Roland D-70 Super LA Synthesizer (#2)

I bought another project Roland D-70 about half a year ago. I’ve fixed one a few years back and this one also has problems with the keys. I thought it would make a nice midi controller for my Roland FA-06 so I bought it.

Technical specifications:

• Polyphony – 30 voices
• Oscillators – Digital ROM samples and DLM (“Differential Loop Modulation”)
• LFO – YES
• Filter – TVF FILTER: low-pass-resonant (like D50).
• VCA – TVA (like D50).
• Effects – Reverb, Chorus, Flanger (like D50)
• #Instruments – 5-parts + 1-percussion
• Keyboard – 76 note keyboard with velocity and aftertouch
• Arpeg/Seq – None
• Memory – 10 user sets, 64 performances, 128 patches, 128 tones.
• Control – MIDI
• Date Produced – 1990-91

I haven’t gotten around to fix this one for about 6 months but I started last night. Overall it looks pretty nice. Hardly any signs of wear and pretty much all the buttons work. It’s a shame they don’t all work well because getting to them and replacing them is a nightmare 🙂

The LCD works fine but the backlight is gone. These LCD displays use an ‘EL-foil’ as backlight and those get dimmer and dimmer after years of use. This synthesizer is about 25 years old and the backlight is completely gone. It’s still perfectly readable in daylight but in the evening it’s not very readable.

So: a few buttons that don’t work, no backlight and only about a dozens keys that actually work.. marvellous 🙂

As I’m going to have to take the entire thing completely apart why not give it the royal treatment… I’ve googled the display and there are a few websites where someone shows a D-70 with a new display. Cool. The display is a standard T6963 controlled 240×64 LCD display and there is only one (Chinese) company that seems to make them (buydisplay.com).

After a little googling I found the cheapest ones on eBay.de. (25 euro’s incl shipping) They make this display in different colors:

I bought the (bottom) black on white one. Should look a lot cooler than the standard yellowish display. (looks a little like the yellow one above)

Swapping it is simply moving all the wires to the connector you can see on the right hand side of the new display. They are suppost to be identical. You only need to add one or two resistors.. More on that later.

First thing to do is to remove the keybed. Before I opened it I noticed a few weird things with the keys. The spacing isn’t the same between all keys and some keys aren’t level with the rest. Two very strong indicators that this synth has been ‘serviced’ before.

When you replace the keys the C’s and the D’s etc are suppost to be identical. But I have found several times that the spacing isn’t good. If you look at the top of the keys you will see markings like CF12 or CF13 or CF14. This means that this key can be used a either a C or and F as they are identical. The 12, 13 or 14 part is support to be the mold number the key came out of. So a CF12 should be 100% identical to a CF13 or a CF14. And yet if you replace the keys by only looking a the C, D, E, F, G, A, B order you can end up with weird gaps between the keys as you can see in the pictures below:

You can see there are uneven gaps between the keys.. swapping out one C with an F or a C from a different octave can fix this.. weird.

Right. Time to break out the screwdrivers.

The D-70’s keybed has two major weak points: the ribbon connectors at both ends. The ones in this D-70 look fine:

This is a closup:

This is a thermally bonded connection between the transparant and the green pcb. Very fragile. DO NOT TOUCH. If you break it, half the keys won’t work anymore. Very difficult to fix (see my other D-70 project..)

I removed the keys and although the notorious ‘red glue’ problem is not happening right now in this D-70 it’s a disaster waiting to happen. So: put all the keys in a caustic soda solution to remove the red glue. Takes a night or two but you permanently remove or prevent this problem.

After I removed the keys I noticed that some of the metal springs underneath the keys were bent. This is probably the reason some of the keys weren’t level with the rest. This can only be caused by incorrect replacement of the keys by the previous ‘tech’:

Easy fix though: just straighten them out and everything should be ok.

Next problem: most of the keys don’t work. The rubber strips look very clean:

Let’s take them off:

Shit. Someone painted all the rubber/carbon contacts with some kind of paint.. I tested the paint with a multi meter and it actually conducts electricity very well. Could be silver paint. But still: hardly any key worked.. could be because of an uneven surface of the paint. I will try to explain with my amazing Paint skills what happens here:

Above you see a cross section of the key contacts. The gray thingies with the black bottoms are the rubber contacts and the two black surfaces below it are the contacts that are on the green circuitboard. Notice the key contacts have a different height. When you press a key both gray contacts are pushed down and make contact with the two black surfaces below it. Because the black (carbon) part of the gray rubber part conducts electricity the circuit is closed and a tone will sound from your keyboard. Because the gray contacts have a different height the one on the left will make contact after the one on the right. The time between these contacts is measured and determine the velocity or ‘how loud’ the tone will sound. So you can play a Piano really gently or REALLY LOUD. Usually (well with Rolands anyway) there are 127 steps in which the velocity is measured. It’s that sensitive. So if you play the piano gently the keybed will tell the sound generating part of your keyboard to play a C with a velocity value of say ’40’. When you hammer the keys the numbers will go up to a max of 127. If you have a keyboard where one or two keys always sound really loud one of the two contacts is dirty. (I guess it will be the one on the right in de above image). You press a key and the contact on the right doesn’t close the circuit. A fraction of a second later the contact on the left closes. The keyboard has no way of knowing how hard you pressed the key so the note will sound at a velocity value of 127. If the contact on the left is dirty the note will not sound at all. (although I might be mixing up left and right here.. not sure :-))

So: one note always sounds loud or doesn’t work at all? Clean the contacts underneath the keys.

In this case the keys where not working properly at some point but instead of cleaning the contacts the previous owner of tech decided to paint the contacts with conductive paint. This didn’t work out very well as I will try to explain in the next picture:

If you paint these surfaces you better make sure the pain is really really smooth because an uneven surface will cause problems. This is what I think happened to my D-70. All contacts were painted and my multimeter showed the paint conducted electricity very well. Still hardly any key worked.. If the paint surface is uneven you will get the situation of the above picture where the red color is the paint. If you press that key it might not close the circuit.. no sound from that key. Painting the contacts might also completely mess up the velocity curve.. Because the distance between the contact surfaces changes. Even if the paint-job is successful you might end up with a Piano that sounds horribly.

The D-70, D-5, U-20, JD-800 and probably some other models share the exact same technology for the keybed. The keys between these models are interchangeable. The D-70 has 76 keys where as the others have a 61 key keybed.

My experience this type of keybed is as follows: it is very common to see these advertised with a description like ‘many keys stopped working’. In the projects I have bought it was not uncommon that only 5 keys worked. However: once I cleaned the contacts (96% cleaning alcohol and q-tips) I always got every key working again and I have never had to take that synth apart again. Even my first project (the Roland U-20): don’t use it a lot but every time I do: all the keys still work years after I’ve taken it apart. And I only use it a couple of times each year… So don’t be afraid that you will have to take these Roland apart every 6 months to clean the contacts.. this is not the case.

The only Roland synth where cleaning the contacts did not work for me was the Roland Juno-D. These are also very commonly advertised with unresponsive keys: just buy new contactrubbers from Roland.. Costs are around 25 euro’s for the entire keybed.

Back to my D-70:

Luckily it is relatively easy to remove the paint. It only takes a few seconds to scratch it off with my nails. I’m going to clean all this mess and then give the contacts a good clean with q-tips and cleaning alcohol.

Stay tuned 🙂

Update November 8th 2017:

I cleaned all the contacts with alcohol and q-tips. It took hours 😐 Everything looks clean again so I reassembled the keybed. I removed the red glue weeks ago and I glued the weights back in. I straightened all the metal springs and put all the keys back on the frame. All the keys are level now and no more weird gaps between the keys. Looks great 🙂

I installed the keybed in the D-70. Tedious job. Be careful not to break the connectors which are exposed at both ends.. I delayed this job for a few evenings because if after all this work you find out that some keys still don’t work you can take the keybed out again..

It’s frustrating when you do all this work to find out that there is one key that doesn’t work of isn’t velocity sensitive :’)

So everything is back together, I flicked the switch, crossed my fingers and plugged in my headphones…

 

 

 

Every key works again!!!!

😎

Played it for a while and it sounds great. Velocity sensitivity on every key works great too. First part of this rebuild is quite successful 🙂

Now that I’ve played it I noticed a very annoying hum coming from the inverter that powers the non-functioning backlight of the display. It’s like a very faint ‘WheeeeeEEEeeeEEeeeeeEEEEEEEeeeeeeee’ kind of sound.

You don’t hear it over the headphones but you can hear it very clearly when you’re near the D-70. Installing the new display will take care of that. The new display has LED back-light so the inverter module can be removed. Win-win. Also a few buttons need replacing so I’ll have to take all the circuitboards out of the D-70 to fix those issues. To be continued.

 

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