geekhack
geekhack Community => Keyboards => Topic started by: Village_Idiot on Fri, 12 November 2010, 09:17:30
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So I stumbled upon a free IBM clicky keyboard a while ago, which I excitedly assumed was a model M. But when I bought an AT->PS2 adaptor, I found that it was indeed a model F of the XT variety.
So I decided to build an XT->PS2 adapter, either kbdbabel or home-designed, but I have an issue. I cannot for the life of me manage to get any signal out of this keyboard. I've been hooking it up to my oscilloscope for 2 days now trying to find a little bit of life on the clock or data pins (I've had gnd and vcc hooked up respectively to an AC->DC 5V connector) unsuccessfully. I even opened the keyboard and interfaced the wires directly to where the cord plugs into the PCB without luck.
So at this point, I'm figuring one of 3 things has happened:
- A capacitor/resistor is dead somewhere.
- The microcontroller is fried
- It's just plain broke.
I'm hoping that worst case I can replace any fried caps or components, or if desperate interface a new microcontroller into the capacitance matrix, but I haven't seen any guides or information that'd guide me.
Any ideas on what my best next step would be?
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I'm a programmer with a screwdriver, but to start,
- check whether /RST is high
- check whether the oscillator is oscillatin’
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Wait, the RESET pin has to be high on XT? Most pinouts I've seen had it marked as not used, and the internal connector only has 4 wires going to the board, which I assumed were vcc, ground, clock, and data.
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EDIT: I meant reset on the controller, not the connector.
kbdbabel has the schematic. Reset is pin 4 of the 8049, fed by a the 7474 latch (pin 9) fed by an RC pair to delay it a little after power on.