Mike's PCjr Page

Will do,

I will definitely buy one. Please add me to your list.

Chuckphd53 wrote:UPDATE;

I have reviewed the schems and data sheets and I am confident that my board is installed correctly, and that it was initially built with the U1 and U2 swapped.

So with that I will finish the PC-Sprint layout....

But I am still hoping someone will share some pictures of their PCJR PC-Sprint board, top and bottom and installed if possible...
I know its a pain....

lastly has anyone tried anything besides the 22.1Mhz crystal, D. Severson in his docs talked about trying over speeds, would like to know what if any results were gathered.


chuck

https://1drv.ms/u/s!AqVrKLbX9W2f31DZ-8_9aWfyyLIq

Maybe you no longer care, but here's a board I made a while back using the D. Severson schematic. I've used exactly the parts he specified, all I changed in the board layout is the position of the motherboard connection vs. the two DIPs, just as you noted below.

This works perfectly, I've tried a few different crystals and speed just scales accordingly. I get a score of 7 in topbench with the 22.1184MHz crystal, and an 8 with a 24MHz crystal. Jumpman and Loderunner are un-playably fast

Nice!

Desolder the 8088 and replace it with an NEC V20 if you want to get that up to a score of 11 or 12.

I plan on getting back on this project, but life has interrupted...

I want to review the schematic once more before I make boards...

bagelswitch, if you have a schematic I can cross reference with the one I have.
i think the IBM design vs the IBMJr is different at least that is what I remember the chips are on different sides...

but I will review and get this going again..

Chuck

Let me review this and get some feedback....

The original design from Douglas Severson 11/85 was for the IBM 515x series platforms...
Let's look at the issue I am having with moving this to the PCJR platform.
Follow my comments below at each picture, ( if you are interested )

First: This is an original board from Douglas Severson that I have.
I built this board exactly as instructions indicated,
NOTE: you can see that IC2 is where it plugs into the IBM 515x series platform



Looking at the original AD for the board you can see that the install 'header' is actually in IC2 position.




Using this board on the JR will not plug in correctly, as it interferes with the DISK DRIVE frame holder, as you can see below.
I don't have a picture showing the original board plugged in, but you can see that if shifted over to IC2 it will move the board
'ON TOP' of the disk drive hole.
(Below is a picture of Bagleswitch's PCSprint board install from an earlier post, this shows the hole in the mother board
that the DiskDrive plastic leg snaps into the hole
SO: the only way to install the original design for the IBM515x is to use the IC1 position with headers.
This is NOT how the original design was intended.



These are the schematics I've redrawn from the originals, but the PCB still suffers from the incorrect placement of the socket to mother board placement. I need to spend time and review this and move IC1 and IC2 positions correctly after I understand the design better.
this will just take my spare time...




SO: To sum this up.....to fit the original design into the PCJR and not have the interference with the disk drive hole,
IC1 and IC2 need to be swapped on the PCB for proper interfacing the PCSPRINT board to the PCJR mother board socket.

NOW: I have just swapped the header and chip on the original board to make it fit in my PCJR, and YES it seemed to work...
I need to examine the schematics in detail ( I have not had time yet ) to understand why this seems to be working !.
I also did the TOPBENCH testing with the board installed but also had the V20 installed which also gave it a POP in performance.

I still plan on running a batch of these boards for the forum folks soon, but want to get this right before I have 100 boards made up.

So apologies for the delay, as I mentioned Life has interrupted my play time, but hope to get back some time soon..
If you gotten this far..... Thanks for the patience.
Chuck


here is clipping from Doug Severson back in the day describing the PC Sprint ! (unedited )

1. DESCRIPTION

PC-SPRINT is a low cost ($25 - $50) speed up for the IBM PC/XT that
you can build yourself. It can achieve processor performance increases
of up to 2 times normal, does not use an expansion slot, doesn't make
any permanent changes to the computer and maintains software
compatibility without restrictions. As an additional bonus, it adds a
true hardware reset - no more "keyboard lockup".

PC-SPRINT is also an experiment to determine if hardware designs
can be placed in the public domain, as a type of "freeware", and be
distributed by electronic means only. This package contains all the
information needed to build PC-SPRINT, including instructions,
schematics, part placement diagrams, and precision artwork from which
a printed circuit board can be made. Although this sounds rather
formidable, PC-SPRINT should be within the capabilities of the average
electronic hobbyist. I would appreciate your comments on this project,
and the experiment in general. You are welcome to send me a note at
the following address.

Doug Severson
7431 W. Southview Dr.
Franklin, Wi. 53132
2. CAVEATS

As an old "hardware hacker", I consider this project simple and
straight forward - but that's easy for me to say. If you feel nauseous
at the mere thought of removing your PC's cover, pass this up or get
help. Maybe your user's group could arrange to have some made at
reasonable cost.

The claims made here are real - this package was done on a PC
running an 8 megahertz (mhz) V20 processor at 7.37 mhz. The actual
performance increase provided by PC-SPRINT depends on what your
particular computer can handle, and on choice of processor. In my
case, the faster clock provides a factor of 1.55X (7.37/4.77); the V20
is variously rated at 1.1 to 1.4X over an 8088 at the same clock,
giving an overall factor somewhere between 1.7 and 2.1X.

Unfortunately, a 7.37 mhz clock, with no "wait states", pushes the
PC's design to its limit. Your particular setup may not be capable of
full speed, but with a simple component change to PC-SPRINT (explained
later), you can find your machines maximum. If your PC has a 5 mhz
8087 (number cruncher chip), it must also be replaced along with your
original 8088.

If you do decide to give this a try, check one very important
detail before committing any time or money - PC-SPRINT depends on
replacing the PC's 8284A clock IC with a circuit board - on most PC's
and XT's I've seen, this chip is socketed and easily removeable.
However, this is not true for all machines. Using the directions given
in the installation section, open up your PC, locate its 8284A, and
make sure it is in a socket. If not, you must unsolder it from the
motherboard and put a socket in its place. This isn't too difficult,
but may not worth the effort.

here are links to all the above pic's if desired:
http://www.linearlogix.com/PCJR/PCJRSPR ... NT1SML.JPG
http://www.linearlogix.com/PCJR/PCJRSPR ... NT2SML.JPG
http://www.linearlogix.com/PCJR/PCJRSPR ... INTAD2.JPG
http://www.linearlogix.com/PCJR/PCJRSPR ... RINTAD.JPG
http://www.linearlogix.com/PCJR/PCJRSPR ... NTHOLE.JPG
http://www.linearlogix.com/PCJR/PCJRSPRINT/CT1.JPG
http://www.linearlogix.com/PCJR/PCJRSPRINT/CT2.JPG
http://www.linearlogix.com/PCJR/PCJRSPR ... EMATIC.JPG

Trixter wrote:Nice!

Desolder the 8088 and replace it with an NEC V20 if you want to get that up to a score of 11 or 12.

I'm using this w/ a V20 already (a -16, but the floppy controller (I think) isn't happy with anything above 8MHz)

Chuckphd53 wrote: (Below is a picture of Bagleswitch's PCSprint board install from an earlier post, this shows the hole in the mother board
that the DiskDrive plastic leg snaps into the hole
SO: the only way to install the original design for the IBM515x is to use the IC1 position with headers.

My board _just_ clears the drive support leg in the front, the fan shroud in the back, and the side of the case on the right. There's really no other way these components could be placed above the the existing 8284 location without obstructing anything, so that's what I did. I followed the Severson schematic exactly, only swapped the part locations in the physical layout (and let Eagle figure out the trace routing, I'm a novice) - I'll share the schematic and layout files I created somewhere later this weekend.

That is exactly what has to be done to work in the PCjr, so I can understand why yours works well...

The original I have seems to work with the wrong chip position plugged in,,, hmmm

I have re-layed out myboard an will get some units in for testing..
I will post the results when I achieve this

I wonder how many folks are comfortable removing the original 8284 chip from their mother board?



chuck

I'm not great at desoldering; a dedicated desoldering station would make that much better but for now I use a copper braid and a plastic plunger-style solder sucker.

The case plastic is more of a problem; removing the motherboard involves dealing with some brittle plastic. That part is not thrilling.

BTW, excellent write-up ...