hifi engine

Akai 646 problem

Hello .. I am new to this nice place. I actually acquired an AKAI GX 646 . It looks in a very good shape except that it needed a lot of cleaning. the problem is that it fast forwards and rewinds but it doesn't play, although the play lights in both directions light up and I can hear a strong click but it doesn't spin. I had a look at the capstan motor and it doesn't spin although it runs freely when spun by hand. The pinch roller engages verywell. I am frustrated because no repair shop in my country wanted to have a look at it. what could be the reason? can anybody give me ahint. I am suspecting the motor is not recieving orders to spin or this is a bad motor. I also had a look at the service manual but it doesn't contain a troubleshooting table.

please , help me out

some hints

...anyway, first of all check all fuses ( see at service manual p. 24 + 33 ( as counted in adobe reader !). If they are o.k. ....

... remove the rear plate ( s.p.8 ), disconnect the cables of the motor and check the DC resistance of the motor (between red-blue ( 110 ohms) , and brown-yellow ( 170 ohms). Aditionelly there are two cables comming from a coil on the motor ( the value should be about 665 ohms ).
( s. also page 20 ).

The values are mostly not exact , but should be at least in the tolerance of min. 20 % !

If they are o.k. check the DC voltages ( between red-blue and brown yellow ). The value is not given, but I think it will be between 20 and 100 volts DC !

If there is no voltage, have a look at page 42 ( this is the schematics diagramm of the motorcontrol ) and page 46 ( the pcb layoutdiagramm ). In both cases you have to enlarge the pic to min. 125 % . In the upper region of page 42 you will find the capstan motor with the next electronic parts ) and the same on the layout ( left corner ) on page 46.

Check switch and D 9. If they are o.k., it will be getting a little bit difficult. But first you have some good hints , you can follow.

Additional remark: the motor is a pll controlled DC motor. In the coil of the motor is a frequency generated which will be checked on the board to a reference ( adjustable ) and - in case of it´s not proper - the DC voltage to the motor will be a little bit electronically changed.




thank you so much for the help.for taking the time to write me.

As a matter of fact, I know very little about electronics. However, I am going to buy a decent multimeter tomorrow and start with your instructions starting with the simple stuff.
I have a question, what if the 110 ohms and 170 ohms are not O.K. .

another question if I may, in case there are bad parts, are these the kind you can find at a good electronics store?. ofcourse , I know the motor itself is not, but I mean electronic parts like resistors and capacitors..etc.

I checked with Akai who is the same pioneer dealer in my area , and it seems they never brought the later (646,747) models to jordan( my country), but they have tons of parts for all other models .
I also acquired about 12 Revox recording(042),playback (047)and erasing heads and a bunch of brakes from the past Revox dealer in Jordan( brand new) which I will be selling on ebay soon.

Jiries ( Arabic version of George)

... these are the DC

... these are the DC resistance values of the two main motor coils. If they are not o.k., you will have a problem : the motor is defect ( and it´s difficult , to get a new one ). On page 30 you can see an explosive picture of this item. Maybe you can find a problem, but the chance is minimal.

I hope, that the problem is an electronic one.


crazy Akai

Now after two hours I tried it again with 10.5" reels. It played well for a minute. I stopped it and pushed play button again , and gues what, it went abnormally fast in both directions. Could it be the same transistor that a just changed .
I read a thread on FIXYA that this same transistor is responsible for the abnormally high speed in the play position.