Guts of a Korg MS2000

I bought an MS2000 with an issue, described below, because I enjoy a challenge:

1) On power up, the LCD shows “IPL s.p.u [ ]”, as if the synth is in update mode

2) If powered up using e.g. the “Mod Seq On/Off” and “1” buttons, the LCD shows “KORG MS2000” for a short while, then comes up with the A0 Stab Saw patch loaded.

3) When connected over midi, the synth is sending midi data – e.g. the keyboard and the controls send midi messages.

4) Patches can be changed using the numbered buttons, and the various LEDs on the synth change accordingly when patches change, however there is no sound from the headphone jack when the builtin keyboard is played, or an external midi keyboard is played.

5) If I attempt to load the OS 1.07 system update with the synth in “IPL” mode, using the Korg updater, then the LCD display changes to “IPL s.p.u [hrd]” and the update utility shows “Receive Error Timeout MS2000 did not respond”. The Seq 3 and Amp LEDs flash slowly when in this mode.

6) The midi channel the synth is working on appears to be 1, as this is the channel that keyboard messages and control changes get sent out on from the synth.

I’ve been through the synth internally, cleaned all connector contacts, and reseated everything. Nothing looked amiss on either of the main boards (no odd looking solder joints or discoloured components). I’ve checked the voltages on the supply, 3.3V, 5V and 7V and they are fine.

If I send SysEx messages over midi, the synth responds with two or three bytes, the values of which vary.

Here are some photos of the guts of the synth:

After some voltage measurements on the PCBs, it was evident that one of the TTL chips on the keypad circuit was faulty – the chip in question a 74HC138. After replacing that chip, everything improved! All the buttons and LEDs began working, and the synth booted up in the standard mode.

However, it produced no sound. After running a couple of the diagnostic checks, the following dreaded information appeared on the LCD:

IMG_1315

This indicates the DSP chip is probably toast. A replacement DSPB56362AG120 has been ordered, but this is a 144 pin surface mount component, and may be tricky to deal with.

Update: I removed the existing DSP using Quik Chip:

IMG_1321

After soldering in the replacement, and checking for shorts and continuity from each pin to the PCB, I found that the synth still showed the DSP error. I then went around the circuit checking voltages and signals – the DSP appeared to be receiving signals from the CPU, but doing nothing with them. My guess is that either the new DSP was a dud, or I somehow managed to destroy it in the process of soldering it in. So, I ordered a second replacement, de-soldered the “dud”, and replaced it with the fresh one – and success! – everything worked, the MPUtoDSP error was no more, and the synth produced sound.

IMG_1324

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