Category: electronics

Today I made a bunch of progress on the Sequentix P3 I’m currently building. Before today I’d only checked out the parts to be sure most of them were there, looked over everything, and did some general setup to be sure assembly could progress. Today I started fitting pieces, and I’m definitely more than half done at this point.

Because this P3 uses a slightly older board set (v1.5) I had to use this set of older DIY Sequentix P3 directions, but this didn’t prove to be too difficult. While I was able to complete the mainboard, I had to make some slight modifications. It seems that the v1.5 P3 board set only supports MIDI sync or DIN sync. One must read carefully through the main board and IO board pages to figure out what extra components to add, which to leave out, and what to do differently. In short, I had to leave out some parts from the mainboard and fit two capacitors where diodes once went and add in an extra pullup resistor on the bottom of the board.

The two capacitors on the top of the board are intended to add a bit of capacitance to the input lines of the PIC which handles MIDI sync. It is suggested that 220 pF parts be used, but as I didn’t have any of them I fitted some spare 330 pF parts. I don’t think this will cause any problems, and hopefully it won’t. The extra resistor on the bottom of the board is to help work around slow rise times on the MIDI output caused by additional capacitance brought about by the inclusion of RFI filters on the IO board.

I’m hoping to be able to power it up for the first time either tomorrow or Tuesday. How late I get home from work will determine how much I’m able to get done each night.

Here’s a few more photos of parts from tonight:

· Completed Mainboard w/o ICs: Top / Bottom
· Completed upper and lower pot boards.
· Pots for the P3, plus spares, with lugs removed and thick 1/4″ washers fitted for spacing.
· Completed IO board, set up for MIDI sync.
· Completed function switch board.
· Twelve resistors.
· Incomplete keypad board with 1N4148 diodes fitted.

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This afternoon I ran by the local FedEx depot at the intersection of Brown Road and Giddings Road in Auburn Hills to pick up a box containing the next P3 I am to build, for another person from the analogue-sequencer Yahoo! Group. It turns out that this facility doesn’t normally receive in-person pickups, as I had to enter through the employee entrance (metal detectors and all), enter the office, and just sit in a waiting area until the person brought out my package.

After a nice bike ride around Dodge Park with Danielle I opened up the package containing the P3 and started sorting through all of the parts, laying them out on the table for easy access. On initial glance everything seems to be there, except for a couple small screws for holding the enclosure together.

This is actually a slightly older enclosure design than I worked with on on my P3, as it doesn’t include niceties like the subpanel to help with the pot assembly, and the clearance around and mounting of the PLED leave a bit to be desired. That said, I imagine assembly will go pretty smoothly.

I’ll get started with the actual assembly tomorrow, although I might take a break for a bike ride if the weather isn’t too threatening.

Oh, and (per usual) there are a few more photos of Ivan’s P3 here in this album in my gallery: Sequentix P3 for Ivan

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Well, that’s it. Mark Pulver’s Sequentix P3, serial number 008 is complete. I spent a good part of the evening tonight finishing it up. The biggest part was making this custom, reversing DIP28 to DIP28 cable so that the MemX expansion which was giving me problems yesterday could instead be mounted next to the main PCB. I then stuck the MemX down to a freshly cleaned case with two layers of foam adhesive.

I also replaced all of the mounting hardware for PCB which holds the MIDI ports with some slightly taller pieces. This made it so that the DIN5 / MIDI ports are properly centered in the cutout in the enclosure.

After being sure it was working I closed it up and gave it some final tests using a Radium 49 and MIDIbox SID-NUXX for testing the MIDI inputs and outputs. Everything is working, so this means its done and is ready to go back to Mark. That’ll be tomorrow’s task… Hopefully the post office won’t be too crowded.

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It works, it’s running with one of the v4.00 beta OS’, and it’s almost done.

Tonight I did most of the final work on Mark Pulver’s Sequentix P3. This included making the cables, connecting the display, mounting the pots (complete with washers for support as mentioned yesterday, hooking everything up, and fixing any mistakes.

It turns out that I had two small errors which caused me some stress and parts of the P3 to not work, but they were easily sorted out. The first problem was an unsoldered pin 1 (OE) on one of the 74HC573 ICs. This made the whole thing act quirky, almost as if buttons were randomly being pressed. There was even odd garbage appearing on the LCD.

The second problem was that I put the 1N4148 diode on the pot function switch backwards. You can see the error here. The misplaced part is D9. This caused the button not to work and was real easy to troubleshoot.

I also found that the DIN5 MIDI ports on the back of the enclosure sit too low, making plugging and unplugging cables difficult, if they can even reach. Putting an extra M4 nut on each post beneath the PCB raises it up enough, but shorts me on M4 nuts. I’ll see if I can get some more tomorrow.

Upgrading the firmware to the v4.00 beta 26 to support the MemX memory expansion module was a bit of a hassle, simply because I kept receiving a BAD DATA error every time I tried. I originally thought the problem was due to some MIDI routing weirdness caused by new MIDISPORT drivers or MIDIOX, but in the end it was simply a firmware version compatability issue. This was resolved by using a bootloader update found in the analogue-sequencer file section.

After getting to the v4 firmware I ran into two other problems. First, capacitor C3 was tall enough and located in such a place on this old version of the PCB that the MemX board simply wouldn’t plug in. This was resolved by replacing C3 with a new 10μF 25V electrolytic cap, but mounting it on its side to be lower profile.

Then, while putting it all back together, I ran into what’s probably the biggest actual problem of the whole assembly: the case won’t close with the MemX board fitted. The place where the MemX board sits in the enclosure just happens to be directly below an IDC connector and the pot board. With the MemX fitted the case stays open about 1.5cm. With this large of a gap I can’t move the board sideways to avoid the connector because then it’d just hit another PCB.

As you can see above I was able to finish up the knobs and get the case mostly complete. As soon as I talk with Mark and figure out what he’d like to do with the MemX board (leave it out and sell it, or see if I can find another way to fit it in, which may not be possible) I’ll be ready to finish up testing and ship it out. All the buttons and pots work as expected. The display does its thing, and MIDI in works. I just need to test MIDI out and maybe sequence a couple things with it just to be sure it’s working and it’ll be done and on its way back to Mark.

Per usual, there’s a bunch more photos to look at. The ones taken tonight start on page 3, so help yourself if you’d like to see them.

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Last night I did a bunch more work on the Sequentix P3 that I’m building for Mark Pulver. Unfortunately last night was the time where I started to see issues with the project. In short, I now understand why Colin moved away from not very many people used this case design for the P3^†. On top of the poor button / pot / LCD layout, the tolerances on the case just aren’t very good.

Here’s a rundown of the problems:

Step Switches: I fashioned a jig to hold the 1-16 buttons in place on the step switch / LED board, and that worked rather well for aligning all the buttons in a nice row, and they automatically lined themselves up with the holes in the PCB. Unfortunately, the screw holes for mounting the PCB aren’t perfectly in line with the slot cut out for the buttons themselves. The end result is that on the left side of that row the buttons are about 1mm lower than on the right side. The buttons all work fine, but they just look a little off.

Function Switches: The way the holes are drilled for the function switches, along with the alignment of the screw holes, the red (key function) button rubbed a bit in the hole. A little bit of filing cleared this up.

LCD Alignment: With the stock LCD for this original P3 enclosure fitted, it doesn’t quite line up with the hole cut for it, leaving the bottom and left side of its bezel visible. This may not be an issues as the actual displayed data will likely be centered, but it doesn’t look as good as it could. Additionally, the mounting holes are not physically compatible with one of the PLEDs used in later P3s. It may be possible to get the PLED to fit, but this would require a bit rigging, possibly involving cutting the corners out of the PCB and fashioning some sort of mount.

Potentiometers: The P3 uses analog pots for a number of inputs. This works very well, except pots (as seen above or here) have small tabs sticking off of them. These tabs are normally fitted into drilled holes and they keep the pots from rotating during assembly or use. The subpanels for the newer P3 enclosure have holes for these tabs, but the original enclosure on Mark’s P3 doesn’t. Because of this, if I were to tighten down the pots they would be bent to the side. To work around this I’ll just snap off tabs (a trivial process, really) and then stack some washers between the panel and pot body to space things as nicely as possible. This will allow the mounting hardware on the pots to be properly tightened.

Now, that out of the way, the good things: I had no problem getting all the LEDs fitted / mounted / nicely aligned in the panel. These are all soldered into place and the PCBs holding them can pretty much be removed at will. All ICs have been fitted into their sockets, and things are progressing quickly towards the ever-so-scary first powerup.

Oh, I also had no problems making a jig out of cable ties and an old heatsink and blue masking tape to handle alignment of the keypad. I’m really happy with how it came out, and thankfully its mounting is not misaligned in the front panel like the other keys.

Next, and hopefully tonight, comes the boards and pots and switches and such together, finalizing mounting of the pot boards, and hopefully getting it running for the first time.

^† After making this post, Colin Fraser corrected me with regards to the case design. This case is actually the Maddox design. The original Sequentix P3, of which only four exist, can be seen here.

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Thanks to the analogue-sequencer Yahoo! Group, a discussion group for individuals interested in the Sequentix P3, I ended up getting in touch with a guy by the name of Mark Pulver who was in need of having his Sequentix P3 kit assembled. I sent him a link to my Sequentix P3 page at nuxx.net and photos of my P3 assembly and I imagine he liked what he saw because he asked me to assemble his.

After languishing in transit for a week and a half between his place and mine, I stopped off on the way to work and picked up the package from the post office. It was a quite large, well-packed box which should be just about right for safely shipping it back to him once it’s assembled.

Before getting to work I had to dig around for a while and locate the old Sequentix P3 assembly instructions. See, Mark actually has a kit for one of the original P3s, serial number 008, before the restyled and rackmountable case. These older versions also had a different PCB layout and BOM, so I couldn’t use the normal DIY instructions. I find this quite interesting because I’ll now have built both versions of the P3. I’m not sure how many people besides Colin Fraser, the creator of the P3 have actually gotten to see both of them in such detail.

Tonight I managed to assemble most of the easier parts of the PCBs. As can be seen above (or here full size) I fitted the sockets, resistors, caps, diodes, sockets, and other small parts. Tomorrow I hope to get to the pots, switches, LEDs, and other parts which are considerably more particular about placement. Since they are what the user actually interacts with I want to be particularly careful about them. After that it should just be a matter of completing the major component assembly, testing everything, ensuring that the firmware upgrades work as expected, getting the MemX memory expansion working, testing it all thoroughly, then sending it back. Hopefully by the end of the weekend that’s where it’ll be.

After this I may be doing some similar assembly work for another P3 (newer case style), an ASM2, and possibly some Blacet modules.

If you’d like to see all of the photos from this P3 assembly, check out this gallery: Sequentix P3 for Mark Pulver

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