Akai GX4000-D reel-to-reel speed problem

[Nickersby]

Hi,

Looking for advice on fixing this issue. Playback speed is fine until the tape has played about 3/4, then the speed starts fluctuating, as if it can't cope with the weight of tape on the take-up spool.

I've cleaned and lubricated the idler wheels, and also disconnected and tested the motor run capacitor, which read 2.6uf. Could the capacitor be faulty even though it measures the correct capacitance? What should I try next?

Thanks for any help.

[Radio Wrangler]

It could be the increasing tension from the drag brake on the supply spool as the tape diameter on that spool diminishes. This can expose problems with hardened pinch wheels and pinch wheel springs. The Akai 4000 family use a capstan sleeve to get 7.5 ips, which means the pinch wheel position varies a bit and 7.5 ips gets more pressure than 3.75 ips.

Another possibility is the slipping clutch on the take-up spool drive grabbing, but that would be most troublesome at the beginning of playing a tape.

So check feed tension, check pinch wheel condition, check pinch wheel pressure, check take-up tension.

It's probably long past clean and re-lubrication time.

David

[Nickersby]

Thanks David. I'm a novice at all this, but I'll try and check what you suggest.

[ben]

I've always found the backtension on these decks to seem a bit high, but they do not have pressure pads so it is relied upon for good head-tape contact. Might be worth checking according to specs.

My best guess is that the rubber pinch roller is past it. Try gripping it in the chuck of a drill with a nut/both through the centre, sanding it down with fine sandpaper to remove the outer rubber.

[Michael Maurice]

Be careful adjusting the spool tensions as it affects braking as well.