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Tascam 424 Mkii capstan speed control voltage
Old 18th July 2020
  #1
Here for the gear
Tascam 424 Mkii capstan speed control voltage

Hi all, this is my first thread and I am hoping to find a few who venture as far as I do when it comes to taking care of my gear. I have a Tascam 424 Mii that I replaced the capstan motor and belt on. I expected to have to adjust capstan speed with the speed control PCB but when I measured the voltage going to the capstan motor "HOLY JESUS" 14.87 volts! No way. I chased down the reading to the power supply board but found nothing out of the ordinary. I don't have schematics for most gear but methodically measure and check based on education and personal knowledge gained from practical work experience. Has anyone run into this over voltage and what if anything solved this to gain back normal speed operation of the capstan motor?
Old 19th July 2020
  #2
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Rick Dalton's Avatar
Quote:
Originally Posted by hotrod79 View Post
Hi all, this is my first thread and I am hoping to find a few who venture as far as I do when it comes to taking care of my gear. I have a Tascam 424 Mii that I replaced the capstan motor and belt on. I expected to have to adjust capstan speed with the speed control PCB but when I measured the voltage going to the capstan motor "HOLY JESUS" 14.87 volts! No way. I chased down the reading to the power supply board but found nothing out of the ordinary. I don't have schematics for most gear but methodically measure and check based on education and personal knowledge gained from practical work experience. Has anyone run into this over voltage and what if anything solved this to gain back normal speed operation of the capstan motor?
Here is something that may help.

https://music-electronics-forum.com/...t=40752&page=2
Old 23rd July 2020
  #3
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Thanks Rick, I took the original motor apart and the little circuit board inside contained to active elements and three passive elements. The main active element was a Sanyo motor controller devise with 5 legs for controlling compact DC motors and then there was a transistor. I dug up the specs on both devices and checked availability for them. The other parts are two resistors and an inductor. I also picked up three more motors and as it turned out they were not what I ordered and I hope I don't have a problem getting the right ones. The motor that is in the 424 now I think I am just going to employ a voltage divider and lower the voltage to see if I can get the speed down to where it is adjustable. The other thing I think I'll do is order the Sanyo motor controllers and see if the original motors can be fixed.
Old 23rd July 2020
  #4
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Rick Dalton's Avatar
Quote:
Originally Posted by hotrod79 View Post
Thanks Rick, I took the original motor apart and the little circuit board inside contained to active elements and three passive elements. The main active element was a Sanyo motor controller devise with 5 legs for controlling compact DC motors and then there was a transistor. I dug up the specs on both devices and checked availability for them. The other parts are two resistors and an inductor. I also picked up three more motors and as it turned out they were not what I ordered and I hope I don't have a problem getting the right ones. The motor that is in the 424 now I think I am just going to employ a voltage divider and lower the voltage to see if I can get the speed down to where it is adjustable. The other thing I think I'll do is order the Sanyo motor controllers and see if the original motors can be fixed.
voltage divider is a good idea, I read where others have had the same problem with ordering that motor and getting something other.
I rebuilt one for an Tascam 238 a few years ago, i thought i Doc'd it on here, But I was under a different user name,, So? Sounds like you've got a pretty good concept of the workings. That's a Huge Plus. Good Luck, Man.
Old 24th July 2020
  #5
Here for the gear
I forgot to mention that when I took the little board out of the old motor that I used a 9 volt battery to power the motor to check that just the motor was working. It worked. Then I used two 9 volts for 18 volts and the motor spun even faster. I now feel a bit more confident that replacing the Sanyo motor controller device will return the motor to normal operation. I also have 2 464 Tascams with motor and belt problems as well so this is going to get all these machines back up and running. I let you know after I get the parts and put them in and see if the old machines come back to life in the fast lane again.
Old 24th July 2020
  #6
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Rick Dalton's Avatar
Quote:
Originally Posted by hotrod79 View Post
I forgot to mention that when I took the little board out of the old motor that I used a 9 volt battery to power the motor to check that just the motor was working. It worked. Then I used two 9 volts for 18 volts and the motor spun even faster. I now feel a bit more confident that replacing the Sanyo motor controller device will return the motor to normal operation. I also have 2 464 Tascams with motor and belt problems as well so this is going to get all these machines back up and running. I let you know after I get the parts and put them in and see if the old machines come back to life in the fast lane again.
Sounds like a plan, one has to watch those trimpots, they can be a Beeach.
Old 31st July 2020
  #7
Here for the gear
Well I finally got started working on my Tascam machines and looking a the partial schematics that I have I see the symbol for digital transistor switches and they are triangle shapes that have a N or P inside the triangle one line at the base of the triangle and one line at the point of the triangle, and one line from the side of the triangle. Depending whether it is N or P type transistor (NPN&PNP), the N has a circle at the point of the triangle and the P has the circle at the base of the triangle. It dawned on me that I am use to the conventional symbol for transistors so I don't know what the base, emitter, or the collector are for these triangles, I looked at the voltages and tested the logic function and thats where the trouble is coming from but knowing these symbols and what legs of the transistors are what would be a big help. Anyone run into these symbols and know?
Old 21st August 2020
  #8
Here for the gear
Hi All, Well after all this time I finally have everything back up and running like almost new. I would also like to share what I have learned about working on these Tascam Portastudios because I have a lot of them and still find relevancy in using them. First the capstan motors. There are some very easy things anyone can do to repair these if they do not have burned up armatures. I have repaired six of these this past month alone. What I know is this the IC motor controller is what quits and/or malfunctions, it does so eventually because it runs hot closed up inside the small motor housing. Replacing this IC will restore the motor back to working condition. Also unsoldering the little circuit board is a no brainer but you have to be aware of the points to unsolder and be quick about as not to overheat the board and components. Done properly it pops right out. I have also found places inside the machines close to either the tape transport mechanism or the speed controller board to install the motor pcb and connect it successfully to motor and speed controller board as the motor IC will now never overheat again and if you so choose you can even heatsink the IC. These mods also allow for non-original motor replacement should sourcing an original or one of the newer 2000/4000 rpm motors be difficult. I have used newer 2000/4000 rpm motors just to verify they will indeed replace the original and they do! I also have a good supply of belts because I do not know if you can make these last indefinitely even with regular maintenance. So if anyone needs help with one of these portastudios just PM me and I will provide all the info and pics I have aquired so you too can have up and running in no time.
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