I have recently purchased and fixed a WM-EX655 though it still has flutter audible in the higher frequencies and a speed difference between tape sides. - Cleaned belt path/pulleys, head, pinch rollers, and capstans with IPA (isopropyl alcohol) - Replaced belt with proper size and has no visible deviations - Oiled motor and capstan bushings - Cleaned and replaced oil on all gear shafts and pinch roller shafts - The pinch rollers look practically like new, though I have not replaced them - The capstans are rough and not polished. While I'm not able to measure wow & flutter, it's easy to hear higher frequencies wavering. When the tape is played off the larger diameter capstan it's played a little slower. The smaller diameter capstan plays the tape slightly faster. Increasing the spring force on the small capstan pinch roller and oiling all shafts helped with the speed difference but it's still noticeable. Not entirely sure where to go from here besides buying new pinch rollers, though I doubt that will have any effect. Any suggestions?
Some speed difference is normal to exist on most autoreverse walkmans, if it's within 30Hz or so would consider it normal. This difference can be caused by an increased load from the geartrain or significantly higher pressure on one of the pinch rollers. Even corrosion in the capstan bearings can cause a significant slowdown which won't be obvious when spinning the flywheels by hand. This is why it's important to clean the inside of bushings with IPA before re-lubricating. Given you say it's high frequency flutter, I would look into the flywheel (FWD one) drive gear as this is a typical point of failure on EX series which would create this symptom. Wouldn't go for new pinch rollers as those will create low frequency wow not flutter.
I managed to get a hold of donor unit that had an almost new flywheel drive gear which ended up helping a little, but I'm still getting about 0.55% RMS in both directions. I cleaned out the motor pulley again as it had some old belt but had no effect. Any other ideas on what could be causing the flutter?
Fact you have the same 0.55% in both directions is suggesting the geartrain is not the root cause of the problem. This is assuming the belt is not too tight or too stiff, case in which a problem from the geartrain wouldn't be attenuated much by elasticity of the belt. Have you measured the W&F figure before replacing the flywheel ? Would be interesting to know how much it changed. What belt are you using ? Does the motor feel free without any roughness when you rotate it by hand (without a belt installed) ? Can you post a WFGUI screenshot to see the actual waveform ? When looking at the waveform, are there any infrequent (occuring once every couple of seconds) peaks that can be noticed ? I suggest to run the walkman with case removed and carefully listen for any abnormal noises in the mechanism.
