Replacing the LCD display on a Roland MC-505

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

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

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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:

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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;

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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:

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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.

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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.

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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

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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 .

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

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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.

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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

 

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12 thoughts on “Replacing the LCD display on a Roland MC-505

  1. Hi, Im trying this replacement but I dont understand the mc505 tech document – to figure out which of the 14 wires on the cable attaches to which points on the ;lcd screen. could you please help with this?

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  2. hi,

    Try to do the same as you but I think I did not put the connections correctly. It turns on and they seem to me letters but it does not correspond with what should appear. I would love to show you a photo but I think it is not possible. How can I solve my problem?

    Thanks for your dedication.

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  3. hello, I do not know my message arrived since I had problems with the application, I feel if it has doubled. The unit you installed was the same as the one you purchased “arducam 1602 based on the HD 44780 driver”. I do not know if the problem comes from having connected something wrong or that simply the bridge I made between VSS and K. I did it with two pins and I think it is very badly done. thanks for your quick response.

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  4. Thanks for the guide, can you please clarify the way the resistor is used to adjust contrast ratio. The installation is successful but Im having trouble getting a good viewing angle. You wrote:
    “680 Ohm resistor between the Vss pin and the A pin, and the K pin to VDD (ground)”
    The pictures show a resistor between VDD (pin 2) and A (15). I don’t see a second resistor between VSS (1) and K (16) but a bridge that connects to pin 1 of the MC-505.

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    1. The 680 Ohm resistor is for the backlight display. The K pin on the LCD needs to be at ground potential, hence the connection. To adjust the contrast on the MC-505 I think you hold down “shift” and press the keyboard 10 button. Hope this helps!

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  5. Hi JB, thanks for the useful guide. In the photo showing the soldering, am I right assuming the white ribbon is seen from its top (the side with the tiny red mark on the other end)? i don’t want to invert the connections to the PCB !

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    1. On the main board, pin 1 of the ribbon connector is ground, I believe. That conductor on the ribbon cable should end up being connected to Vss on the LCD display board, so just check for continuity between Vss on the board, and pin 1 of the ribbon connector on the main board 🙂

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  6. Thanks JB. It worked. But I think there is a bit of confusion going around since, as darkosis said, the pictures doesn’t illustrate the connections of your text. In fact you inverted VSS and VDD in your explanation, but as we can see in the pictures the correct connections are a resistor between VDD and A (not VSS) and a bridge between K and VSS. I hope you can tweak this little part, because everything you did was so helpful!

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