Well you just gotta love adventures with old cassette decks. Recently I noticed there was some slight speed flutter with recording/playback of this deck. Didn't think too much of it as it was ever so slight on high notes and could have possibly been the tape itself etc. I put my 3khz test tape in and sure enough, clear as day, the flutter was there. It has been annoying me more and more as I record different types of music with this deck, and although the sound quality is up to spec after further adjustments, its just not good enough when it comes to the speed flutter. Its ever so slight, like a vibration in the tape transport mechanism.
Anyways, I did the following to try and fix this:
Pulled down the mechanism, re-lubed and cleaned everything, capstan shafts, flywheels, pinch roller arms and bearings etc.
Cleaned the main capstan slave belt and pulleys.
No difference.....
Cleaned pinch rollers and tape path several times, resurfaced pinch rollers, cleaned again. Checked speed, quartz lock functioning perfectly, but slight flutter still there.
Increased pinch roller pressure on both supply take up rollers individually. No difference. Put it back to stock pressure.
Disengaged supply capstan while playing, made it worse, disengaged take up capstan while playing, made it worse
Stopped take up reel momentarily while playing, flutter goes away for this brief moment.
Excessive take up reel torque suspected.
Voltage check on reel motor, read 4 volts as per manual in play mode.
Check voltage during ff/rew mode, read 5 volts as per manual.
Took off reel motor and cleaned pulley, de-oxed inside of motor, lubed main motor bearing, re-assembled, problem still there.
I have no idea how to reduce the voltage of the reel motor to make the torque less during playback, and even if I did the problem could still be there, as flutter only disappears when reel motor is stopped.
So really, I have no idea how to fix this machine as have tried every trick within my knowledge. The reel motor/pinch rollers could also be replaced but it comes down to money I don't have, and a good possibility that it won't fix this issue.
I did get a quote from a professional to fully restore the deck including audio stage and capacitor upgrades, but after postage is factored in, it would come to over $1000, its just not worth it. Would be much better off buying a Nakamichi BX-300 or ZX-9 and leaving it at that, but that's not going to happen anytime soon.
So, I will be getting my trusty JVC TD-V661 fired up to re-record the 15 hours of tape that I have done in this Denon, at least the speed is true on it and recording quality almost as good, it just doesn't have that lovely Denon sound that I like. I thought I had the Denon sorted until this flutter issue became more obvious as time passed. I guess they can't all be winners, however the JVC was truly a winner indeed as it was cheaper and has been extremely reliable requiring only a capstan belt.
I don't think I will be purchasing any decks off the bay anymore as my luck has simply run out, but have had some good decks come along in the past that only needed basic tuning, unfortunately not this Denon DR-M4. My next purchase (much later down the track) will be from a Professional who restores decks for a living.
Time for some rest, am exhausted from troubleshooting this thing.