Jun
11
2013

Repairing and Restoring an Alesis Quadraverb/GT LCD Display

NOTE: Use at your own risk. Author is not liable or responsible for mishaps.

This is a re-post from http:/www.johanforrer.net/Guitars/QuadraverbFix.html as this site is no longer available

–UPDATE–(December 2010)–
Since I wrote this article, many repaired LCD displays have found their way into Quads all over the world. I am grateful to all that took the time to write to me about their experiences — am pleased to hear the material was useful.

PLEASE NOTE THAT I DO NOT HAVE ANY MORE DISPLAYS AVAILABLE FOR SALE.

The Alesis Quadraverb is one of my favorite guitar effects units. These vintage units regularly show up on eBay, often listed in “AS IS” condition with the LCD display being dead or erratic. Nowadays, replacement LCDs are hard to come by, probably cost more than the Quadraverb is worth.

Here is how I fixed my broken display.

After reading various discussions on lists regarding replacing these LCD displays, it was evident that almost any 2×16 LCD module that followed the HD44780 LCD controller protocol would work. However, most OEM LCD modules has a 14-pin (or 16-pin) inline connector instead of the 14 pin header found on the stock module. This is an eazy fix as its just a matter of reworking the Quadraverb connection to the LCD.

I did a search for a suitable LCD module, something that looked like a good physical fit, a greenish/yellow backlight, and inexpensive. The KEST 1602A-01 LCD display available from All Electronics (www.allelectronics.com, CAT# LCD-120) looked like a good prospect. I believe these are all gone by now, but there are several available on eBay (search for “16×2 LCD”). Just check that it is HD44780 compatible and the size of the module is something like “80 x 36 x 13.5mm”. You’ll have choices for color preference. Also make sure about how to power the backlight. Ideally you’ll want something that will work off 5V. Some backlights will need an external resistor to regulate the backlight current to manufacturer’s spec. If you are not careful about this, the backlight might have a very short life!

Note the 1602A is slightly smaller than the stock module, however, loosening the LCD fixing screws on the Quadraverb panel just slightly, allows the 1602A module to fit snugly in position. While you are at it, using small fiber washers on the screws will help tighten the display in position. A dab of glue on the screws holds the module in place permanently.

Reworking the electrical connection is fairly straight forward. There are two ways to do this; either cut off the connector at the display side and solder the ends to the new LCD, or make up a transition cable. For more on how to directly wire the display, see the note at the end of this page.

I made up a transition connection using a short piece of 14-way ribbon cable and attached a 14-pin female IDC header at one end.

TO avoid a lot of confusion: NOTE THE IDC HEADER ORIENTATION. AS SHOWN, START COUNTING FROM THE BLUE STRIPE SIDE OF THE RIBBON CABLE … that will be wire #1. Wire #2 will lay next to it and so on. Strip and tin the other end of the transitional 14-way ribbon cable wire ends as these need to be soldered to the 1602A module. 

Solder the 14-way ribbon as follows (check your work wiring with an ohm meter).

IDC-end —– LCD-end
————————–
2 ……………….. 1 (GND)…[NOTE POLARITY SWITCH!!]
1 ……………….. 2 (+5V)….[NOTE POLARITY SWITCH!!]
3 ……………….. 3 leave unconnected (see backlight wiring below)
4 ……………….. 4 (R/S)
5 ……………….. 5 (R/W)
6 ……………….. 6 (E)
7 ……………….. 7 (D0)
8 ……………….. 8 (D1)
9 ……………….. 9 (D2)
10 ……………..10 (D3)
11 ……………..11 (D4)
12 ……………..12 (D5)
13 ……………..13 (D6)
14 ……………..14 (D7)
— ……………..15 backlight, connect to +5V (pin 2 above)
— ……………..16 Backlight, connect to GND (pin 1 above)

Finish off the backlight wiring at the 1602A module (you are sure about power requirements for the backlight. Yes??): Wire +5V (pin 2, LCD) to pin 15 (backlight), and GND (pin 1, LCD) to pin 16 (backlight). Note the 1602A module has a built-in series resistor to accomodate a 5V supply. No external current-limiting resistor is needed for this particular LCD module.
On my pictures, these wires for the backlight is actually on the display-side of the module and not visible on the picture.

One final bit of wiring to set the contrast of the 1602A: Connect the ends of a 20K trimpot to LCD pins 1 and 2 respectively, the wiper goes to LCD pin 3. I used a 3/8″ square pot and soldered the legs directly to the LCD. Besure that the trimpot does not interfere with the covers or other nearby components or wiring. Alternatively, connect a 1N4148 diode between pins 1 and 3 (the diode’s ring/stripe end goes to pin 1).

Install the 1602A replacement LCD module and put a dab of glue on the screw heads.

Now there are two female 14-pin headers, one from the Quadraverb side, the other from the replacement LCD. Snap off a piece of 0.1″-pitch, double-header stock (14-pins worth) and use it to interconnect the two 14-pin IDC headers.

NOTE: The Quadraverb’s ribbon cable is a bit unconventional: the red stripe side and the alignment notch on the IDC header are opposite to usual convention. The Quadraverb cable has pin 1 (5V) and 2 (GND) on the opposite side to the red stripe. Be sure to align the LCD header correctly .

Power up the Quadraverb. If you installed a contrast trimpot, adjust for best contrast. Otherwise, for the diode modification, contrast should be good to go.

NOTE: Wiring the replacement display directly:
As mentioned above, the new display can be wired directly to the ribbon cable coming off the Quad PCB to the display. This requres swapping all odd and even-numbered wires. For example wires #1,2 goes to LCD pins 2,1 … wires #3,4 goes to LCD pins 4,3 and so on. The power connections to the backlight remains as above, i.e., LCD pin 1->16 and 2->15. Just ensure your backlight works off 5V, else you will need to determine a proper-valued series dropper resistor.

A final note: Judging from the scratches on the covers of my unit, it has seen a fair share of handling. I stripped all the paint and resprayed with Crylon black “Textured Shimmer” aerosol paint. Looks respectable and sounds great.

Good Luck!

About the Author: Neil Frost

Husband to Laura, Dad to Adam. Follower of Jesus

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