Akai 1720L solid state

[Dorian27]

The above machine on rewind of a 6"tape stops rewinding about an inch before end of tape it refuses to rewind the last inch or so I here a click like a relay going and it stops rewinding.But if I change the tape speed switch on the top it will rewind the tape all the way with no problem any ideas what it may be please

[Michael Maurice]

When it stops rewinding, is the capstan still rotating? If it is then its mechanical, if it isn’t then the motor is stalling. Replace the motor run capacitor if it hasn’t been done already.

[Dorian27]

No the capstan is rotating ok

[Michael Maurice]

More likely the idler wheel rubbers have gone hard an are slipping, there's more inertia at the faster speed to carry it through.

[Dorian27]

I slakend the tape guide bearing and it seemed then to rewind ok whether it was a coincidence or not I don't know

[Dorian27]

It rewinds ok as I said if I change tape speed to slow from fast

[Radio Wrangler]

I'm trying to remember.... I think the 1720/1721 changes the number of motor poles to change its speed, so there may be more torque available on the lower speed setting. The 4000 series keeps the same motor speed and adds a sleeve to the capstan itself.

David

[joebog1]

The 1700 series of recorders changed capacitors on the motors to change speeds as per my attached photo. Michael has the problem explained. Rubbers in Akai equipment always went hard and were renowned for slipping.
These motors also ran on 100 volts ( about) directly connected to mains on 110 volts, and connected to the 110 volt primary tap of the power transformer when connected to 240 volts.

They also had two other very common faults:
1: there is a monkeymetal/zinc diecast cam that operates the moving parts when changing from play to fast forward and rewind that is famous for crumbling into small pieces
2: the record/playback slide switch frequently went open or partly open circuit. This caused low level recording, or low level playback and is a real $%^$& to diagnose!!.

Joe

[ms660]

Originally Posted by joebog1

The 1700 series of recorders changed capacitors on the motors to change speeds as per my attached photo.

Not according to a schematic I'm looking at unless I'm mistaken, they switched windings.

Lawrence.

[Michael Maurice]

There are two motor run capacitors, the main one and another smaller one which is switched in for 50Hz operation. Capacitors are NOT changed for speed switching.

Speed change is effected by switching from 4 - 8 pole operation.

[joebog1]

Apologies gentlemen!!
I do stand corrected.

Joe