So if you were a rich kid in the 80's you might have had a DG-10 or DG-20 a digital guitar made by Casio. ($350 for the DG-10...I am guessing the DG-20 was $50 to $100 more)
I was not a rich kid in the 80's and I hadn't even heard of this until I saw one on the remake of the Take On Me video by Weezer.
So I did so looking around, figured out what the device was, then tried to by one.
I lucked out and picked up a DG-10 (like in the video) that needed a bit of work but operated just fine...for dirt cheap...
So I got it running and played with it a bit, as I dug through the documents available I learned that I had the stripped down version, but there was also a DG-20 that had line out and MIDI out. (as well as some other sound and manual percussion switches).
Well I was jealous of the MIDI output...so I popped mine open to see how hard it would be to modify mine to add MIDI support.
I noticed that in the Service manual that the main parts seemed to be identical and even the circuits were almost identical except for some minor differences and some passive components.
I took pictures of the circuit boards top and bottom and happened to find a few pictures of a DG-20's guts.
I realized that those geniuses at Casio had built both keyboards with the same chips and almost identical circuit boards except for about 3 modified traces...depending on which version you got, some traces were whole and some were cut.
The circuit boards even had the drill holes...the only thing missing was labeling and some of the pads were coated and had to be cleaned.
So based on the schematic (they did not have board photos unlike most electronics service manuals) I basically reverse engineered the circuit boards and figured out where to add passives and jumpers, and where to remove them to convert the DG-10 into the DG-20.
(luckily mine is a DG-10 so no worries)
I can say that it was actually an easy mod...time consuming for the planning and reverse engineering, but the actual mod went pretty quickly with no problems, except for missing a jumper, and 4 passives for the line out circuit.
So the total number of parts required for the mod were:
1 slide switch
1 midi port
1 1/4" mono port
8 momentary pushbutton switches
4 ferrite bead filters
9 diodes
3 ceramic capacitors
3 electrolytic capacitors
6 resistors
So depending on what you have on hand...$10 to $20 worth of parts...you know the Casio factory got them at bulk...so I am guessing the DG-20 cost at most $5 to $10 more to build...total cost. (some more rubber switches, two more circuit boards, and a completely different sound selector in the actual DG-10)
The result is other than how the switches and outputs look, my DG-10 is a DG-20.
I am sure nobody else is dumb enough to do this mod, but I include the photos I used and modified to show the original circuit and components and the ones requited to modify the DG-10.
I will say you don't really need the line out, but I thought bypassing the amp circuits might sound better?
Anywho the following are my modifications to the board photos I did.
Lineout mod to schematics (not complete...just showing what I missed...
In all cases the pink (salmon?) colored lines are what needs to be added or modified, the red is the existing circuit topside components (to help me trace the circuits)
Amp circuit mods to get line out
Tone control and rhythm select panel...needed to be modified to add 4 tone switches.
If someone really gets a desire to do this mod, drop me a line and I will send all my photos and documents...
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