Hi Jack
I worked on these years ago when I first started with HP. I remember these being only a few MB. They used an encoder glass to sync the head positioning. I think you needed an oscilloscope to align the heads. Can you send me some pictures? Does it spin up and the heads mount? The heads must be cleaned. We used a dental mirror to look up at them. Look for dirt on the edges. Clean with alcohol and a pad wrapped around a plastic flexible part that looks like a tongue depressor a doctor might use. Maybe you don't have to clean the platter. Good luck
Jim Maher
Saratoga Computers
888-999-7479
-----Original Message-----
From: HP-3000 Systems Discussion <[log in to unmask]> On Behalf Of Gary Robillard
Sent: Monday, November 23, 2020 6:08 PM
To: [log in to unmask]
Subject: Re: [HP3000-L] [EXT]: Fwd: HP 7900A drive maintenance
I’m sure you would need to remove the belt, it’s been almost 40 years though...I am pretty sure I have a 7900 head alignment tool... but it isn’t important for the lower platter... At least it had the optical encoder so no servo code to write like a 7905/6 lower platter...
Thanks,
Gary Robillard
Sent from my iPhone
> On Nov 22, 2020, at 11:13 PM, Stan Sieler <[log in to unmask]> wrote:
>
> External Email
> Jack Rubin ([log in to unmask]<mailto:[log in to unmask]>) writes:
>
> ---------- Forwarded message ---------
> From: Jack Rubin <[log in to unmask]<mailto:[log in to unmask]>>
> Date: Sun, Nov 22, 2020 at 9:45 AM
> Subject: HP 7900A drive maintenance
>
> Hello -
>
> I'm bringing a 7900A back online and cleaning it prior to spin up. I've renewed the foam gasket that feeds filtered air to the removable disc, but I'm not sure how to get to the fixed disc for inspection/cleaning. As part of the maintenance procedure, the manual says to clean the lower disc assembly. My question is how? HP says to "Remove the lower disc assembly." That's it - no further details.
>
> Can you provide any clues? It looks like there is a shield that may or may not retain the assembly but removing it seems to require removing the drive pulley. If it comes to that, is there anything special about mounting/unmounting the pulley (Loctite, torque spec, etc.)? Changing the pulley was clearly a field operation to allow for 50/60 Hz operation but again no details in the manual. I've also got the CE Handbook but no hardware specs there.
>
> Any thoughts or help would be appreciated. Any retired CE's around who might have more info?
>
> Thanks,
> Jack
> ----------
>
> If anyone can help him, that would be great!
>
> thanks,
>
> Stan
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