Very hard to say as it looks like it's been cut and scraped away between the pins with something sharp.
I'm surprised I didn't notice this before when I removed the MCU from it's DIL socket and soldered it directly into the board.
It's now linked to pin 22 as shown in the schematic but I can't be sure what is correct.
I'm surprised I didn't notice this before when I removed the MCU from it's DIL socket and soldered it directly into the board.
It's now linked to pin 22 as shown in the schematic but I can't be sure what is correct.
It's nice to learn this is a "stable" state. The problem, of course, is with getting into this state...
Working backwards:
The MCU is happy when both the "tray closed" and "clamper down" signals are at logic level 0 (ground), when both of these sensor switches are closed on the mechanism.
The MCU is also happy when the tray is open and the clamper is up. At this time the "tray closed" and "clamper down" switches are both open. So these 2 MCU pins are both at logic level 1.
Could there be a short circuit between these 2 MCU pins which detect "tray closed" and "clamper down?"
I suggest monitoring both of these pins with the scope.These two signals should never change state at the same time.
Also check for unwanted continuity or resistive leakage between these 2 pins.
Finally I thought of one other useful test:
First get the machine into the "stable" condition where the tray is closed and the clamper is down.
For this test it would be interesting to try it with the tray belt installed, so perhaps put the belt on before the next step.
Then press the "open/close" button.
Does the clamper rise up, followed by the tray opening normally?
Without any oscillation?
-EB
MCU pins 22 and 23 are also connected to MCU pin 15. These 3 pins share a 100k pullup resistor. They also connect to a pin on the CXD1135 labeled "SENSE." The service manual says this pin is an output from the CXD1135
What is the purpose of this signal?
There's a section in the service manual describing all the pin functions for the MCU. It's page 38 of the .pdf file I have. It states MCU pin 23 (\INT2) is "not used."
The logic state of MCU pin 23 might have no effect on the oscillation problem. But it's wise to consider the signals on every pin of the MCU just in case there is something really odd happening. One way to check would be to see if any other MCU pins are following the state of of the "tray oscillation mode" signals(e.g. synchronized with them).
-EB
Your question regarding a possible short or some electrical path between tray closed and clamp down switches got me thinking about a previous attempt at fixing this a few years ago.
I had taken the player to work while on late shift to have a look at it. I removed all four leaf switches to clean them up and took the digital PCB out to fit a new motor controller chip.
When I put it back together, much to my surprise the tray operated normally without oscillation and much to the amusement of my colleagues, I sat there opening and closing it repeatedly in disbelief. I didn't use the player for a while after this and the fault returned.
I wrongly assumed it was the controller chip that had got it going. The leaf switches are very small and completely open construction. Could it be some mould or corrosion creating a resistive path between them or to the chassis that's just enough to falsely trigger the MCU inputs?
I need to remove all 4 switches again and get them under a magnifier, clean them and make sure there is no electrical breakdown anywhere.
I had taken the player to work while on late shift to have a look at it. I removed all four leaf switches to clean them up and took the digital PCB out to fit a new motor controller chip.
When I put it back together, much to my surprise the tray operated normally without oscillation and much to the amusement of my colleagues, I sat there opening and closing it repeatedly in disbelief. I didn't use the player for a while after this and the fault returned.
I wrongly assumed it was the controller chip that had got it going. The leaf switches are very small and completely open construction. Could it be some mould or corrosion creating a resistive path between them or to the chassis that's just enough to falsely trigger the MCU inputs?
I need to remove all 4 switches again and get them under a magnifier, clean them and make sure there is no electrical breakdown anywhere.
I suggest using the scope to look at the signals coming from all 4 switches.
In particular you will want to confirm the voltage cleanly drops all the way to 0V when the switch closes. And also that the logic signal transitions cleanly up to 5V when the switch opens. Do this for each switch.
The pullup resistors are in a SIP package mounted right next to the MCU. It would probably be a good idea to check the resistances on every pin and between pins. Probably wouldn't hurt to simply replace the pullup resistor module. These things are a standard item and cost very little.
I would also take a really close look at how the mechanism actuates those 4 switches. Just in case there is something unusual about how the parts move which actuate the switches.
At this point I'm very suspicious of the switches for the clamper. Although the oscillation starts up when the tray operates the "tray closed" switch, keep in mind that the MCU may be checking the signals from the clamper switches at the same time. The clamper is supposed to be in the "up" position whenever the tray is moving. That means the "clamper up" switch should be closed and stay closed. And the "clamper down" switch is supposed to be open and stay open. But what if something "jiggles" either of these switches at about the same time as the tray reaches the fully closed position?
I'm thinking the MCU firmware might reverse the tray (open it) if it detects the clamper isn't staying fully open.
As for the clamper oscillating when it approaches the closed position, this could be a result of the MCU firmware getting into an "undefined state" after the tray oscillated. This is what made me curious to learn what happens if the tray is fully closed and the clamper is fully open "statically" prior to switching on the power to the CD player. Ideally one would expect the clamper to close without oscillation.
Finally when I was looking at the Akai CD-73 PC board layout in the service manual I saw several jumper wires on the component side of the PC board located around that corner of the PC board where the connectors are for the detector switches. A bad solder connection at a jumper wire which carries the ground bus to an entire section of the PC board could cause all sorts of wacky issues.
Speaking of jumper wires, I've recently begun bench work on my collection of 1980's Philips CD players. There are numerous posts about bad solder connections where jumpers bridge between top/bottom PC board foils, especially "ground" jumpers.
These Philips PC boards are "2 sided" but the holes aren't plated through.
I have one Philips CD player which cannot initialize a CD with a "known to be good" CDM4 optical pickup mechanism installed in it. So I'm going to check intensively for bad connections and bad solder on that PC board before I do anything else.
-EB
When this problem first occurred I had just got divorced and was living in a property that suffered a lot of condensation due to lack of proper heating. I took the player to a local repair outfit that was an authorised warranty service centre for Panasonic and all the other big names.
The guy who got it working said it was corrosion on the MCU DIL socket. Your comment about the switches made me wonder if this problem has returned either at the open switches themselves or around the MCU pins which is now directly mounted to the board. I always clean up anything soldering work with IPA after to remove flux and it may even have been that which briefly cured the problem several years ago. It didn't last very long.
The pull up resistor pack was replaced some time ago too and I even tried swapping it to 4K7 instead of 47K so that shouldn't be a problem. I will concentrate my efforts today on the switches and the area around the MCU where they are connected.
My first CD player was a Phillips CD204. It too developed an annoying and intermittent fault out of warranty. I spent ages trying to find the problem and discovered that gently pressing on the main board would make it burst into life. I eventually found a tiny split in a PCB track but only by scraping away the green solder resist and inspecting it under a magnifier. A small wire link fixed it and it worked fine for years after. I eventually gave it away after I acquired the Akai CD73.
I was scanning through your thread on the Onkyo player you've been working on and noticed the comments about the KSS-151A laser. I think this is the one in my CD73?
The guy who got it working said it was corrosion on the MCU DIL socket. Your comment about the switches made me wonder if this problem has returned either at the open switches themselves or around the MCU pins which is now directly mounted to the board. I always clean up anything soldering work with IPA after to remove flux and it may even have been that which briefly cured the problem several years ago. It didn't last very long.
The pull up resistor pack was replaced some time ago too and I even tried swapping it to 4K7 instead of 47K so that shouldn't be a problem. I will concentrate my efforts today on the switches and the area around the MCU where they are connected.
My first CD player was a Phillips CD204. It too developed an annoying and intermittent fault out of warranty. I spent ages trying to find the problem and discovered that gently pressing on the main board would make it burst into life. I eventually found a tiny split in a PCB track but only by scraping away the green solder resist and inspecting it under a magnifier. A small wire link fixed it and it worked fine for years after. I eventually gave it away after I acquired the Akai CD73.
I was scanning through your thread on the Onkyo player you've been working on and noticed the comments about the KSS-151A laser. I think this is the one in my CD73?
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Today, I removed the complete mech again and took all 4 switches off to clean and inspect them all (again...) to eliminate them as the problem. They all test ok and the only one I rewired was the tray closed switch as there was some minor damage to the insulation but the conductors were not exposed. It's now connected with some very nice mil spec silver plated copper, ptfe insulated wire I happened to have lying around.
I've checked them in operation and all are giving a good 0V when closed and there are no shorts or circuit paths between them. The only anomaly I found today was the front panel timer switch, which is connected to pin 60 of the MCU was giving a poor contact resistance. It is closed in the off position and should read 0 ohms to ground but was showing 28 ohms. I cleaned it with some servisol and tried the player with it in circuit and removed. The oscillation is still present.
Looking at the 4 x MCU switch inputs the logic levels are good and switch correctly unless the tray belt is in place and the oscillation starts and then they follow it as expected. The pull up resistors all measure correct to +5V rail and to each other so I can't see any issues there either.
The problem remains stubbornly unresolved again!
I've checked them in operation and all are giving a good 0V when closed and there are no shorts or circuit paths between them. The only anomaly I found today was the front panel timer switch, which is connected to pin 60 of the MCU was giving a poor contact resistance. It is closed in the off position and should read 0 ohms to ground but was showing 28 ohms. I cleaned it with some servisol and tried the player with it in circuit and removed. The oscillation is still present.
Looking at the 4 x MCU switch inputs the logic levels are good and switch correctly unless the tray belt is in place and the oscillation starts and then they follow it as expected. The pull up resistors all measure correct to +5V rail and to each other so I can't see any issues there either.
The problem remains stubbornly unresolved again!
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I'm thinking our discussion of this project is more popular than the Akai CD-73 itself!
I browsed through my archive (hoard) of old CD players. I don't have a single Akai item.
What do I have? Philips, Magnavox, Marantz, Sony, Carver, Onkyo, Denon, Mission, Proton, Harman-Kardon, Toshiba, TEAC, BSR...
I don't recall any Akai dealers in my area (central Illinois).
-EB
Bad solder joints are a frequent issue in old Philips CD players. Philips was ahead of the technology curve then, using mostly SMD (surface mount) resistors and 2-sided PC boards. Unfortunately the holes weren't plated through. Other companies had problems with that too. Tascam (TEAC's pro side) sold tons of recording studio reel-reel machines (models 32, 34, 38 & others) where every single "through the PC board" connection had to be carefully resoldered on both sides. Some of these PC boards were rather large & inaccessible. Back in the day I spent many hours resoldering them for my clients. That worked. To the best of my knowledge none went "intermittent" again.
Yes, it is the KSS-151A. Check page 12 of the Akai service manual. This alone makes this machine a "keeper." But if you ever decide to part it out, the KSS-151A is one of the most sought-after vintage optical CD pickups. I recently saw people asking $500 USD for used KSS-151A on ebay. It is also said that the KSS-151A rarely fails.
-EB
I had and still have quite a lot of Akai equipment and generally it was quite reliable. I have two integrated amps, AMU61 and AM55, both of which are powerful and still work well but have now been replaced with more modern multi channel receivers.
In the cupboard unused are a couple of GX32 cassette decks and a couple of matching tuners to the amps, all of which still worked when last powered up. Behind them are two VSA77 vcrs and a very rare VS12 vcr from 1985.
The CD73 is the only one I've had any serious problem with. The vcrs had the usual drive belt, mode switch and clutch failure problems after a lot of use (not unusual for any brand) and some of the PSU caps were prone to leaking electrolyte after a few years.
My day jobs have mainly been in military, marine and aerospace electronics with audio/video as my hobby, so I haven't worked on that many CD players. I've never seen a mech like this one though or a peculiar fault like it, even on other Akai units.
As for the KSS-151A, it should be in good condition because the player has mostly been in a faulty state since 2008 and hasn't had a great deal of use since then. Due to this ongoing problem, I swapped it for my other Akai (CD55) some time ago for use on my main system and when that recently developed a problem reading discs I started looking at the CD73 again.
In the cupboard unused are a couple of GX32 cassette decks and a couple of matching tuners to the amps, all of which still worked when last powered up. Behind them are two VSA77 vcrs and a very rare VS12 vcr from 1985.
The CD73 is the only one I've had any serious problem with. The vcrs had the usual drive belt, mode switch and clutch failure problems after a lot of use (not unusual for any brand) and some of the PSU caps were prone to leaking electrolyte after a few years.
My day jobs have mainly been in military, marine and aerospace electronics with audio/video as my hobby, so I haven't worked on that many CD players. I've never seen a mech like this one though or a peculiar fault like it, even on other Akai units.
As for the KSS-151A, it should be in good condition because the player has mostly been in a faulty state since 2008 and hasn't had a great deal of use since then. Due to this ongoing problem, I swapped it for my other Akai (CD55) some time ago for use on my main system and when that recently developed a problem reading discs I started looking at the CD73 again.
With that excellent DSO you should get some images of the eye pattern from the RF test point.
I hooked my works DSO up to the relevant test point before I reluctantly take it back tomorrow.
I 'persuaded' the CD73 to play a disc by cycling the power until it loaded. Screen capture attached.
I hooked my works DSO up to the relevant test point before I reluctantly take it back tomorrow.
I 'persuaded' the CD73 to play a disc by cycling the power until it loaded. Screen capture attached.
Attachments
Somebody else is out there working on a CD73 with the same fault... they just haven't joined the discussion yet!
Akai CD-73 Vintage CD Player with Wood Cheek! visually Top! as defect to hobbyists! | eBay
There's also another up for auction in the UK that's faulty:
Akai CD-73 Vintage CD Player HiFi Separate foulty | eBay
I sent a message to find out if the tray operates correctly and the reply was it is loose, which would indicate one or both belts are broken or missing... or they have been taken off to get the disc loaded.
Not sure if I want another faulty one...
Akai CD-73 Vintage CD Player with Wood Cheek! visually Top! as defect to hobbyists! | eBay
There's also another up for auction in the UK that's faulty:
Akai CD-73 Vintage CD Player HiFi Separate foulty | eBay
I sent a message to find out if the tray operates correctly and the reply was it is loose, which would indicate one or both belts are broken or missing... or they have been taken off to get the disc loaded.
Not sure if I want another faulty one...
I’ve often succeeded at fixing challenging issues when I had multiple units of the same model.
However this works best when each unit has a different fault.
I’m not sure I would enjoy having a row of Akai CD-73 units with oscillating trays on my workbench!
When I look for inexpensive “for parts or repair only” items on ebay my favorite symptom to see in the listing is “totally dead - no power.” My Sony DVP-NS999V was advertised that way. When I received it and popped off the cover, the obvious bulging/vented electrolytic capacitor in the power supply made initial diagnosis quite simple.
-EB
However this works best when each unit has a different fault.
I’m not sure I would enjoy having a row of Akai CD-73 units with oscillating trays on my workbench!
When I look for inexpensive “for parts or repair only” items on ebay my favorite symptom to see in the listing is “totally dead - no power.” My Sony DVP-NS999V was advertised that way. When I received it and popped off the cover, the obvious bulging/vented electrolytic capacitor in the power supply made initial diagnosis quite simple.
-EB
It's a shame I can't be sure whether the eBay one has a working tray mech or not before deciding whether to bid on it. Given the high value of the laser and looking at the few that have sold recently, I think it's unlikely to end at a bargain price.
Faults in a defined state are far easier to deal with than the one like mine, which only happens for a few seconds at a time and is inconsistent.
Faults in a defined state are far easier to deal with than the one like mine, which only happens for a few seconds at a time and is inconsistent.
Hello andyb1712 , Mooly and electricboyo.
What a monumental effort to get the CD73 going! This thread and the fact that I have recently acquired AKAI CD-93 with exact same fault made me stay up until ~5AM reading and finally, registering in this forum. I haven't registered in a forum for at least 20 years!
Am now crashing and need to go to bed, have to work tomorrow/today, however just wanted to post my initial comment to let you know there are others out there.
I am in Australia so my comms will be likely delayed (or shall I say "ahead" ) of yours.
Quick summary. Picked up AKAI CD-93 about 2 months ago (free) as broken. Was told about the tray open/close issue, was hoping it would be just a leaf switch (ha!). tried to power on the unit a couple of days ago. In addition to tray issue the VFD was dead. That was a simple fix - C62 clearly has leaked (but luckily didn't damage the PCB) and was open. Replaced with 220uF (didn't have a 50V 330uF in stock) and the VFD is working now.
There is also a cracked in half zener D24 on the analog board, but I'll get to it if manage to fix the tray issue. Currently analog board is removed.
Switching the power quickly sometimes keeps the cd loaded and start spinning but it doesn't appear to be playing. It doesn't read the TOC. So it is possible my unit also have a pickup issue Haven't checked if laser fires up yet.
And the reason I haven't checked "the laser" is this. I thought that maybe if one of the motors is too stiff - it may cause issues pulling too much current and possibly causing voltage to drop. So I tried to add a drop of oil to both loading and clamp motor shafts and run them off 9V for a bit of time to let the oil get in.
Here is where I possibly killed my motor driver IC8... rookie mistake. With unit powered off I connected 9V lab power supply directly to clamp motor without checking the polarity. and BOTH loading motor and clamp started to spin. Not sure if it's normal, haven't analyzed the internal schematic of the IC8. I then unplugged the motors from the PCB and let them separately run off 9V for about 30-45 seconds each. Also added some silicone lube to the clamp gear.
After assembly, the issue was of course still there (would be too easy, after reading 18 pages of this thread), the sound clamp motor +gear make gotten much quieter due to lubrication. However, I now got myself the same problem as Andy had with wrong motors (only I did not change motors) - a smoking R71. I've powered off the unit when noticed the smoke. Did try one more time to identify where the smoke is coming from. The motors still operate but R71 (and probably IC8) are getting very hot very fast so I cut the power after ~5-7 seconds.
So yes, there are people out there who read every single post in this thread, and yes, AKAI CD-93 is also cursed. I will try my best to help Andy (and myself ) to resolve the problem. Of course Andy has been dealing with this literally for months (years?) , huge respect for your perseverance. Not sure how long will I last, but will try.
What a monumental effort to get the CD73 going! This thread and the fact that I have recently acquired AKAI CD-93 with exact same fault made me stay up until ~5AM reading and finally, registering in this forum. I haven't registered in a forum for at least 20 years!
Am now crashing and need to go to bed, have to work tomorrow/today, however just wanted to post my initial comment to let you know there are others out there.
I am in Australia so my comms will be likely delayed (or shall I say "ahead"
) of yours.Quick summary. Picked up AKAI CD-93 about 2 months ago (free) as broken. Was told about the tray open/close issue, was hoping it would be just a leaf switch (ha!). tried to power on the unit a couple of days ago. In addition to tray issue the VFD was dead. That was a simple fix - C62 clearly has leaked (but luckily didn't damage the PCB) and was open. Replaced with 220uF (didn't have a 50V 330uF in stock) and the VFD is working now.
There is also a cracked in half zener D24 on the analog board, but I'll get to it if manage to fix the tray issue. Currently analog board is removed.
Switching the power quickly sometimes keeps the cd loaded and start spinning but it doesn't appear to be playing. It doesn't read the TOC. So it is possible my unit also have a pickup issue
Haven't checked if laser fires up yet. And the reason I haven't checked "the laser" is this. I thought that maybe if one of the motors is too stiff - it may cause issues pulling too much current and possibly causing voltage to drop. So I tried to add a drop of oil to both loading and clamp motor shafts and run them off 9V for a bit of time to let the oil get in.
Here is where I possibly killed my motor driver IC8... rookie mistake. With unit powered off I connected 9V lab power supply directly to clamp motor without checking the polarity. and BOTH loading motor and clamp started to spin. Not sure if it's normal, haven't analyzed the internal schematic of the IC8. I then unplugged the motors from the PCB and let them separately run off 9V for about 30-45 seconds each. Also added some silicone lube to the clamp gear.
After assembly, the issue was of course still there (would be too easy, after reading 18 pages of this thread), the sound clamp motor +gear make gotten much quieter due to lubrication. However, I now got myself the same problem as Andy had with wrong motors (only I did not change motors) - a smoking R71. I've powered off the unit when noticed the smoke. Did try one more time to identify where the smoke is coming from. The motors still operate but R71 (and probably IC8) are getting very hot very fast so I cut the power after ~5-7 seconds.
So yes, there are people out there who read every single post in this thread, and yes, AKAI CD-93 is also cursed. I will try my best to help Andy (and myself
) to resolve the problem. Of course Andy has been dealing with this literally for months (years?) , huge respect for your perseverance. Not sure how long will I last, but will try.
Things like that are easily done. It's quite likely applying voltage has zapped the drive chip and tbh worst case scenario is that it allow a reverse polarity to appear across the rail that the drive chip runs on. That said you would be unlucky if that caused further issue beside the drive chip. I bet there are diodes in the chip output across the motor feed to suppress back spikes and so with luck they protected everything, even they themselves fail short.
Something I just thought of... did I mention it earlier, not re-reading it all though... is to look with a scope of the output ports of any uP or syscon chips that are not changing state as expected and look closely to see if there is a minute change in level indicating a failed output stage on the port.
I remember once a VCR that had something like that. A port was stuck but did shift a few hundred millivolts. It was a one off but we fixed it by using a couple of transistors to restore the levels. It was a bodge and the customer knew and was happy for us to do it. There were never any comebacks from it.
Something I just thought of... did I mention it earlier, not re-reading it all though... is to look with a scope of the output ports of any uP or syscon chips that are not changing state as expected and look closely to see if there is a minute change in level indicating a failed output stage on the port.
I remember once a VCR that had something like that. A port was stuck but did shift a few hundred millivolts. It was a one off but we fixed it by using a couple of transistors to restore the levels. It was a bodge and the customer knew and was happy for us to do it. There were never any comebacks from it.