As it is a microprocessor declared "obsolete" you will have a hard to time to find one. I think a realistic option is a obtaining a second ( defective ) CD73/93.
http://www.xs4all.nl/~ganswijk/chipdir/pinusr/m50747.txt
http://www.alldatasheet.com/datasheet-pdf/pdf/MITSUBISHI/M50747.html
You could try to mail various Akai companies in Europe for a start.
http://www.xs4all.nl/~ganswijk/chipdir/pinusr/m50747.txt
http://www.alldatasheet.com/datasheet-pdf/pdf/MITSUBISHI/M50747.html
You could try to mail various Akai companies in Europe for a start.
Akai CD73
Hello!
I have tracking problem with akai CD73.
There are linear tracking motor with two coils.
Motor and sensor coil.
Sensor coil was broken.
Sensor coils electrical resistivity is now about 10 kiloohm.
Too high I think.(In denon this is about 2 kiloohm)
Player cant perform track jump function.
But from beginning plays well.
Can eny body help with right resistivity.
Hello!
I have tracking problem with akai CD73.
There are linear tracking motor with two coils.
Motor and sensor coil.
Sensor coil was broken.
Sensor coils electrical resistivity is now about 10 kiloohm.
Too high I think.(In denon this is about 2 kiloohm)
Player cant perform track jump function.
But from beginning plays well.
Can eny body help with right resistivity.
I have Akai CD73 with a loading tray problem.
The tray reaches end of travel, either open or closed and hammers back and forth. The disc can be made to load by cycling power, after which it will play.
I've replaced the bi-directional motor driver and cleaned the sense switches but it still doesn't work.
The switches feed directly into the micro mentioned before, M50747-433SP. I think this device is faulty.
Has anyone else encountered this problem and/or found a solution??
The tray reaches end of travel, either open or closed and hammers back and forth. The disc can be made to load by cycling power, after which it will play.
I've replaced the bi-directional motor driver and cleaned the sense switches but it still doesn't work.
The switches feed directly into the micro mentioned before, M50747-433SP. I think this device is faulty.
Has anyone else encountered this problem and/or found a solution??
These kind of faults are rarely caused by the uP, so in practice that means that while it is not impossible for it to be faulty, it would normally be about the last thing to suspect.
You need to check everything else first. That means using a scope to look at the rails and make sure they are clean under load and something like that could 'spike' the uP.
When you say it 'hammers back and forth' do you mean the tray motor continues to run in the same direction or do you mean the tray is going in and out constantly.
Again a scope would be used to look at the microswitch logic levels as applied to the uP.
You need to check everything else first. That means using a scope to look at the rails and make sure they are clean under load and something like that could 'spike' the uP.
When you say it 'hammers back and forth' do you mean the tray motor continues to run in the same direction or do you mean the tray is going in and out constantly.
Again a scope would be used to look at the microswitch logic levels as applied to the uP.
The problem first appeared about 10 years ago. I reflowed all solder joints and replaced all electrolytic capacitors due to the age of the unit.
Eventually I took it to a local repair shop as I could not figure out the erratic behaviour. The engineer who repaired it said the micro was in a cheap DIL socket and the contacts needed cleaning. He advised that if the problem returned, I should remove the socket and mount the IC directly to the board, which I have. This cured the problem again a few years later but it has returned again.
The tray reaches end of travel and jumps back and forth about 10mm repeatedly. I thought it was contact 'bounce' and built a de-bounce circuit using schmitt trigger buffers but this made no difference. The logic levels into the micro look good and are correct.
Eventually I took it to a local repair shop as I could not figure out the erratic behaviour. The engineer who repaired it said the micro was in a cheap DIL socket and the contacts needed cleaning. He advised that if the problem returned, I should remove the socket and mount the IC directly to the board, which I have. This cured the problem again a few years later but it has returned again.
The tray reaches end of travel and jumps back and forth about 10mm repeatedly. I thought it was contact 'bounce' and built a de-bounce circuit using schmitt trigger buffers but this made no difference. The logic levels into the micro look good and are correct.
You've gone to considerable lengths if you've built a de-bounce circuit. The fact it started working again after a previous repair attempt reinforces my own opinion that the uP is not at fault here... they don't normally fail like that.
What would I do... probably return the player to standard configuration and perhaps look at disconnecting the tray motor and rigging up some external switches to simulate the tray microswitches. Then see how the feed to the disconnected motor responds in relation to the logic levels from the external switches.
Wild thought... is the motor electrically noisy and causing odd issues. Be careful checking with a scope because the motor will probably be tied into an H bridge driver and so you need to be careful over test equipment grounds if there is also another ground return on the player via the mains lead etc.
What would I do... probably return the player to standard configuration and perhaps look at disconnecting the tray motor and rigging up some external switches to simulate the tray microswitches. Then see how the feed to the disconnected motor responds in relation to the logic levels from the external switches.
Wild thought... is the motor electrically noisy and causing odd issues. Be careful checking with a scope because the motor will probably be tied into an H bridge driver and so you need to be careful over test equipment grounds if there is also another ground return on the player via the mains lead etc.
I did spend quite a lot of time on trying to trace the fault. The built in PSU is quite noisy with high ripple, so I disconnected it and ran the unit from external bench supplies but that didn't make any difference either.
The de-bounce circuit was my last try a while back (it's now removed) but I've decided to have another go at it because it is a nice unit when running.
I like your idea of disconnecting the tray motor and rigging up external switches for the open/close control to monitor the control circuit. The tray has two other switches that control the up/down clamping function too. That sometimes goes into the same unstable state after the draw has closed too.
I'm aware of H bridge motor drive circuits and will be careful with grounding the scope probe when looking at the motor control. I'll check the mains lead but from memory it is a two core cable with just L and N connections.
Thanks for the suggestions!
The de-bounce circuit was my last try a while back (it's now removed) but I've decided to have another go at it because it is a nice unit when running.
I like your idea of disconnecting the tray motor and rigging up external switches for the open/close control to monitor the control circuit. The tray has two other switches that control the up/down clamping function too. That sometimes goes into the same unstable state after the draw has closed too.
I'm aware of H bridge motor drive circuits and will be careful with grounding the scope probe when looking at the motor control. I'll check the mains lead but from memory it is a two core cable with just L and N connections.
Thanks for the suggestions!
Have you cleaned the microswitches properly?
By that I mean pulling a strip of paper through the contacts (paper soaked in ISO) while gently holding the contacts closed. Just a squirt with something doesn't always work.
Something mechanical like that would be the first thoughts in a problem like this.
Microswitches are a common issue across the board... happened to me here:
Sony CDP790 and KSS240 Restoration Project
Good luck anyhow
By that I mean pulling a strip of paper through the contacts (paper soaked in ISO) while gently holding the contacts closed. Just a squirt with something doesn't always work.
Something mechanical like that would be the first thoughts in a problem like this.
Microswitches are a common issue across the board... happened to me here:
Sony CDP790 and KSS240 Restoration Project
Good luck anyhow
First thing I did was remove the tray switches and clean them. They are very basic open frame leaf switches and they were quite grubby. I cleaned the contacts and then tested them on a micro ohmmeter to make sure they were making good contact.
It surprised me that they were connected directly to the micro, which was why I put the de-bounce circuit in. I figured all 4 couldn't be defective, which was why I started to suspect the micro itself.
The switches are plugged into the PCB with connectors, so I can unplug them and wire in some external switches to allow for manual control as you suggested. It will be interesting to see how it behaves.
It surprised me that they were connected directly to the micro, which was why I put the de-bounce circuit in. I figured all 4 couldn't be defective, which was why I started to suspect the micro itself.
The switches are plugged into the PCB with connectors, so I can unplug them and wire in some external switches to allow for manual control as you suggested. It will be interesting to see how it behaves.
I've removed, cleaned and double checked contact resistance of the 4 switches that provide open/close and up/down signals for the micro controlling the CD tray and all are good.
Disconnecting the motors and monitoring the loading tray motor output with a scope, while activating the tray sense switches manually, shows a good clean DC level switching on and off as it should.
Connecting the motor, the clean DC level changes to a signal that oscillates when the tray reaches each end of the travel. I've already replaced the motor driver chip and eliminated the PSU as a problem so I'm only left with the possibility of motor noise interfering with the micro.
There are capacitors (47nF) across each motor to prevent parasitic oscillation but these are on the PCB near the driver chip. I think these would be better located directly across the motor terminals with a couple of others from the terminals to the case for good measure, so will try this.
The tray loading mech uses two rubber drive belts, both of which are past their best and tend to slip a bit, so I have ordered some suitable replacements, which should also help.
Other than this, I'm at a loss to what is causing the problem.
Disconnecting the motors and monitoring the loading tray motor output with a scope, while activating the tray sense switches manually, shows a good clean DC level switching on and off as it should.
Connecting the motor, the clean DC level changes to a signal that oscillates when the tray reaches each end of the travel. I've already replaced the motor driver chip and eliminated the PSU as a problem so I'm only left with the possibility of motor noise interfering with the micro.
There are capacitors (47nF) across each motor to prevent parasitic oscillation but these are on the PCB near the driver chip. I think these would be better located directly across the motor terminals with a couple of others from the terminals to the case for good measure, so will try this.
The tray loading mech uses two rubber drive belts, both of which are past their best and tend to slip a bit, so I have ordered some suitable replacements, which should also help.
Other than this, I'm at a loss to what is causing the problem.
Try a dummy resistive load in place of the motor. I would guess something that pulls say 100ma and see if the voltage holds up and stays clean.
A quick bodge with suspect motors is to isolate them (mechanically as well as electrically) and zap it on a 9 volt battery each way a few times. That can clean the commutator up.
(Electrically noisy small DC drum motors used in the first generation VHS recorders used to cause lots of trouble with the servo failing to lock and the picture 'swinging' left and right)
You could try adding a series resistor to the motor as a well as a cap across it. Maybe a bipolar cap or you could try to electrolytics as a quick test with them wired in series back to back to make a bipolar type.
You mention belts slipping. That kind of thing can be an issue if it cause the tray not to quite fully complete its operation. It could be something as simple as that.
A quick bodge with suspect motors is to isolate them (mechanically as well as electrically) and zap it on a 9 volt battery each way a few times. That can clean the commutator up.
(Electrically noisy small DC drum motors used in the first generation VHS recorders used to cause lots of trouble with the servo failing to lock and the picture 'swinging' left and right)
You could try adding a series resistor to the motor as a well as a cap across it. Maybe a bipolar cap or you could try to electrolytics as a quick test with them wired in series back to back to make a bipolar type.
You mention belts slipping. That kind of thing can be an issue if it cause the tray not to quite fully complete its operation. It could be something as simple as that.
I'm at work at present but will sort out a suitable resistive load to put in place of the motors and hook the scope up again. I'll also try the 9V battery 'zap' on the motors as that will be easy enough plus add some suitable caps their terminals.
It seems strange that both motors are exhibiting the same problem though. When I eventually get the tray to stay closed, either by cycling power or physically holding the tray in, the clamp motor runs and then does the same oscillation thing. Cycling the main power a couple of times eventually gets that to lock down and the disc starts to play normally.
The disc clamp mech is purely gear driven unlike the tray loading, so although the slipping belts don't help, I don't think its the issue. The belts are odd sizes but I've managed to source a couple that should do the job.
It seems strange that both motors are exhibiting the same problem though. When I eventually get the tray to stay closed, either by cycling power or physically holding the tray in, the clamp motor runs and then does the same oscillation thing. Cycling the main power a couple of times eventually gets that to lock down and the disc starts to play normally.
The disc clamp mech is purely gear driven unlike the tray loading, so although the slipping belts don't help, I don't think its the issue. The belts are odd sizes but I've managed to source a couple that should do the job.
OK, I guess all you can do is work your way through it and see what shows up as you try all these things out. I think it is going to be something like this though.
It is also worth looking at the rails on the scope when the motors run and see if they still hold up cleanly and are not being modulated by the motor current.
It is also worth looking at the rails on the scope when the motors run and see if they still hold up cleanly and are not being modulated by the motor current.
It's become a bit of a challenge now, especially as it plays fine when it eventually loads the disc!
The main PSU is fairly basic with an unregulated 12V rail and a 5V regulated one derived from it. I tried running it from external individual bench supplies to try and eliminate noise from one rail getting to the other. The problem persisted.
All electrolytic caps have been replaced with good quality ones, Panasonic or similar as I've learnt my lesson with cheap caps on tv repairs.
The motor drive chip is a BA6247 and the circuit is as shown in the data sheet except the Vr (pin 8) signal. This is normally set at just over half + supply volts but Akai are controlling the voltage at this with a transistor and zener diode driven from the micro. I tried changing this to the simple two resistor divider but again it made no difference.
The main PSU is fairly basic with an unregulated 12V rail and a 5V regulated one derived from it. I tried running it from external individual bench supplies to try and eliminate noise from one rail getting to the other. The problem persisted.
All electrolytic caps have been replaced with good quality ones, Panasonic or similar as I've learnt my lesson with cheap caps on tv repairs.
The motor drive chip is a BA6247 and the circuit is as shown in the data sheet except the Vr (pin 8) signal. This is normally set at just over half + supply volts but Akai are controlling the voltage at this with a transistor and zener diode driven from the micro. I tried changing this to the simple two resistor divider but again it made no difference.
Fair enough
The noisy motor scenario definitely needs investigating then. A series 10 ohm and suitable caps might work wonders... you just have to try it.
Although you have looked at the rails and used external PSU's it might also still be worth looking at the rails on the motor drive chip. Sometimes something like a low value safety resistor in a rail could be playing up and have gone a little high in value (that is quite common) and that would cause the rails to fall under load at their destination.
The noisy motor scenario definitely needs investigating then. A series 10 ohm and suitable caps might work wonders... you just have to try it.
Although you have looked at the rails and used external PSU's it might also still be worth looking at the rails on the motor drive chip. Sometimes something like a low value safety resistor in a rail could be playing up and have gone a little high in value (that is quite common) and that would cause the rails to fall under load at their destination.