Ensoniq ASR-10 Right Channel Analog Input Dead


I have an Ensoniq ASR-10 which I’m bringing back from the dead (OS 3.53).

One final issue I have is that the right analog input is dead - notes below.

Maybe an issue with analog to digital conversion for one channel - no idea which board that’s on.

Any ideas?

Thanks, Tim.


  • Input level LEDs are not showing any incomming signal on right channel
  • Rigth channel is not sampled

The left analog input channel is working wonderfully (input/monitoring/output) and digital input/output/monitoring is working for both channels. Analog output for the right channel appears tro be fine (e.g. playback of disk samples).

I have tried the follwing:

  1. Replaced the analog jack board

The jack board I bought did not seem to work at all. When I tuned the ASR on, the input level LEDs for signal and peak were both lit with no imcomming signal, but only for the left channel. Looks like the board I got is not working\compatible, but strange that only left channel LEDs were lit.

  1. Replaced the analog board (+ original analog jack board)

The different analog board worked fine, but again only left analog input working.

  1. Cables

Continuity test of analog jack board and display board ribbon cables - passed.

  1. Display LEDs

Diode test of right channel input level LEDs - passed.

This is not specific to your synth, but is a technique that works.

look at the sound generation chip in your synth. It will have opamps feeding the signal to the output.

if you have an oscilloscope check if the signal is on the input and output of each op amp from the sound generation chip to the output. where ever the signal is missing in a stereo Left-Right circuit, or not where it should be, that is the fault.

Op amps fail mostly because of power supply glitches such as spikes or grounding faults, so always start with inspecting and verifying the power supply is correct first.

Hey, thanks for replying to my post.

Sounds like good general advice for diagnosing output issues, appreciated. However, my issue is an input issue, both left and right output channels are working fine.

I do have an oscilascope, but have not yet used it for diagnostics work - the next step up for my limited skills.

One of the problems I have is that schematics do not seem to be available for the ASR-10.

Sounds like your problem is on the analog jack board if after replacing the analog board you still have the dead channel. As far as having to troubleshoot without a schematic goes, it may not be too bad on that board. Luckily, you have a working channel to inspect with your oscilloscope so you can spot what’s wrong on the other channel.

You will want to check the inputs and outputs of the ICs that make up the left and right inputs. You may have to remove the board and follow traces to determine which they are or it may be more obvious, depends how many ICs are on that board and how they’re laid out.

With the unit on, try running audio into the left and right channels. Follow the audio signal with your scope through each IC or transistor it travels through. Check datasheets for ICs to know which pins are the inputs and outputs. Or go pin by pin comparing to the other channel and note any weirdness. It’s likely a bad opamp and when you probe it with your scope you will see audio at the input and then nothing at the output.

issuing a service manual without a schematic is criminal in my books.

But my advice is the same, insert an audio signal and follow it through the circuit the same as described.

Google the ic chips to find their pin outs so you know (or have an idea) where the signal is going.

Where the signal should be and isn’t, is the problem. That’s how any tech would go about searching through an unknown device.

Hey, thanks for the advice. All sounds logical.

Signal tracing is something I haven’t attempted yet - it will open up loads of opportunities for diagnosing and fixing stuff. I live in the middle of nowhere so I have to get on with it really - no gear techs out here :slight_smile:

Fingers crossed I get to the bottom of it - will report back here for posterity.

Good luck! Just be careful not to short IC or transistor pins to one another with your oscilloscope probes. Also never put the ground clip of your probe on anything other than ground, this can damage the oscilloscope or device under test. The chassis is a fine place to clip it to.