LGP-30 Memory Drum Update

On Tue, 3 Jan 2017, Cory Heisterkamp wrote: We relocated some of the heads on our second LGP-30. This is not difficult. We put 3 or 4 layers of 3 micro-meter kitchen aluminium between head and drum. If I remember right, the distance is 12 micro- meter. Maybe, that we made a fine adjustment 3 or 4 layers with the oscilloscope, to get the same output voltage at the head, than the other heads. Maybe that 3 layers of 3 micro-meter Al have something more than 9 micro-meters. If I counted right on every head bar are 3 unused positions as spare tracks. > For kicks, I tried to use a piece of cheap (=thin) (0.004?) notebook paper > as a feeler gage to see if I could identify the offending heads prior to > support removal. This was a no-go as clearance was too tight. So, is it > true these ride 0.001? off the surface? The (german) maintenance manual whose scan is on our website speaks about 12 micro.meters. There are 64 data tracks, 4 timing tracks (including the main clock at the rightmost position) and 3 tracks for the registers. Most problematic are the timing tracks. If they are faulty, there is no simple solution to change the heads, because there is no provision to write them in the machine. If there are only few tracks defective, and not exchangeable, I would try to get most of them in the lower adress-room of the machine, and at least the last track. The first 3 tracks are used by the "operating-system", program 10.4, and the last track is used by the initial loader, that loads 10.4 itself. But timing tracks S1, S2, S3 and the registers themselves must be functional. If this is not, a semiconductor drum-emulator ist indeed the only solution. If you lift all the head bars 1 or 2 mm, then the drum can rotate even with this fake. Klemens > Any input is welcome. -C -- klemens krause Stuttgarter KompetenzZentrum fyr Minimal- & Retrocomputing. http://computermuseum.informatik.uni-stuttgart.de