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Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 3:08 am
by Jeff
Aa part of my C4P Replica, described here: viewtopic.php?f=3&t=413,

I am building up a 502 CPU board.

Does anyone know how to configure the Monitor Rom Selects at U15? I have searched for documentation and cannot find any.
Monitor Rom Selects.png
Monitor Rom Selects.png (1.29 MiB) Viewed 173133 times

EDIT: Found my answer in an earlier post: viewtopic.php?t=327

/Jeff

Re: Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 4:05 am
by Jeff
Here is a layout I have created.
502 Layout small.jpg
502 Layout small.jpg (1.44 MiB) Viewed 171571 times
[REVISED to show R74, missing trace, and needed mods and jumpers.]

/Jeff

Re: Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 10:51 am
by waltermixxx
Damn I soldered in my 24 pin sockets last night before this post, what are the mods with the little x and gray wires?

Re: Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 2:36 pm
by Jeff
To use 2716's in 502 board

U6
1 cut trace between U6-18 and U6-21 topside
2 connect U6-18 to U5-18 on bottomside

Above U7
3 cut bridge at W4 topside
4 connect center of W4 to other position (gnd)

Above U9
3 cut bridge at W8A topside
4 connect U9-18 to U8-18 on bottomside

U17
6 remove U17 (74LS04)
7 add jumpers on U17 socket
3-4, 5-6, 8-9, 10-11, 12-13

Layout:
502 Board 2716 Mod.jpeg
502 Board 2716 Mod.jpeg (1.05 MiB) Viewed 173120 times
Instructions:
502 Use 2716 Eproms.pdf
(30.56 KiB) Downloaded 9198 times

An earlier post on this topic: viewtopic.php?t=111

/Jeff

Re: Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 10:31 pm
by waltermixxx
Thank you for the added details on it, very much appreciated. :) (and the PDF)
Looks like I will either have to take my board to my buddies place who has a vacuum type desoldering station and try and remove the 24 pin socket, or drill a hole in the Augot socket, over the cut, and cut the exposed (hopefully) track. (the 24 pin socket is one of those solid sockets.)

I'm worried about the de-soldering station, as the machined pins will be making contact with the top of the pad it rests on, so I dont think the socket will pop off. grummble grumble. :)

Re: Building an OSI 502B CPU Board

Posted: Tue Apr 02, 2019 11:56 pm
by Jeff
You could lift the leg of pin 18 out of the socket and tack a jumper to it.

Or build a socket adapter: Plug the eprom into the adaptor, and the adaptor into the U6 socket.
2716 Adaptor1.png
2716 Adaptor1.png (1.55 MiB) Viewed 173109 times
2716 Adaptor2.png
2716 Adaptor2.png (432.09 KiB) Viewed 173109 times
/Jeff

Re: Building an OSI 502B CPU Board

Posted: Wed Apr 03, 2019 2:11 am
by Jeff
My progress so far.
C488A37A-C4D9-4384-B0A1-A7D33ABB81BE.jpeg
C488A37A-C4D9-4384-B0A1-A7D33ABB81BE.jpeg (617.92 KiB) Viewed 173104 times
/Jeff

Re: Building an OSI 502B CPU Board

Posted: Thu Apr 04, 2019 3:38 am
by waltermixxx
here is my progress thus far, i was able to cut the track under the socket by dremeling out an oval,
and cutting the track. It's not too pretty, but you wont see it with the roms on board. :)

if you prefer I start my own thread on the 502 I can :) sorry to but in, let me know and I will delete this post
:)


IMG_0236.jpeg
IMG_0236.jpeg (1.35 MiB) Viewed 173097 times
IMG_0235.jpeg
IMG_0235.jpeg (770.92 KiB) Viewed 173097 times

Re: Building an OSI 502B CPU Board

Posted: Thu Apr 04, 2019 5:25 am
by Jeff
It’s all good Walter, feel free to post πŸ˜€πŸ˜ƒ. Makes a more complete story πŸ‘πŸ»

Well done on the cut trace. Just needs a band-aid now.

/Jeff

Re: Building an OSI 502B CPU Board

Posted: Thu Apr 04, 2019 5:35 pm
by waltermixxx
As a dentist, i should fill that hole.

But alas I am not a dentist....

perhaps I will even out the hole a bit and then3d print a plug or "filling".

if I do, I will post pics. :)