Re: how to fix a weak and jumpy QS display

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Posted by Woody on September 10, 1999 at 23:46:15:

In Reply to: how to fix a weak and jumpy QS display posted by sav on September 10, 1999 at 01:29:33:

Nice tips, since you've had the cover off and seem to know the insides of these things, I've got a QS6, and i assume the key actions are relatively the same, I've got a chipped key and want to replace it, tears the crud out of my middle finger on a good fast honky tonk tune. But does this look like an easy task or do i need to just let it be and maybe use some liquid plastic to fix it back up??



: oh, about a year ago, bought a used QS, pretty good condition, but some minor flaws. think i might've
: put in a post here asking how to fix it, but i don't remember when. anyways, here the flaws, and how
: i quickly (and cheaply) fixed them. i have no idea how applicable this stuff is for newer QS's, but i
: can't imagine the guts being too different.

: needless to say, if you choose to do this operation yourself, be sensible-- use ES protection, mark
: all wires & connectors before you unplug them, etc.... and take all of this with a grain of salt. i'm not
: a professional technician, just a guy trying to save some bucks. perhaps you have a better way.


: symptoms: the display sucks. it's very dim, tooling around with the Global Parameter doesn't help.
: perhaps it is unevenly lit too. if actual digits are crazy or don't show up, then you probably have
: a different problem, like a broken LCD. sorry, no help here. search the posts.

: -- turn the synth upside down, remove the 13 large black Phillips head screws. do not remove the
: smaller ones, for they seem to hold the keyboard action assembly together, as well as the circuit
: boards. the keys are not going to fall out or anything.

: --holding the synth together with your hands, turn it rightside up (keys up). take top off, but not too far.
: it is connected to the bottom by (2) grey ribbon cables, and one pair of wires (which appear to attach to
: the key sensing assembly). you can disconnect the 2-wire cable in the middle. there is enough slack on
: the ribbon cables to be able to flip the top over and work on the electronics without disconnecting them.
: putting a towel down on the keys, and resting the semi-connected top on the towel seemed to work
: for me.

: --while you're at it, clean the poor thing! i found a spider's nest and some really weird hair in my QS case.
: i'm not asking, and the QS isn't telling.


: -- in the middle of the synth, where the display is, is a tent-shaped piece of white plastic. this is the
: back of the display. apparently, the LCD display is semi-transparent, and a tiny (0.5"x5.0") circuit board
: with 6 small incandescent bulbs shines through the display. remove the board by separating the
: white prongs that hold it in place. when i opened my QS up, only one of six of
: these lights was still working. i had to use a flashlight at gigs to see what program i was using!
: this display board disconnects from the "mother"board of the synth by gently pulling on the orange
: and yellow wires at its connector on the MB. be careful to support everything and not break anything!

: -- i measured the voltage and current going to the bulbs: 60mA across 5V. looking up these in a
: Newark Electronics (18004639275; no, i don't work for them, but they have good service, and will
: sell to anyone with a credit card) catalog, they are Type 2200 (part number 50N8156), T-1 /34, 2-wire
: terminal base. i bought a pack of 10 of them, came in about 3 days, total cost: $10.44. not too bad.
: Radio Shack does not stock these bulbs, i called.

: -- replace the old bulbs with the new ones! this will require a soldering iron and a good touch. the
: original lighting board is probably assembled by machine, with pretty tight solder lines, so
: removing the old bulbs and putting in new ones is probably tight work. i chose to make another one
: from scratch rather than risk screwing up the old one. you can buy one-sided copper circuit boards
: from Radio Shack or Newark for pretty cheap. or make it out of cardboard, if you want. use your
: imagination.

: --reinstall the new board with new lights and enjoy the blaring visual display! (may want to
: reassemble the synth first, going in opposite order from above)


: this isn't really a true "fix", but a semi-permanent solution. symptoms of the problem:
: doing nothing, the display would go berserk, as if one were spinning the Quad knobs back and
: forth. this really sucks during the middle of a tune, as my beautiful organ patch suddenly sounds
: like a wet fart, then a marimba, then a flute...

: --open up the synth as above-- one cannot clean the potentiometers (pots) when the synth is
: assembled. at least i haven't figured out how to remove the rubbery knobs from the shafts of the
: pots without destroying both.

: -- on the right side is the board which holds the Quad knobs. get yourself some good
: contact cleaner (111 Trichloro, Freon, etc)-- i used stuff called SPRA KLEEN 10-8666-16 from
: GC ELectronics, Rockford Illinois 61101. spray the crap out of the Quad pots from the backside.
: there's a little hole in the back for just this purpose. be careful about dripping solvent-- it can
: probably eat plastic if you let some sit for too long, but clean the pots well. i did this, and haven't
: had a "jumpy" problem again. could probably replace the pots entirely, but that seems unnecessary.

: and that's all, folks. any other good home-repair tips or suggestions?

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