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

Advertisements

Replacing the LCD display on a Roland MC-505

Here’s my MC-505 as it arrived from the seller on Reverb:

4

The LCD display (the orange rectangle top centre) shows the common problem that these units suffer: many pixels are inoperative. A closer look:

3

The first thing to try as a fix is to re-heat the LCD ribbon cable, to re-make the electrical contacts. We need to extract the LCD from the unit first. Start by removing all knobs from the front of the unit (they just pull off) and opening the case:

Photo Jun 09, 13 59 22

The white ribbon cable  attached to the upper main board is for the LCD – it just pulls out. To extract the LCD itself we need to get access to the screws which attach it: these are underneath the plastic screen at the front of the MC-505. Some people use a knife and pry it off from the front: a bit risky, as the screen could bend and break. Instead, remove the mainboard, which involves detaching all the ribbon cables, all the jack sockets, and several screws. Take photos of everything as you gut the machine:

Photo Jun 09, 14 01 37

Cut any cable ties as necessary, such as the one in the photo above (and remember to replace them on final reassembly). Here we see the interior after removal of the main board;

photo-jun-09-15-45-30.jpg

We can see the rear of the LCD display top centre. Now remove the large board that holds all the keys and switches. No need to detach the ribbon cables from it. There are many small screws that attach this board to the case. Here’s the key switch board removed:

Photo Jun 09, 16 22 41

If you are going to clean the switches etc., remove them from the board – the plastic piano key switches have small latches that hook them to the board, but are not hard to remove. Be very careful, as they are quite flimsy. Here’s a view of the case, without the boards, but with the various switches still in position. Remove them for cleaning if desired. With access to the rear of the plastic screen, it can be gently pushed outwards by applying firm pressure through the aperture – it’s only held in by double sided tape, so little effort is required.

Photo Jun 09, 15 57 01

With the screen removed, the LCD display unit can be accessed and removed from the front of the unit – it’s held in place by four small screws. Here’s the case with all switches, knobs etc. and the LCD display removed.

Photo Jun 09, 16 15 49

With the LCD display removed, re-assemble the unit’s circuit boards, including the power supply board, but leave the back of the unit’s case off so that the innards can be accessed. From the front, feed the LCD display’s ribbon cable through the aperture and attach the ribbon cable to the main board. Now the machine can be powered up again.

If you are lucky, you can fix the missing LCD pixels by heating. There is a wide ribbon cable that connects the LCD display at the front to the LCD circuit board at the back. This ribbon cable is poorly connected. Using a soldering iron, and while the machine is powered on, so you can see the results, run the tip of the iron slowly backwards and forwards along the ribbon cable where it attaches to the circuit board. You should see pixels reappear as the connections get re-made.

In my case, I could get most of the display back using this method, but parts were still missing no matter how many times I applied heat.

I ordered the following:

Arducam 1602 16×2 LCD Display Module Based on HD44780 Controller Character White on Blue with Backlight for Arduino

61vgjCFcKWL._SL1000_.jpg

for $5.99 on Amazon. I then removed the ribbon cable from the old LCD display by de-soldering it, opened up the individual wires in the cable, and soldered it to the pinouts on the Arducam unit, referring to the Arducam datasheet and the MC-505_groovebox_SM .

Photo Jun 11, 17 17 44

I added a 680 Ohm resistor between the Vss pin and the A pin,  and the K pin to VDD (ground) which adjusted the brightness of the backlight on the LCD to a good level. The display worked:

Photo Jun 11, 17 17 38

Now all that remained was to position the new display in the aperture, drill a couple of new holes at the left for mounting purposes, and fix it into position.

Photo Jun 11, 17 52 13

Finally, I reattached the plastic cover using some double sided tape. The LCD unit stands a little higher than the original, so the cover sits a bit proud of the unit – not a big deal. It certainly looks a lot better than the original, and is fully readable!

Photo Jun 11, 18 00 08

 

Puzzles of the Voynich Manuscript

I just published the guide “Puzzles of the Voynich Manuscript” on Amazon.

This illustrated guide to the Voynich Manuscript is targeted mainly at those who have recently come across the book and are wondering what all the fuss is about, and why, after more than a century of effort, nobody has cracked its code yet. It should also be useful as a set of tests for those who believe they may have cracked the code, so that they can see how their solution matches up against each of the puzzles or notable features described. And finally, it is hopefully of interest to those already familiar with the manuscript – perhaps they will find something new or thought provoking within.

 

 

Trying the Sitar

I’ve always been entranced by the sound of the sitar, and wanted to try it for myself. If you do some research on beginner sitars, you will find a lot of people pontificating in a most discouraging way, e.g. by saying that it’s incredibly hard and painful to play, that every sitar costing less than $1000 is rubbish, and so on. You get the picture.

Casting these admonitions aside, I ordered a 1/2 size sitar on Amazon. It’s probably about 3-4 feet total length.

17596560349_d29d9a0901_m
The 1/2 size sitar. This has 7 main strings, and 11 sympathetic strings. There are two toombas: one at the base (the big, round object that is made from a gourd/pumpkin), and the one on the neck, which looks a bit like an upturned salad bowl. Never rest the sitar as shown!

Although it was advertised as “blemished”, what I got was an unblemished model. It arrived well packed, inside a soft carry bag, and complete with a set of new strings, some mezrabs (the little wire things you put on your forefinger to pluck the strings), a learning sitar book, and another soft cloth bag.

There are seven main strings that are played, and a set of 11 “sympathetic” strings, which lie underneath the main strings, and aren’t played, but vibrate in sympathy with the main strings. I spent quite some time tuning *all* the strings to the Ravi Shankar C# settings, which you can find online. I used an Android tuning app to do this. Take extreme care, as it’s easy to over-tighten a string when tuning it, and thus create a crack around the tuning peg hole (I did this on the third main string, and had to repair the crack using wood glue and clamps overnight – now it is fine). Another thing that can happen is that a string can break – this also happened on mine, just after I started tuning one of the main strings. Replacing it was easy, but make sure you replace the string with one of the correct gauge (I used a micrometer to measure the snapped string diameter, and then selected a new string of the same diameter from the set sent with the sitar).

Another tuning tip is to remove each tuning peg carefully and rub some pavement chalk on it, before carefully reinserting it – this helps to avoid the peg slipping. After tuning all the strings, the effect is striking – if you pluck any of the main strings, the whole instrument resonates and produces that very characteristic buzzy sitar sound. With the strings un-tuned, the sound is dull and lifeless.

What is great about beginning the sitar is the fact that it sounds good even when a novice is plucking it, unlike most other instruments (the violin is a particularly bad offender). So, you can sit plucking and strumming and bending notes randomly on the sitar and it actually sounds very pleasant.

One other issue I’ve found is that the strings dig deeply into your finger ends, when you press them against the fretboard. It’s like playing an egg-slicer! The first main string (tuned to F# in the Shankar tunings) is the one that sees most finger pressing action, and it is thin! After a while of playing, it becomes almost unbearable, so I’m hoping that I develop some callouses soon.

Mitsubishi LT-70 Linear Tracking Turntable

This is an LT-70 that at one time was part of the Mitsubishi “Audio Intelligent System Model DA-L70/LT-70”. I am trying to get it to work standalone.

LT-70

On the back panel, there are phono outputs for the cartridge, and an 8-pin DIN plug that connected to the rest of the system.

DIN plug

The wiring is as follows:

  1. Pin 1: Yellow -12V
  2. Pin 2:  N/C
  3. Pin 3: White (“AF”?)
  4. Pin 4: Orange +12V
  5. Pin 5: Black (“SYNC”?)
  6. Pin 6: Braid 0V
  7. Pin 7: Red (“STP”?)
  8. Pin 8: N/C

This plug is marked “TO CACEIVER” J106 on the following schematic for the turntable:

LT-70 schematic (part)

The same plug is marked “PL CONT” on the schematic for the main unit:

DA-L70 Schematic (part)

Working from the schematics, I saw that the turntable uses a -12 0 +12 power supply, which I’ve duly connected to pins 1-6-4 on the plug (29,28,27 on the turntable schematic). Sure enough, the unit powers up, the track indicator 7seg LED lights up, and I can operate the tray using the “Open” button on it, the fwd/rev buttons that move the cartridge left/right, and the various programming buttons on the tray (track select, program, etc.)

However, the turntable never spins, the “Start” button has no effect. I think this is because I am not providing the correct signals on the pins marked “SYNC”, “AF” and “STP” (shown on the main unit schematic).

Two of these three pins (24 & 25) are connected to IC151, a BA612 quad driver, on the turntable circuit board: 24 seems to be an input signal to the turntable (since it goes to a BA612 driver input, pin 2). The other, 25, looks like an output signal from the turntable to the main unit, and measures +12V when the turntable is powered up. Finally, pin 26 also looks like an output, some sort of current source from Q221?

EDIT (April 2016): I don’t know what I was doing wrong above, but I just checked three years later, and the unit works fine using the connections specified above. I was able to play and listen to an LP without problem.

Summary: open the DIN plug connector on the cable coming out of the unit, and connect the following wires to a 12-0-12 power supply.

  • Yellow to -ve 12V
  • Orange to +ve 12V
  • Braid to Ground

Connect the RCA plugs (left and right) to your amplifier.

The red wire, if touched to +12V, will stop playback, but it’s not required.