LGP-30 Memory Drum Update

[Cory Heisterkamp]

On Tue, Jan 3, 2017 at 1:47 PM, Brian L. Stuart <blstuart at bellsouth.net>
wrote:

> On Tue, 1/3/17, Cory Heisterkamp <coryheisterkamp at gmail.com> wrote:
> > What I’m wondering is if anyone is familiar with the setup/adjustment
> > procedure for getting the heads set correctly. There *might* be a couple
> of
> > unused tracks I can relocate heads to, but my thought is that if half a
> > dozen heads were already in contact, then the rest may be perilously
> close
> > as well (swelled drum?). My odds of setting 71 heads perfectly on a 50
> year
> > old worn drum is…well…not great.
>
> A while back I read a procedure (probably in reference to the G-15).
> Quite frankly, it scared me a little, but I'll pass it on.  The idea is to
> use sound.  The tech would use a screwdriver as a sounding bar
> between the casing and his ear.  Then the head was tightened down
> until you could just hear it start to brush.  I don't remember for sure,
> but I'd have to think that you would then back off just enough for
> the brushing sound to stop.  I don't recall whether the article said
> that this was done with the motor running or the drum was being turned
> by hand, but if it were my machine, I'd set the heads turning the drum
> slowly by hand and then check for any brushing sound when the motor
> comes up.
>

This sounds believable (but scary). With the 64 main heads out of the way,
I pulled out a mechanic's stethoscope last night and carefully rocked with
the drum back and forth listening to the recirculating register heads. One
may need backed off just a little, but the adjustment screws are a little
crude.


>
> Whether or not the drum is restorable, I'd still plan on building a drum
> simulator.  That way you can get the rest of the machine up and
> running without stressing or depending on the drum too much.  Plus
> if the drum does turn out to be unrestorable, you'll still be able to
> run the rest of the machine.  As to how to approach the simulator,
> I would have to think a C.H.I.P. or a Pi would have plenty of horsepower,
> especially if you drop Linux and either run on the bare metal or
> as an in-kernel driver in something lighter weight.
>
> BLS


Once I can make sense of the timing tracks, I think I'll proceed with this.
Not sure how I feel about using a micro-based solution though. Just seems
wrong : )   -C

>