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Yamaha DX100 Repair and Review


Hello, and welcome back to 8-Bit Keys. In this episode, I’m going to be taking
a look at this Yamaha DX-100. This was recently donated to me Naoki Saito,
and normally I don’t take professional keyboards for reasons I’ve talked about before, but
I just couldn’t resist on this one. This one is basically like a relative of the
Yamaha DX-7 only it’s really small and it’s basically the size of like, you know, a toy
keyboard. And so, I thought this would be really cool
to play around with. And it’s actually in really good condition
too. It needs a little bit of cleaning, which I’m
going to do here in a minute, but the main issue is that it doesn’t actually work right,
however, I’m hoping that it’s a problem I can fix. Let me show you what’s wrong with it. So here it is, the DX-100. This was made in 1985. I said it was related to the DX-7, which is
one of the most famous keyboards from the 80s, but this is really more closely related
to the DX-27. The 27 is a full sized keyboard and you could
call this DX-100 a miniature version of that. I’ll give you an overview of the ports on
the rear. Starting off, this is the power switch, a
12V DC power port, a line output and headphones. Keep in mind this keyboard has no internal
speakers. This is a foot switch, most likely used for
a sustain pedal, but may be configurable to other things, I’m not sure yet. These 3 are for MIDI, and this one is actually
for a cassette drive. I actually couldn’t find a pin diagram for
this port, but I found one for some other Yamaha keyboards and it appears it may be
wired the same as the cassette port found on the Tandy Model-100 and several other Japanese
made computers from the time period. So, hopefully, I can use the same cable with
it. The last two things here are the LCD contrast
knob, and a port for a breath controller. I’m also probably going to remove these
things as I have no intention of wearing this keyboard to play it, and these are always
in the way. OK, so let’s give it some power and then
a connect the line output. Keep in mind this keyboard is not stereo,
it outputs in mono. OK, let’s power it on. Welcome to DX. OK, so at first I couldn’t hear any sound
at all. It doesn’t seem to matter if the volume
is all the way up or down. Now, if you look at the recording I made,
and you do an extreme amplification on it, you’ll find that there is in fact a hint
of actual sound there. So this suggests the FM chip is working. So, the other problem is that most of the
instruments are just garbage. And this is most likely due to the internal
battery being dead. I’m going to do a factory reset by holding
down the 1 and 2 buttons like this, and then powering it on. And, he first thing it says is change RAM
battery. Ok, so what I hope to do here is I’m going
to take it apart in just a second and I’m going to replace that battery, of course,
and then I’m going to see if I can find some kind of problem with maybe the amplifier
circuit or something. So, let’s dig right in. Well, let’s turn this thing over and start
unscrewing it. OK, let’s pull the cover off. This is an interesting board. It looks like somebody has been in here before
because they scratched some letters onto the board to help remind them which port was which. Fortunately, being this is a Yamaha it appears
all of the cables have disconnects. That will make it a lot easier to work on. OK, I think it’s time to remove this main
board. OK, so one of the things I find immediately
interesting about this board is that it is a single-sided board. In other words there are only traces on one
side. That’s why you see all of those little metal
pieces, these are substituted for traces on this side. Another interesting thing is that apparently
this same board is used in the DX-27. I guess they just used a marker to cross off
the 27 since this board was going into a 100. I’m pretty sure this is where the battery
is supposed to go. It looks like it was directly soldered to
the board and somebody just snipped it off, probably because it was leaking. So that’ll be an interesting challenge to
undertake. Over here, this is a separate board just for
the LCD, and it’s a true HD44780, which is unusual because most of the time I just
see clones of it. This is the exact same kind of LCD that I
showed how to control in a previous video series. Now, this board here is just for the volume
and data slider controls. There are just two potentiometers on this
board and nothing else. However, since I am not sure the volume control
slider isn’t the source of our problem, I’d better test it. I’m just going to use some alligator clips
here. And then I’ll watch the resistance on the
meter as I slide the control. OK, so it looks like it goes from about 3
ohms all the way to 34 kilo-ohms Next I’m going to test these voltage regulators. This 7095 is outputting almost a perfect 3
volts. Which I thought was weird at first, but then
I realized that they are using this 7808 to get a perfect 8 volts and they are using the
difference to get 5 volts for the digital electronics on this thing. I found a copy of the service manual for this
thing online, but is only 30 pages long and to be honest, it leaves a lot to be desired. It doesn’t even show most of the information
that would actually be useful to me. So, to be honest, I’m going to have to troubleshoot
this as if I didn’t even have a copy of the service manual. One thing I’m going to need to do is peel
up this plastic piece, which is where the battery compartment rests, so that I can see
where all of the traces go. I did a lot of sleuthing on this board and
I have determined that this is the FM synthesizer chip, but it outputs a digital signal. So it sends that signal over to this tiny
digital to analog converter, which then feeds the analog signal into this little pre-amp. So I want to find out if I can get any signal
from that chip. So, I hooked up some alligator clips to the
line input to my boom box. And I’m going to clip this one to ground. And as you can see here, this one here is
the audio signal. OK, so this is the sound chip here, and over
here this is the digital to analog converter. And then over here is the amplifier circuit. And this is the output. I’m going to just touch it right here. And I’m going to push some keys on the keyboard. Hear that? I’m pushing keys on the keyboard. So yeah, I think we’re onto something! OK, so we know we have sound here, so I followed
the traces up to yet another amplifier chip. I’m not sure why it needs two of them, since
this thing doesn’t even have any internal speakers. Anyway, this chip is also interwoven with
a bunch of other circuitry including these wires here, which go to the volume control
slider. I had to look up a schematic for all of these
chips online because they weren’t in the service manual. Anyway, so this chip has two inputs and two
outputs. Now, with more poking around I found that
I get sound out of this output here on pin 1. However, I can’t figure out where this actually
goes. However, I did discover that moving the volume
control slider will change the volume for me at this output. However, this second output here on pin 7
is what actually goes to the line output jack on the back of the keyboard, and it is dead. I can’t get any audio signal here. So I’m thinking I need to replace this chip. I looked on ebay and found somebody selling
4 of these for 4 dollars and 25 cents, with free shipping. The sad part is, I could order a single chip
like this from mouser or digikey but I’d probably wind up paying 5 or 6 dollars just
for shipping. So I ordered this. Ebay has really become by go-to shopping for
parts like this when I just need one or two. Two days later I had these in the mail. I didn’t even realize they were going to
come with the little sockets, so that’s even better. Since I don’t really have proper equipment
for desoldering chips, I’ve found the easiest way to remove them is to just cut the leads. That way I can use pliers and desolder the
little left-over pins one at a time. I couldn’t find my smaller wire cutters
at the moment, so this proved to be a little irritating, but in the end I got it removed. The only problem is I didn’t leave much
to get ahold of. I tried heating and pulling these but the
cold pliers would cause the solder to re-solidify before I could pull them out. So instead I just used some desoldering braid
and since this is a single-sided board there were no copper parts going all the way through
the board to the other side, so it actually made it very easy to desolder. I should have just left the chip in there. Anyway, it doesn’t look super beautiful
but the chip is removed. Next I’ll just insert this socket. It appears there is plenty of clearance for
the socket and chip together, so why not? That way if I realize I got the wrong chip
or something I won’t have to solder this area again. So, I’ll just solder this socket in place. There we go. Now I’ll just flip the board over, and insert
the little chip. Now it’s time to test it. So, I’ve put the board back in the keyboard
and the only thing I have hooked up right now is the regular line output, which is the
orange one, which is going to the boombox. The gray is not connected right now. OK, let’s try some keys. Hey, guess what? It works! I’d say that problem is fixed. ——NEW STUFF OK, to tackle this battery problem the first
thing I need to do is remove these old battery leads that are still here. For that I’ll just hold them with pliers
and desolder from the other side. This is how I had intended to do the chip
I desoldered earlier, but didn’t have enough to grab onto. Anyway, it worked fine for these. I’ll soak up the remaining solder with some
desoldering braid and remove the flux with some alcohol. And there we go, nice and clean. Ok, so I bought these CR2032 battery holders
on ebay for like 5 bucks for all of these. As you can see, these just have two leads,
and the battery snaps in like this. Now, in case this doesn’t fit, I also ordered
some of these as well. I think these were also around 5 bucks for
the whole pack. These are designed to mount anywhere you want
and have external wires. Hopefully I won’t have to use these. Unfortunately, as you can see the battery
holders do not actually fit. The leads are too far apart. However, on the bright side this is a single
layer board and the ground trace covers a large area, so I should be able to use a small
drill bit like this and just make a new hole in the correct spot. I went nice and slow with the drill, with
gentle pressure in order to make sure I didn’t crack anything. OK, so I think that hole is going to work,
but I’ll also need to scratch away some of the protective layer over the copper so
that I’ll be able to solder to it. OK, let’s see if this fits. And it does. Unfortunately, I guess I didn’t have the
camera rolling when I was soldering, but here’s the finished solder job. So all I need to do now is flip the board
over and insert the battery. I did double check the polarity was correct
before I soldered this thing in, by the way. The next step was to re-attach all of the
cables yet one more time to the main board. I also said I was going to remove these strap
lugs or whatever they are. They are in my way. Also the keyboard needs just a bit of cleaning,
but nothing serious. I haven’t put all of the bottom screws in
yet, because I wanted to test it out a bit first. Oh, and I’d better put the slider knobs
back on. OK, so I’m going to power it up with the
factory reset again. This time it doesn’t mention anything about
the battery. Of course, I can’t do most of these tests
because I don’t have the correct things attached, but let’s power cycle again and
see if the battery is working. I think it is, since we have actual instruments
now instead of garbage. Well, let’s screw it back together. All right guys, so as I have said before,
I’m not really an expert when it comes to these professional style keyboards so I thought
I’d bring over somebody who is. This is Brandon, he actually lives here in
town and he actually does a YouTube channel himself and it’s called Zibbybone and I’ll
put a link down in the description for that. He’s brought several things with him to
help demonstrate this and the first thing he brought is a Yamaha DX7 so that we can
compare exactly the size difference. Because, you know, a lot of times I tell people
something is big or small, sometimes it helps to have a frame of reference to actually see
you know what the difference is. So you can see, yeah, this is definitely quite
a bit smaller than a DX7. But there are some other technological differences
between them as well, why don’t you tell us a little bit about that? Well, the DX100 has four operators per voice
as opposed to six operators per voice on the DX7. An operator is basically a sine-wave that
can either be a sound source or modulator for that sound source to create more complex
sounds. Now, even though the DX100 only has four operators
per voice, it’s still capable of producing some pretty complex sounds. Well, he has brought with him a breath controller
and a foot pedal and I’m going to let him demonstrate some of those complex sounds for
you, so let’s check that out. Bank A number 4 electric grand. It’s a rendition of the Yamaha CP80 electric
grand piano. High Tines, this is going to be like a Rhodes
piano sound. The sound we were looking for. No that’s not it. That’s not it. But I think that is ported over from the,
yeah I heard it earlier. There it is, electric bass. This one’s ported over from the DX7. You’ll probably recognize this. Flugal horn. Hard brass. Power Brass. Strings. Patch 11. Silk Cello. Rich strings. Let’s see, what would be a good one for
that? Fuzz Clav. Celeste. Feed Lead. Bank D has got a bunch of sound effects, I
think. This is a glockenspiel. Marimba. Steel drums. Doesn’t sound like steel drums to me. There is the tubular bell sound that we were
looking for. That’s weird. It’s got a little low frequency oscillation
going on. Helicopter. Every synthesizer needs a helicopter sound. Metal keys. Heavy synth, did I do this one already? Smoosh. Pan flute. As you saw earlier in the video, the DX100
has these guitar strap pegs and an input for a breath controller. So, I brought these from home to show the
DX100’s portability and performance ability. It will also operate off of six C-cell batteries
so that way you don’t have to have it plugged into a wall and you could jump around on stage
without having to be plugged into power. So, there’s a few patches already programmed
into the DX100 that are specifically designed to be used with this breath controller. As I blow harder into the mouthpiece, it will
make the sound louder and sometimes even make the timber brighter. So, let me demonstrate a couple of those real
quick. There it is, breath controller sax. All right guys, I think we’ve reached just
about the end of this video, there are a few other things I wanted to tell you. First of all, the voices in the keyboard are,
of course, programmable. Now there’s quite a few built-in factory
voices which we’ve demonstrated for you, but you could theoretically program in hundreds
if not thousands of other patches either that you could create yourself or download off
the internet. And those can be programmed in either through
MIDI or through the cassette interface, because this was designed to save your patches onto
a cassette tape. And, of course, that’s one of the reasons
I don’t like to do reviews on professional keyboards because it could take hours to show
you all of the different features of a keyboard like this. I also wanted to thank Brandon for being on
the show. And he does a lot of reviews and just playing
around with professional keyboards on his channel, so if you’re more interested in
those, that would be the place to go and again the link is down in the description field. Also if you liked having Brandon on the show,
say something about it in the comments, I’d like to bring him back for future episodes,
particularly for the fancier keyboards, so let me know what you thought about that. Anyway, stick around until next month, and
thanks for watching!

Bernard Jenkins

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