Hi all,
I've come here really hoping that someone can help as i can't find anyone to work on my AKAI in the UK.
I don't know a lot about this unit, it only recently came into my possession and in mint boxed new condition with the exception of one fault.
Regardless of where the tape speed switch is set, the tape plays back at one speed.
If i play a tape, it seems to start off at a speed and very gradually reduce speed over a reasonably long period...say 30 seconds?
It doesn't grind to a halt or anything; There's just a notable pitch drop.
The pitch control knob on the unit has no effect either.
Another symptom of what i imagine to be one golbal fault is that if i play a tape back from the start, the capstan will feed tape through faster than the take up can receive it, so it gets chewed.
If i FF a bit and play again, it'll be fine as the diameter of the tape on the take up now great enough that take up speed is sufficient.
The physical switches and potsare fine, this fault goes deeper than that.
I've guessed that tape speed and pitch are both voltage controlled and perhaps that something in both their paths has shorted out allowing full voltage to the motor at all times. Does this sound reasonable?
There are markings on some internal connectors that say 9.5 and 4.75. Again, i guess that these are voltage outputs for the two speeds.
If i even knew what the voltages are meant to be i could trace the fault a little farther.
Anything at all is helpful on this guys.
Many thanks in advance.
I've come here really hoping that someone can help as i can't find anyone to work on my AKAI in the UK.
I don't know a lot about this unit, it only recently came into my possession and in mint boxed new condition with the exception of one fault.
Regardless of where the tape speed switch is set, the tape plays back at one speed.
If i play a tape, it seems to start off at a speed and very gradually reduce speed over a reasonably long period...say 30 seconds?
It doesn't grind to a halt or anything; There's just a notable pitch drop.
The pitch control knob on the unit has no effect either.
Another symptom of what i imagine to be one golbal fault is that if i play a tape back from the start, the capstan will feed tape through faster than the take up can receive it, so it gets chewed.
If i FF a bit and play again, it'll be fine as the diameter of the tape on the take up now great enough that take up speed is sufficient.
The physical switches and potsare fine, this fault goes deeper than that.
I've guessed that tape speed and pitch are both voltage controlled and perhaps that something in both their paths has shorted out allowing full voltage to the motor at all times. Does this sound reasonable?
There are markings on some internal connectors that say 9.5 and 4.75. Again, i guess that these are voltage outputs for the two speeds.
If i even knew what the voltages are meant to be i could trace the fault a little farther.
Anything at all is helpful on this guys.
Many thanks in advance.
I don`t know anything about this particular machine but the markings 9.5 and 4.75 are likely to refer to tape speed, 3.75 and 1.875 inches per second respectively. It certainly sounds as if there is no control on the capstan motor. Check for any loose wire or connectors in the vicinity of the motor.
Barry
Barry
Thanks for the advice Barry. I can see all the wires that disappear off to the motor, but getting at the back of the motor itself is looking tricky.
I might have to bite the bullet and just do that.
I might have to bite the bullet and just do that.
Ok, i took a look.
The motor is getting 2.9v on two wires at all times.
There is a top board with all the controls, a lower board beside the psu and the motor/cassette assembly.
It seems that the top board is sending 15.8v and -16.6v out to the lower board.
These voltages swap places if I toggle the speed switch.
a range of 1.3v to 2.2v is sent out on different wires and this range corresponds to pitch control position.
These voltages all arrive at the lower board, but the output from that board which goes straight to the motor is just a constant 2.9
Would it be safe to assume i'm chasing a fault on the lower board?
The motor is getting 2.9v on two wires at all times.
There is a top board with all the controls, a lower board beside the psu and the motor/cassette assembly.
It seems that the top board is sending 15.8v and -16.6v out to the lower board.
These voltages swap places if I toggle the speed switch.
a range of 1.3v to 2.2v is sent out on different wires and this range corresponds to pitch control position.
These voltages all arrive at the lower board, but the output from that board which goes straight to the motor is just a constant 2.9
Would it be safe to assume i'm chasing a fault on the lower board?
Pics of that board are at
www.steenaudio.com/1.png
www.steenaudio.com/2.png
The capstan speed voltage comes out of the top left connecter, at the pins labelled FG (5th and 6th from left)
The chip below that connector is UPC1043C.
I've flipped image 1 so that solder side and component side are visually comparable.
www.steenaudio.com/1.png
www.steenaudio.com/2.png
The capstan speed voltage comes out of the top left connecter, at the pins labelled FG (5th and 6th from left)
The chip below that connector is UPC1043C.
I've flipped image 1 so that solder side and component side are visually comparable.
No, it's all new/tight.
Like i say, voltage to motor doesn't change when speed switch is changed.
I'll label the pics later when i figure out some more.
Like i say, voltage to motor doesn't change when speed switch is changed.
I'll label the pics later when i figure out some more.
Presumably the UPC1043 feeds the tabbed power chip. You may be able to measure whether the voltage out of the UPC1043 is being controlled and therefore deduce whether the power chip is O.K.
Ok, i'm not really sure how to do that, But...
voltages at chip (viewed from above) are
Low speed
2.9........4.9
2.8........2.9
3.00........0
2.8........5.4
2.8........4.2
2.9........1.5
10.8........0.8
0...........5.8
High speed
2.9........4.9
2.8........2.9
3.00........0
2.8........5.0
2.8........4.1
2.9........1.5
10.8........0.8
0...........5.8
The terminals for the motor (FG) read 2.9v each, but if motor is disconnected they read 2.9 and 0.5.
It seems motor speed is controlled by whatever returns to FG right? so what would make that change?
voltages at chip (viewed from above) are
Low speed
2.9........4.9
2.8........2.9
3.00........0
2.8........5.4
2.8........4.2
2.9........1.5
10.8........0.8
0...........5.8
High speed
2.9........4.9
2.8........2.9
3.00........0
2.8........5.0
2.8........4.1
2.9........1.5
10.8........0.8
0...........5.8
The terminals for the motor (FG) read 2.9v each, but if motor is disconnected they read 2.9 and 0.5.
It seems motor speed is controlled by whatever returns to FG right? so what would make that change?
Last edited:
Hi everyone.
I know I'm bumping an old thread here, but I thought that was better than starting a new one on the same topic.
I'm thinking of hoking this unit out and having another blast at it.
Around the time when this thread was active, I found out that there are little hall effect sensors on a board in the mecha block.
These sensors were being blown from what I can tell, which I guess means there is too much current getting to them?
I replaced the board and all was fine for a brief period until the fault developed again.
This makes me think I'm looking for too high a voltage, or too much current, on the way into the mechablock. I think this info might really narrow down the search.
I pmd a chap who I believe has a service manual for this unit.
I'll post back if/when I get the service manual, but if any one else out there has it, I'd be super grateful if you'd share.
Any thoughts on this?
Thank you.
I know I'm bumping an old thread here, but I thought that was better than starting a new one on the same topic.
I'm thinking of hoking this unit out and having another blast at it.
Around the time when this thread was active, I found out that there are little hall effect sensors on a board in the mecha block.
These sensors were being blown from what I can tell, which I guess means there is too much current getting to them?
I replaced the board and all was fine for a brief period until the fault developed again.
This makes me think I'm looking for too high a voltage, or too much current, on the way into the mechablock. I think this info might really narrow down the search.
I pmd a chap who I believe has a service manual for this unit.
I'll post back if/when I get the service manual, but if any one else out there has it, I'd be super grateful if you'd share.
Any thoughts on this?
Thank you.
Wow this is an old thread but I know we all sometimes end up at dead threads looking for advice. This is only my second AKAI on my bench (mostly TEAC, TASCAM and Yamaha)...
I just spent the day with an Akai MG614 and ended up with similar speed issue (too fast, no control). It started with logic issues (buttons and LEDs random) due to an open ribbon cable connection. Bad door mecha. Wouldn't play due to stuck "break" mechanism. Wouldn't FF/RR due to stuck idler (did not need to replace). Heads stuck....
After a few hours it seemed almost there but when I played a tape it was inconsistent and much too fast... 🙁
The UNCONTROLLABLE FAST playback was caused by, as others suggested way back, the take up reel driving the playback since the capstan motor had an issue. My machine was playing excessively fast (but not quite FF) and no pitch control had an effect.
The problem in my case was simply the SMALL PLASTIC bushing that the capstan (brushless, beltless) rests its butt on. During disassembly I guess it was dislodged and become crooked. The capstan would spin easily enough with my finger, but when the block was back in the machine friction would keep it from working well. If that piece is missing or crooked it will affect the capstan motors ability to spin with low friction and the take-up-reel would pull the tape through at an arbitrarily faster than playback speed.
I spent many hours yesterday checking voltages only to pop this back in place this morning (fresh eyes), restoring the playback function. There was a degree of randomness to the symptoms because it was physical not electrical in nature....
NOTES:
This is not a pleasant machine to work on.
The FG wires are not motor voltage, they are Frequency Generator signal pair that uses the wee board in the mecha and a magnetic ring to send rotational info back to the big board. The capstan motor voltages are in the larger buss.
The HALL effect sensor is for the take up reel auto-stop detector, I think, not associated with the capstan.
The components on the main mecha board are op amps (2) and transistors (4) making up the oscillator that drives the motor coils.
I just spent the day with an Akai MG614 and ended up with similar speed issue (too fast, no control). It started with logic issues (buttons and LEDs random) due to an open ribbon cable connection. Bad door mecha. Wouldn't play due to stuck "break" mechanism. Wouldn't FF/RR due to stuck idler (did not need to replace). Heads stuck....
After a few hours it seemed almost there but when I played a tape it was inconsistent and much too fast... 🙁
The UNCONTROLLABLE FAST playback was caused by, as others suggested way back, the take up reel driving the playback since the capstan motor had an issue. My machine was playing excessively fast (but not quite FF) and no pitch control had an effect.
The problem in my case was simply the SMALL PLASTIC bushing that the capstan (brushless, beltless) rests its butt on. During disassembly I guess it was dislodged and become crooked. The capstan would spin easily enough with my finger, but when the block was back in the machine friction would keep it from working well. If that piece is missing or crooked it will affect the capstan motors ability to spin with low friction and the take-up-reel would pull the tape through at an arbitrarily faster than playback speed.
I spent many hours yesterday checking voltages only to pop this back in place this morning (fresh eyes), restoring the playback function. There was a degree of randomness to the symptoms because it was physical not electrical in nature....
NOTES:
This is not a pleasant machine to work on.
The FG wires are not motor voltage, they are Frequency Generator signal pair that uses the wee board in the mecha and a magnetic ring to send rotational info back to the big board. The capstan motor voltages are in the larger buss.
The HALL effect sensor is for the take up reel auto-stop detector, I think, not associated with the capstan.
The components on the main mecha board are op amps (2) and transistors (4) making up the oscillator that drives the motor coils.