Otari 5050 tech tips – Various Transport Problems

Transport Problems……Dead Capstan Motor……Dead Reel Motors…….Only one speed working etc.

Equipment Needed

 Method # 1 and 2

  • Philips screwdriver
  • DeOxIt D5, either in a spray can, or better yet, in the liquid small bottle with the precision dispenser
  • ohmmeter (optional)

Method 2 only

  • All items for Method 1, plus,
  • Dremel drill tool, with a small round abrasive bit in it

There are a bunch of transport problems in the Otari 5050 MkI and MKII models that are all related to the reel size switches, the tape speed switch, and the ‘edit’ switch. These are the three push buttons that are located to the right of the main power switch on these models.  (the later MkIII is not affected, as the construction of the deck is different). Faults include, but are not limited to:

  • dead capstan motor (may pulse a bit when the deck is powered up but is otherwise dead. The capstan shaft spins freely though).
  • only one speed works, the other speed is dead
  • Rewind and fast forward do not work
  • takeup reel not spinning in play mode
  • tape tension is incorrect, or intermittent
  • All of these problems can be traced back to bad switch contacts on the three switches. This is most common when these decks have been sitting unattended for years. The switch contacts corrode or oxidize within the switch, causing dead or intermittent contacts, which cause the aforementioned transport problems.

A typical MX5050 Mk1 with the top knobs removed

All of these switches are DPDT, and can be accessed by removing the Philips screws that hold the electronics in place. The metal cover plate over the switches, held in place with two Philips screws should be removed as well.

Method # 1 (quick and dirty)

The Otari 5050 comes apart easily, as it was designed to be serviced. Remove the top knobs of the level controls with an Allen key (the Allen heads appear to be imperial sized for some reason, my metric Allen keys didn’t fit), which will then allow the removal of the lower knobs, which pull off. The front panel comes off at that point, and two additional screws at the bottom front of the deck also unscrew, which allows you to tilt down the whole electronics section, away from the transport.

Front panel removed, showing the two small brass Philips screws at the bottom that need to be taken out so the electronics can swing down out of the way

You can now see the underside of the power, reel size and speed control switches. With the power off, you can use an ohmmeter to verify that the switch contacts are not working in either speed mode. (the deck should be unplugged while you measure the switch contacts with an ohmmeter)The switch is in a DPDT configuration, all 6 contacts need to be working properly.

Electronics removed, showing the switch PC board where defective speed control switch is located

The cover over the switches comes off with the one Philips screws on each side, but the head cover of the deck may also need to come off to take that switch cover off completely.

The quick and dirty fix if you’re in a pinch or rush, is to simply shoot DeOxIt contact cleaner down the switch shaft in the middle top of the switches, and work the latching pushbutton switches rapidly up and down about 30-50 times in a row. The DeOxIt should be moved around by the constant action of the switch, and hit the switch contacts. As the DeOxIt cleans the switch contacts, they will come back to life, and the various transport problems will cure themselves. Check both speeds, to make sure the capstan motor changes speeds appropriately, and that the reel tension changes when you change the reel size switch. Finally, in ‘edit’ mode, the takeup reel should stop turning, so that you can spool tape through the deck.

Method 2 – a more thorough cleaning

While method 1 works most of the time, I’ve found over the last 5 years that decks that have been sitting for a long time in a poor, damp environment, may not respond to DeOxIt shot down the switch shaft. More drastic measured are needed. Fortunately, this second method has worked flawlessly for me, and I now do this with every Otari 5050 that I sell.

With this method, a tiny hole is drilled into the front of each switch, on the left and right sides of the  switch contacts, so that you can spray, or drip DeOxIt directly on the switch contacts.

Using a small round abrasive bit in the Dremel tool, drill a tiny hole into the front of each switch. The switch body will drill perfectly, and there’s no chance of the switch housing shattering under the pressure of the drill bit. Beware however, that the  drill bit will break through the switch, and you want to limit the drill bit once it’s broken through the plastic housing, otherwise you will hit the switch contacts and potentially bend or shatter them. Proceed with caution,  and drill 6 holes into the 3 switches as shown below:

Blow away the plastic residue so it doesn’t fall into the switches.
Shoot a liberal amount of DeOxIt D5 into each hole. A ½ second shot at the lowest setting of the nozzle will do it. Put the switch in the other position (up or down), and shoot another ½ second blast of DeOxIt into the switch. Do that on both sides of each switch, and then rapidly work that switch up and down 30-50 times. That will move the DeOxIt around, and the contacts will be cleaned. Do that with each switch.

The switch contacts should now be clean, and the deck transport functions should work fine.

Note that I have had two out of about 30 decks where the spray DeOxIt didn’t do the trick, the switches were too oxidized. I ordered in a bottle of the DeOxIt liquid, with the precision steel applicator, and put a few drops of that version of DeOxIt into each hole in both positions of the switch, then worked each switch again 30-50 times. On those two switches, the liquid DeOxIt restored the switch contacts perfectly.

NOTE:  A dirty/intermittent pitch control and switch will also cause a capstan motor to be dead at both speeds. In that case, access the pitch control through the back of the deck by taking off the back of the 5050, flip down the back motherboard by removing 6 Philips screws, 3 down each side of the motherboard, and up against the front panel of the deck is the pitch control pot and switch located on the top of it. Clean that switch with DeOxIt spray, and work the switch and the pot to move the DeOxIt around.

Method 3- replace the 1, 2 or 3 switches that won’t clean via methods 1 and 2.

NOTE: Since implementing method 2 of cleaning the switches, I have not had to replace any of the DPDT switches, since every one of these was cleaned successfully. If however you have a bad speed, tape size or edit switch, that won’t clean itself, and you’ve confirmed that the contacts are open in one or both positions, you can always replace the switch via the below method:

Here’s the challenging part: On one deck I recently worked on, the glue that Otari used to hold the plastic knobs to the switch shaft hardens up, making removal of the switch covers exceptionally difficult, and you need to remove the knobs to get the switches out! I used a bit of heat (not enough to melt the knobs!) to soften the glue, along with some careful pressure with a flat blade screwdriver between the switch and knob will release that knob.

Switch PC board removed from deck, ready for switch to be unsoldered

Switch knobs removed, switch screws removed, PC board is ready to drop down

Showing the glue that holds the knobs to the switch shafts

One the knobs are off, you can undo the Philips screws that hold the switches and the Pc board to the front of the deck. The switches unsolder nicely, but you’ll likely need a replacement switch (found on ebay from time to time).  These are getting hard to find.

Reassemble, and verify that the tape functions are now restored.