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My gear position lights on my '78 GS750c just started acting strange. Each gear still is indicated with a unique number and 1st and neutral are fine but 2 through 5 all have an extra LED line lit up. The 2 looks a backward 9, 3 looks like 8, 4 looks like 9, 5 looks like 6. Any ideas?
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Sounds like the display itself is damaged in some fashion, or the controller(?) is sending a wacked signal to the display. Possibly the voltage to the display unit is too high or low? I'm just tossing out free-association ideas as they arrive. -
I've built a numerical display in electronics and my first thought is that you have either a bad ground on your pins somewhere or you are bleeding voltage onto them when you shouldn't.Comment
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It is pretty easy to check the if the problem is the display, or the contact at the gearlever.
Somewhere below the tank, you will find a 6 point connector and a single blue wire.
As i recall, your bike has 5 gear + neutral, which means that you will probably find only 5 pins in the connector house.
Each of these pins equals one of the gears (1-5) and the blue wire goes to the green neutral light in the instrument panel.
Separate the connector, and with a voltmeter, or a testlamp, you measure from a 12V source, to the pin in the connectorpart going towards the gearbox.
The switch at the lever makes contact to ground (0V), and for each gear one, and only one, pin should give connection. Which pin doesn't matter for now, because if twisted, you would just get a wrong figure in the display - not garbage numbers.
It is likely, that the switch is o.k., in that case it could be the wiring or the displayunit itself causing you troubles.
Most likely the displayunit. (Which requires total dismantling of instrument console to get at)
The displayunit is a 7-segment display, and a Toshiba TD6011BP IC. The 7-segment number is easy to get a replacement for, but I have seached high and low for the Toshiba IC - it is not available nor can i find i decent replacement.
3 options:
1: Find a complete replacement. I was not able to find a new replacement, but now and then they will turn up at Ebay (Unfortunately just as old, as your own).
2: Solder up the circuit from diodes and resistors. It takes about 15 components for a 6-gear circuit. I took it to a danish engineer forum, and it reduced the number from 32 diodes to app. 15. Let me know if you are interested in this solution - I have a diagram.
3: (What i chose) make a fixture with 7 LED (Light Emmitent Diodes) with built in resistor for 12V, and place them in a circle with one in the middle (or any other pattern of your choise).
The fixture with LEDs goes into the housing, replacing the original display.
Connect each of the LEDs with a cable to the contact at the gearlever. You will now have a display, indicating the gear with one of the 7 LEDs.
Connect them in a way, that makes sense to you. (Idle in the middle, 1st bottom, 2nd lower left, 3rd lower rigth a.s.o.)
If interested you can find the principle at my lousy homepage http://home20.inet.tele.dk/xxxxx/ but this is for a 77' GS550 (6 gear) with changed wiring harness.
(Look under wiring, documentation page 8 )
The 4th option is running without the indicator, like at many other bikes - but once getting used to the feature, it is hard to miss.
Stig77 GS550BComment
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