Capacitor values for original PET power supply?

Josh Dersch derschjo at msu.edu
Tue May 20 22:13:12 CDT 2008


> ----------Reply:
>
> Well, if it were mine I'd clean it up and figure out what's what and how to use
> it instead of returning it to the boring "original" spec.
>   
I plan to use the Expandamem board (once I get the basic machine 
running) but the hacked up stuff is ugly (and falling apart -- hot glue 
doesn't work so well in the place of solder).  The prototype board with 
the EPROMS is all wired together on the bottom and tons of them are 
dangling loose at this point :).  It could be repaired, but I'll wait 
until I'm feeling really ambitious before I take that one on.

> Don't know why you need to replace the cap or rewire the transformer, but 
> FWIW the original cap is 23,000 at 15; presumably it was increased to deal
> with the increased current required by the extra boards. Don't know specs
> for the transformer but it and the wiring look stock as far as I can see aside
> from being heavier than the original so I don't see why you'd need the specs.
>   
I mostly need to replace the capacitor because as it is, if I ever do 
find an original cassette drive for this thing, it won't fit with that 
huge thing in place :).  That and I'm afraid of what a capacitor like 
that might do if it dries up/shorts out.  The wiring needs to be redone 
in places because a significant portion of it was hot glued/electrical 
taped together (not entirely obvious from the photos) and it's since 
fallen apart. 

> FWIW, there should be 5 secondary terminals: 7 & 8 are the AC supply for 
> the monitor, 5 is ground, and 4 & 6 are the two ends of the 8-0-8 secondary.
>   
Thanks for the info.
> The EPROMS may be interesting; there were a number of monitors, utilities
> etc. supplied in EPROMs, and some disk/tape software packages also used
> EPROMs for extra memory and copy protection; at least some of those 
> switches will be for selecting the EPROM to use. Dump 'em if you can;
> they may be rare/useful.
>   
I've dumped them, see http://yahozna.dyndns.org/computers/pet/ if you're 
interested.
> If the keyboard isn't an obvious hack, i.e. if it fits the case and has the PET
> graphics characters, it may be original; only the early models had the chiclet
> keys and integrated tape drive.
>   
It's an obvious hack, though it's the one modification that's done 
fairly well.  It's mounted on top of the case above the mounting holes 
for the original cassette drive & keyboard.  Unfortunately someone 
spilled glue on it at some point :).

Thanks again for the info...
Josh
> mike
>
> m
>
>
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