Paul Fox's Casio Horn Page

(Launched 16 November 2003

Last update 19 June 2010: further additions to the DH-800 squeal fix section)

CASIO Digital Horns were made in the late 1980's. They can be used independently (they have six different built-in voices), or they can be used as a breath controller for MIDI synthesizers. Shown here are two DH-100's (silver) and a DH-200 (black). Other models were made, including the DH-500 and DH-800.


Does your horn squeal? These horns have a common fault: they start to squeal due to a component failure. Dorian Rose's web page about fixing this fault is no longer available, but the instructions for fixing DH-100, 200, 500 and 800 horns can now be found here: Fix the Squeal


Do you want to know how to turn off the vibrato? Kerry Bradley has a webpage that will show you how. Go to http://home.earthlink.net/~kerrybradley/id1.html for details.


There are three other problems that I have found in Casio horns. Here's how to fix them:

BREATH SENSOR ADJUSTMENT

NO SOUND (due to a damaged clock pulse circuit).

NO SOUND WITH BREATH MODE ON

Click on the links or scroll down for details. Email me to ask about other faults. I may be able to help.

The information on these pages is provided free, but if you have found it helpful, you may like to:


Do you have a broken horn? I may be able to help, or I might be interested in buying it for spares if it's beyond repair.

I also have a small stock of SPARE PARTS: keys, springs, tubes and other internal parts. Email me to ask if there's something you need. Sorry but I don't sell mouthpieces.

By the way, I'm in England. If you're in the USA and need a horn repaired, take a look at Ted Keys' website. Ted knows more about these things than anyone I know, and he's fixed loads of them. He's a genuine nice guy too.

I'VE GOT LOTS OF INFORMATION ABOUT THESE THINGS THAT ISN'T ON THE WEB PAGE YET.

INSTRUCTION MANUALS: I HAVE THESE IN ENGLISH, SPANISH, FRENCH (PDF), ITALIAN, DUTCH (PDF) AND GERMAN (PDF) - PHOTOCOPIES AVAILABLE FOR COST OF COPYING AND POSTAGE. I will add more pdf versions as and when I get time.

You can email me about problems, fixes or anything else to do with Casio horns at: paul.fox4@ntlworld.com

Let me know if the information on this page has helped. I Look forward to hearing from you!

DISCLAIMER: THE ADVICE GIVEN ON THESE PAGES IS TO BE TAKEN AT YOUR OWN RISK. I AM NOT AN ELECTRONICS EXPERT, THIS IS JUST A HOBBY FOR ME. I AM JUST SHARING THINGS I'VE FOUND TO WORK, BUT I CAN'T BE HELD RESPONSIBLE FOR ANY DAMAGE CAUSED THROUGH ATTEMPTING THE REPAIRS / ADJUSTMENTS GIVEN HERE.


BREATH SENSOR ADJUSTMENT.

If the sensor is adjusted correctly, you should get a graduation in volume, from very quiet to very loud, when the volume is turned up fully. The sensor should be very sensitive to changes in breath pressure. If the sensor is NOT adjusted correctly, you may feel you have to blow very hard to produce a note, and that the horn only plays quietly. This is probably caused by a badly adjusted variable resistor (VR) on the circuit board.

Check the breath mode switch is in the ON position. Remove the mouthpiece and the six screws holding the two horn shells together (one of these is in the battery compartment). You'll need a small cross-head screwdriver to remove the six screws . You'll also need a small flat-bladed screwdriver to adjust the VRs. With the horn open, you will see two circuit boards stacked inside the back half of the horn. The top board, labelled M263-MA1M, has two variable resistors on it, labelled VR1 and VR2. These should be easy to find, there's no need to take the horn apart any further (See photo below.)

(The ceramic resonator is labelled for the next fix; for now you're just interested in VR1 and VR2.)

To reset the breath sensor to factory settings, follow this link.

To adjust the sensor by ear, use the following instructions:

To begin with, leave VR1 at its current position. Power up the horn and turn the volume up FULL. (You'll be listening for sound and silence, and you'll need to know when the horn is really silent). There are 2 ways you can adjust VR2.

EITHER:

Blow hard into the tube and adjust VR2 until the horn is playing its loudest. (It's a bit tricky with the horn in pieces held together by cables, but you'll soon get used to it.) Stop blowing and the horn should be silent.

OR:

Adjust VR2 until the horn starts to produce a note without any breath, then back off slightly so it's silent again.

In both cases, you shouldn't need to alter VR2 by more than half a turn.

Try blowing the horn again, and you should find that you have a full range of volume and sensitivity. If you think it should still be louder, try small adjustments of VR1 to see what effect it has, until you're happy. (Basically VR2 sets the threshold between "no breath" and "breath", and VR1 controls the maximum volume available. Email me (paul.fox4@ntlworld.com) if you want more details.)


POWER BUT NO SOUND.

I came across this in one horn, and the fault was obvious when I examined the circuit board.

Symptom: the horn powers up, the power light stays on and you can hear a quiet background hiss in the speaker (if the volume is turned up full.) This is normal. However the horn would not produce a sound, either with breath mode on or off.

The problem: a damaged component. The 12 MHz crystal on the board M263-MA1M had been broken. This looks like a blue ceramic capacitor (see top photo) and is part of the clock pulse circuit for the CPU. Without the circuit producing a clock pulse, the CPU won't do anything. I desoldered the legs and removed the parts of this component.

The board with the resonator removed.

Casio's specification for this component is "CSA12.0MT18". It's a ceramic-encased crystal with a frequency of 12.0 MHz. I couldn't find a ceramic one but I managed to get some crystals housed in cans (see photos). I tried both of these unsoldered and they both worked, so I soldered the small one in place and trimmed off the legs.

An original ceramic crystal (blue) with two different style "cans"

The repaired board in a DH-200

INCIDENTALLY, I also tried a 4.0 MHz crystal instead of a 12.0 MHz one. As you might expect, the horn worked perfectly but the pitch was much lower. Normally the base note of the horn when it's first switched on is Middle C, but with the 4.0 MHz crystal it was a low F, about one and a half octaves lower.


NO SOUND WITH BREATH MODE ON.

Thanks to Martin in Germany for working this one out and sending pictures of his repair.

[Please note, I haven't performed this repair myself yet, but will try to give more details when I have. For now, here's the basic information.]

Symptom: WIth the Breath Mode switch set to ON, the horn makes no sound when you blow into it, but with the switch OFF the horn plays when you press the keys.

The problem: a damaged component. The transistor T6 has failed. This is a small surface mounted transistor, at the top right of the board when you first open the horn up. It can be replaced with a BC547 for just a few pence. Unfortunately it has to be soldered onto the board surface, there are no convenient holes to use. Bend the legs into an 'L' shape to get a good contact on the pads on the board. Adjust the sensitivity as described above when the repair is complete.

BC547 transistor.

BC547 in place.


HOW TO FIX THE SQUEAL (DH-100 and DH-200.)

Follow these instructions:-

Remove the mouthpiece, batteries and all the case screws (don't forget the one in the battery compartment).

Once opened you will see two printed circuit boards in a stack. Remove the screws from the top board and carefully turn the board over. At one edge of the board you will see the offending capacitor. (C39 which is 33uF)

Very carefully and without damaging the circuit board, either unsolder or cut the capacitor out. I usually wriggle the capacitor with a small pair of pliers until it breaks free. Then unsolder or cut off any remaining legs. Double check with a magnifying glass if possible to be really sure that you have not left a short circuit here! The capacitor can also leak a corrosive fluid, so make sure the circuit board is dry before continuing. A cloth soaked with alcohol will clean it.

Insert a 33uF electrolytic capacitor in the feed through holes on the board. (see photos)

Any type of capacitor will do as long as its small enough to fit in the the space available. The working voltage should be at least 6V.

 

Before........ ....and after.

 

Make sure you use the right holes!

Double check the polarity before soldering in place. Trim the excess wire off the legs of the capacitor and that's it!!

Re-assemble your horn and enjoy.


  SQUEAL FIX FOR THE DH-500:

In the DH-500, the capacitor that causes the squeal is C37. Here's the board before and after repair. As you can see in the photo, the positive side of the capacitor goes into the hole just below the old capacitor - there's a "+" in a circle printed on the board right next to it. The negative side can go into either of the 2 holes just above the lettering "R37".


  SQUEAL FIX FOR THE DH-800:

The DH-800 isn't quite as easy to fix. In the DH-800, the capacitor that causes the squeal is C20 (in the centre of this picture). It's on the green circuit board you see when you open up the horn, and it is located between VR3 and the ribbon cable that's soldered to the edge of the board. The capacitor is marked "33 6V". As in the other models, it's a surface-mounted component so when you remove it, it leaves two solder "pads" on the copper tracks.

The black edges on the capacitors mark the negative side, so the negative side of your replacement can be soldered into the hole near the ribbon cable (or the other hole in that broad “ground” track - see photo below).

The thin track from the "positive" pad goes to a small black resistor marked 272, between C19 and C20. I don't think there is a suitable hole for the positive side, so we have to try and bend a small “L” shape in the leg and solder it onto the pad that the old component came off. Tricky, but it can be done. It will be easier if you solder the negative leg in first.

You could try soldering the capacitor to the end of the resistor, but be careful not to overheat and dislodge the whole resistor. Just try to melt the solder at the end enough to “grab” the capacitor leg when you take the heat off. Probably better to use the pad if you can.

 

Allen Talbot has kindly supplied me with his instructions and photos of a DH800 repair: Allen's DH-800 Instructions

 

If this information has helped you, please let me know at paul.fox4@ntlworld.com