[sdiy] EFM MIDI-Gate?

[Dave Kendall]

That is definitely not right. Pin 5 is GND, and Pin 8 is +V. If 
healthy, pin 6 should show very short pulses when MIDI is sent to it. 
(IIRC, negative going pulses)
They are quite fast - 320uSec or so for each byte, so make sure the 
scope scan rate is fast enough to pick that up, and that the soundcard 
can handle DC (which may affect it's operation if it's AC coupled).

With the optocoupler removed, do a continuity test on the traces 
leading to the 6n138, check that they are going to the right places.

Also check your input bypass caps are doing what they should, and there 
is not a dead short across +V and GND.

6n138/9s can be a little twitchy - I lost a couple for unknown reasons 
while testing a MIDI circuit - couldn't replicate the fault.
one of PINS 2 and 3 had come loose, and at the time I suspected that 
*might* have had something to do with it.


good luck

Dave

On Nov 13, 2009, at 15:47, Chromatest J. Pantsmaker wrote:

> I think I may have a dead optocoupler, so I'm gonna buy some
> replacements and see if that helps.  I'm not really sure how to check
> the one I have.  I'm using the o-scope software (freeware) that uses
> your soundcard as an interface.  Pins 5, 6, 7, and 8 all show the same
> waveform which doesn't seem right to me at all.
>
> On Fri, Nov 13, 2009 at 7:16 AM, Dave Kendall 
> <davekendall at ntlworld.com> wrote:
>> Hi.
>>
>> FWIW, I stuffed the board years ago, but never tested it. However I 
>> made a
>> couple of notes when examining the circuit traces.
>>
>> Silkscreen error:  +5V and GND down near the 7805 voltage regulator 
>> are
>> incorrectly swapped over. +5V should be nearest the edge of the board.
>> It works, but the silkscreen is wrong..... (batch number H&L - 1 5100)
>>
>> D1 should be jumpered. LED is not used. (don't know why - I think I 
>> got that
>> from Tom G's notes some time....) The pad nearest to the legend J1 is
>> ground, the pad connected to junction of D1 and R1 is +15V or +12V.
>>
>> C2 is a 10uF electro (25V ). The negative is connected to GND, ie. 
>> facing in
>> towards R8. (did I sub the ceramic caps? Hmmmm)
>>
>> I haven't got the board in front of me, so can't check exactly why I 
>> wrote
>> this stuff.
>>
>> Hope this helps anyway...
>>
>> cheers,
>> Dave
>>
>>
>>
>> On Nov 12, 2009, at 06:08, Chromatest J. Pantsmaker wrote:
>>
>>> So, I'm starting to revisit some old projects... The first of which 
>>> is
>>> the EFM MIDI-Gate interface.
>>>
>>> I have one built, but at the time when I built it, I couldn't get it
>>> to work.  That was roughly in 2000 or so.
>>>
>>> I have the original PDF file, but as I remember, there were often
>>> extensive re-work notes for each EFM board produced.
>>>
>>> Does anybody have those notes?
>>>
>>> Does anybody have a working MIDI-gate who could help me troubleshoot 
>>> mine?
>>>
>>> --
>>> .sig
>>> -Chromatest J. Pantsmaker
>>> http://www.chromatest.net
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
>>
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>
>
>
> -- 
> .sig
> -Chromatest J. Pantsmaker
> http://www.chromatest.net
>