Sunday, April 17, 2016

Yamaha DGX-620 LCD Repair/Retrofit

UPDATE: Ulrich Borghoff did his repair slightly different and sent in photos. Thanks Ulrich!

Here's a Yamaha DGX-620 keyboard with a broken LCD. Judging from the fact that there are quite a few videos and tutorials on how to exchange a broken LCD with the proper spare part, I'd reckon these LCDs break quite easily and often.

 (Broken LCD)

(Original LCD module: The slightly kink in the flexfoil is enough to ruin the module, this slight damage is, unfortunately, not repairable.) 

I was a little surprised to get a quote of 130€ ($150) for the replacement (Yamaha Part # WG299100), and I was looking for a replacement that's cheaper. As this is a fill-in instrument, and long out of warranty, I wouldn't mind not getting the original part. Also I don't mind the tinkering.

Enter Pollin, a company selling electronic remnants, such as bags with 1kg of capacitors, sold as “perfect for tinkering”. By chance, they sell a “LCD-Modul NAN YA LTC79H202T50K, 240x320” (order #121307, €4/$5) which, on closer examination, is electrically 100% compatible to the Yamaha display. Only with a slightly different, smaller shape, and with a different pinout. Also, they sell the exact same flex-cable that Yamaha uses to connect the LCD to the CPU board: Flexprint-Kabel AXON FFC1.00A14/0200L5-5-10-10 (#562251) (€1).

(Pollin: Product Page)

(cheap replacement LCD)

Looking into the datasheet of the LCD provided by Pollin and the Yamaha DGX-620 service manual easily found online, it's clear that electrically the display is compatible.


(Pollin LCD Module)

FR (first row) is FLM (first line marker), LP (line pulse?) is CL1 (data latch), XCK (x? clock) is CL2 (shift clock). Everything else has identical designators. Sanding off the back of the replacement LCDs PCB a little to have good bonding to epoxy glue...

(replacement LCD, before gluing down flex cable)

(sanding off the back of the PCB and the white flex-cable, so that the epoxy sticks better, you can see the residue from a first attempt: The blue plastic on the flex cable didn't stick)

(jumper wires)

Ugly patching of wires from the 14-in cable to the pads on the LCD according to pinouts shown above. After soldering the wires (which is hard on the flexfoil, as the plastic melts and the copper traces of the flexfoil will move around, creating shorts) and emitting a few prayers to the deity of choice, a picture appears! :-)

(first signal on replacement LCD screen)

Then I added the display to the original plastic part from which I removed both the LCD logic and all the light spreading works. The complete LCD module almost fits in the cutout for the old glass, only a small plastic ridge had to be removed with a xacto-knive.  I had to add a small slot for the flexcable, to feed through and added a hole for the big blob of goo by which I glued down the cables so that they don't become loose.

(cutout for big lump of wires and goo)

The end result: A replaced LCD screen for €4. But I had to invest a few hours of work, which in this case I didn't mind.

(replaced screen on the Yamaha keyboard)

Update: As Ulrich pointed out, one can directly solder the cables for the LCD backlight to the cables going to the two-bin connector on the power supply on more recent models of the keyboard. Some onlder ones have high-voltage for an electroluminiscent foil, though, so beware.

Here are Ulrich's Photos:

Saturday, April 02, 2016

Superlux HMC660 Headset and PS 418-S Phantom Power Adapter

The HMC660 Headset made by Superlux is dirt-cheap, and not that bad, for the price. Certainly beats some other headphones sold for €39. But even though it has a XLR connector, it doesn't really work that well with phantom powered microphone inputs. That's because its Electret Capsule is directly connected to the XLR pins, which sometimes works, but generally doesn't.

From Chris’ Miscellanea

The microphone part is glued, but after heating it gently to about ~40..50 °C with a hair-dryer or a heating gun used for heat-shrink-tubing, it can just be pulled apart by hand.

From Chris’ Miscellanea

The proper way to adress the connection issue is to use a proper phantom-power adapter for electret microphones, luckily this taiwanese producer of cheap (and a little crappy) audio electronics also has something in store. The Superlux PS 418-S adapter!

Inside, this little marvel looks like this: Mostly through hole, one-sided PCB, waves-soldered.

From Chris’ Miscellanea

The schematics mostly adheres to the often copied "Schoeps" design, here's my attempt at the schematics.

From Chris’ Miscellanea

I think I got the type of Q1 wrong. It's probably wired as an emitter follower (the voltage gain of the drawn common emitter amp of 22x would be unreasonably high) with Q1 being a KSA1015 PNP Epitaxial Silicon Transistor. Q2 and Q3 are likely KTA1268

The PCB is small enough to fit it inside one of the earcups of the HMC660. Just cut open the direct connection that go from the 6-conductor XLR & TRS cable (braided copper, yellow, green) to the 3 wires that make their way into the gooseneck (white, black, red).

From Chris’ Miscellanea

From Chris’ Miscellanea

Here's the PCB inside a piece of heat-shrink tubing, but in the end, I opted to just hot-glue the bare PCB into the cup. Also some foam (from inside the PS-418's small shipping box) was added to prevent the whole thing from rattling around.

From Chris’ Miscellanea

Here you go. 39€ + 19,90€ for a only halfway crappy headset ;-).