Hello, or Bonjour,
Your e-mail address has the extension .fr, which I believe means France. Are you in France? Est-il plus confortable à correspondre à vous en français ? J'emploie www.systranet.com pour des traductions d'email.
Before discussing the TX81Z, tell us about yourself. Do you know electronics? Do you know MIDI or musical instrument digital electronics? Do you have tools like a soldering iron, a voltmeter, or an oscilloscope available? If this is a hardware problem, how much money would you be willing to pay to fix it?
Working TX81-Zs go for $60 US on eBay (USA) with about a $15-$20 shipping fee to send a TX81Z each way across the USA. Don't pay some shop $50 just to look at the TX81Z, because it will be cheaper to buy and ship a working one from eBay. Your broken TX81Z will sell on eBay for about half the price of a good one. If you do take the TX81Z to a shop, download and print out the schematic from the file section on this web site. Include it with the TX81Z when you bring it in to them. They charge by the hour, and it is a lot faster and cheaper to fix old electronics when you have a schematic of the unit. Be aware that the microprocessor (a 63B03, a semi-custom clone of the Motorola 6803) and the sound ICs are nearly impossible to obtain if they are the parts that are broken.
Electronically the TX81Z is a 1980s microprocessor-based device that gets user input from front panel buttons and a serial port (the MIDI interface). The CPU reads the serial port and buttons to get selected blocks of data from ROM chips. This data is loaded into a custom digital sound generator IC. This IC gets data from the CPU bus and outputs two pulse streams to a serial Digital-To-Analog (DAC) IC. The DAC outputs are stereo audio output waveforms that go to the amplifiers.
The good news is that this is not likely to be a hardware problem. Disconnect the headphones or audio put cables and power up the TX unit. High pitched sound still coming from the unit? Probably something in the power supply.
All the sound-generating parameters of the TX81Z are accessible through the front panel buttons. Find the LCD display screen for the output levels of the four operators. Start with operator four and reduce the output level of each operator to zero. Does the high pitch sound go away?
There are eight 'algorythms' on the TX81Z. These are the ways that the operators can be arranged to make sounds. On algorythms one through four, operator one is the main sound generator. Does the high pitch sound change when selecting different algorythms? (they can be changed by the front panel).
The test here is to find whether the high-pitch sound is made by the settings of the sound generating ICs, or if it comes from the analog circuitry that is after the sound generators. After the DAC chip, there are audio op-amps. Maybe they are oscillating because of worn out capacitors.
Can you record about about 15 seconds of several TX voices with this high-pitched audio (using an audio capture program), compress this recording into a SMALL MP3 or OGG file, and post it for download somewhere? You may want to ask the moderator of this site before posting a file like this into the files section here.
Please keep us updated. We might be able to help you fix this.
-Alan Probandt Portland, Oregon USA (1000 kilometers north of San Francisco)