[sdiy] lovely 'glitch' puzzle...siel DK600 74HC923 key matrix read

[Bob Weigel]

On 12/27/2011 7:43 PM, Veronica Merryfield wrote:
> What sort of scope?
>
> On 2011-12-27, at 5:55 PM, Bob Weigel wrote:
>
>    
>> Hmm.  Here's the correlation after getting everything *else* working I think on this synth. Grounds to front panels seem good.  But that front panel board has the 74HC923 on there to code the buttons.  Now... I see that if I hit say a waveform button it'll cause other buttons to act like they've been hit as well.  The outputs are called A, B, C, D, and E however E isn't used it appears.  Not sure why they didn't use the 922 chip since it would have been find I think..but whatever.  Anyway so I notice that all the buttons are being affected that have common 1's in the code.  For instance the LFO pitch A and B routing switch is never affected since it's code is 01000 EXCEPT when another button with that same 1 in the code is being hit.  All responses are somewhat intermittent too.  Sometimes you'll see no affect.  Sometimes it's like another button got hit twice etc..  The "B" in other words is the only output high during the read.  (Data available of the chip goes to interrupt the cpu and tell it to do a read on the panel codes coming in to a 74HC244 latch that interfaces to the data buss)
>>
>> The 923 chip has a timing capacitor for a schmidt trigger input inverter clock (ie. a f/b resistor charges the capacitor and discharges it when it crosses threshhold) and this sets the scan rate.  There is also a bounce mask timing capacitor.  But I'm thinking... that wouldn't be relevant probably.  I'm having trouble triggering a scope on the signals out of this for some reason also so anyone with a thought would be appreciated.
>>
>> Sadly the panel board is a little hard to pull.  And I had a spare and tried it but it doesn't work at all it appears so... hoping to trouble shoot it w/out ripping it apart.
>>
>> -Bob
>>
>> -- 
>> Check out sounddoctorin.com for songs, a studio tour, help
>> repairing old synthesizers and parts or thought provoking
>> articles that could help make your eternity!
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>>      
>
>    
Tekrtonics 466 I use on digital stuff often.  I should try my little 
computer one... but just thought someone might have seen this type of 
thing before

-- 
Check out sounddoctorin.com for songs, a studio tour, help
repairing old synthesizers and parts or thought provoking
articles that could help make your eternity!