2 - The Solution

The first thing i noticed when i came up with the problem was that if i gave a little "help" to the machine, just forcing the feeding spool to run faster with my hand, the take up loading spool would then also start to run faster, so, if i managed to change the electric spool control mechanism to do something in this way, maybe i would solve the problem... definitely!

And that's what it's all about.

I started looking for a solution, browsing the internet, and found some interesting posts in related forums, but none of those provided a real complete answer with detailed and precise procedures, so, based on it i started looking myself for an answer.

I got my hands to the service manual and after studying schematics and processes of the spool control, i have found a solution that basically makes use of two relays that will be interconnected with the two spool motors and came up with a prototype board. The process for including the board in the machine would, of course, imply some re-wiring, but nothing too much complicated.

Below you can see a detailed photo of the prototype board and a set of few wires that will be necessary to do some re-wiring in the machine:

After doing all the re-wiring you can see bellow some details about the connections in the proto board and installation on the machine:

Installation is very simple and for doing it you don't need to be an expert in electronics! You just need to have basic skills about using a simple soldering iron and a couple of tools to cut some wires and deal with some screws!

UNDERSTANDING THE PRINCIPLES OF FFWD/FRWD:

Before understanding what the mod changes in the machine we must first take a short view to understand how the machine works.

Let's start by the PLAY function - when you press the RIGHT PLAY button, the RIGHT spool motor will be fed with 5V DC wich will make it run in counter-clockwise direction, thus pulling the tape from the feeding spool on the left side. At the same time the RIGHT pinch roller is atached, making the capstan motor to drive and also pull the tape towards the right side spool. The same principle applies when you press the LEFT PLAY button.

Now, let's talk about the FFWD function - when you press the FFWD button (>>), the RIGHT side spool motor will be fed with 16V DC wich will make it run in counter-clockwise direction, thus pulling the tape from the feeding spool on the left side. At the same time the RIGHT side pinch roller is DETACHED, thus removing the capstan motor from the process. So, only the RIGHT side spool motor will be pulling the tape towards the right side spool. This motor has a big job to do, because it has to deal against all the mechanical inertia forces, plus the friction caused by the tape passing through all the 6 heads and the tape counter roller, plus having to "drag" the weight of the LEFT side spool. You must also understand that the LEFT side spool motor will then be free-running (no DC voltage is applied to the motor). If you have some basic electronics knowledge you know that when a DC motor is free-running it will act as a DC generator, so, the LEFT side motor will generate a DC voltage that may vary between 4-8V, depending on its speed. That's why those little boards by the side of each motor (see pictures above) have those famous 3W blue resistor in series with a diode - the only function of this 2 components is to "burn" that generated voltage thus preventing it not to damage the motor control driving transistors. It has the same function that the free-wheel diodes often placed in parallel with a relay coil.

The same principle applies when you press the FRWD button (<<) - the LEFTside spool motor will be fed with 16V DC wich will make it run in clockwise direction, thus pulling the tape from the feeding spool on the right side. At the same time the LEFT side pinch roller is DETACHED, thus removing the capstan motor from the process.

UNDERSTANDING THE PRINCIPLES OF THE MOD:

What we want to do is just making the feeding spool motor to give a little help to the pulling spool motor, so, instead of being free-running, acting like a DC generator, the feeding spool motor will be acting as a 2º motor thus helping the pulling spool motor in its job.

To do this, we have to change the wiring circuit and include the above board with the two relays.

Let's examine the particular situation when the FFWD button (>>) will be pressed on:

The RIGHT spool motor will be fed with 16V DC wich will make it run in counter-clockwise direction. The LEFT motor will also run in counter-clockwise direction. The relays board is connected in such a way that it will fed the LEFT spool motor with a certain DC voltage, thus helping the RIGHT motor in it's job. This DC voltage is taken out directly from the machine PSU, through the mod board. This will dramatically increase the tape spooling speed. Please note that this modification will not cause the tape to scramble or pull off the tape path. That will not happen, because the amount of DC voltage applied to the LEFT spool motor was calculated taking that in account.

In the particular situation when the FRWD button (<<) will be pressed on:

The same principle is applied. The LEFT spool motor will be fed with 16V DC wich will make it run in clockwise direction. The RIGHT motor will also run in clockwise direction. The relays board is connected in such a way that it will fed the RIGHT spool motor with a certain DC voltage, thus helping the LEFT motor in it's job.

In the particular situation when the PLAY button (<) or (>) will be pressed on:

In this situation, the voltage applied to the pulling motor is only about 5V DC, and the mod relay board does nothing at all.

Also, when you use the button to activate or deactivate the vertical tape loading/unloading mechanism, nothing will happen with the mod board.

And that's it!

As i told before, my AKAI GX-77 is modded with this prototype relay board for several months ago. Since then, i've been using it for about 2 or 3 times per week. FFWD/FRWD speed is excellent (i think it's much better than when it was new) and the mod continues to work flawlessly. I'm very pleased with this solution.