IMSAI Score update/Spare BYTEs/Got an Altair too

Hi Rich, The "IMSAI 8080" does not light up and should appear clearly visible in white. Sounds like the logo was removed for some reason ... hopefully it was covered with a bit of black paper and not "backed out with a marker". I have a decent picture of an IMSAI front panel by itself on my website. For now, the easiest way to get to it is to click on "Vector 1+" which will take you to my general S-100 section, and scroll up ... the photo just before the Vector is an IMSAI panel. (at the time I did the last update I only had the panel which is why there is no listing for a machine - I have since acquired a complete IMSAI which will have it's own section at my next major update which should be within the next couple of weeks). The panel is quite easy to take off/apart. First remove the power switch connections from the upper corner of the panel in front of the power supply (live AC - do this unplugged obviously) and umbilical cable from the CPU board. There are 8 small hex screws in the front of the panel - when you remove them, be careful as the spacers from the rear and center boards will drop out (Took me 1/2 hour of searching the floor of my workshop the first time I "discovered" this. After that, the panel should just unplug from the S-100 bus and come out. The various pieces will separate, you should be able to remove the plexiglass front and get at the insert which has the labels and logo - Be VERY careful as the layers can stick together, take them apart slowly to avoid damage. Behind the insert is a "foil" paper which blocks light to all but the desired places. At this point you should be able to determine what was done to the logo, and if it is recoverable. Putting it together is the reverse - Assemble the layers and internal spacers, and insert the hex screws far enough to just stick out the back, then carefully plug the panel into the S-100 bus, making sure not to pull the screws out and' drop the internal spaces. I found it easiest to install the two middle/bottom spaces first, using thin long nose pliers to slide them in place while extracting the screws just enough to let them pass - then put the screws in enough to catch in the threads but leave them out far enough that you can still rock the panel back and forth. After that, it's easy to put in the remaining spaces around the edges, and once all is in place and looking good, you can snug them in. I've had both of my panels apart without too much difficulty. As it's a linear supply, you don't really nead to load it initially. I highly recommend powering it through a series light bulb and bring up the line voltage slowly. Monitor the DC levels and you should see +8, +/-16 coming up as the line voltage rises. With something this old, it's a good idea to bring it up in steps allowing plenty of time for the capacitors to reform at each step. With no load on the supply, the light bulb should not glow at all, except briefly during initial charging of the capactors (which you won't see if you are bringing it up slowly). If the light glows as you bring up the supplies, you likely have a shorted filter capactor or failed rectifier diodes. (sometimes the chassis fan draws enough power to cause the lamp to glow dimmly buy it should not glow brightly with an unloaded supply). Once you have it running at operational voltages, it's a good idea to test it under a load and observe the waveform at the filter capacitors with a scope. A 20-40 watt 12v bulb works pretty good for this. Get it up and running and delivering a few amps of power and look for excessive ripple - this would indicate dried out capactiors. Btw, be sure to remove the series light bulb before attempting load tests. Always be careful when working on the IMSAI as it has AC line voltage to the front panel which is unprotected when the cover is off. Regards, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html