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Crazy PCB Layout from the Big Hair Decade

Check out the bizarre PCB layout on this power supply. A Pulse Instruments PI-702, I bought it for a few dollars at a hamfest. It was made in the mid-80’s and plugs into Tektronix TM500-series mainframes. When I powered it up, BANG!, after which it had no output. Here is what I found when I opened it up for a look:

The curvy, hand-taped traces are typical for the period, but look at how few components are in the two-thirds closest to the front panel compared to the number of pads! Plenty of those pads look like they have an 0.3″ DIP pattern, but have either discretes or nothing soldered to them. The layout is also full of dead-ends and traces that don’t go anywhere, and there is no silkscreen. The back third is neat and tidy — it is all a bit Dr. Jekyl and Mr. Hyde.

All of this leaves me wondering what the crazy layout is for! If it is meant to dissuade reverse-engineering, it might work (it worked for me, so far…), but who would want to protect something as simple as a linear power supply? It is even stranger that the digital-to-analog conversion circuitry near the edge connector gets so little of the board, and is laid out quite cleanly compared to the power supply. I suppose that this might be a case of multiple models using a single PCB, but what a devious mind it would take to merge multiple schematics into something that looks like this!

The problem itself was easy enough to find. One electrolytic capacitor dried out and blew up. You can see it at the lower-left of the second photo. It will be easy to fix, assuming it didn’t take any other components with it.

The device itself is interesting. It has three outputs, two of which are bipolar, each covering -25 V to +25 V continuously. They can be independently set with front panel controls, track an external input, or be controlled digitally. The bipolar outputs are limited to a wimpy 25 mA each, which is undoubtedly why it is called a bias supply. It also has a fixed +5 V output at up to 0.5 A.

Now I know that the 80’s were not only the decade of MTV and big hair, but at least one rather strange PCB layout.

FPGA breakout board PCB errors

I’ve recovered from the busy last few months and that means I can spend a little more time at my workbench. The first of the A3PN250 (ProASIC3 nano) FPGA breakout boards is built. Here it is, in all its glory:

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Building the ProASIC 3 nano FPGA board

After a busy week spent traveling for work and a morning digging out from a surprise snowstorm, I had a great weekend with my family. It was Sunday night before I heated up the soldering iron and got down to business building the ProASIC 3 nano FPGA board.

I started with the toughest component, the FPGA. Its central location and low height means ….

I started with the toughest component, the FPGA. Its central location and low height means that I will have an easier time accessing it before other components are mounted. That is not likely to be a big problem for this board, with plenty of space around the chip, but I would still prefer not to have to work around the filter capacitors if I can avoid it. On the other hand, its 100 pins and 0.5 mm pin pitch makes it far and away the most difficult soldering job on the PCB.

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The FPGA boards are here… and they’re purple!

Despite my last post mentioning the lateness of the breakout boards, it turns out they had already arrived. The mailer was stuck between two magazines in the mail, so my wife and I missed seeing it. I had hoped to get the PCBs by February 26. They were here the 22nd. Oops!

They came out quite nicely, with no obvious defects, and they look quite regal with gold plating and Laen’s signature purple solder mask. How often do you see purple circuit boards? The gold is nice, too. Laen’s standard boards are have a solder finish, but sometimes some of his customers pay the extra for gold, in which case all the boards on that order come back with gold.

A3PN250 board — The FPGA board, gleaming and ready for some solder.

I’m looking forward to building up these boards and writing some Verilog to bring them to life.

No PCBs this week

I had hoped to be able to write about the new printed circuit boards this weekend, and maybe even show one built up, but they didn’t arrive. I had guessed that it would take them 9 days to get to Ohio from Oregon, which would have made them arrive yesterday. There have been several snowstorms in areas they would be passing through, so it’s quite possible they were delayed by weather.

I’m still working on getting the Actel Microsemi development environment set up at home. When I tried to register for a free license key, the web site was down for maintenance. I’m looking forward to getting it installed and starting work on some Verilog code. First up will be an iambic keyer.

FPGA Breakout Board Layout

Here at last is the printed circuit board layout for the FPGA breakout board. I’m planning a series of projects involving FPGA-based DSP for ham radio, and in order to build them, I need an FPGA and a PCB on which to mount it….

The goals for this layout constrained it to be a nearly single-sided layout, …

The goals for this layout constrained it to be a nearly single-sided layout, with a ground plane on the back. That way, the board could be mounted directly on a piece of copperclad with no short circuits to ground. My budget limited me to a double-sided board, so all signal and power traces had to go on the top side.

That said, here is the layout, top and bottom.

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