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.

Hey just following up as I have the exactly same problem with my ASR, have you managed to fix it?

Hey @drumbait, no I have not solved the issue as yet. Have not had the time (nor the enthusiasm!) to commit to the diagnostics tracing.

Yeah electronics is not my forte unfortunately so might have to consider saving up to send it to a pro. If I beat you to it I’ll post in here. On the plus side it’s got me digging in mono which has its own benefits I guess.

Just to clarify… you are aware that the ASR 10 can use either left or right in mono mode as well as stereo input. Are you only trying to sample in mono L? Have you tried stereo? Have you tried changing both your input cable jacks just to make sure it’s not the cables themselves. I’ve had bad 1/4" cables before where only one side works. Try that first. Also, if you change to new cables and still getting no signal on one side, make sure you’re sampling in stereo to see if you get signal on both. If all that fails I’d think you need to open it up and check for loose solder connections on the input jacks going to the input board. If it’s loose it may not be making the connection. Just reheat the solder connections on the loose jack carefully and if it needs more solder purchase some at Radio Shack. Hope this helps. P.S. after you fix the input connector. Pick up a patchbay… this way you can connect the ASR 10 inputs to the patchbay and use the patchbay to plug into the ASR 10 instead of pulling and pushing different sources into the direct input connectors of the ASR 10. The patchbay will act as your middle man to make connections going into your ASR 10 without ever causing future damage. Patchbays are cheap. $60. at Sweetwater Sound. My entire studio inputs and outputs all connect via patchbays. There are 6 patchbays because I want to spare all the connectors on my machines and have one central place to make any connection I want from any machine to another. Enjoy!

Hey y’all,
My ASR-10 is suffering the same right channel issue. I’m no electrical engineer but I did go through checking continuity on the jack board and found that U3 (tl072cp) showed continuity through pins 1&8. Looking at the pin out below we can see that pin 1 is the output and pin 8 is where all our current is coming in. I don’t know much but my hypothesis is that output is our right channel input. I’ve ordered a new one from syntaur (along with a replacement decoder IC for the right coil board) and I’ll let you know if it fixes it.

This is where it is located on the board. If you’ve got a multimeter set it to continuity and check the two top pins. If it yells at you you’ve got the same problem I do.

You don’t have to remove the ic to test it, it’ll show continuity in-circuit. I pulled mine after to make sure those through holes weren’t still continuous (they were not).

TLDR: check that IC

Hey @terrorboss that sounds very promising and appreciated you adding to this thread. Will try and get my board on the bench this week to confirm. Let us know how you get on too.

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