Akai X360-D Smoke/Slow Speed

Disclaimer

This is not a detailed troubleshooting write up. I did not discover this problem, rather I learned about it via  many online forums. The only reason I am blogging it here is to help someone identify the offending component/part easily, as it is not easy to trace its location, neither I could find any place where it is documented  All credits to the folks who identified the root cause and updated various forums.  I am just summarizing what I found/learned from them.

Akai X360-D,  a very nice reel to reel player for its look. I got it with some other vintage gear in a swap meet, like the 80 year old T80 RCA above it. This is a very heavy unit, so be careful while carrying it around. That is why it is kept at the bottom.

This model, like many other reel to reels use snubbers, to protect the relay and switch contacts. Reason being the load switched are the motors and are  inductive. These snubbers  do leak/short due to age and smoke. In this specific model, they  short out and slow the motor down, causing symptoms of a run capacitor failure. Not that the run capacitor will not fail, but  this is the main culprit. The motor winding is also done using two different color enameled copper wire, making you think one set of winding got burned. It is not.

So typical failure mode is that it  smokes as you operate any switch and motor slows down drastically.  Nothing to worry, it is the snubbers. Basically they are a resistor and capacitor in one box. Snubber type  capacitor, which is usually with very low inductance and large dv/dt.

Now, as always, check all paper caps, there are few (2-3) in the relay board. Then to the main offender, the snubbers.

There are about 20 snubbers in the unit.  Main relay board carries about 12 or so, one under power switch  (of different value) and 8 of them totally deep inside the unit attached to main  control switches.

Relay board is right behind the unit, you can remove and replace them easily. However the most failed snubbers are deep inside the unit.

Here is the flow. Remove the unit from wooden case. And remove front panel knobs, and plate. Details in service manual.

Then remove the amplifier unit.

And keep the unit on its side, you can see the main switch PCB where all snubbers are mounted.

 

Here in the picture, I have removed the PCB. You need to de-solder wires to take out the PCB so that you can easily replace the snubbers.

Here is what I did, I used a cap + resistor. The grey ones are my replacement caps, orange is the original snubber, they are blown out.

And the PCB wiring for reference, in case you removed it and cant put it back together.

Here is the mountain of snubbers  replaced in the unit.

Also, found a user named “Derfie”  posted wiring info about the all confusing running capacitor with 5 leads. Here it is –

http://audiokarma.org/forums/index.php?threads/akai-x-360d.324675/

== The two terminals on the top of motor cap with blu/blk and grn/blk wires are dummy terms to connect the motor wires with the harness wires leading to the relay board. The common is red dot, sky colored wire, the white dot white wire (1 mfd) and the yellow dot yel/blk wire (2 mfd) ==