I've not seen the schematic for the motor drives as Akai implemented it, but let us assume they used double pole relays to switch the 16v supply to the motors. As built, when in FF, the FR motor is isolated and is being spun in the reverse direction to its usual 'standard' rotation when the machine is in FR mode. The extra 'helping' voltage must be applied, via another double pole relay, to make this motor actually run in that same direction, but which is the opposite to how it would be energised if FR were selected. Simply adding a diode in series with the coils of each of the extra 'helping' relays would ensure that they are not energised when the motors to which they are connected are running in their 'standard' directions.
no need to do that ...
It will only take a couple of relays that actually are 24 volt and a specific resistance to be able to click with some 16 volt that are produced from the motor PSU
Now this will require some thinking one may as well use 12 volt relays or regulate some voltage to work with 12 volt relays Looks closer to work with 12 volt relays when voltage is 16 rather than 24 volt relays
Problem is that voltage present there at RW or FFW mode is something like 16 volt but also there is some voltage produced when the motor is at free spin condition ( the other motor is pulling ) so some 4-9 volts may be present there and this may as well activate the relay and obviously we don't want that .Also it is not safe to operate 12 V relay from 16 V power supply ... Let us not forget that a free spinning DC motor will work as a generator So 24V relays it will be my friends .
Notice that motors are driven by regulated power supply but voltage is engaged by relays so in any chance there is no harm to be done in electronics by reverse voltage since an open contact is in between .
Also you dont need a reverse diode on the relay since this one already exists on the motor that gives the power together with the notorious blue resistors .
Low power supply exists all ready in the machine and its the one that feeds unstabilized the motors at PLAY mode with a bit of power just to wind the tape after the pinch roller done all the pulling job , voltage is low and PSU doesn't feature electronics just a good bridge and a capacitor that obviously doesn't get damaged when a few very little more voltage is around ( at free spin motor may produce some voltage that will be a bit higher than the low voltage power supply produced but this as said can do no harm and comes in the correct polarity )
Brakes are mechanical so absolutely no side effects and working like a charm ...see the Video !!!
Low voltage is so low that in absolutely no case will end up un-winding the tape faster than the pulling motor ....
It will only take a couple of relays that actually are 24 volt and a specific resistance to be able to click with some 16 volt that are produced from the motor PSU
Now this will require some thinking one may as well use 12 volt relays or regulate some voltage to work with 12 volt relays Looks closer to work with 12 volt relays when voltage is 16 rather than 24 volt relays
Problem is that voltage present there at RW or FFW mode is something like 16 volt but also there is some voltage produced when the motor is at free spin condition ( the other motor is pulling ) so some 4-9 volts may be present there and this may as well activate the relay and obviously we don't want that .Also it is not safe to operate 12 V relay from 16 V power supply ... Let us not forget that a free spinning DC motor will work as a generator So 24V relays it will be my friends .
Notice that motors are driven by regulated power supply but voltage is engaged by relays so in any chance there is no harm to be done in electronics by reverse voltage since an open contact is in between .
Also you dont need a reverse diode on the relay since this one already exists on the motor that gives the power together with the notorious blue resistors .
Low power supply exists all ready in the machine and its the one that feeds unstabilized the motors at PLAY mode with a bit of power just to wind the tape after the pinch roller done all the pulling job , voltage is low and PSU doesn't feature electronics just a good bridge and a capacitor that obviously doesn't get damaged when a few very little more voltage is around ( at free spin motor may produce some voltage that will be a bit higher than the low voltage power supply produced but this as said can do no harm and comes in the correct polarity )
Brakes are mechanical so absolutely no side effects and working like a charm ...see the Video !!!
Low voltage is so low that in absolutely no case will end up un-winding the tape faster than the pulling motor ....
When left motor is on play back then the right motor is on rest position accidentally the PSU of the left motor together with the voltage drop presented from the operation is not enough to trigger a 24V relay ...that simple ...
Yes this is what practice showed 4 machines so far are operating like a charm for a year now
TBH i was ready to face problems like that after the idea was achieved but it seems that even though bit unorthodox works like a charm as seen on the video plus that out of the blue it is simply not important any more the condition of the belts Even belts that are almost dead will play with no probs
Kindest regards
Sakis
TBH i was ready to face problems like that after the idea was achieved but it seems that even though bit unorthodox works like a charm as seen on the video plus that out of the blue it is simply not important any more the condition of the belts Even belts that are almost dead will play with no probs
Kindest regards
Sakis
It would be trivial to do this if each motor were controlled by a relay, but that's not the case. Looking at the schematic, both motors have power, and whichever is grounded depends on a handful of transistors and diodes. Doesn't appear the motors are ever truly isolated from one another.
Charles.
Charles.
In this case you should quit since its obvious that you cannot read the schematic properly which brings us to the one of the first posts saying that if you feel that you are not able to manage this may someone with more experience should do it for you ....
I see RL1 either provides low voltage to both motors at all times, or when switched provides high voltage to both motors. This is the only relay in the area of the motors, and both motors are connected to it. The ground side of the intermediate PC board that the motors are on goes through a couple of transistors which are switched on and off by IC1.
I don't know how to read how those transistors effect the ground state of the motors, but I can tell there aren't two individual relays controlling power to each motor. Your insult is invalid.
Charles.
I don't know how to read how those transistors effect the ground state of the motors, but I can tell there aren't two individual relays controlling power to each motor. Your insult is invalid.
Charles.
If i am a helpful person or not can be seen from thousands of posts that i have in this forum ...
But injecting knowledge to another person cannot be done the way you like to have it
Especially when language might be an issue
on the other hand the last thing i could do is to make a schematic for you to execute either you understand the principal of operation or not ...
But injecting knowledge to another person cannot be done the way you like to have it
Especially when language might be an issue
on the other hand the last thing i could do is to make a schematic for you to execute either you understand the principal of operation or not ...
I've been reading this thread right by now, trying to understand it. As I don't have the machine's service manual Handy, I assume the following:
1st: Both reel motoers are permanent magnetic field DC motors. Right?
2nd: There's a chain in parallel with each reel motor, consisting of a reversely polarized diode and those ominous blue resistors. Right?
There are still some questions left:
1st: DC motors act as generators, when their shaft is driven externally. So, if the voltage of the non-pulling motors exceeds the diode's knee voltage, this motor is shunted by those blue resistors and acts as a break. Shouldn't this be desirable in order to avoid tape loops?
2nd: When the reel on the pulling side is almost full and the other one almost empty, the non-pulling motor spins at very high rpm, thus producing a high DC voltage, which may even exceed the pulling motor's supply voltage. So you're only relying on the characteristics of the individual relays you're using. As the pull-in voltage seldomly, if ever, is published in the relay's data sheet, installing a randomly chosen relay may end as some kind of vabanque game. A diode in series with the relay solenoid definitively would cure this issue. Which type of relay did you use exactly?
3rd: I don't assume that the GX-77 had the FF/FR issue when new. So there is no design flaw. Am I right in assuming that your remedy just tries to cure the symptoms, but not the cause?
4th: Your refusal (at least up to now) in showing or explaining details makes me wonder if you're just trying to source customers rather than really trying to help. Am I right? Btw, the topic of this forum reads do it yourself!
Best regards!
1st: Both reel motoers are permanent magnetic field DC motors. Right?
2nd: There's a chain in parallel with each reel motor, consisting of a reversely polarized diode and those ominous blue resistors. Right?
There are still some questions left:
1st: DC motors act as generators, when their shaft is driven externally. So, if the voltage of the non-pulling motors exceeds the diode's knee voltage, this motor is shunted by those blue resistors and acts as a break. Shouldn't this be desirable in order to avoid tape loops?
2nd: When the reel on the pulling side is almost full and the other one almost empty, the non-pulling motor spins at very high rpm, thus producing a high DC voltage, which may even exceed the pulling motor's supply voltage. So you're only relying on the characteristics of the individual relays you're using. As the pull-in voltage seldomly, if ever, is published in the relay's data sheet, installing a randomly chosen relay may end as some kind of vabanque game. A diode in series with the relay solenoid definitively would cure this issue. Which type of relay did you use exactly?
3rd: I don't assume that the GX-77 had the FF/FR issue when new. So there is no design flaw. Am I right in assuming that your remedy just tries to cure the symptoms, but not the cause?
4th: Your refusal (at least up to now) in showing or explaining details makes me wonder if you're just trying to source customers rather than really trying to help. Am I right? Btw, the topic of this forum reads do it yourself!
Best regards!
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Your study is wrong , you come up with study taking as a fact that the reel is working that is wrong it has a mechanical flaw ...
1st Actually not ...it will not act as a brake ( notice that eventhough pretty simple idea it is never done in any other reel since it doesn't work as a brake ) diode is there for the same reason reverse diodes exist in transistor driven relays . Secondly if voltage exceeds the diode knee voltage then diode will become a "wire" and power will be consumed on the resistor ( the reversed one ).
Existing brake techniques is either mechanical brakes or reversed voltage brakes
That will apply though in the case the free motor is spinning in high speed which clearly its not the case here and at any condition FFW or REW the pulling motor of the other side since tape is traveling through a lot , motion is given by DC motors and belts , then there no mechanical power to actually pull the tape and reel it from one reel to the other and finally drive the free motor in high speed .
That is the original problem of the machine
2nd That is the problem this condition you describe DOESN'T happen in this machine ...IE for any reason there is no chance that the full reel has enough mechanical power to pull the tape and force the opposite motor to spin free in high speed and produce as a generator a good amount of voltage.
Notice Please that if you skip the local power supply and try to force more voltage to the pulling motor this also deosn't work and even if you do so still there is not enough torque to produce enough mechanical power to pull a complete reel side to side
Read please the principal of operation once more carefully please:
Since there is nothing possible to do with the pulling motor from either electrical aspect or mechanical aspect the only thing left to do is to apply some voltage to the free motor to help it UNREEL the tape so the pulling motor together with its electrical and mechanical assembly has less load to carry
At this condition the voltage produced by the free spinning motor and the voltage applied from the low side power supply is the same polarity so you get absolutely no issues there except that at a very extreme condition you might go up to the voltage of the rectifying capacitor which as long as this is in the same polarity this will cause absolutely no problem .
Yet again the relays work as transfer switches over the motor in condition FFW or REW only to provide power from the low side of the existing power supply ( one bridge and one capacitor ) in the correct polarity to assist the free motor to UNREEL the non pulling side of the tape
3rd
Well i cannot talk about that supply me with a couple of brand new motors , brand new original belts fresh also , and a few other things and i will let you know.
A design flaw doesn't mean that the machine had problems since day one ...It means that Japanese most of the times designed things that will work for about 400 years , details are never missed in Japanese Audio and often tests enough have been done to Japanese audio since they had the working people to do so and the feeling required to produce everlasting machines ....Something that the Germans never managed or thought to do .There is a very good chance that in this machine everlasting was overlooked .
4th being a member since 2006 having thousands of posts in various threads while above 50% is about helping other people troubleshoot their audio systems makes your statement clearly insulting .....at least
Finally you can clearly blame me for not being able to describe my work properly since English is not my native language but other than that the rest is crap....
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couple of details more
To come up with this solution took a lot of work and obviously the first thing to do was to increase the voltage on the pulling motors to gain some torque and mechanical power ...
Voltage Given from external power supply reached almost double the existing voltage but had no usable effect on the operation of the machine .
We also had the ability to temporary play with the ratio of the gear and try to reduce that in order to trade speed for torque .... Obviously there is a small margin to play with that still that had no usable effect
Other thickness on belts or other tightness on belts tested made the thing worst
Kind regards
Sakis
To come up with this solution took a lot of work and obviously the first thing to do was to increase the voltage on the pulling motors to gain some torque and mechanical power ...
Voltage Given from external power supply reached almost double the existing voltage but had no usable effect on the operation of the machine .
We also had the ability to temporary play with the ratio of the gear and try to reduce that in order to trade speed for torque .... Obviously there is a small margin to play with that still that had no usable effect
Other thickness on belts or other tightness on belts tested made the thing worst
Kind regards
Sakis
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One small detail ....
Helping voltage is very low and its enough to just "start" the pulling motor to pull. Luckily this is working without creating any mess since unreeling the tape from the other side could easily create a tape mess all over the machine
Clearly there i was lucky and the helping voltage provided was just enough to start supporting the pulling motor without creating a mess Tested in all possible reels all possible reel size and the all spectra of tape at all conditions
Tape full from one or the other side
Tape empty from one or the other side
And many possible test points in the middle loads of tapes
Helping voltage is very low and its enough to just "start" the pulling motor to pull. Luckily this is working without creating any mess since unreeling the tape from the other side could easily create a tape mess all over the machine
Clearly there i was lucky and the helping voltage provided was just enough to start supporting the pulling motor without creating a mess Tested in all possible reels all possible reel size and the all spectra of tape at all conditions
Tape full from one or the other side
Tape empty from one or the other side
And many possible test points in the middle loads of tapes
I was able to fix mine. it is all mechanical. All needs to be disassembled, cleaned, degreases, lubricated, readjusted as per service manual. Do not expect to just turn a screw and see it working. No way this is a simple job. Took me 4 days but it is all in perfect condition. I live in Toronto Canada. If anyone needs one repaired I can do it. Contact me if you want.
Th1 Thermistor is ABSOLUTELY NOT the cause for this. Don't waste your time and money
You may have encountered a post mentioning that TH1 Thermistor is the cause - it runs burning hot. It is ABSOLUTELY NOT the cause. It runs hot normally. In troubleshooting my Akai GX77 I swapped TH1 and TH2 (same type). Still TH1 remained hot, TH2 continued to be cold as ice. After I was finally able to repair it and it now works perfectly hours after hours, TH1 remains hot, and it is not creating any issues. Forget about it.
You may have encountered a post mentioning that TH1 Thermistor is the cause - it runs burning hot. It is ABSOLUTELY NOT the cause. It runs hot normally. In troubleshooting my Akai GX77 I swapped TH1 and TH2 (same type). Still TH1 remained hot, TH2 continued to be cold as ice. After I was finally able to repair it and it now works perfectly hours after hours, TH1 remains hot, and it is not creating any issues. Forget about it.
Hey, glad to see someone making sense to me in resolving this issue. I am also in GTA and I'd like to give this a try. I have the service manual and a very good hands on experience with these things. Can you please indicate what exactly you cleaned/greased to regain the hub motors' power? I just got my GX-77 recently and I also need to do a heads alignment, if I can find a decent calibration tape