HP7879B tape again

[Tony Duell]

> 
> Hi,
> 
> > I asusme there's nothing of use on http://www.hpmuseum.net/ ?
> Don't think so.... :-(
> 
> >>But I still and urgently need the schematics for the 7978 drive. My
> > I sould be suprised if any published manual contained full schematics.
> For the 7970 tape drive there ARE the full schematics on bitsavers... So 

That's interesting... I will take a look.

> I think it should be possible to get the complete 7978B docs, too.

Hmmm... I've found some HP manuals contain schematics, some for 
closely-related devices do not.  And before you ask, I don't have any 
'large' HP tape drives, so schematics will not be appearing on the HPCC 
CD-ROM.

> 
> > By that period, HP comptuers were 'repaired' by board-swapping. If you're 
> > lucky there will be _some_ useful info in the boardswapper guide, like 
> > pinouts or testpoints.
> You are too pessimistic :-) I hope to find good documentation of 
> everything I need.

I've found it often takes less time to trace out schematics than to play 
telephone tag round the manufacturers only to be told they're not 
available. It's certainly less stressful and more interesting (and you 
learn a lot more about the device).

> 
> > 
> > I hate to say this, but you may be reduced to producing your own 
> > schematics. It can't be that difficult, I've managed to do it a few times.
> But there is one small problem: I don't have the time to do that for an 
> old switching power supply. And by the way I'm not very good in 

If I can manage the 9845B supply, you can do this one :-). 

> repairing switching power supplies. These devices scare me a bit.....

Well, they're not too bad when they're turned off. I would check the 
mains smoothing capacitors (likely to be a couple of 200V units at a few 
hundred uF's each) with a voltmeter to make sure they're discharged 
before diving in.

-tony