[sdiy] Diagnosing Fatman problem

[Scott Gravenhorst]

I assume that you are certain all 3 power supplies are working and providing
the correct voltages.  Especially +5 volts.

One thing I would try is to start with the keyboard controller on channel 1,
play notes watching GATE, then switch the keyboard to channel 2 and repeat,
channel 3, etc. to 16.  If there is a problem with the FatMan channel
switches, it may respond to an unexpected channel number.  That's pretty easy
to fix if that turns out to be the problem.

The MIDI LED indicates the presence of any MIDI activity, regardless of the
channel or even the message type.  The GATE LED turning on is a function of
the firmware and hardware, i.e., it is the program that turns it on.  If the
MIDI message's channel number matches the channel setting on the board, the
LED should light.  If it does not, then a problem exists with the
microcontroller part of the system.  Any of the logic parts: IC1, IC2, IC3,
IC4, could be at fault.  I would inspect your soldering work with a magnifier
such as a loupe.  Also look at the traces themselves, I've seen etched boards
that have discontinuous traces.  Any solder connection that doesn't look
right can be reflowed.  For socketed ICs, make sure that there are no folded
pins.  Pins can fold under the IC body and be difficult to see, remove and
reinsert each one to make sure this didn't happen.

There's not much else you can do without more specialized equipment, such as
a device to verify the contents of the EPROM or to verify the functioning of
the MCU.


"James Howe" <jwh at allencreek.com> wrote:
>I've just completed building a Paia Fatman synthesizer as my first DIY  
>synth.  Unfortunately it's not completely working.  It powers on just  
>fine, no overheating or smoking.  The MIDI input works just fine (the MIDI  
>light flashes as expected in response to keyboard input), as does the MIDI  
>thru.  My current problem is that the Gate LED does not light up when a  
>key is struck on the keyboard.  Since I am fairly new to doing electronics  
>work I fully expected that I might have some bad solder joints, but I've  
>looked and have yet to find one that might be causing a problem.
>
>Based on some tips from Paia, I checked voltages on various IC's (1, 2, 3  
>and 4) and the values seem to be consistent with the schematic (e.g. I'm  
>not finding a voltage on Pin X of IC1 and no voltage on the related pins  
>on the other IC's)  I know that the Gate LED will in fact light up since  
>it lit up on me when I accidentally shorted out pins 4 and 5 (I think it  
>was those two) on IC1, when I was trying to get a meter reading for one of  
>the pins.
>
>I'm also fairly confident that the keyboard is transmitting on channel 1,  
>and that is how my DIP switches are configured.  I'm hoping that someone  
>out there has some suggestions for ways that I can diagnose this problem.   
>Unfortunately I don't have access to scope, only a digital multimeter.   
>Are there specific places that I should be seeing certain voltages (or not  
>seeing voltages) that would help me locate places where I may have a bad  
>solder joint?
>
>Any tips would be appreciated.
>
>Thanks.
>
>-- 
>James Howe
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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