HybrisBehemoth

Starting MB6582 build

96 posts in this topic

thanks.... and I was wondering about the negative voltage bit.....
Need to decide how wedded to White on Black I am I guess and maybe get a different lcd if I can't work it out....

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thanks for the help with this... I should probably just get another screen, but I did like the idea of white on black text....

it seems relatively simple to make the circuit:

http://www.shellyinc.com/techDCtoDC.htm

I am still a bit confused as to what pins 15 & 16 do though? 

do you think it is it expecting -5V dc at 15 or 16? And what does the other one get? 
the tech spec seems to show an optional "negative voltage generator" providing negative voltage from Vee, almost as if I just need to hook pin 15 to pin 16.... that can't be it though surely?

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Okay, double-reading the data sheet and I don’t think it needs negative voltage for the backlight. But pin 15 seems to be used for something other than powering the backlight, which is odd. According to the data sheet, it supplies negative voltage as part of an external contrast adjustment circuit.

The backlight seems to run on normal +5V running into A (+) and K (gnd)...but I can’t figure out where pin A is supposed to be from the pinout in the datasheet.

I’m guessing the LCD itself doesn’t have any more helpful labels or anything, just pins 1 and 16 marked probably?

 

edit: I think the backlight power is connected internally somewhere, as opposed to needing a separate supply.

Edited by jaytee

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nothing more helpful than that. 

that's where I was arriving as well at looking at the sheet  -  pin 15 is out from the negative voltage generator.
tbh I might just order a white on black version, which appears to be the right configuration rather than try and mess around too much......

thanks for helping I would have just had suspicions about it, but you kinda confirmed what I was thinking.

 

Edited by the_duckchild

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8 minutes ago, jaytee said:

 

 

edit: I think the backlight power is connected internally somewhere, as opposed to needing a separate supply.

I was wondering this. So I could in theory skip that pin, but then I think it still needs the contrast circuit.... I think another screen is going to be easier.

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I’m pretty sure you want to leave Pin 15 disconnected. Seems like a bad idea to be injecting negative voltages into your MIDIbox. But I’m not sure that having it connected would be enough to keep your backlight from turning on, as that seems to rely solely on proper voltage at Pin 1 and Pin 16, which you should have.

So I would disconnect the LCD entirely and double check that all your voltages are still correct (ie double checking that nothing went wonky from applying -5V to pin 4 of J15). If that looks good, snip the wire attached to Pin 15 and see if anything changes.

Disclaimer: We’re already a bit beyond my full understanding, so consider these comments as rough guesses rather than truth. Still, this is more or less what I would be doing to troubleshoot.

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You may be able to get contrast working with a jumper wire from pin 15 to the contrast trimmer (and cutting a trace on the board), or it might work as-is with the ideal setting all the way to one end of the trimmer’s range instead of somewhere in the middle, but tbh if it were me, I would certainly be tempted to just get a different LCD.

Edited by jaytee

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thanks - pretty sure, I can live with a black on white screen, so am going to order one now I think. I'm sure it's possible to mod it to work, but I'm worried enough about it all working properly anyway tbh!

fingers crossed I didn't fry anything except the resistor I already replaced.

not sure I hold out much hope for the transistor in the contrast circuit!

Edited by the_duckchild

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Hi,

Mounted a Midas LCD on my MB6582 and I remember that I encountered the same problem...

I first made the "standard" wiring and burned the backlight...

Figured it out (after having bought a second LCD :/ ) by simply following this little scheme in the spec :

Capture.PNG.85a901209e10f285d1c04cffc297

... and made some rewiring around P2 trimmer :

Capture2.PNG.55b5600886278d24e79d5914fc6

20181203_193126_redim.thumb.jpg.392028c3

Finally, check the wiring on LCD side. Pins 15 and 16 should be inverted, but double check with the LCD pinout.

 

Hope that will help you.

Cheers!

 

 

Edited by WilHelm*
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thanks Wilhelm! Much appreciated - I think I probably blew my screen as well, so am going to try ordering a replacement that doesn't require the rewiring, but if I decide I must have the white on black in the future this might come in very handy! 

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big thanks for the help people, feeling a step closer for sure now!

 

screen.JPG

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Congrats! I remember that moment when I finally got a legible message on my screen ;) all downhill from here.

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hmmm, I'm on the point of actually putting some SIDs in.... unfortunately it seems like the colour change LEDS are maybe not going to work... or at least not properly!

the ones in the Matrix seem to do three colours, rather than cycle all of them. 

the other LEDs are staying resolutely red.... not quite sure what's going on here.

Have tried 1k/220 and a resistor leg bridge... the lower the resistance the more the matrix seems to change colour, but it's still not right. Using resistor legs seems to mess with the LCD so that it displays random characters, which doesn't sound brilliant.... bit more exploring to do I guess... shame if they are going to stay red forever!

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Do you have a datasheet on the color-cycling LEDs?

If a LED is matrix-driven with 1/8th duty cycle, that means on - off - off - off - off - off - off - off -on - off - ... - so they might actually reset their color cycling because they are powered up all the time again?

Many greets,
Peter

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ok, so something even weirder now.....

Sometimes it doesn't boot up MIOS, but it does do a pretty thrilling light show. I assume it should not do what it is doing in video 1 in the below instagram post?

When this happens (usually when it's been turned off a while, it never seems to boot. Then a quick restart or two will make it do what happens in video 2......

Is video 2 a bit closer to what is supposed to happen when you turn it on?

I also seem to be getting some slightly weird LCD screen stuff going on

Do you think this might be fried Shift registers from the LCD incident? I think maybe I have to try replacing them anyway.... ho hum...

Still, the light show is nice!


 

 

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Will try and find the data sheet - are both sets of leds matrixed that way? I did wonder if that was why the selection leds were not changing - they are slow change so maybe get reset before they can change. Annoying, but not the end of the world I guess. The matrix ones are fast change, and they seem to be working in some ways when MIOS is running. No idea what the fancy light show is about! Kinda odd. 

Going to try switching out the shift registers first I think, unless I can think of a better idea! 

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The second video looks more or less correct. Hard to tell exactly because of the bright LEDs and otherwise dark video, but it should definitely start up with a quick light show on the matrix. IIRC, the boot-up lightshow has two stages, one with the LEDs in a more-or-less randomly flashing pattern, and one where the LEDs alternate a checkerboard pattern—I forget which comes first.

You have the new Step E power circuit, right, with the sVreg? I had a little trouble with excess power draw on start-up causing issues with my boot up, but it was solved IIRC by changing to a smaller cap on the input of the sVreg. Might be a similar issue if your fancy LEDs draw too much current?

It doesn’t seem like the shift registers are the problem, as least from what little I’ve seen in those videos.

Edited by jaytee

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My bad, it was too big of a capacitor on the output of the sVreg, coupled with too much current draw on start-up.

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ah, thanks - so the cap at C3?

c3.thumb.png.c5e01b44654d6d83c0a3454e99b
Pretty sure I only have 10uf in there already, can I go even smaller? It's just smoothing the already regulated 5V right? 
Do you remember what you used, or did you mean you'd changed it to 10uf? I wonder if it can go even lower, sounds from your thread here that it isn't actually doing very much...>
 



thanks for the help. 

I guess it might be the current draw is just too big. Although it does start up sometimes - both this and the screen misbehaving seem worse when all the LEDs are connected.

I think Hawkeye is probably right about the slow cycle LEDS being retriggered too often to colour change. 
So I guess I will see if I can get it to reliably start up with the colour change LEDs in before thinking about changing all the slow ones for fast ones!

I guess I might try some bigger resistors and see if I can get the current draw down..

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I forget exactly what I put in there, probably a 10uF. It’s probably not even necessary tbh. Otoh, I don’t think the capacitor is your problem, especially if you only put in a 10uF.

Something related to current draw seems likely though, since it seems like your main deviation from a typical build are those LEDs.

Did you socket your current limiting resistors? You could try pulling those and seeing if you get a consistent good boot up. If you didn’t socket them, you could cut/desolder the board connections that go with the LEDs, or if you wanted to try bigger resistors anyway, just clip them.

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thanks - yeah, I have sockets for the resistors. have tried a few combinations now - the fast changes in the matrix get through all the colours only when they are about 150R..... any higher and they don't operate very well, if the resistance gets high enough they just stay red, which I guess suggests they are probably drawing a lot of current to do the change..

There seems to be another issue as well though, as sometimes it starts and sometimes it doesn't and it feels like some of that is maybe to do with a loose connection/shorting in the cables joining the two halves. I can't shut the lid the way it is at the moment anyway, so need to give that some attention and remove it from the possible causes!

Hoping not to have to start the control surface again, but not sure I am going to avoid it if I can't get all the LEDs on without fritzing the LCD or the buttons or something!... desoldering 100 LEDs may not go perfectly I am guessing!
Also: there should be more than one patch in the memory banks on start up right? Something seems to be awry there too..... 

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Random restarts (or the unit sometimes not starting up) remind me of a 5V rail problem i had early on, back then still with the original C64 PSU.
The current draw on 5V (using a VFD) was just too high and it went under 4.7V or so on the 5V rail, the PSU was overloaded.
So, which PSU are you using and can you measure your 5V rail voltage during operation?

Patches need to be uploaded with a Sysex transfer, so all should be good there as long as you can access all banks.

Many greets and good luck!
Peter

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ah, great, thanks - didn't realise that about the patches

Am using PSU Option "E"  from this thread: 

so the 5v rail is coming from this - RECOM POWER R-78B5.0-1.5L SWITCHING REGULATOR, 5V, 1.5A

I'm just trying to desolder the connections from the CB to the base as the way I had attached them did not leave room for the case to shut. Once I have had chance to reconnect them i will take some voltage measurements and see what's happening to the 5v rail. 
There are no SIDs at all in at the moment, and only three PICs, so if it is insufficient current it might be quite an issue to deal with.. but then is there any reason I couldn't use a larger switching regulator?
Say this?

https://uk.rs-online.com/web/p/switching-regulators/1392821/

i'm not all that learned about power supplies tbh....  would this have knock on effects on the capacitors required? I think not.... just wondering if anyone sees any obstacle!

Edited by the_duckchild

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Before you order a new regulator, run some tests, find it if your current regulator is drooping, measure current draw with and without LEDs, etc.

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