Have you managed to locate a DX21 service manual yet?? What problem are you experiancing with the 21?? From your request notes you mention 'all audio sections are live', do you mean that you have no audio from the 21?? Most faults i have experienced with the 21 are, failure of the main OPP YM2164 fm chip and associated D/A convertor(YM3102). In some cases YM3102 is ok .When the YM2164 fails, DX21 will boot as normal but no sound whatsoever from the audio out's. YM2164 is the main tone generation ic. Also when YM2164 is replaced, if sounds are reloaded back into the memory areas from ROM and the display reads gibberish in certain memory areas then a ram or rams have failed also. The crunch, Don't expect to get a YM2164 and Associated components easily, these things are very rare. I have seen the YM2164 fetch £35!! Best way around this, if you are eager to repair the synth is to purchase a working YAMAHA FBO1 FM MODULE ,not a popiular module and sell for about £20 - £50 on ebay. You can rip the parts out of the unit and use them in the 21. Sell whats left on EBAY spares or repairs.
The damaged (i believe) is caused by failure in the powersuppy causing voltage rails to 'spike'. What is strange is the cpu stays in tact. Capaitor replacements can cure this problem. I have a complete circuit diagram i can scan and email to you for a small fee for my time if required . email me:- firstname.lastname@example.org
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NO power light or audio from Digitech Vocalist 2 live. Check that your power adapter is for 9 Volts AC (not DC like most pedals) and is rated at 1300ma or more. A DC adapter MAY light up the unit but not make it pass audio. Lights can be lit but that is NOT an indication thaat correct power is applied. They likely use the AC input to generate both positive and negative voltage within the unit. The use of a DC adapter will prevent generating one of these required voltages and prevent audio from passing.
Suspect a broken circuit trace or broken solder. If they use a 7805 three terminal regulator, check the solder around those pins...
Berhinger does NOT release schematics except to their service facilities... I know... I have tried... I repaair a lot of their stuff and have to trace out the circuits.
Power supply circuits are rather easy except for the switching regulators if they have failed totally.
If only the +5 is dead, you should be only a filter cap and a diode or two away from the problem... Transformer leads and electrolytic leads with their weight are favorite to pull out of solder... On Behringer, often the traces are narrow and can have a crack in them.
Try looking for the voltage rectifier or bridge diode that converts the A.C. supply into D.C. to power the circuits. Test it with your multimeter using the diode test function if you have one.Hope this helps.
You have to remember that the voltages coming out of the power transformer are A.C. and the voltages used by the devices in the keyboard are D.C. Check for voltage rectifier I.C.s between the transformer and the rtest of the circuits. They should look like squares with 3 pins coming out of the bottom of them and metal backs that protrude above the top of the black squares. Use a volt ohm meter on direct current range and clip the black lead to a circuit ground such as a ground on an output jack. Touch each pin one at a time taking note of the voltage. If you find one that has the same voltage on all 3 pins it is probably shorted. I think the voltage should be about 12volts direct current positive or negative depending on the circuit. Each one will have a code that you can cross reference on the net to find the pinouts and specs. The same thing goes for all the I.C.s If you can find the pinouts for any that you suspect look for the power supply pins and check what the voltage is. Some will have two supplies, one negative and the other positive. If you find an I.C. with power at all pins or ones that should have no power only signal then it is likely shorted. Go slowly and don't bridge two pins at once by accident and you might be able to find the problem without the schematic or a service manual. There is a memory battery (CR2032) that power the memory that might be dead but that should only affect the programmed sounds not the LED or the amp chip. Hope this helps. Do not measure A.C. with the D.C. range or you'll burn out your meter. Use safety precautions with a live device.
How familiar are you with schematics? I've just found my CT-670, There where marker marks on the keys. I cleaned it up. I took it apart as one channels had no sound. I love this machine. I want to find a manual for it also schematics would be very helpful for me too. I would suggest looking inside for burns on semiconductors. or loose soldering. I need to replace a chip that has no cross reference... that I've found yet... I think it's an amplifier but need to spend more time on it....
An answer, but likely not a solution. I believe all Yamaha PSR series keyboards use the same 12 VDC adaptor, so I looked at the electrical schematic for another model I have. There seems to be no fuse on the power input. There are two components shown on the positive and negative wires off the power socket, but the symbols do not look like anything I have seen for fuses - they may be resistors. Power goes directly to a 5 VDC voltage regulator, which powers all of the solid state componenents. Too much voltage of the wrong type could have easily ruined many of the sensitive components.
Your only hope is to check the power socket area for the possibility of having fuses. My drawing shows the power socket, voltage regulator, and audio power amplifier being on one circuit board. That may not actually be the way it is in your model.