Nord's classical Virtual Analog Synth Nord LEAD 1/2/2x/3/4/A1 and Nord Rack versions

Nord Rack 2X New 3 Digit Display Needed...

Postby Mr Misfit » 05 May 2013, 21:28

Hey there to everyone here. This is my first time here and I have come with a problem.

My Nord Rack 2X has come out of storage and the 3 digit display is not functioning properly. Only the 2 lines on the side of each number illuminate consistently. The rest either do not light, light very dimly or periodically light.

Is there a remedy for this or do I need to purchase a new display component? If so, where can I purchase one from and what is it called, component number etc.

Thanks a lot in advance to anyone who chooses to off any assistance here.

M
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Nord Rack 2X New 3 Digit Display Needed...


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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby mjbrands » 06 May 2013, 00:40

I expect the display is a fairly standard part; it looks like the rack and the keyboard version use the same display. I don't have a Nord Lead 2X anymore so can't check anything myself and I don't have any info on the type, nor was I able to find something with some quick googling (same as you, probably).

I think those three numbers are part of a single display, something like this one:

http://pt.farnell.com/lumex/ldt-m2806ri ... dp/2062178

Note the something in my previous sentence. I very much expect it to be a through-hole component. You'd need to find a part with the same footprint and size (can be done from the back of the PCB without taking the whole Rack apart). Additionally, you need to find out if it is a common anode (probably) or common cathode display and what the forward current and forward voltage are (you can measure these, but it may be easier to do this once the old display is removed).

Desoldering a through-hole part with multiple legs is pretty easy to screw up (I know from experience :thumbdown:). Lifting a solder pad or even part of a trace off of the PCB is a substantial risk (but maybe I'm the only one who botches stuff like this 8-)). It does get a lot easier if you can clip the legs off of the component, so you can remove individual legs instead of the whole thing in one go.

Anyway, are you sure it is actually the display that is acting up? LED displays do fade, but this quickly seems a bit suspect. Maybe there's an issue with the power supply? On the other hand, the 3V3 supply that's probably used for powering the LEDs is also used for other electronics, maybe even the DSPs. If that 3V3 supplyl were flakey, I'd expect there would be more issues than just the LED display.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby Mr Misfit » 06 May 2013, 23:05

Hi there.

Thanks for your detailed reply. :)

The keyboard and rack are pretty much identical apart from the keys and pitch bend.

I'm a little apprehensive about desoldering a multi legged component as I do not wish to cause more damage, but hey, if needs a must.

The LEDs on the display were playing up a little last time it came out of storage but it was just the middle row and they had faded to half brightness. After a week or so they returned to full brightness and a week later were dim again. Now the problem is more severe as I cannot tell what patch number I am on. My assumption was that it was the display but I could be wrong if there is another possible cause for this problem. Everything else works perfectly though as far as I can tell.

I try emailing clavia customer support to see if they can shed any light on it.

Thanks again.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby mjbrands » 06 May 2013, 23:09

Do you have a multimeter or even better, access to an oscilloscope?
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby Mr Misfit » 06 May 2013, 23:44

I do have a multi meter yes. But not an oscilloscope.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby mjbrands » 07 May 2013, 21:38

I did some poking around in my own Nord Rack 3, but I fear I'm out of my depth here.

I first measured the voltages in my power supply. The 3.3V one was smack on and the other ones within say 1-1.5% of the intended voltage (probably well within spec). I measured the potential difference between ground and the indicated legs of the power transistors.

Note that the 3.3V supply could do with more capacitance on the output, as I've measured short dips as low as 1.4V when I abuse it (= plug a vacuum cleaner in the power socket next to the synth and then start turning that on and off). The values shown in the image below aren't as dramatic however, but still far from ideal. I've never had hangs I didn't cause myself, but there are quite a few reports of people who have had hangs during normal use.

Image

Voltages in the PSU:
Image

This isn't particularly useful or exciting, but it might be of use to someone.

Next was figuring out what type of LED display was used.

The front of the panel:
Image

The rear of the panel (top of the panel is actually at the bottom of the image):
Image

I thought it would be using a 3-digit display, but clearly they're using three separate 7-segment displays, each with their own set of 10 legs. It looks to me the through-hole components on the board were hand-soldered, as there's still flux residue on the board and the amount of it differs quite a bit for the different pins.

In this image the pin at the bottom-left of each of the three display is pin 1, the common anode. Pin 6 is also an anode (for the decimal point) and pins 1 and 6 are connected together. I've verified that segment B lights up when I put my multimeter in diode testing mode, with the positive probe on pin 1 and the negative one on pin 9. The multimeter puts out about 2.9 volt while doing that and the LED segment certainly isn't lit at full brightness.

Here's the service manual for the Nord Electro 2. Have a look at the LED displays on the page about the panel board.

http://www.workhousepoets.com/NE2%20Ser ... matics.pdf

It seems to me that my NR3 uses roughly the same setup, with a power transistor feeding 5V to the LEDs. The power transistors are turned 'on' using one of those 74HC374 octal flipflops, while they use a second octal flipflop to sink the 15-35 mA required for/available to the LED. They must be 'scanning' the LEDs, as a single output pin on the HC374 is only able to sink enough current for one (maybe two, but that's pushing it) LED. They're probably 'scanning' over the rows, turning on a maximum of 9 LEDs (in the case of the Electro 2, but it might be different on my NR3) per column. With a scope I should be able to see at what frequency, but that'd mean soldering (no room for the probes without first soldering on some wires) but something like 175-200 Hz seems to be good enough to achieve 'full' brightness on an LED.

Btw. the Lead 3 has a ridiculous amount of LEDs. It has 26 knobs with a 15-LED ring around them (so 390 LEDs) and then another 132 LEDs and 3 x 8 in the LED displays, so about 550 in total. :o

I wasn't able to determine with 100% certainty the LEDs displays actually run on 5V and not 3.3V. However, I measured values over 3.3V in some cases. Since there is a fairly beefy transistor (with heatsink) for the 5V supply and since the six DSPs (DSPB56362PV120) run on 3.3V, I'm fairly certain the LEDs run on 5V. The micro controller (MC68331CFC25) taking care of the panel, MIDI, etc. is probably running at 5V, though that part seems extremely lenient as far as what voltage it runs on, so it might as well run on 3.3V.

I wasn't able to determine the forward voltage for the LED displays. If I had to guestimate, I'd say 3.2-3.3V but it might even be as low as 2.7V or as high 3.8V.

I think you'll need to do some measurements of your own. Desoldering one of those displays would allow you to properly determine forward voltage and current. My guestimate for the forward current would be 15-25 mA. You'd also need to measure the (SMD) current limiting resistors - they were on the side of the board that could only be reached if I disassembled the entire panel board (which I'm not going to do but you'll have to do it anyway). They might be 100 ohm, as in the Electro 2.

As mentioned earlier (the remarks about pin 1, 6 and segment b) I've verified the pinout for the displays in my NR3 is the same as the ones used in the Electro 2. Strangely, when looking up parts on the internet, the pinouts seem to be different. I didn't really put a lot of effort into finding a compatible part though.

If you're going to do this yourself, your next step should probably be to carefully desolder one of those displays so you can do some measurements. If you google for 'determine led forward voltage current' (or something like that), you'll find descriptions of how to do that. Ideally you'd use two multimeters, but with some trial and error you can probably do it with one.

Anyway, quite a bit speculation on my part and fairly little hard data. Proceed with caution. :mrgreen:
Last edited by mjbrands on 07 May 2013, 22:12, edited 3 times in total.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby Mr Misfit » 19 Jun 2013, 18:06

Hey there. Been a lttile while since I was able to spend any time with this issue. it seems that over time the display leds are improving.

I appreciate the time and detail that you put into providing your previous answer.

As the problem does not seem to be having any effect on the actual performance of the Nord I have shied away from pulling it apart until I have time to reallt dedicate my self to seeing the job through.

I think it may be a connection problem directly with the display so this is where I shall look first. Certain leds are flashing and randomly turning on and off and others are only dimly lit.

Thanks again for your help. I will keep you posted.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby mjbrands » 19 Jun 2013, 23:27

Mr Misfit wrote:As the problem does not seem to be having any effect on the actual performance of the Nord I have shied away from pulling it apart until I have time to reallt dedicate my self to seeing the job through.

Sound like a very good idea. Even if the display were to fail completely, it indeed shouldn't have an impact on other functions.

Mr Misfit wrote:I think it may be a connection problem directly with the display so this is where I shall look first. Certain leds are flashing and randomly turning on and off and others are only dimly lit.

You could try re-heating the solder joints of the display to see if that helps; maybe one of them has gone bad.
Last edited by mjbrands on 20 Jun 2013, 17:06, edited 1 time in total.
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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby pablomastodon » 20 Jun 2013, 05:54

Re-reading this thread I just gotta say that I am completely blown away by MJ's lengthy, detailed and photographed response. Honestly dude, when do you sleep? Removing that NR3 from the rack and then taking it apart just to try to help out a fellow Nordesian some 6000 miles away! Wow...is there another forum online this friendly and helpful? Anywhere?

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Re: Nord Rack 2X New 3 Digit Display Needed...

Postby Mr_-G- » 21 Jun 2013, 21:15

I am certainly no expert on this, but leds either work or do not work. I guess that it is not the led panel which is faulty, but what controls it or some problem in the printed circuit (i.e. metal conductors corroded/broken). The comment that they are "faded" made me think this. If only some segments only light up, I guess that some of the "bits" are not being transmitted? Maybe you can map which traces to test this way? Hope you find a fix!
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