After I repaired the memory backup battery on my Alesis DM Pro, it’s time to (try to) fix the faulty audio outputs.
Each voice in a kit can be assigned among the DM pro has 6 outputs, in addition to being routed to EITHER of its for Reverb (room, hall plate) OR MultiFx (distortion into fixed delay into mod-delay into EQ).
- Main L and R, with panning, and routing to reverb OR the MFX. LR also acts as output for
- Aux 1 and 2, with panning, routing to either FX bus.
- Aux 3 and 4, only for direct selection, with no FX bus routing.
All the stock kits never used the “other four”, and just sent all voices a stereo spread out the Mains with preset FX bussing.
Over the years, I’d build up a system of routing and grouping electronic drum voices into 6 channels.
- Kick(s) isolate on 3
- Snare(s) isolated on 4
- Tom(s) in stereo image on 1/2; sending “dry”
- Everything else (cymbals, perc) and internal “FX returns” out the on L/R.
By putting these 2 mono and 2 stereo channels into a rack mixer, I could quickly adjust levels and change FX routing (to some rack gear) for a very live instrument.
UNFORTUNATELY; over the years, I lost outputs 3, then R (even though the headphone output still gave proper LR stereo)… then everything. All 6 outputs (plus the stereo headphones) would only emit a simple whine.
Like any good surgery, we start with tests. The headphone outputs were the last to go, so I tested them by playing the demo sequence.
The DM Pro has a debug mode, where you can run
- test on RAM integrity
- test buttons and lights
- Audio Test: test audio outputs (with a 0 dBFS square wave pushed out all ports).
I ran the Audio Test.
Sure enough, there’s a square wave, but it’s weak, and intermittent when I flex or push on the paneling.
Perhaps this was a problem of the MANY jacks that were hard-soldered to the motherboard (not even separated to an IO board).
To the Bench
Opening the DM Pro (back) up, I se that the (many) audio out and trigger input jacks are are soldered directly onto the motherboard. There is a possibility some (or now all) of these outputs could have become open solder joints.
The Heat is ON
I gave the motherboard a once-over with my solder reworking blower (set to 650 F, kept 2-4 cm from board). This made many of the blown points liquify and re-solidify.
No Dice…too small ?
After re-assembly, and re-testing, I found this did not fixe the problem.
So, this is where I start tracing (with eye and probe) where the audio lead from, to see if there is any obviously burned or open component.
The back corner shows 3 stereo DACs (Digital to Analog Converters for LR, 12, and 34) fed off some small chops labeled CS4390KSEP on top, and JNAWEA9834 below.
Internet search determines these are 2 channel 24-bit converters by Cirrus Logic, which are now discontinued. These chips fed outward to some electrolytic capacitors, which tested fine, and showed the Audio Test square wave at MUCH greater strength. These ten led to a maze of surface mount resistors (attenuator/mixer circuits) toward the output jacks.
Since I don’t (yet) have the experience or tools to work productively with surface-mount components, this is where I throw up my (large) hands.
Luckily, I’d bought a spare DM-Pro from a pro-audio auction a few months ago, but it had it’s share of problems. Time to consider Frankenstein-ing the good remainders of my “old” unit into the “new” one.