Civil War Controversy: The Relieving of General Warren Before Five Forks

June 4th, 2015

A while back, I created a web page with some of my views on controversial topics of American Civil War history. The first topic talks about my view of the efficiency of Army of Potomac Corps commanders in both 1864 and 1865. One of the most controversial changes was on April 1, 1865, when General Phil Sheridan relieved General Warren of command of the V corps. To this day, the correctness of this decision is debated by civil war buffs.

The website has a number blog entries covering both sides of the controversy. What is especially interesting is reading the blog entry covering messages between various Union generals on May 30th and April 1st.

My view is that Generals Grant, Meade and Sheridan had every right to relieve Warren. In my view, Grant didn’t trust Warren to do the right thing in a crisis. The messages captured in the Official Records clearly indicate that Generals Grant and Meade were attempting to micro-manage Warren’s actions. If Grant had confidence in Warren, I believe that he would have given Warren general directions to work with Sheridan in order to turn the Confederate left and cut the South Side Railroad. A commanders lack of confidence in a subordinate should be enough to justify removing a person from such an important role.

Whether Warren was a competent corp commander or not, really is quite a different discussion. Even if he was actually the best corps commander in the world, if he didn’t have the confidence of his boss, relieving him of command, was the right thing to do. No commander should be saddled with a subordinate that he can’t trust in a crisis.

Web Page Unique Visitors

June 3rd, 2015

I’ve been using the same hosting service since 2009 and just went back and collected yearly stats for “unique visitors”.

Web Page Unique Visitors

Web Page Unique Visitors

The data for 2009 was only for 11 months so I multiplied by 12/11. The data for 2015 is for 5 months so I multiplied by 12/5.

The overall trend is for a general increase in activity, but this year could be slightly down over the past couple. However one real popular blog posting could affect the yearly results in a big way. November of 2014 had a major temporary increase in hits with my report of Steve Wozniak still thinking about improving the Apple II design generating over 26,000 visits for that month alone.

The total number of “unique visitors” over the last 6+ years is 537,704.

Dr. Galfo’s Integer BASIC Compiler

June 1st, 2015

I just put up a web page with documentation and DSK images of Dr Galfo’s Integer BASIC Compiler (IBC). This compiler was used in development of some well known Apple II games. It runs around six times faster than WOZ’s BASIC interpreter, so it’s worth trying out. Compiling an Integer BASIC program is easy. You simply load the program in the standard Apple interpreter and then run the compiler. You will be prompted for a few options and then, after the compiler is run, are given the option of running the program.

New Version of SCELBI OS/X Emulator Released

May 28th, 2015

The release of a new version of my OS/X SCELBI/8008 emulator was motivated to provide support of the Modified Creed Monitor for the 8008. To do this, I added menu options to support to optionally setting (input) and clearing (output) the most significant bit of input and output serial data. For the MCMON, the input menu for set the bit should NOT be set. The output setting doesn’t matter.

8008 Mini Monitor and EPROM support for the SCELBI-8H

May 25th, 2015

I just finished adding two new web pages to the 8008/SCELBI area of my website. Take a look, if you want to see what can be done with 256 bytes in an 8008 and how to add a monitor and EPROM to your SCELBI-8H.

SCELBI Main CPU/DBB/INPUT and Front Panel Boards restocked

May 18th, 2015

I did add a silk screen/legend to the front panel. Some original boards had it, and some didn’t. I figured I’d add it on this batch.

Front Panel with Legend

Front Panel with Legend

Only other difference from first batch is slightly large holes for Zener diodes.

Another SCELBI Cassette Write Board (with logic changes/fixes)

May 13th, 2015

While working on the SCELBI cassette write board, I found some issues which were reported in this blog post. I found that I had detailed images of a second cassette write board, and it looks like the problems on that first board that I looked at, were corrected on the second board.

The first board is the one found at the CHM, and was photographed a while back by Jack Rubin. The serial numbers on the SCELBI associated with that unit are in the single digits, so that unit was apparently a very early unit. The second, corrected board, was part of the collection of Nat Wadsworth. I am only aware of one other cassette interface, but I don’t have images of that unit. I don’t know how many were made before the corrections were made.

Here are partial images of the front and back of relevant sections of both boards. Red arrows on images of the Nat Wadsworth unit show where visible changes were made.

Cassette Write Board Changes

Cassette Write Board Changes

Note that the changes are somewhat different than the what was done in rework on the CHM unit. These changes don’t match the schematics, but I was able to piece together what was done and why.

First, let’s talk a bit about what is going on, by reviewing this section of the schematics.

Cassette Schematics - Z1

Cassette Schematics – Z1

The chip associated with all these changes is a 7475, a part that has 4 bi-stable latches. Here is the key part of the data sheet – the truth table and the pinout.

7475 Data Sheet

7475 Data Sheet

The function of this chip is pretty simple. Whenever clock input 13 is high, the chip’s output pins, 16 and 15 follow the input on pins 2 and 3, respecitively. Also, output pins 10 and 9 follow inputs 6 and 7, respectively, when clock input 4 is high. When inputs 4 or 13 go low, the associated pair of outputs, are “frozen” or are “latched” into their current state at the time the clocks inputs go low. Note that there are normal and inverted outputs for each latch.

In the schematics, three inputs are connected from a SCELBI output port to this chip. There are two data bits and the port’s output strobe. The output strobe is a high going pulse that occurs when an 8008 OUT instruction addressed to this port. The data bits are connected to the SCELBI write data bus, so will change rapidly, as the 8008 writes to memory or output ports. The strobe is connected to the clock input (pin 13) of the 7475 latches 1 and 2. This circuit allows the 7475 chip to capture 2 bits of the SCELBI output data onto latches 1 and 2 whenever an out instruction is directed to the output port connected to the cassette interface.

What about the two other latches of the 7475? In the schematics, the clock (on pin 4) for outputs 3 and 4 is not connected. What usually happens on unconnected inputs of 74XX series logic is that the input will “float” high. As mentioned before, if the clock inputs are high on the 7475, then the outputs will simply track the state of the inputs. The 3rd latch of this chip is not connected or used. However the 4th latch (pin 7) is connected to the strobe input, so the output will follow the strobe all the time. The inverted output on pin 8 is used as a clock elsewhere on the board. The function is a buffer and inverter of the strobe input to the board. Note that letting an input “float” high is not a good design practice and it’s possible that clock input on pin 4 was directly tied to +5 volts, which is connected to pin 5. It is not connected on the bottom of the board, but could be connected on the top of the board, which is obscured by the chip. The only way to know for sure, would be to use an ohm meter to determine if pin 4 is connected somewhere by a trace that is obscured by the chip. I don’t presently have access to this board, which is in storage at the CHM, so I can’t do this. My best guess, based on the extensive use of pull up’s elsewhere on the SCEBLI boards, and lack of a connection in the schematics, is that it was left to float high and was not connected.

As mentioned in the previous blog post, the first version of the layout has two significant problems.

1) The strobe output wasn’t connected to pin 7 of the 7475. This is rectified with a jumper wire.
2) The output on pin 8 (which is the inverted strobe signal), is not correctly connected to the rest of the circuit. This is rectified by a cut and jumper as can be seen in the image of the back of the board.

So what did the people at SCELBI do, to fix the problems in revised layout.

1) Power and ground connections to the chip were rerouted to make room for signal traces that needed to be added.
2) The inverted strobe output which was supposed to be on pin 8 was moved to pin 11, which is the inverted latch 3 output. This was done to make it easier to connect to the rest of the circuit. It was also disconnected from the strobe input connection.
3) The floating clock input on pin 4 was tied to an existing pull up resistor.
4) The latch 3 input was connected to strobe input by running a trace under the chip to pin 13, which was already connected to strobe. I actually can’t verify this change, but I can be fairly certain that it exists, since the circuit would not work without this trace.

Note that this change to use latch 3 instead of latch 4 for buffering and inverting the strobe is not reflected in any schematics that I have seen. The schematics actually don’t match either of the boards described in this description.

If you look at CAD images of this section of the board, you can see how the changes were made. Blue traces are on the bottom layer and red traces are on the top layer of the PCB.

Write Board Changes

Write Board Changes

I have repeated this sort of exercise numberous times over the years to solve various inconsistencies in schematics and PCB layouts in a number of vintage computers. Understanding a vintage design frequently requires detailed detective work, but with time and patience, most mysteries can be solved.

One last comment about the nature of the problems with this board. Of the thirteen SCELBI boards that I have investigated in detail, this is the first significant layout problem I have run across. There is an issue on the DBB board with a single missing trace. In this case, the connections to the 7475 were botched and had to be redone. This is a very unusual and unexpected mistake from the engineers at SCELBI.

Cassette Write Board Rework

May 10th, 2015

More progress on the SCELBI cassette write board. I have figured out the reason for the rework seen on at least one board.

Cassette Write Board Rework

Cassette Write Board Rework

There are two wires and a cut on this board. In both these cases, the PCB didn’t follow the schematics. Both changes are related to chip Z1 connections.

In case 1, pin Z1-7 should have been connected to Port A, pin T. Port A, pin T is already correctly connected to Z1-13 and Z2-13 and Z2-4. I’m not sure if this omission was on purpose or not. Routing to Z1, pin 7 would require running a trace on the top of board, from Z1-13 out the top of Z1 around the outside of Z1 to Z1-7. This would also require re-routing a couple of other traces on the top side of the board to make room for this new trace. It’s very unlikely, but possible the layout person didn’t want to mess with this and decided to just require the board builder to add a wire.

In the second case, Z1-8 is not connected to Z11-3. Instead Z11-3 is connected to Port A, pin T. The fix requires cutting the trace from Port A, pin T, after it splits and runs through a via to go to Z2. Then a wire can be soldered from the cut trace to Z1-8. This is clearly a layout error.

I still have at least one more mystery to solve on the cassette write board, before I’m done with it, but the layout is shaping up real well.

Economics of Selling Vintage Computers/Kits/Components

May 9th, 2015

In March of 2011, on the MARCH Yahoo Forum, I suggested that having a PCB fab build a batch of reproduction boards for the MARK-8 would cost a small fortune.

Perhaps I should follow my own advice. In Feburary of 2013, I invested a small fortune in a similar project, the SCELBI-8H. It has taken over 2 years to sell 19 pcb sets for the SCELBI-8H and SCELBI-8B. I’ve kept track of my investment in PCBs, as well as all the other components and materials that it took to build a working example of each system. Despite selling individual boards for a profit over their cost, I can honestly report that the overall project has cost me a significant amount of money. Now this investment has been worth every cent, but almost entirely due to the fun that I’ve had and friends that I’ve made, not due to any financial reward.

Now it’s possible that after a few more years of selling SCELBI PCBs, I’ll have managed to break even on the project, but it will always be a work of passion, not profit.

Many retro products only come to the market for a short period of time and then disappear. I believe that this is due to the tiny market and low profit realized. Once you have built something, the excitement of creation is replaced by the routine work of handling inquiries, ordering parts, packing, shipping products and supporting customers. If you are only making a few dollars and would rather be spending your spare time on a new project, it is easy to see why new batches are not made once inventory is sold off. It wouldn’t surprise me that some products are pulled off the market, even when the inventory still exists, just because the developer just doesn’t want to deal with the hassle.

There are a few products that seem to have defied the odds – but they are very few in number. An example is the series of CFFA cards for the Apple ][ computer. Rich Dreher routinely makes and sells batches of hundreds of them. The numbers of units he sells, absolutely amaze me. He also has an Apple 1 version of this card, but according to his web site, it appears that he has only sold a little over half of a batch of 200 that were made two years ago. I wonder if he will make another batch of the Apple 1 version, when the current batch is finally sold. Vince Briel has had some very good success with his vintage work-alike kits, but I don’t think it’s enough for him to live on. Just doing a little basic math shows how how many would need to be sold to make a living at it. A Replica 1 kit currently lists for $149. Assume that you could make $75 per kit after costs. Then, assume you needed a $100,000 annual income, which is a fairly low income for an experienced engineer. Then divide the annual income requirement by the $75 revenue from each kit. The result would be a minimum of 1333 kits sold. Then, keep in mind that you would have to do that year after year in order to sustain a business. I just don’t think that the market is that large. In fact, Frank Achatz had a similar product to the Replica-1 on the market for a while called the A-ONE. It appears that he quit selling them and closed down his website a while back, which should tell you something about how difficult it is to either have fun or make a decent profit selling vintage kits.

New batch SCELBI FP, CPU, DBB & Input PCBs on order

May 8th, 2015

I finally sold my 19th set of SCELBI boards. There were 20 sets made in the original batch for the 8H that were made in January of 2013. There were about an even number of 8H and 8B sets sold, and the boards I’m reordering are common between the sets, as I still have plenty of the boards that are unique to each system. There are only two differences between these new boards and the original set of boards.

1) The size of the holes for the zener diodes is being made a little bigger. Note that if you can find them, the leads for the original style zeners in the cans will fit in the original holes, but more modern zeners have thicker leads may not. Older boards will work fine with the more modern zeners, but the holes will have to be reamed out a bit and the leads soldered on both sides of the PCB.

2) This time around, I’m adding a silkscreened legend on the front panel board. The original SCELBI front panel boards came both with and without the legend, but I see more original units with the legend. This is why I’m adding the legend to this batch. When I made the first set, I thought that only early boards that were made before the advent of the aluminum front bezel had the legend. Later on, I discovered that a number of systems with the front bezel, also had a front panel board with a legend silk-screened onto it.