Alesis Ion Troubleshooting Suggestions

Hi everyone. I bought an Ion knowing it was busted. I like to post here because I love this forum and all the knowledgeable members. So just looking for general thoughts. The output is random and super glitchy and changes by applying pressure to keys and the panel. Some keys don’t work and some buttons appear dead. Some leds dead as well. All pots work. I don’t think it’s the standard output problem, but that’s an easy fix. Doesn’t seem like a dsp problem either. What do you all think? Bad solder joints, some other fried components? I might re flow the entire board. The worst part is that a factory reset is not possible because the global button does not respond.

Thanks

First of all - do you have access to a scope?

Measuring the supply rails for ripple and voltage drops is usually a good way to start when a device has all sorts of random glitches. Digital circuits can behave very strange if the supplies are broken. I don’t know about the power supply in the Ion - does it use an internally mounted wall-wart supply like the Blofeld? In that case you might want to try exchanging it for another supply and check if it changes something. If it has an external supply - try chaning that as well. It might internally use some DC/DC convertors or other regulator circuits. Those might be broken - you can try to measure the voltages by finding datasheets for some of the chips and measuring on their respective supply pins.
I would check all of that supply stuff first.

Do you see any sign of mechanical problems? Corrosion, signs of water damage, etc. ? If the unit looks fine optically, you are likely to find a single defect that fixes all of the problems at once, e.g. worn out capacitors or a defective DSP.
If there are obvious signs of water damage or mechanical damage you migh have different sources of trouble all over the place. That can become hard to repair.

You can try to find out if the DSP is okay by sending MIDI messages and checking if it reacts accordingly - e.g. Sysex patch dump requests. If that works fine, you have a good DSP/CPU.

Regarding the defective buttons: It could be a defective DSP/CPU or a problem on other parts of the hardware. Chances are high that the button is scanned by a simple shift register or a button matrix - maybe you can follow the traces and find out if the signal actually arrives at the processor. For a button matrix you won’t be able to find it out without a scope, though. I wouldn’t bother about this before I could tell for sure that the supplies are fine, though.

I hope that helps a little. Its hard to give any specific advice without more details.

Thanks for the reply. The unit has a built in ac/dc supply. It’s open and it’s very easy to access. I do have a scope. I’ll look at the power ripple.

I completely disassembled it and cleaned the boards and inspected the damage. Many pots are corroded at the base but still work. The dead buttons are still dead after a de-oxit cleaning. They are common e-switch tactiles so no problem there. The control boards look really clean except for the pots. The main board shows corrosion, oxidation near the outputs so I was guessing that maybe the DACs were damaged. Luckily those can still be found on ebay.