TU56 fun and games

We've been working to connect a second TU56 to our PDP-8/e and TC08. Unfortunately, our second TU56 had been configured for a TD8-E. The good news is that we surmounted our lack of a M531 negative bus converter module - by making our own. The module worked partially (it did boot OS/8) on its first test, but further testing discovered one missing trace, which was easily ECO'ed. With that in place, I discovered that our second TU56 had a defective M040, and fortunately we did have a spare to replace that. Each TU56 runs appropriate MAINDECs successfully. The bad news is that we still don't have two TU56s on our PDP-8/e. The extant TU56 and TC08 documentation (thanks, Bitsavers!) aren't particularly clear on this, but the cable that connects the TC08 to a TU56 is NOT the same cable to 'daisy-chain' to another TU56. The TC08-TU56 cable, 70-6223, has several crossovers on the paddles - it's not A to A, B to B, etc. The TC08 documentation *hints* at that, but only states that connecting two TU56s requires a "M908 to M908" cable. The M908 is the paddle itself. There are at least two cables made using those paddles. The correct one to connect two TU56 drives (and I finally thought to confirm this in the FSTM) is a BC02X, which comes in various lengths. It, too, has M908 ends, but the wiring is direct, A to A, etc. (except for four low-value resistors in four of the lines). We do have a 70-6223, and I suppose we could rewire it - but I really really hate to do things like that. Frankly, I'd rather make some M908s. But I'd really like to find an original BC02X, if anyone has a spare in any length. Please contact me privately if you have one and would be interested in making a deal. Hey, we have some more M531 replicas.... Thanks -- Ian Ian King, Vintage Systems Engineer <iank at vulcan.com> Living Computer Museum A project of Vulcan, Inc. http://www.livingcomputermuseum.org