9700midi2cv8 troubleshooting help please
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Author:  James [ Sun Oct 02, 2016 8:54 am ]
Post subject:  9700midi2cv8 troubleshooting help please

self-test WITH midi works:
LED gives "status on basic channel" blinking when sending midi.
when switched to Mode 3 LED blinks as expected when sending notes & pitch wheel, etc. messages

self-test WITHOUT midi does not work.
I get a constant 10v at all connectors, when testing with DVM across tip & sleeve. No strobing of voltage and no ramping of voltage at

I am powering the unit from 9771-15 power supply and it powers up fine. No smoke, nothing hot to touch.

I did NOT install the following: (since it is being powered by 9771-15)
NO wire from point "G"
NO wire from point "S"
NO switch installed
NO power LED installed
NO wall wart used

I tested the voltage across pins 4 & 7 at all 3 Op Amps and get +14v & -12v on each
if I turn the trimmer on the board, the 10v measured at the T & S connector points moves as I turn the trimmer, but the voltage is still fixed. (no fluctuation during self-test)
I re seated both uC & PROM (no change)
while in Mode 3 I patched the gate output to cv in on my filter and just get a constant held gate at 10v.

Author:  RoyGwinn [ Mon Oct 03, 2016 3:29 am ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

The MIDI self test is good, so the processor is running. Just to be certain here, when self test sees a MIDI byte the flashing is bright, bold and regular and continues after the MIDI in has stopped. A little blip on the LED when MIDI is received, in any mode, is a hardware effect and doesn't by itself prove the processor is running.

The DAC tune preset changes the voltage at all of the outputs. That is encouraging. It means the 4051 demultiplexer and all of the output opamps are working. It looks like the DAC is stuck on FF (the code for maximum out).

I would look for shorts or opens around IC7 (the HC373 data latch for the DAC) and IC6:D which drives the latch. I would pay particular attention to anything that could affect all eight bits together, like the G which comes from IC3p16, and the /OC input to the HC373.

It might be a faulty chip in IC7 or IC8, but a soldering issue is more likely.

Give the back of the board a good scrub with flux solvent or isopropyl alcohol. That can clear small problems, and make it easier to see big ones.


Author:  James [ Mon Oct 03, 2016 9:18 am ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

thanks for the help Roy,

during the MIDI test, yes, the LED continues to blink in the proper sequence after sending a note. When switching to any other mode OTHER than self-test, the LED blinks briefly, as expected, when sending notes, cc changes, etc and only when sending data. So that section of the module appears to be working properly.

I'll check out the locations you've pointed out, and try and clean the board as well.

Will report back

thanks again for the help

Author:  PAiA-Scott [ Mon Oct 03, 2016 9:55 am ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

There are some extra connections to be made on the MIDI2CV8 board when the v3.0 is in place (illustrated on page 28 of the v3.0 supplement). Did you get these added?

Author:  James [ Mon Oct 03, 2016 10:32 am ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

I'll double check. I definitely remember NOT doing any instructions in the 3.0 manual that came in the kit. I just thought it was a programming reference. :oops:

Author:  PAiA-Scott [ Mon Oct 03, 2016 4:04 pm ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

Sorry, but sometimes a light goes off in my head, hours later or overnight.

Not long ago, we had some micro-controller ICs that exhibited the trouble as you've described. I believe I emailed all that could have been impacted, but...

The part in question has the mfrg marking ATMEL 80C51 RD2-UM.

Author:  James [ Mon Oct 03, 2016 4:32 pm ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

That's the manufacturing number I have on IC3 ;)

Is it necessary to also add the jumpers to activate dip #8?

please e-mail me for address to mail new IC to


Author:  PAiA-Scott [ Tue Oct 04, 2016 11:07 am ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

Replacing the uC is the first step.

The extra connections for v3.0 are only for accessing the extra features and had I been thinking right, would not have mentioned this as a solution to the trouble symptoms : /

Thanks for the help here Roy! About cleaning flux to help see the board joints, this is something that should be done with caution so as to avoid the solution running around edges or through holes to the top side of the board and getting in socket receptacles or switch/connector contacts (if there is a area of concern that is obscured by blackened touch-ups or resoldering, a dull scribe can be used to scrape/flake away hardened flux and a dampened cotton swab used to wipe the area clean).

Author:  James [ Sun Oct 09, 2016 4:01 pm ]
Post subject:  Re: 9700midi2cv8 troubleshooting help please

Changed out the IC today and module works perfectly!

thanks for the quick part replacement and help.


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