Yamaha MT120 Tear Down

[@briankeenan4901]

The part in the beginning when you say that knob removal was not necessary when changing belts is absolutely priceless. Thanks for being so knowledgeable and considerate.

[@EgoShredder]

I had the MT100 MkII predecessor in 1991 until 1997. Went digital with a Fostex DMT 8 v2 after that, but the Yamaha was an excellent machine and taught me a lot about recording. I got the nostalgia bug back in 2016 and bought a used Yamaha MT3X in mint condition for £60. Love the meterbridge and extra features that mine lacked like sync and mixer channels for feeding in live stuff. Managed to find a cheap Yamaha FSK sync box for £12, and got an old Yamaha SY55 keyboard sequencer and RY30 drum machine to all sync to the four track. Worked like a charm. There is something about the old era of doing recording, that had a bit of magic to it which is missing for me in the digital age.

[@DagoSanDiego]

Thanks, Ive been waiting for something as informative as this on the MT120 for years. I made a bunch of tapes in the mid 90's of S.F. bands playing in their practice spaces, and you have helped me ressurect them!

[@Tetrakan]

That's great, if any of those recordings find their way to youtube share a link here please

[@BlazeONEANdChill]

A good day when you pick up one of these for 20 and you find out tetrakan already has a video up.

[@lawrencerasmus]

What drives the play, FF and Rewind ? My belts are good but they don't turn

[@peterdosa7342]

Great video!do you know what would cause the reels not spinning in either direction?the capstan spins all right but the reels don't engage. The belt looks all right. Update!!the source of the issue is the clutch assembly. Any idea why it won't t engege?

[@kvfive]

Your teardown vids are always helpful, I’ve changed belts on a few cassette multitrackers now - always refer to what you show. Fostex XR7 is one I wish you had a vid on, belts are tired on mine. Cheers for what you do :-)

[@Tetrakan]

Thanks. I'll get to the XR7 eventually....isn't the XR5 which I ahve covered very similar though? Apart fromt he mechanical transport buttons I mean?

[@lawrencerasmus]

I have no eq , could it just be the connection? Other than that it works except it needs a counter belt

[@normalkills]

The belt disc (with the felt) of my clutch assembly does not engage / move the gears. Seems like there’s a tiny bit of space between the belt disc and the gear ⚙️ disc. Any ideas? I didn’t see a spring or clamp to add tension in your teardown or in the manual.

[@mutetouretteshimself]

Same here

[@senorfrio]

I'm working on one of these right now and a mystery spring just fell out when I removed the transport assembly. I can't find it on the exploded view parts list in the service manual. It is a conical spring with no hooks or loops to attach it anywhere. About 9mm wide and 7mm tall uncompressed. About 10 turns. Not a very stiff spring. Any idea where it may have fallen from? I thought maybe it went under the smaller black plastic belt pully but again, I couldn't see how it attached to anything.

[@StevenHadfield]

Nice tear down and channel. Thanks. DON'T DISTURB THE RIBBON CABLES - Wise words. Luckily I'd decided to replace these anyway as I've a feeling I'm going to be in and out of this thing, but wow these are horrible, couldn't get the ribbon out, never mind back in. For replacements JST PH cables have the correct 2.0mm pin spacing, for anyone looking to do the same. The primary issue with mine is the right side of the mixer is attenuated on all sources in the mixer section, with noise on the fader. The monitored tape signal is fine. Cleaning and a brand new master fader from RS has not resolved this, so I'm suspecting it's a bad capacitor leaking DC current into the pre-fader summing Op Amp (IC10). Does this sound correct? Anything else I should investigate? Regarding the issue with the door mechanism in the video, It looks like you have everything, the door just extends past the pivot and is restricted from moving by the L shaped metal spring. The post which is broken on yours, doesn't have anything attached to it, on mine. Cheers!

[@Tetrakan]

Thanks. What you are saying seems plausible. When faced with those sorts of problems I also replace the (usually) 10uf 16v electrolytic capacitors, which separate the buffers on either side of the master fader from preceding and following gain stages. My theory is that leaky caps here interfere with the impedance relationship between gain stages, but whatever thd actual reason, I have a very high rate of success replacing these in addition to any caps between the opamps and Ground or power rails.

[@StevenHadfield]

@@Tetrakan I'll do that. Thanks.

[@bonistik]

Is it at all possible to source those long chassis screws nowadays, for a unit that's missing some?

[@Tetrakan]

I'm afaraid I haven't researched that, I rely on spares donors.

[@ocean457]

So if you made it with the JSP-HX connectors, that means the connector's pitch of the MT120 are different from the japanese CMX100II. (They look like coming from the same product line so I was assuming they're the same internally somehow). My Yamaha CMX100II have these bord-in connectors with a Pitch of 2mm, in which case the JSP-HX (with the pitch of 2.5mm) wouldn't fit.

[@StevenHadfield]

I found JST-PH 2.0mm fitted my MT120.

[@ocean457]

@@StevenHadfield Yes, PH is the correct one, it cannot be the HX. Tetrakan made a mistake here.

[@lehesson]

Hi, thanks for the video. I have the Yamaha MT100 II and it plays warped. Is the anything I could do or do I need a new motor?

[@Tetrakan]

First replace all rubber parts and lubricate all moving parts. If the problem persists, you might need a new motor

[@lehesson]

Thank you, I’ll give it a go.

[@thespots]

VERY helpful video! Thanks so much. I noticed at the end, you re-attached the door with the unit intact. I need to replace my door. Do I need to take the entire panel off first? Much appreciated!

[@pieta9097]

Hello! a bit unrelated to this video but i recently got a portastudio 488. the original motor is beyond repair so i replaced it with a mabuchi 2400 rpm 12v motor i got from ebay. it's running almost 70% too fast. is there anything i can do?

[@Tetrakan]

I'm not totally clear on the answer to this but I might be able to make some educated suggestions if you could tell me which model of motor your replacement is, and does it have 4 or 2 input cables?

[@shawnlennon1947]

look at that built in transformer lol. that probably adds some weight.

[@kaerustation]

Hey! I wanted to ask you if the mt120 got a built in auto stop feature that prevent tapeloop like some other yamaha models. Thanks a lot for your input :)

[@Tetrakan]

There's a switch on the front panel to defeat autostop, so I'm fairly sure you could use loop cassettes provided that switch was set to "off"?

[@rayh72]

Excellent explanation and much appreciated. I have just bought mine back into action after 20 years and found that my channell 1 input would not record (plays back and bounces to fine). This video helped me to get to see the input jack in question to see if I could repair/replace it. However, not sure I can as the pin solder point seems to have pushed through and broken away from the circuit board and so broken the connection running through the circuit board. Just wondering if I could solder some external wires across somewhere to compensate... do you think that might fix it?

[@Tetrakan]

Thanks. Yes you could glue the socket in place and solder a section of wire from the base of the socket to the next un damaged lug on the circuit board, follow the lifted trace on the board to see where the far end of the wire should go.

[@MichaelJ023]

Any idea on how to adjust the bias on these to accept type I tapes? Hopefully they labeled the bias adjust pot.

[@Tetrakan]

The bias has two parameters, frequency and amplitude. Usually you adjust frequency once at the oscillator, but must set the amplitude in 5 places, one adjustable component sets overall level for all four erase tracks, and four separate adjustments one for each segment of the record head. On this model those components are well annotated. I don't know what the amplitude and frequency requirements are for type 1 tape, you'd need to research that, please share the information if you find it.

[@MichaelJ023]

@@Tetrakan Thanks for the info. I have an MT100 II which hopefully is similar inside, with labeling. I can’t remember the setting for Type I. A few years ago it was more popular to convert the decks to use type I tapes. But now I can’t seem to find the details. I’m sure it’s still much better to use Type II tapes anyway, but it would be nice to know how to do it.

[@mutetouretteshimself]

Hi there, thanks for the very informative vids. This mechanism doesn’t look like the normal gec mech.. do you have a teardown for this one? Is it similar to a mech found elsewhere?

[@Tetrakan]

It's really similar to the transport found in the Marantz PMD 740, I think I talk about it a bit more in the playlust of videos for that unit?

[@mutetouretteshimself]

Cheers!! Looks like the pmd740 has a doohickey pushing the idler pulley clutch together, where the yamaha seems not to. Is that right? What pushes the clutch together on the yamaha?

[@Tetrakan]

Pass! Sorry, it's been at least 18 months since I deconstructed either transport, and neither is a model I've worked on very often. Hopefully, there are enough clues in my footage to help you resolve yourproblem? If not, comparing exploded views from service manuals can help...

[@JamesTurner-sb5ib]

Love your videos, thank you for providing so much useful info. I recently purchased one of these units but the monitor/mix/stereo switch is very scratchy and makes a racket when used. The overall output volume is very low and I have to have all sliders up all the way. This is during playback and general monitoring of instruments. Would a good clean of the mixer maybe fix this issue? Thanks

[@Tetrakan]

Thank you. It definitely is the first step in a process of elimination, I wouldn't meddle with the electronics or pay anyone else to do so until the unit has been cleaned thoroughly, it could resolve your issue.

[@JamesTurner-sb5ib]

@@Tetrakan bloody good advice I reckon. Just gave it a good clean and that fixed the horrible switch. The only issue it has now is low output volume when listening in stereo mode. I can red line channel one through mic line but it barely tickles the ear drums. Looks in pretty good nick though so ain’t giving up on it. It’s got more joy to bring

[@richiedagger733]

Can we get a tutorial on use? I just bought one but I have no idea how to work it hahaha

[@Tetrakan]

Eventually, but not soon...the one in the video got cannibalised for parts, so I'd need to buy another. The next video I publish will be a 1 hour tutorial on 4 track recording demonstrated on a not dissimilar Fostex, keep your eyes peeled....

[@gerry5265]

I'm following along at home and I noticed that you dont really need to mark the mixer pcb screws as yamaha labeled them with a little screw icon themselves, also the reason why the plastic casing on yours is melted a bit could be because from the factory the loktite-ish stuff they put on the screws makes them pretty tough to remove, i had to use a soldering iron to try melt the adhesive stuff. thanks

[@Tetrakan]

Noted, thanks

[@gerry5265]

@@Tetrakan hey, thanks for the quick reply! while I've got you here I was wondering if you could help me with mine! It plays back fine but any input in all channels is super attenuated and gainy, it's like that while monitoring and recording. lmk if you have any idea what could be wrong with it, I've already tried cleaning out the pots and sliders but hasn't done anything :/

[@Tetrakan]

@gerry5265 try first actually desoldering disassembling and deep cleaning replacing the master fader. If you're still having problems, something that comes up often is the audio coupling capacitors on the pre - and post master fader buffer go bad. You're looking for 8 electrolytic caps of the same value near the master fader. They tend to be 10uf on tascam units, I imagine they'd be the same on yamaha stuff...

[@gerry5265]

@@Tetrakan thanks that's a lot of help, I'll give that a go!

[@bas1cbas1c]

Urgh - that unit looks like a real ball-ache. Yamaha must have been really trying to save pennies - the MT-2X is a breeze by comparison.

[@Tetrakan]

In a lot of ways the quality is pretty nice, its just the ribbon cables make me want to puke. Tascam went through a phase of including those in their builds too - 424 MK I and porta 07 for instance.