The Quarky Engineer

I recently got a Televideo 1605 PC, which was one of the original early ‘PC compatible’ clones. It was also the first PC I had, so I have lots of good memories learning X86 assembly on it. It was a very ‘compatible’ clone of the day as it could run Microsoft flight simulator, a benchmark of sorts. I got it off eBay, and the seller says the machine was booting when it was packed. It arrived in good condition with no obvious damage, but does not boot.

The Televideo has an attached monitor, plus a sidebar floppy/hard drive combo. The machine appears to not POST at all. No beeps, no activity. My first thought was that perhaps the monitor was just dead, but even with no monitor you would still get the POST beep and floppy seek. I removed the floppy and hard drive module, and check the primary power supply. Good power on +5,+12, and -12. I checked the speaker, which is good.

I removed the motherboard and did a visual. A few blue wire mods that are probably factory, plus 4 ICs that look to have been removed and replaced based on the flux residue. I clean up the residue and verified the IC connections.. all look good. Still no POST. I removed the processor (8088) and tested with my dedicated processor tester, and it works fine. Replace, no POST. I replace each of the major subsystem ICs that are socketed with known goods, and still no POST. I also removed RAM down to the system minimum, but even no RAM would not prevent POST (since POST is from the EPROM BIOS).

I did a bit of debugging with the scope and the CLK signal is a good 4.77Mhz 33% duty cycle clock, and the processor does seem to be sequencing. It looks like code runs for a bit then executes a HALT instruction, which is typical in the original IBM PC BIOS when doing system tests that fail. I pulled the BIOS EPROM out and downloaded it so I could reverse engineer the BIOS.

Next up is to hook up a logic analyzer so I can watch the processor execute instructions and see where things are going off the rails. This BIOS mostly likely doesn’t output POST codes to 0x80 like the later IBM AT, so I will probably have to dig into the BIOS initialization to figure out what is wrong. I have a copy of the Televideo Technical Manual, which has a schematic, so it will be easy to track things down.

Any other obvious paths I am missing? Anyone have, or know someone who has a 1605?

I made my first try at retrobrighting. It a process for turning older ‘yellowed’ plastic back to the original white. I made a UV exposure bin with UV LEDs and some reflective foil, and then filled it with a mix of hydrogen peroxide and distilled water.

This is an old Mac SE that needs some restoration work. I’ll recap the main board as well since those electrolytics are old. The floppy drive also needs some cleaning and lubrication.

Let’s see who can name all of the machines in this picture and the processors that are in them.

A bit of CPM playing today. I was able to build a Kaypro CPM disk on my 5150 PC, and use that to transfer over a few things including MBASIC and STARTREK.BAS. All seems to be working well.

The Osborn booted right up as well and I was able to run a few programs. That little screen is very cool. NIce to see 40 year old hardware work so well.

Commodore 64 time!

A little retro-gaming. It brings back memories of playing Space Invaders and Parsec when I was a wee lad.

Thanks to Aaron Morris for feeding my retro-habit. The Amiga is such a fantastic platform with so many really great design ideas and cool aftermarket support.

I added a TV in my lower garage today. I thought a 65″ TV would be too large, but no, it is about right.

I recently acquired a small gamma spectrometer that I can used for radioactive sample profiling. A simple Geiger counter can detect alpha, beta, and gamma emissions but does not have way to measure the energy level of the detected emissions. A gamma spectrometer can measure the energy of a gamma emission which provides a profile of the sample under test.

As a first test I used a Cesium 137 sample from Oak Ridge. This is a sample I have had since 2011 and used for misc calibration. Cesium decay is a great source since it has a nice mono energetic emission at 662 keV. You can see that emission on the chart, as well as a few other cool things. On the far left you can see an emission at 32 keV that is the result of internal conversion where an electron in the 1s orbital is energized and an an electron from an upper orbital replenished it, releasing the 32keV X-ray.

A second cool effect is the bump at 184keV which is the result of Compton Backscatter. The Compton effect is the result of electromagnetic radiation passing thru and interacting with matter.

I pulled some radioactive samples out from my nuclear archive to test, and I included a couple of them here. I have some excellent Radium-226 samples that are inside radioactive vacuum tubes from the early 1950s. That spectrum shows the Bismuth 214 peak, and a bit of the Radium 226 peak. I also tested a Thorium Ore sample which had the PB-212, Ti208, and Ac228 lines present.

A cool tool to add to my tool chest. One never knows when a radioactive sample might need to be identified!

My friend Dan Martin pointed out that if you have local pressure recorders you can see the pressure wave from the Tonga Volcanic explosion. Sure enough just past 4am you can see the jump in the sensor in my shop. Pretty cool to see how it can be detected.