Whining LCD display

I have a 128x64 ks0108 controlled lcd which makes a quiet but annoying high pitched whine. I assume this is coming from the circuit that generates the high voltage for the LCD panel. Sounds like 10~20KHz.

Had anyone experienced this and fixed it? How?

Thanks!

I have had that issue. It can be really bad on EL backlights.
I've not found anything to fix it.

--- bill

bperrybap:
I've not found anything to fix it.

Dip it in hot wax?
OK, that might cause other issues.

PerryBebbington:
Dip it in hot wax?

I suppose if I can identify the component(s) making the sound, I could blob hot glue on them. Which is it likely to be? I can see some caps. I can't see an inductor...

If it is generating high voltage, there is an inductor! :cold_sweat:



There are no components under the backpack.


I see nothing in your photos that would obviously produce any sound.

You could try touching the components one by one and see if the sound changes.

Is it possible that the sound is not coming from the display but comes from the power supply and changes in the load from the display cause the sound to change, and that is what you are noticing? I agree with Paul__B about the need for an inductor for high voltages. I would not think the display in your photos needs any high voltages.

I am reminded of when I was about 20 working in a repair workshop and I said to an older colleague: "What did you just do, the buzzing sound changed?", He replied: "What buzzing sound?".

Oh, and what is a 'liquid crystal display display'? :confused:

A voltage doubler doesn't need an inductance, and a capacitor or the panel glass might have some piezo-electric effect.

Yes, I think the LCD needs a "high" voltage, meaning higher than the input voltage, but probably in the tens of volts, not hundreds. So maybe the board has one or more voltage doubler stages.

I found that touching the pins of that small 8 pin chip at the top right stopped the high pitch whine for a moment. There was a 50~100Hz buzz and the display went blank, until I removed my finger. So that chip is involved in the high voltage circuit. I'll try to read the codes printed on the chip.

LCD display? Well, is a bit like Mount Fuji or River Avon :wink:

Yes, I think the LCD needs a "high" voltage, meaning higher than the input voltage, but probably in the tens of volts, not hundreds. So maybe the board has one or more voltage doubler stages.

I can't confidently say you are wrong but I think you are wrong. LCDs don't need high voltages. You could settle this by checking around the circuit with a DVM. There are people on here who know this stuff better than me and I invite one of them to comment.

I found that touching the pins of that small 8 pin chip at the top right stopped the high pitch whine for a moment. There was a 50~100Hz buzz and the display went blank, until I removed my finger.

That makes me suspect a faulty chip or a dry joint or a broken track, I suggest you check for any of these. If touching the chip silences it then maybe, just maybe, some glue will do the job. My comment about wax was only half a joke, wax has the advantage of being easy to remove.

LCD display? Well, is a bit like Mount Fuji or River Avon

Or my (least) favourite 'personal identification PIN number' :o

OK, now this is a recent product, so it must use LEDs, not EL for illumination. The "A" and "K" on the PCB are consistent with that. It should be easy to check that these connect directly to the corresponding pins on the backpack with a resistor somewhere. So no high voltage there.

"U5" and the two capacitors definitely looks like a charge pump IC such as an ICL7660 or clone and would be present to generate a higher contrast voltage for the LCD. I cannot read the chip label on that photo.

As such it is - due to piezoelectricity in the capacitors, not magnetostriction - the likely source of the noise. Perhaps exchange the capacitors C5 and C6 (possibly C4 which is not so clearly related) and see what happens.

The ks0108 typically needs a negative voltage feed to the Vo input pin.
The source of that can be derived using a pot as a voltage divider using the voltage the from Vee output pin.
The Vee voltage output can be low as -18v.

Something on the board has to create that negative voltage for the Vee output.
That is likely the source of the noise.

--- bill

Oh and for backlights. KS0108 modules usually use just simple LEDs not EL.
The ones with LED backlights sometimes have very inefficient LEDs, drawing as much a 500-600ma.

EL needs high voltage like 90v+ Some have onboard generators that often whine but some don't have onboard high voltage generators and you have to create & supply it yourself.

That backpack is interesting. Who makes it?

--- bill

Paul__B and bperrybap,
Thank you both for teaching me something about the displays.
++Karma;

Thanks Bill, I knew high voltage was needed for these lcd but had forgotten it was negative.

Here's that chip. (Data sheet)

I was thinking, is the fault with this display not that it is making the sound, but that it is making the sound in the audible range? Perhaps it is supposed to be in the 30KHz+ range.
I have a couple of similar displays which don't make a sound. They are not identical to this one, they too are ks0108 but the circuits on the board are different. I could take a look at them with my logic analyser to see if I can find what frequency their voltage generators use compared to this one.

EDIT: the data sheet says typical oscillator Freq 10KHz...

Yep it is indeed an ICL7660. Datasheet. :grinning:

@Bill, the adaptor is made by DiyMore and is a very similar design to one made by Nick Gammon here, but using different pins, so Nick's library is not compatible, but I forked it and made the bare necessary changes here.

I just ordered one of those backpacks. There are more than 6 different pinouts for ks0108 LCDs.
I'm not so lucky in that the backlight power connections for the GLCD I have do not line up with the anode and cathode pins on the backpack.
I'll have do some surgery to make it work.

I think I'll revive openGLCD and get it working with this backpack and then get it added to the IDE library manager.

--- bill