[sdiy] TR-909 dead tom

[Adam Inglis]

On 26/07/2014, at 9:52 AM, greg at gzifcak.net wrote:

> I forgot to mention, I've also verified that there is no trigger  
> signal
> coming out of the 4174 (IC1) on the voicing board at the pin for the  
> low
> tom.


IC 1 is right at the corner of the voice board. Check the area  
carefully for a hairline, because 909 boards have been known to crack  
at the mounts on the corners when dropped, causing all sorts of lovely  
madness.





>
>> Hi guys,
>> Just joining the list again after a few years away. I'm working on  
>> my 909
>> and kind of stumped by my dead low tom.
>>
>> I've determined that it's not the voice circuitry since I can  
>> trigger it
>> from the trigger lines of the other sounds. I've verified the  
>> trigger line
>> connection between the voicing board and switch board, and from the
>> connector back to IC604 and the other ICs to which it should  
>> connect. At
>> this point I'm not sure where else to look except to try every other
>> connection on the switch board. My only other thought is to drag  
>> out my
>> scope and look at the trigger lines, but it's tough to power the  
>> switch
>> board and still have enough room to probe around.
>>
>> Can anyone offer any insight into the workings of the switch board  
>> so I
>> can narrow down my hunting?
>>
>> service manual here if you need it:
>> http://www.gzifcak.net/TR-909_SERVICE_NOTES.pdf
>>
>> Thanks in advance,
>> Greg
>>
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>
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