[sdiy] ENSONIQ keyboard woes

[cheater cheater]

> tom mentioned that when we was workin' the polysix diodes he flipped it
> upside down to have the keys pressed then tested....

I assume he was testing the inputs and the outputs of the diode
matrix. I'm assuming you're testing the diodes themselves, i.e. the
elements that make up the diode matrix.

Isopropyl won't do if a diode tests as open on both polarities, you'll
have to scrape the leads with an exacto knife. Don't use chemicals on
boards, especially old ones, they can be abrasive. Again, only do this
if the diode tests open on both polarities. If it's closed on both
polarities, you might have to replace it; however, depending on the
circuit, a diode in that circuit could test like it's closed when it's
not.

Cheers
D.

On Thu, Jan 22, 2009 at 4:19 PM, Nathan M. Reeves <djservs at comcast.net> wrote:
> so to test the diodes, i dont have to close the switches?
>
> tom mentioned that when we was workin' the polysix diodes he flipped it
> upside down to have the keys pressed then tested....
>
> i guess they can be tested with or without the switch closed?
>
> after leaving the unit on all night and looking at it this morning I see
> (well, feel) that U6 is fairly warm to the touch, though this might be
> normal behavior...
>
> ok i will check the diodes again, also i found out you can lift the end of
> the ribbon cable to expose the terminal leads on them so i guess i can check
> each for continuity....phew
>
> thanks for all the advice if anything its a valuable learning lesson!
>
> cheers
>
> nate
>
> On Jan 22, 2009, at 9:15 AM, cheater cheater wrote:
>
>> Hi Nate,
>> *don't* go reseating uC's! you can fry them just like that, by
>> touching them, even indirectly. Leave this up to an experienced
>> tech... unless you put no value in your item, then feel free to fry it
>> :P
>>
>> Shouldn't a diode (meaning: its terminals) read open in (at least) one
>> direction even if it's in a circuit?
>> What is the point of holding the keys down?
>>
>>> How do I read through the archives again? 08^)
>>
>> http://img178.imageshack.us/my.php?image=sdiyfw4.jpg
>> 8-)
>>
>> HTH
>> D.
>>
>> On Wed, Jan 21, 2009 at 9:43 PM, Nathan M. Reeves <djservs at comcast.net>
>> wrote:
>>>
>>> yes it seems like a long shot for the diode check.....
>>>
>>> i remember the korg polysix thing vaguely....
>>>
>>> fortunately my DMM has a diode/continuity check built into it
>>>
>>> its says to:
>>>
>>> 1. Remove all power from the circuit under test and discharge all caps.
>>> 2. Set to proper selection on switch, looks like a little diode icon.
>>> 3. Connect test leads to device you want to check.
>>> 4. Reverse test leads and note second reading.
>>>
>>> If one reading shows a value and the other is over-range (0.F appears)
>>> the
>>> device is good.  If 0.F appears during both readings, the device is open.
>>> If
>>> both values are very small or zero, the device is shorted.
>>>
>>> I did this and got 0.F for both readings.... though I am not sure if the
>>> diode I was testing had the key pressed (maybe i will tape all keys down
>>> while i do this...)
>>>
>>> Tom Wiltshire says
>>>
>>> "You can buzz them through with a multimeter continuity checker, assuming
>>> it
>>> uses enough voltage to overcome the diode drop. Sometimes they don't.
>>> This
>>> is why
>>>
>>> they also include a "diode test" setting on the multimeter. Still, I've
>>> found it easier with an audible clue.
>>>
>>> I tested a Polysix keyboard by taking it out of the instrument and lying
>>> it
>>> down upside down. This meant I could get to the PCB and connector, but
>>> more
>>> importantly
>>>
>>> meant all the keys were pressed down so I could test the diodes. To avoid
>>> the multimeter problem I just mentioned, I tested it with a 9V battery
>>> and a
>>> buzzer."
>>>
>>> what type of buzzer, just one from a PC will do?  i have PLENTY of those
>>> lol
>>>
>>> so it looks like if its not the diodes, keyboard contacts, nor the ribbon
>>> connector than its most likely the MCU
>>>
>>> i rather not pull the other MCU i have out of the working one.....
>>>
>>> Are these obscure and rare  (read expensive) to find?
>>>
>>> 8^(
>>>
>>> how do you check the ribbon cable for continuity?
>>>
>>> What ended up being the problem with your Polysix Tom?  Did you resolve
>>> it?
>>>
>>> How do I read through the archives again? 08^)
>>>
>>> Cheers,
>>>
>>> Nate
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>>>
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