LGP-30 Update

[Cory Heisterkamp]

Hey guys, figured it was time for an update on the LGP-30 resuscitation. 

Some further detective work found a leaky 1500uF cap in one of the B+ supplies which was causing the 'surging' issue on the scope. For good measure I replaced all six 1500 and 3000uF caps even though ripple was low. Better safe than sorry and if it means pulling that chassis and its covers again, all the better. I attempted to weigh it on my shipping scale, but it only registers to 100 lbs and the indicator flew right past that. 

There had been a small thermal event in the AC junction box that the twist lock connector mounts to, and I suspect it occurred pre-60's refurb. It's not too surprising as the wiring on the computer side is aluminum and the feed is copper. The box needed replacing but was a unique Hubbell variation of a std 4" box with special ears. I couldn't find anything even close to that at any of the supply houses online, probably because it violates today's conductor fill rules (it's only 1" deep but the socket consumes most of that depth and 75% of the area). I eventually settled on drilling/tapping a standard box and cleaned up the wiring.

The sequencer unit is now working correctly after I found an NOS relay to R&R contacts with. The blower is still steady and quiet with its new bearings, and no issues (knock on wood) with the drum after greasing the end bearing, belt and 'tightening' up the tolerances on the timing and short register heads.

Some good news- I now have three horizontal lines on the scope, rock solid and where they should be. I can get the occasional pattern for Instruction contents, but Order and Accumulator still aren't reading/writing/displaying. All in good time.

http://radar58.com/LGP30/wp-content/uploads/2017/03/lgp.jpg

Even better news is that the three timing tracks appear to be intact on the drum and the supporting hardware is working.

http://radar58.com/LGP30/wp-content/uploads/2017/03/scope-e1489957963176.jpg
(1, 2 and 3 correspond to S1, S2 and S3)

Now to investigate those short registers...  -Cory