BREATH SENSOR ADJUSTMENT.

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.