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Alesis MMT-8 Mods

The Problems

"Alesis MMT-8, Like new, Gray, $100" was the ad I answered...the machine I recieved was an MMT-8, was gray, but was definitely not 'like new'! My secondhand MMT-8 came with no power supply, and since it has no battery power, I was unable to use it. MMT-8 uses a very un-standard 9v AC power adapter, and Alesis put an odd sized connector on it. The only way to get a proper power supply would be directly from Alesis, and if they even still sold parts for the aging sequencer, they are notorious for charging outragous prices for their parts. As if that weren't bad enough, the buttons on the face of the machine could be pushed down about an inch into the plastic cover. Given the bad reputation of the MMT-8/HR-16 buttons, it was going to be a miracle if these things worked at all (and that's only IF i can get power to it)!

The Solutions

Part one, Power Supply...

Luckily, I had a bunch of spare parts left over from my last semester digital circuit lab...I knew all those left-overs from Jameco orders would come in handy...I just happened to have a 9v AC power adapter and matching surface mount plug.
-insert part numbers here-
First, remove the 4 screws on the bottom of the MMT-8's case. The case comes apart into two halves; the top half with the buttons and the LCD, and the bottom half with all the main circuitry and jacks. They're connected with three ribbon cables...I suggest you mark them with permenant marker on both sides of the ribbon-connectors so there is no confusion when it comes to re-connecting them. Leave the ribbons connected to the top half of the MMT-8 for now. The next step is to remove the PCB from the bottom half of the case. It is held in place by 5 (?) screws, then should pull up and out of the case with no problem. Unsoldering the old jack was harder than I thought it would be, partly because it's held in place by 3 soldered tabs. I had to apply heat to each connection while pulling on the jack while trying to pull the old solder off with the solder-sucker. I was eventually able to rock it off the PCB and clean the excess solder off the board. Soldering the new one in place was no problem, but make sure to get it flush with the board and sitting level with it so that it will properly line up with the cut-out in the case. Reseat the PCB in the bottom half of the case and replace the screws. Plug in the 3 ribbon cables, then the power supply and throw the power switch. If it boots up normally with the '***Alesis MMT-8***' screen, then Congratulations! If it's sparking/smoking/shocking you, the un-plug it, and check to make sure you didn't accidently short any of the 3 leads from the jack or any of the surrounding traces on the PCB.

Part two, MMT-8 Buttons and PCB...

After opening the MMT-8, I saw the damage that had been done to the underside. The buttons had been hit so hard that the plastic threads that the PCB were screwed into had been cracked and broken. Almost every single standoff showed signs of being broken. My solution to this was to drill completely through the top half of the case and replace each screw with a machine screw and nut. I went with 1/2" 4-40 Machine Screws and Nuts from my local hardware store. I drilled slightly smaller holes with my dremel on it's slowest setting. I wanted the holes a smaller bore so that the screws were securely threaded into the case. Make sure that the screws are 1/2", as they are exactly long enough to thread the nuts on all the way, and anything longer will not fit flushly in the smaller height of the case front. I tightened everything as much as possible and re-assembled the case. The MMT-8 feels much sturdier than before surgery, and the buttons press down and firmly stop.

MMT8 Button repairs; concrete fix.

To: analogue@hyperreal.com,
From: "Matthew S. Padden m.s.padden@hud.ac.uk
Subject: MMT8 Button repairs; concrete fix.
Date: 14 Nov 1996 12:07:32 +0000

--------------------------------------------------------------------------------
Hi..

>
>My MMT8 is now down for the count. I have to open it up and clean it 
>everytime I use it more than one day. I called allessis and they do *not* 
>sell the ciorcuit board anymore but they do sell the rubber pads for 
>around $30 or so.
>
>Has anyone replaced their rubber pads in the MMT8 with a new one and seen 
>the problem go away? Or is it a combination of the Circuit board as well?
>

I had this problem , along with the dreaded 'button bounce'; when you press 
PLAY the MMT8 will stutter terribly before getting going. I tried varuous 
cleaning solutions, and then got fed up with forever cleaning the board. So 
I added tactile switches under all the buttons to fix the problem once and 
for all. Here's what I did.

1. You need to buy the switches; Maplin, RS, Farnell will all do something 
suitable. I dod this mod a few years ago and have since sold the MMT8, so 
I'm afraid I can't give the part numbers. What you're looking for is a small 
click-action momentary switch, such as you might find in (for instance) 
QUAD's system remote control from their 66 range of hifi. They have a low 
profile body, and a peg which protrudes upward, to which you can attach keys 
etc. There are four pins; the switch is a DPST type. Use a meter to find 
which pins connect when the switch is pressed.

2. Cut off the pegs from the switches so there is just the flat switch 
surface. Lay the pins flat. There are some little lugs on the bottom corners 
of the switches; carefully remove those, making sure you don't destroy the 
integrity of the case.

3. Pop open the MMT8. On the underside of the button membrane, each button 
has either 1 (small buttons) or 3 (track and transport buttons) black 
conductive pads. VERY carefully slice these off to leave a smooth underside 
to the button. Make sure you don't puncture the membrane, as rips tend to 
spread rapidly.

4. Now for the tricky bit. Lay all the switches in position over the PCB 
'fingers' which would normally be shorted by the conductive pads. Shape the 
pins so that a connecting pair lies over each side of the finger set. Cut 
off the two unused pins, then solder the others direct to the fingers. The 
switch now acts as the short between the fingers.

5. Once all the switches are in place, test fit the button board back into 
the casework. You will need to cut off some of the front edge of the board 
to make it fit (don't worry, there are no tracks down at the front edge). 
You'll need some slightly longer screws to hold the board and membrane in 
place. Tighten the screws so that no buttons are jammed down, and so that 
all buttons have a similar sensitivity.

That's it! My unit performed faultlessly after that; all the buttons had a 
positive feel and NO bounce. They also worked every time. It's a bit of a 
fiddly job siting the switches on the board, but it's definitely worth it. I 
wonder if I should do the same for my Atari...

Bye for now

--
Matthew S. Padden
Computer Music Research Group
Music Dept.
Huddersfield University
e: m.s.padden@hud.ac.uk

More button repair ideas

From: GIMBO@pulse-service.co.uk, (Gimbo In Limbo)
Date: Thu, 1 Oct 1998 13:47:28 +0000

--------------------------------------------------------------------------------
(Warning: Long-ish and no analogue. Good for MMT-8 freaks, though).

OK... MMT-8 fixing information...

Adam Phillips  wrote:

> On Wed, 30 Sep 1998, George Cochrane wrote:
> 
> > MIDIMEL wrote:
> > 
> > > If you send the unit to alesis + $50 they will replace all the buttons
> > > and you will have a great unit-Love Mel
> > >
> > Do you mean they'll install a new rubber button sheet? or actually
> > replace the contact switches with real, mechanical switches or a
> > better designed version of a contact switch?
> > 
> For $50 you could get a new MMT8 (just a thought).
> 
> - -Adam

Yeah! Then send your old defunct unit to me! I'll fix it and give it 
a good home! I'll even pay the postage!

Seriously though, $50 is a little under the odds for an MMT-8, isn't 
it? I thought $100 was more like it. It won't be "new", either, just 
another 2nd-hand one that's probably just about to get exactly the 
same problem.

For that $50 (so I understand), Alesis will replace the button sheet, 
and also ensure that you have the latest ROM (v1.11?). Not a bad deal 
really. And I really don't see anyone replacing all 40 or so buttons 
with mechanical ones at that price. BTW, does anyone know if you'd 
have to ship to Alesis US to get this service? I haven't looked into 
it myself.

The alternative to shipping to Alesis is fixing the pads yourself... 
This whole topic comes up every few months so there's some stuff in 
the archives you might wanna check out. I'll try to summarise it 
here, and add some more.

The MMT-8's buttons have little round pads on the bottom (between one 
& three pads, depending on the size of the button). The pads make 
electrical contact between two sections of circuitry on the PCB, 
conceptually closing a switch. So the bottom of the pad has to be 
electrically conductive otherwise this just doesn't work. The problem 
you get is that the conductive surface wears away over time, so the 
switches become "dodgy" then "dead".

The solutions all involve restoring the bottoms of the pads to a 
conductive state in some manner. Suggestions include using conductive 
silver paint, and even hole-punched aluminium foil stuck to the 
pads... The best (by which I mean, the least "hacky") idea I've seen 
comes from Rob Hukin, who I hope won't mind me quoting his private 
email here, since this little tidbit isn't in the archives yet...

Rob said:

> 'If you're looking to refurbish keyboard rubber contact strips, i've 
> had good results using some stuff called Circuit Works Rubber Keypad 
> Repair kit. It's a 'two part carbon/silver coating that cures to 
> form a tough, flexible, wear resistant surface which provides 
> excellent adhesion and electrical conductivity...Testing has shown 
> repairs can withstand over 500 000 simulated keystrokes' (from the 
> literature that comes with it). It's quite expensive (about 20ukp 
> for a kit) and rather irritatingly comes in two sets of two-part 
> mixtures that have to be mixed all in one go, and will only stay 
> usable for 72 hours (less in my experience), so make sure you have 
> plenty to do to make it economical. It's made by a company called 
> Chemtronics Inc, Kennesaw, GA 30152-4370 USA, 800-645-5244. I've 
> used it on an HR-16, MMT-8 and my OB8 and it seems to work pretty 
> well.'
>
> Try cleaning the contacts with isolpropyl alchohol (available from 
> all good chemists) first and see if that improves things, otherwise 
> you can get the kepad repair kit from CPC in Preston - I thinks it's 
> on offer this month at about 14quid (which works out to nearer 20 
> once VAT and P&P are added), but it's probably only worthwhile 
> either if you've got other stuff that needs doing or the MMT-8 
> becomes unusable (which is what happened to my HR-16).

BTW, I don't recommend using isopropyl alcohol... That seemed to 
utterly kill my pads. I know alcohol perishes rubber, so that's 
probably got something to do with it, but according to the archives 
the MMT-8 pads aren't actually rubber, they're some sort of 
conductive carbon. Anyway, be warned, I used isopropyl on *dodgy* 
buttons and they became *totally dead* buttons. *8-)

Last week, I used the aluminium foil/hole punch method with 
*excellent* results, ie my buttons are all better than they've ever 
been. My hole punch makes little circles of foil that are just the 
right size to fit over the pads (actually, if they'd been slightly 
smaller it would have been perfect, but they're good enough). I used 
Pritt-stick to fix them on - hardly industrial quality but I was 
experimenting really. No doubt this fix will be fairly short lived 
and soon I'll need to ring CRC in Preston for the kit above. Rest 
assured that I'll let you know when that happens :-)

Apologies, again, that this isn't analogue, but I thought the 
archives needed this info. The MMT-8 does seem to crop up fairly 
regularly on AH - it must have something to do with it's immediate 
interface, rock solid timing, and general coolness I guess. As 
digital sequencers go, it's got a lot of what we love about analogue 
gear - including the maintenance responsibilities!

Take it easy,

Andy

Yet another

From:Vertical 8 ka6zud@mindspring.com,

OK, the best fix, which costs nothing but time, is to open the
machine, rub graphite dust on the plastic switch components and clean 
the PCB contacts with denatured alcohol. I found this search on an 
old hyperreal directory and it REALLY WORKED WELL!!


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