My GM5 adventure

[Breeze]

Hi all! A little post for the benefit of anyone jumping into the GM5 kit blind. I've been DIYing electronics for many years, but I never did SMD till now.

Having moved to Win7-64, my $1k Unitor 8 mkII suddenly became a piece of junk (so much for "many years to come", Emagic...). I heard of the GM5 looking for an alternative, and ordered 2 of the small PC boards and 2 GM5s. I had never done SMD, but it stayed on my desk for a couple of weeks while I mustered the knowledge and courage to tackle soldering this tiny chip. To make a long story short, what worked for me was:

1. 
   
   
2. Having a 10X loupe and a magnifying lamp.
   
3. Gluing the chip to the board with a tiny drop of epoxy! I couldn't get the damn thing to stop slipping after many, many tries.
   
4. Using Flux! I tried going pin-by-pin flux-less, but it didn't seem to work well for me. I ended up damaging one of the traces on the board close to the GM5 and had to use a wire strand to fix it.
   
5. Using the Flood and Suck Technique! Even with the flux, pin-by-pin was a PITA. So out of frustration I just flooded one side of the chip with solder, and then just used my desoldering pump to suck the excess. And it worked!!
   

I had this old MIDI distribution box which I chose to convert to use with the GM5. When I started mapping my extension board, it occurred to me that having LEDs would be a good thing. So I came back here to order the 5x5x5 PCB, but there were none left! So I bit the bullet and built my own: I strongly recommend anyone wanting to do this to be patient and get the 5x5x5 PCB because I spent a ridiculous amount of time hand routing a project PCB. However, the benefit of designing custom is that I added a few things:

1. 
   
   
2. I wanted to use a dual color LED because it was easier to mount single LEDs in the box I had. Ideally, common-anode 3-pin dual-colored would have been perfect, but I only found common cathode red/green ones. So I used two additional 74HC14's to invert the LED signals for them. BTW: I did end up using a single 1/2 watt 100 ohm resistor in series with a 1k multi-turn and connected all the cathodes together through them to ground; it turns out though that the Red is slightly brighter than the green but though it isn't optimal, it's fine for the occasional checking they're useful for.
   
3. I needed a couple of thru circuits so I tapped the connections of all five channels where the 6N138 connects to the 74HC14 to 2 multi-turn switches, and used another 74HC14 to get two independent 3-channel thru's whose input can be any of the 5 channels.
   
4. I included a 5 volt regulator circuit for independent operation for when the computer is off. This turned out to be a useless mod because it's plugged into a powered USB hub which stays on all the time. So far it hasn't needed any additional power at all, despite the addition of 3 74HC14's and a power LED.
   

In the end, other than a stupid problem where one of the standoffs was touching a trace on my custom board, everything works perfectly. I had a minor issue where the name of the first port was different than the others but installing the Ploytec drivers fixed that.

A big thanks to Midibox and Ploytec for making this available. I hope some of this can help someone. It's a great little box!

Edited February 8, 2010 by Breeze