AKAI mg614 tape speed/pitch fault.

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 of the take up side is now great enough that take up speed is sufficient.

The physical switch and pot are fine, this problem 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.

I am in communication with Dave at VST. He is certainly very helpful but the times zones are making comms slow, plus i don't feel right tapping a company for free advice.


Many thanks in advance.

I've worked out that the board which houses the pitch pot and speed switch sends out -9.8v and 10.9v for tape speed,
and a range of 1.3v to 2.2v for pitch control.

If i flick the speed switch, the tape speed voltages are swapped around.


These voltages arrive at another board where it seems like they are fed to a chip (UPC1043C), which then sends voltages out directly to the motor.
The pins marked FG go to straight to/from the motor and are always 2.9v always. Nothing alters this.

Pics of this board are at
www.steenaudio.com/1.png
www.steenaudio.com/2.png

white/black and white yellow are where 10.9v and -9.8v comes in.

I've flipped the solder side pic so that they are directly comparable.

Any ideas what i'm looking at here?

My problem is, I expect that the FG voltage is responsible for motor speed, but i don't understand what should change these voltages.

I think your motor drive voltage goes out on the terminal marked HALL. The 2 FG terminals are where the motors speed is measured by means of a varying frequency signal. Google the UPC1043C chip and you will find a data sheet for it showing a typical control circuit.

i've been lookin into it today and yeh, you're right.

F.G seems to be loop that's responsible for 'reporting' the speed of the capstan.

The capstan power comes from +15/-15.

It seems a small voltage has to be present at hall too though.

Are you sure the pinch roller is actually controlling the speed? The symptoms are of a recorder with insufficient pinch wheel pressure. Also when you change speeds, you should be able to observe the capstan motor speed change.

i figured that the capstan controls the speed and the take up should be capable of taking up at either speed. Is that not how it works?

Either way, my capstan has since ceased to operate at all.
The 1.5v that used to be observed at 'hall'  is no longer present.


Due to my limited knowledge, i'm going to replace the mentioned chip, and if that's not it i'm gona have to search for someone to work on this for me.

Well, it seems the chip was fine..

Sick of it.

Hi again.
I know it's been a long time since I posted about this, but i came across the unit again during a clear out and can bring myself to just bin it.

I thought I'd update incase anyone can help.
After replacing that chip, I left it into a repair shop.
They wanted a ridiculous amount of money to replace the mecha block, so I paid for the estimate and took it home.

I found a replacement mechablock for £20 online and put it in.
I was over the moon to find the unit worked absolutely perfectly.........for about two days, after which the same fault developed.

Does anyone have a service manual, or any suggestions?

Hello,
Sorry to hear of your AKAI woes.  It is a fun machine when functioning.  Which brings me here!  Mine I picked up at a pawn shop some years back and it worked excellently the last time I used it and recorded a couple tracks.  In fact yesterday I fired it up and it seemed to be working.  Now however, it won't play.  It FFs & RWs fine, but when I push play it engages but won't turn.  I know the plasticky/springy thing on the left side turns (goes into the hole of the cassette--not sure what the term is for that) b/c when I pull the pinch roller back with a screwdriver the tape will play though it's not music coming through the headphones! 

My question is:  Isn't the capstan supposed to be spinning?  It no longer is.  Any idea of the culprit?  Could that just be a simple belt change?  You didn't happen to find a good source on rubber for your 614 did you?  Any further progress with yours or did you throw in the towel?

http://www.ebay.co.uk/itm/Akai-MG614-Service-Manual-MG-614-MG-614-copy-/150672695654