Casio HT-700 Repair and Review

Hello, and welcome to another episode of 8-Bit Keys.
Today, I’m going to be taking a look at this old Casio HT-700.
Now, this keyboard has two problems.
One, the pitch-bend wheel is broken.
And also, one of the speakers doesn’t work.
So, I’m going to take this thing apart and find out if I can fix one and maybe, hopefully,
both of the problems.
And then, I’ll give you a demonstration and see if I can put some multi-track recording
together for you.
So you can see a little closer here that the pitch bend wheel is pretty messed up.
And you can hear that only one speaker is working.
The first order of business is to unscrew this thing and take it apart.
It was at this point I realized it was actually missing all of the bottom screws.
I’m surprised it didn’t fall apart when I was carrying it home.
So anyway, here’s our first look inside.
And you can see the pitch bend wheel here.
So let’s take a look at that speaker.
I was sort of hoping to see a broken solder joint or something, but everything looks fine.
So let’s have a look at the logic board.
So there’s this one chip here, and I think it is the CPU or possibly the synth chip or
maybe both.
So, let’s have a look at the other side.
These chips have proven to be very difficult for me to identify.
These 3 chips appear to be ROM chips, but the one on the left might be a static RAM.
This one on the bottom might be a CPU or possibly a synth chip.
And this one is a MIDI controller chip.
So, I decided to start looking at the speaker problem.
The first thing I wanted to do was trace the connections and check for continuity.
OK, so what I figured out is the speaker is attached to the board here and then there
are some traces that it follows all of the way over here and it goes through this ribbon
cable.
And then, it goes over here where the main amplifier is, presumably where the other speaker
connects.
However, I found that there is no connection between here and there.
So, I got to looking around and you can actually see a crack in the board right here.
So I decided to just remove this cable completely from the keyboard, starting by desoldering
it from the board and then removing it from the speaker.
I also used some desoldering braid to remove the solder on these connections.
Then I soldered a brand new wire to the speaker.
I tinned the leads on the other side of the wire since it is going to surface mount on
the board.
And this is where I decided to connect the other side.
These connections were large and easy to solder to.
And here’s the result.
if this works, I’ll hot glue the cable down.
Next, I wanted to turn my attention to this wheel.
You can see the little plastic stalks are broken off the main case.
It’s really not the greatest design since the wheel essentially hangs from the top of
the case.
So two options I considered was super glue, which does work on plastics, but I’ve not
had great luck with super glue on these types of problems.
So I’m going to try this special plastic epoxy instead and see if it works any better.
This is a two-part mixture so I’ll mix it up.
I think one problem with super glue is that it is too runny and doesn’t fill in gaps
very well.
This stuff is thick and with any luck it will work better.
I went ahead and applied the epoxy to both sides of the break.
And fortunately the thing will sit there on its own without needing any support, which
is good because it takes 15 minutes to cure.
So, next it was time to close it up and test it out.
OK, I think both speakers are working now!
Also the pitch bend wheel is working.
So I took the back off and took a moment to hot glue this wire into place so it isn’t
flopping all around inside.
So that looks a lot better.
So, The next issue I wanted to tackle was the lack of screws.
I noticed the similarity between this keyboard and one of my more amateur casio keyboards
from the same time period, so I decided to see if the screws were the same.
And it does appear the screws are the same.
So now I know what the screws look like.
So I went to the Home Depot and had a look at the screws there.
They have a little tool to help you find the diameter and it looks like I needed a #3.
However, the smallest screws they carried in stock were #4.
Not only were they too thick, but they were also just a bit too long.
I noticed this little hinge came with screws the right length, but were still slightly
too thick.
So I went to Ace Hardware and looked at their impressive selection of screws.
Unfortunately, I ran into much the same issue.
#4 seems to be about as small as anyone carries.
They did have some smaller ones but they were machine screws and I didn’t think they’d
work well in plastic.
So, I know I could have probably bought the correct screws online somewhere if I were
willing to wait, possibly weeks.
But I decided to go a different route.
I bought these #4 screws of the correct length.
As I suspected, the diameter was too large and I’m sure they would have cracked the
plastic.
So I took a drill and just made the holes slightly larger.
Then they fit perfectly.
So I was able to close it up and screw this thing back together.
OK, so now that it is repaired, let me give you a little bit more technical detail on
this thing.
It was first produced in 1987.
It has 8 voices and 49 mini keys.
It has 40 built-in sounds but you can program additional sounds yourself.
And, it has PCM sampled drum sounds.
The HT-700 was supposed to be a “prosumer” keyboard.
I think I would place it just about here on my scale, as it does have many professional
type features, but is clearly built as cheaply as possible.
It has a sustain port, which is something typically only seen with professional keyboards
during this time period.
It also has MIDI, another thing making it professional.
Next is a tuning knob, and RCA line outputs.
Now an interesting thing about line inputs and outputs is that typically consumer equipment
uses RCA jacks like this and professional equipment usually uses either XLR or quarter-inch
phone jacks like these.
So this particular trait suggest consumer equipment.
And the same with the headphone jack, since one-eighth inch jacks like this were typical
of consumer equipment.
And last is your power jack.
I will be using the RCA jacks to record all of the rest of the sounds from this point
forward, so you can hear everything clearly.
So, as you can see, it is quite a mixed bag of features.
Now, let’s talk a little bit about how it sounds.
So, this thing does not use digital PCM samples.
Instead it actually uses a hybrid analog/digital synthesizer chip, which can produce some interesting
sounds.
But, it doesn’t sound very realistic.
This is clear by listening to the piano sound.
Even the electric piano doesn’t sound that great, which is ironic.
Also the Harpsichord sounds pretty synthetic.
However, if synthetic is what you are after, there are definitely some neat sounds to play
with here.
Notice how this sound grows as you hold it.
That’s something PCM sampling keyboards are not good at doing, because it would require
a really long sample.
So, theres actually lots of things that old-school synthesizers can do better than, say, PCM
samplers because when you want a sound to be able to change, or grow, or change based
on how hard you press the key, or how long you hold the key, or things like aftertouch,
you need an actual synthesizer, not just a sample.
So, it looks like there are only 20 built in sounds, but if you press the “internal”
button, then the entire row of sounds here changes to a totally different 20 sounds.
And here are some of those.
Also there is this RAM slot where you could store additional sounds, but these are pretty
rare and hard to find, and obviously I don’t have one.
And of course, it has several built in drum rhythms as well.
You can change the temp with the big knob.
Speaking of the big knob, practically everything else on the keyboard is controlled with this,
and I don’t care for it.
Unlike most keyboards, this knob is just a potentiometer and it has a very specific range
of motion and comes to a hard stop.
so you can’t just keep rotating it in one direction indefinitely.
Also it is hard to turn with one finger, and its really annoying to be honest.
Here are some of the things you can do with it, though.
If you move it to mode 92, you can design custom rhythms or just play the drums manually
using these keys.
These are all PCM samples.
You can also edit or create your own sounds.
Here are some of the waveforms you can start with.
After you pick a waveform there are all sorts of other attributes you can define to refine
the sound exactly how you want it.
Anyway, so I put together a little multi-track recording, big surprise there, huh?
And so here goes.
All right, So that just about wraps it up for this episode.
I did want to mention a few things, though.
I actually get quite a few emails from people who are asking me repair tips on their various
keyboards.
And, I just wanted to mention that since I’ve been repairing keyboards the last few years,
I’ve found that most of the keyboards that need repair are pretty simple things.
You know, like broken plastics, corrosion from batteries, or corrosion on traces, or
in this case a little bit of a crack on a PCB, you know, sometimes just cosmetic things
like yellowed keys, and you know things like that.
And so, surprisingly a lot of the problems on these old keyboards can be fixed if you
want to take the time and put the effort into fixing them.
And it’s actually pretty rare, in fact I’ve never really encountered a keyboard that has
like a burned out CPU or RAM chip or something like that.
Not to say it can’t happen, just, I think all of the other problems are considerably
more common.
I want to thank my friend Brandon who let me borrow this keyboard from him, although
I don’t think he should mind since I’m going to be returning it in better condition
than I borrowed it.
Also, I want to apologize for the lack of content on this channel lately.
I have a lot of projects piling up on my other channel and since my other channel is my primary
source of income now, I do have to concentrate more on that channel.
But don’t worry, I do have quite a few things planned for this channel.
Hopefully i’ll be getting to more of those soon, so stick around for that, and see you
next time!

Casio HT-700 Repair and Review

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