Troubleshooting AJT MidiMod: Common Issues and FixesAJT MidiMod is a compact MIDI modification board popular among musicians and hobbyists for adding MIDI control and flexibility to electronic instruments. While generally reliable, users can run into a range of issues — from basic connectivity problems to tricky timing or mapping errors. This article walks through the most common problems, diagnostic steps, and practical fixes so you can get your MidiMod back to stable operation quickly.
Quick checklist before troubleshooting
- Confirm power: ensure the host device and any external power supplies are on and within spec.
- Cables and connectors: use known-good MIDI or USB cables and try different ports.
- Firmware: check whether firmware is up to date; many bugs are fixed via updates.
- Backup settings: if you can access configuration, export or note your settings before making changes.
1 — No MIDI signal / device not recognized
Symptoms: Host device doesn’t see the MidiMod, or MIDI messages aren’t received.
Steps & fixes:
- Hardware connections
- Re-seat the MidiMod board and confirm all ribbon/header/solder connections are solid.
- Try a different MIDI cable or USB cable and different ports on your computer or host device.
- If using a USB-MIDI adapter, ensure that adapter is class-compliant and powered (if required).
- Power issues
- Verify the host provides the correct voltage/current. Some mods require stable 5V from the host or separate supply.
- Drivers & OS
- On Windows, check Device Manager for unknown devices; install or update the driver if the MidiMod requires one.
- On macOS and Linux, class-compliant devices typically need no driver; restart the MIDI subsystem (replug or reboot).
- Firmware and boot mode
- Put the MidiMod into bootloader/DFU mode (per device instructions) and reflash firmware if the device is unresponsive.
- Test loopback
- Use a MIDI monitor utility (e.g., MIDI-OX on Windows, MIDI Monitor on macOS, or a DAW) to see if any messages are being sent. If nothing appears, the issue is likely hardware or firmware.
2 — Intermittent MIDI dropouts or latency
Symptoms: Notes or CCs drop occasionally; unexpected lag between input and output.
Causes & fixes:
- Cable/connector fault: replace suspect cables and check connectors for dirt/corrosion.
- USB bandwidth/CPU overload: close other USB devices or software processes; try a direct USB port (avoid hubs).
- MIDI clock conflicts: if multiple devices are sending clock, ensure only one master clock or properly configure clock routing.
- MIDI throttling in firmware: check settings for message filtering/rate limits; increase throughput or disable filtering if safe.
- Ground loop/noise: ensure proper grounding; try isolating the MidiMod with an optical or transformer MIDI isolator.
3 — Wrong notes/CCs sent or mapping errors
Symptoms: Controls send unexpected MIDI messages or notes.
Diagnosis & fixes:
- Check mapping/configuration
- Verify the mapping table on the MidiMod (via its editor or config file) matches your controller layout.
- Restore a default map to see if custom mapping caused the issue.
- Bounce/ghosting from hardware
- Mechanical switches/encoders can generate spurious signals. Use debounce settings in firmware or add hardware debouncing.
- MIDI channel mismatch
- Confirm the sending and receiving channels are aligned; use a MIDI monitor to view channel numbers.
- Velocity/scale conversions
- Some mods apply transformations (velocity curves, transposition). Disable or adjust these features if outputs look incorrect.
4 — Erratic behavior after firmware update
Symptoms: Device behaves strangely, features missing, or crashes after an update.
Steps & fixes:
- Reflash stable firmware
- Re-download the official stable firmware and reflash using the recommended tool. Avoid beta builds unless you’re testing.
- Factory reset
- Perform a factory reset to clear incompatible settings left by a previous version.
- Check release notes
- Read firmware changelogs for breaking changes (e.g., changed default MIDI channels, renamed controls).
- Roll back
- If problems persist, roll back to the last known-good firmware version.
5 — Settings not saving or random resets
Symptoms: After power cycle, mappings or preferences revert.
Causes & fixes:
- Faulty non-volatile memory (EEPROM/FRAM)
- Verify writes are occurring: some MidiMods expose settings through a config utility which shows save status. If writes fail, NVM chip could be bad or improperly soldered.
- Insufficient shutdown time
- Ensure the host fully removes power only after the device has finished writing settings; add a short delay before removing power.
- Power brownouts during write
- Provide stable power or add a small capacitor to prevent brownouts during EEPROM writes.
- Corrupt config file
- Load a fresh config file and save; delete old corrupted files if applicable.
6 — MIDI clock/sync problems
Symptoms: Tempo drifts, sequencers lose sync, or timing feels off.
Fixes:
- Single master clock
- Ensure only one master is sending MIDI clock. Configure the MidiMod to be slave or master explicitly.
- Buffering/latency
- Reduce any buffering settings and disable message throttling that might affect clock messages.
- Clock jitter from USB-to-MIDI adapters
- Use a high-quality adapter or native DIN-MIDI hardware where timing accuracy matters.
- Use DIN MIDI for critical timing
- DIN connections often have more consistent timing than USB MIDI in complex setups.
7 — USB enumeration errors (device shows as unknown or “USB device not recognized”)
Troubleshooting:
- Try another computer and cable to rule out host issues.
- Replace the USB connector or check solder joints on the board; micro-USB/USB-C ports can develop cracked solder pads.
- Inspect for bent pins, damaged traces, or shorts on the board.
- Reflash USB descriptors if corrupted (advanced) or restore factory firmware.
8 — MIDI through / routing issues
Symptoms: Messages not passing through the MidiMod to downstream devices, or double-transmitted messages.
Fixes:
- Confirm routing mode: many MidiMods offer passthrough, merge, and routing modes—ensure correct one selected.
- Avoid loops: ensure you don’t create a feedback loop where device A sends to B and B sends back to A.
- Merge behavior: when merging, messages may be duplicated—enable deduplication or use routing rules to filter duplicates.
9 — Hardware symptoms: overheating or visible damage
Immediate actions:
- Power down and disconnect. Inspect visually for burnt components, bulging capacitors, or cracked traces.
- Smell for burnt electronics (careful) and do not power on if damage is apparent.
- Replace damaged components or seek warranty/repair service.
10 — Advanced debugging tips (for tech-savvy users)
- Use a logic analyzer to capture MIDI signal timing and identify malformed packets or framing issues.
- Connect a MIDI loopback with a known-good device to isolate whether the problem is upstream or downstream.
- Enable verbose logging in the MidiMod’s editor (if available) to capture internal events and errors.
- Use a breadboard test harness to power and test individual components (IO pins, MCU, clock crystal) separately.
When to seek professional repair or replacement
- Visible physical damage, persistent non-volatile memory failures, or suspected MCU faults are usually beyond simple home repair.
- If the device is under warranty, contact the manufacturer with serial number, a clear description of the issue, and steps already taken.
Example troubleshooting flow (quick recipe)
- Swap cables and ports.
- Test with MIDI monitor to confirm no messages.
- Reflash firmware; if still failing, factory reset.
- Inspect solder joints and connectors.
- Replace suspect hardware or contact manufacturer.
If you want, tell me the exact symptom you’re seeing (including host device, cables used, whether DIN or USB MIDI, firmware version if known) and I’ll give step-by-step commands and checks tailored to your situation.