressure on the tape, more stable and clearer the Sound was, but only on Reverse Playback. It didn't matter much on FWD Playback. I made a macro Picture of the Reverse Capstan for you to take a look:
I see, those capstans are the type that already have a deep roughening from the factory. The macro picture is a very good reference in this regard, so a potential capstan/roller issue can be excluded. The fact that when you press on the cassette the situation improves may indicate the cassette itself does not stay straight into the carriage. There should be some metal springs in the carriage itself and also one on the back of the cassette (where recording tabs are located). Double check that those are keeping the cassette firmly in place (and also not on an angle) when the door is in closed position. Something mechanically bent (carriage, frame) can't be excluded.
UPDATE: With @Valentin 's valuable help and Advice i checked some things out and realized the Reverse Pinch Roller wasn't perfectly aligned to the capstan. By flipping the Pinch Roller, the alignment became much better and Sound Quality became somewhat better. Then i grabbed my EX-678 and compared the Quality on it and saw a pattern. On Reverse, the Treble Levels on it are also slightly lower in Comparison to Forward Playback! Maybe this is how it is on these units which share this Mechanism?? Can someone test it and report back?
