Tektronix 4097 GPIB 8" Floppy Drive

Bob R. wrote: it Yes, the unpopulated socket is a 24-pin, near the edge of the ROM board. It's a relief to know that the fault being reported is not due to a missing chip. actually Wow! Ten? With as huge and heavy as these things are, I can imagine that you must have a lot of storage space! That'd be most appreciated! I don't want to put pressure on Al, but it'd be great if the 4907 Service Manual could be on the priority list to be scanned and put on Bitsavers. Schematics and other service information would make the job much easier. Tony D. asked what type of RAM is used. It uses 18 MK4127 (Mostek) 4Kx1 Dynamic RAM chips with 150ns access time. They are all socketed. I was able to find the datasheet for the parts online. They need to be refreshed a maximum of every 2ms. I figure that if worse comes to worse, I could simply build a little circuit with the address latches (the address lines are multiplexed) to grab the address, then use fast Static RAM to replace the DRAM. Wouldn't be too tough to build, and would get rid of the reliance on DRAM. I'm willing to bet that the problem is probably with the DRAM. It would make sense that the firmware would do a quick RAM test at initialization after perhaps performing a ROM checksum test, and if either test fails, lighting the FAULT light. Tony also asked how the fault light is driven. The four LEDs are connected to the main controller board with a ribbon cable, that plugs into the controller board with a harmonica connector. It looks like the LEDs are driven by a latch that is probably driven by the 6800. So, like Tony posited, the microprocessor is probably running, and is actually detecting some fault condition that prevents it from getting through its power-on self tests. It would have been nice if the LEDs could somehow have been used to indicate the part of self test routines that was failing -- it'd at least be a good clue for troubleshooting. On another topic related to the 4051...many of the 1/4" (Tektronix-branded) cartridge tapes that came with the machine have busted drive bands. The tapes are OK, but they won't work in the 4051's drive because of the broken drive band. I've re-banded one of them ("Version 5 Loads-Of-Fun Game Tape (Binary Version") and it works good now, after I did a little o'scope-assisted tweaking of the tape head azimuth to get the signal strength a little stronger. The games tape has a lot of really neat games that appear to be derivations of various common BASIC games, but modified for use on the 4051 with its graphics capabilities. There's a fun little artillery game when you take turns trying to launch artillery shells at your opponent (or the computer). There's also a game called "Weather Wars" where you try to destroy your enemy with lightning strikes and tornados. There is a BASIC version of Chess (not graphical) that appears to be a re-write in BASIC of a minicomputer chess program (the board listing looks a lot like the Chess for the PDP/8 under OS-8). It's painfully slow to play...computer takes about 6 minutes to make its move. It'd play faster (probably about 3 times faster) on a 4052 that uses the bit slice implementation of the 6800). There's a music box program that uses 6800 machine language code (the CALL EXEC function) to manipulate the bit that drives the speaker to play music. Anyone know of a source for the drive bands in these 1/4" cartridges? I've got a stock of spare DC300 and DC600 tapes that have good drive bands, but I don't want to pillage them for drive bands to try to repair the 4051 cartridges that have broken bands. Rick Bensene The Old Calculator Museum http://oldcalculatormuseum.com