Akai M8

MRL_Audio

RIP 2022
Subscriber
Couple of questions. Just picked up a nice example of the Akai M8. Looking to restore it and not bust out the amps... just yet. Plays fine and for more than 30 minutes, however it gets quite hot. Hot enough that the take up reel got so hot it warped the plastic take up reel. A clear Audiotape brand reel and tape. The play function never stopped or slowed but I stopped it as soon as I noticed it. Never have seen anything like this before. My general understanding is this could be from the motor cap needing to be replaced. I have looked for a match but have not been able to locate one. Appreciate any help locating the proper cap. In the service manual it's listed as a "Condenser 2.2uF + 0.6uF". Is there a way to check it with a dvm to actually confirm it's bad?

On a secondary note I have a couple of these. They both arrived set to 110v. The set options for US 60hz and 110v. Options for voltage is 100, 110, 120, 200, 220 and 240. I realize the US standard household voltage is 120 but I have looked at many pictures of these online and I have yet to see one set at 120. If the pic is a US picture it's set for 110. Is this correct and what's the logic since the US is 120v 60Hz. Thanks.
 
Classic deck. Though I've never owned one, I've always admired the amp pair on those. I, like you, vote for the motor run cap being ca-put. It has done it's job for decades, is past it's prime, and deserves a proper burial. Shouldn't be hot enough to warp reels! I wouldn't even bother testing it, just replace. Have you tried Ebay or Mouser for a replacement? Not sure why 120V setting wouldn't work, has to be many of these in the US.
 
Make sure it’s sctually the motor that’s getting hot, kind of unusual for the motor to get hot without also slowing down or stalling out altogether. Also make sure the 50/60 cycle switch is set to 60, if it’s set to 50hz that’ll heat things up.

The motor might need ludrication after all these years too (they didn’t plan on them still being in service after 50 years so lifetime lubrucation is kind of a relative term). You can open those motors up and lubricate them even though they don’t have oiling tubes but don’t try to remove the bearing caps on the back of the motor as the screws are threadlocked in place. Instead you remove the four screws around the perimeter of the motor and then slide the outer band off, motor comes apart in two pieces.

If you need a 2.2uf motor cap you can replace it a standard ceiling fan cap available on feebay. You don’t need to worry about the smaller .06uf value unless you plan on using it with 50hz power since its only for the 50hz setting, just cap off the wire that went to that side of the old capacitor. New motor caps look like this:
universal_ceiling_fan_capacitor_22uf__3_wires__1515584368_73f760db.jpg
 
@audiojones - appreciate any other thoughts on why the take up reel table gets so hot. As I mentioned the motor keeps right on happily turning and the tape plays fine, it's just that the take up reel table gets really hot. Is there anything in particular I need to watch out for is I serve that side? I need to do a little more testing and I have not lubricated the deck yet. I'll make time to do that this week. I noticed you have posted many time on the Akai/Roberts decks so I assume you have a great working knowledge. Thanks
 
I’d say open ‘er up and see what’s getting hot in the vicinity of the take up reel table when it’s running, maybe the transformer or some other component nearby is having an issue. I believe there is a back tension clutch under the reel table that operates from an idler wheel, could be problems there but I kind of doubt it would heat things up that much. Take the faceplate off and make sure it’s not the automatic cut off switch or one of the spark suppressor caps burning up. That’s a weird one for sure!
 
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Figured this one out but still have questions @audiojones, others. First - the issue with the heat was that the "Take-up Roller A" was stuck to "Take-up Roller B". I took the whole thing apart. Clean it, lubricated, reassembled and was back up and running properly. When I noticed the heat issue last weekend it was tied to the take-up reel. Reading was about 115F. Much too hot. Supply reel was at 89F. Now both reels are at 89F after 2 hours of play time. Perfect. I did not change the motor cap while I was in there but I have what is needed to do the job. I have a 2.2uf and I have a 0.5uf and 0.1uf cap. That should give me the required capacitance and leave it to use both 60hz and 50hz if I move to another country... ;) I am confused on the three wires coming out of the cap and how to hook them up to what I purchased though. They are red, green and yellow. They all go to the speed switch. I was assuming that all three wires of the caps I purchased would be tied back to a ground wire, the green one? The two other ends of the 0.5 and 0.1 would be tied together to either the yellow or red wire. The remaining end of the 2.2 would go to the remaining wire, again yellow or red. I have no idea how these wires would be used with the new caps. I am also confused by the schematic since it shows a third cap. Listed as C29 0.5u on mine. The 2.2 is listed as C30b and 0.6 is listed as C30a. Where is C29 physically? I am not a pro at reading schematics but it makes it looks like it is part of the can. Physically there is another cap off to the side of the speed switch but that is a 1uf cap on the cap itself. I suppose it could have been replaced at one point. Below is a copy of the schematic reference.

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Where is C29 physically? I am not a pro at reading schematics but it makes it looks like it is part of the can. Physically there is another cap off to the side of the speed switch but that is a 1uf cap on the cap itself. I suppose it could have been replaced at one point. Below is a copy of the schematic reference.

I think you are correct that C29 may have replaced at some point with a 1uF capacitor. It should be possible to verify this if the other end of the capacitor is connected to switch SW8. The 0.6 and 2.2 uF capacitors are labeled as C30a and C30b which normally indicates that they are two sections of the same capacitor. The wire colors you mentioned are not shown on the schematic which makes it difficult to advise you about how the 0.1, 0.5 and 2.2 uF should be connected. The schematic does not show any of the capacitors being connected to ground. One end of them is connected to the speed switch (SW9) which connects them to different sections of the motor windings depending on the position of that switch. Their other ends are connected to line frequency switch (SW7) which connects one or both of them to the motor windings depending on whether 50 or 60 Hz operation is selected.
 
One end of all three caps get tied together and connected to the wire that was connected to the common terminal of the original can capacitor (tied to the center terminal of the speed switch). The 2.2uf gets connected to the wire that was originally connected to the 2.2uf terminal on the old metal can capacitor and the .6uf gets tied to the wire that was originally connected to the .6uf terminal on the old metal can capacitor. The original can is marked on the side as to which terminal is which uf value and which terminal is the common. You can't use .1uf in place of the .6uf though if that's what you were going to do, the values for motor phasing need to be right on the money.

The .5uf (c29) is for the fast forward / rewind speed and should be connected to a microswitch that is operated by the FF/REW lever (switch is under the faceplate I believe). I don't know if it's part of the multi section can capacitor or not but I'm pretty sure it's a separate capacitor. Follow the wiring and you'll find it, it's connected between the common connection of the original motor capacitor mentioned above and the FF/REW switch and it should be a can capacitor because of the voltage requirements.
 
I've got a feeling the manual has an error in it and that C30 is the multi section can and C29 is the little cap mounted on the bracket in this pic. They're calling that little cap C30A, so if that's the case then C29 is part of the multi section can. Take a look at the uf values stamped on the side of the can, see if they're 2.2uf and .6uf or 2.2uf and .5uf. You can see how close these values have to be, there's no wiggle room between .5uf and .6uf or Akai would have just used the same value capacitor and saved the trouble and expense of stocking and installing a slightly different value.
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Here's another question. Looking thru the owners manual the V4 tube is listed as 6AR"S". You can see that below.

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In the service manual V4 is stated to be a 6AR"5". What the... which is it?

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I pulled the tube. It's the original NEC 6AR5. I find it odd that the Operations Manual says "S" and I can find not other reference to that on the net... I am a trailblazer!
 
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On to yet another question... when I utilize the internal speakers the VU meters deflect as expected. But now I have the unit connected to my amplifier and am using the "Pre-Amp Out" 1/4 inch connections to go to the amp. Works great but the VU meters do not function when I do this. Is this normal and by design? Thanks for continuing to entertain my questions.
 
Hello everyone, I would like to use my akai M8 without the recorder part, but I don't know where to connect my power plug to the left amp.
Thanks for your help.
 
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