Apple IIc keyboard issue

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Apple IIc keyboard issue

Hi - I recently picked up a descent IIc  and it booted fine but the keys didn't work. I checked to ensure the keyboard button was engaged and disengaged but still no keys work. However, control and reset does reboot the machine. 
 

I have tore the machine apart to clean up the components and inspect them. I also took all the keys off and cleaned up the key connectors and also checked for continuity. All seems fine. 
 

After reassembly I have the same issue. The keys simply won't work except the control and reset. 
 

Does this seem like a bad keyboard chip on the logic board?

 

Thank you in advance. 

 

 

 

 

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Could be.

Could be.

 

Grab the schematic (https://archive.org/details/Schematic_Diagram_of_the_Apple_IIc/page/n1/mode/2up) and check the encoder IC for +5 and -12V. Also look at the KSTRB signal at the IOU. Should be easy to track down the issue.

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Thanks I'm going to be back

Thanks I'm going to be back to testing it tonight. I did plug another confirmed working keyboard in and had the same result so I know it's something going on with the logic board/chips.

 

I'll check out the schematic and start testing. 

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Curious - I don't have an

Curious - I don't have an oscilloscope but have a multimeter. If I set my multimeter to 20v DC can I still test for the +5 and -12v readings?

 

 I swapped the IOU and still had the same results.

 

I want to verify the encoder IC and also recheck all the PCB traces. 

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Northband wrote:Curious - I
Northband wrote:

Curious - I don't have an oscilloscope but have a multimeter. If I set my multimeter to 20v DC can I still test for the +5 and -12v readings?

 

 Sure. You might be able to see the strobe pulse as well if you look close.

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Northband wrote:Curious - I
Northband wrote:

Curious - I don't have an oscilloscope but have a multimeter. If I set my multimeter to 20v DC can I still test for the +5 and -12v readings?

 

 I swapped the IOU and still had the same results.

 

I want to verify the encoder IC and also recheck all the PCB traces. 

 

20VDC means that it uses a 20V DC baseline: It will 'max out' at 20VCD on that setting. You can check 0.2VCD on that setting, or 5VDC, or 12VDC. It doesn't matter. Negative and positive polarity from - 20VCD to + 20 VDC is the range for that. 

 

Most units max out much higher than that, and have settings at least to 400VDC for very limited and cheap models. Likewise, most units have lower thresholds of 2V, 0.2V, and so on. 

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