Yamaha dx100 blank display

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Tiger Jackson
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Yamaha dx100 blank display

Post by Tiger Jackson » Thu Jul 18, 2019 8:05 am

So ever since I got this years ago, it had an issue with the output cutting off, temporarily solved by adjusting the cable.
I took the dx100 out recently to play with but now I've had enough, so I opened the dx100 up to see if the soldering on the output was bad, couldn't see anything off so I just put it back together. But now the display is blank. Doubled checked, no connection on the display is loose. What do you think could have happened? It still produces sound so I know the whole thing didnt just die.

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Weirdofromouterspace
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Re: Yamaha dx100 blank display

Post by Weirdofromouterspace » Thu Jul 18, 2019 1:30 pm

Tiger Jackson wrote:
Thu Jul 18, 2019 8:05 am
I just put it back together. But now the display is blank. Doubled checked, no connection on the display is loose. What do you think could have happened? It still produces sound so I know the whole thing didnt just die.
Sounds like there is either a connection mistake (triple check, and possibly have someone else look as well - we often don't see our own mistakes), or a broken cable/wire. Check voltages on the display connectors. Are those OK?
Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you get no sound out of it. - ARP 2600 manual, 1971

Tiger Jackson
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Re: Yamaha dx100 blank display

Post by Tiger Jackson » Thu Jul 18, 2019 6:19 pm

Weirdofromouterspace wrote:
Thu Jul 18, 2019 1:30 pm
Tiger Jackson wrote:
Thu Jul 18, 2019 8:05 am
I just put it back together. But now the display is blank. Doubled checked, no connection on the display is loose. What do you think could have happened? It still produces sound so I know the whole thing didnt just die.
Sounds like there is either a connection mistake (triple check, and possibly have someone else look as well - we often don't see our own mistakes), or a broken cable/wire. Check voltages on the display connectors. Are those OK?
I didn't unplug anything. Maybe mismatched some screws with their screwholes, it seemed like it was missing a few. I don't have a voltage meter to check with right now but I'll try opening up the dx100 again.

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Re: Yamaha dx100 blank display

Post by Rasputin » Fri Jul 19, 2019 7:22 am

If it's 100% blank then it's likely either not getting 5V or something happened with the contrast. Can you see any hint of text from any angle at all?

Tiger Jackson
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Re: Yamaha dx100 blank display

Post by Tiger Jackson » Fri Jul 19, 2019 10:11 pm

Rasputin wrote:
Fri Jul 19, 2019 7:22 am
If it's 100% blank then it's likely either not getting 5V or something happened with the contrast. Can you see any hint of text from any angle at all?
Well I'll be damned you're right, if I tilt it in a well-lit room I can see the text. So what do I do now?

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Re: Yamaha dx100 blank display

Post by Rasputin » Sat Jul 20, 2019 12:19 am

Tiger Jackson wrote:
Fri Jul 19, 2019 10:11 pm
Well I'll be damned you're right, if I tilt it in a well-lit room I can see the text. So what do I do now?
Standard LCD character displays (yes, I know that's like saying PIN number...) use pin 3 to read voltage which determines the contrast.

My guess is that the value of pin 3 is buried at 0V, and the ideal contrast is usually non-zero but less than 5V. In other words.... pin 3 is flaky somehow, either in the display cable, or the header the cable plugs into, or there is a contrast setting (knob or variable resistor?) which has been moved out of the "sweet spot" somehow.

I'm not intimately familiar with the DX100, but I'm guessing pin 3 just isn't making good connection.

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Re: Yamaha dx100 blank display

Post by Tiger Jackson » Sat Jul 20, 2019 1:56 am

Alright this is gonna be super embarassing but I had JUST noticed the DX100 has a contrast dial wheel on its back panel. It's even printed at the top... https://www.synthmania.com/dx100.html I completely disregarded what it even was for the entire time I had it. Guess It had just got knocked back to the lowest position while working on it. Just kicked it back to the highest setting and the text is back. So it was a complete non-issue :lol:

But now, about that output cutting off issue...

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Re: Yamaha dx100 blank display

Post by Rasputin » Sat Jul 20, 2019 4:31 pm

Tiger Jackson wrote:
Sat Jul 20, 2019 1:56 am
But now, about that output cutting off issue...
If you didn't notice any cold solder joints on the intermittent jack, yet the jack functions okay when fiddling with it then there are two potential problems which come to mind:

1) The metal contacts are corroded and wiggling the plug within the jack makes/breaks the connection.
2) The jack is physically damaged internally and the contacts are displaced.

Problem #1 can be solved with something like Deoxit, or perhaps some light sandpaper usage on an appropriately sized dowel, etc.

Problem #2 requires finding a replacement jack, desoldering the old jack, and then soldering the new jack onto the PCB without lifting any pads or traces.

That said, cold solder joints can sometimes be hard to see, especially if you don't know exactly what you're looking for. I would rule that out with very careful inspection (magnifying glass in bright natural light if your eyesight isn't perfect, or maybe even if it is).

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Re: Yamaha dx100 blank display

Post by Tiger Jackson » Sat Jul 20, 2019 7:18 pm

I'll look into those options, thanks.
Is this the correct replacement part? https://www.syntaur.com/Items.php?Item=4546 though it's out of stock, don't know where to find it.

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Re: Yamaha dx100 blank display

Post by Rasputin » Sun Jul 21, 2019 6:55 pm

Tiger Jackson wrote:
Sat Jul 20, 2019 7:18 pm
I don't know where to find it.
I'm pretty sure these jacks will fit most Yamaha mono jacks (output, footswitch) of the era, like the DX, RX and TG series. I can't guarantee it, but I know they are 3-pin PCB mount, and if your original jack has that "black front with red rear" color scheme then they should be Yamaha LB202330 jacks, I believe.

https://www.ebay.com/itm/Audio-6-35mm-1 ... SwtOZcfImk

I'm also fairly confident that Jalco PJ3 (style B) jacks are the same. There are a lot of Jalco jacks which are all black and don't have the blade-style pins, though, so make sure to take a good look first.

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