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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 (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 (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 (1.05 MiB) Viewed 173120 times
Instructions:
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 (1.55 MiB) Viewed 173109 times
- 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 (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 (1.35 MiB) Viewed 173097 times
- 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
Itβs all good Walter, feel free to post
. Makes a more complete story
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.