other SS-50 or SWTPC boards

other SS-50 or SWTPC boards

This page last updated Sept 28 2024. It covers a number SS-50/30 bus boards, from SWTPC and others. My Web page on my STWPC 6800 system recieved 2010 is at this link. When I work on it again, I'll update that Web page. Also, look at all my 6800/6809 work on a page of Web links.

What restarted my interest? In 2023-24, my friend Neil Cherry got me interested in 6800 again. This new work began in June 2024, including reviewing some boards obtained in the last several years. - Herb Johnson

MP-A board de/repopulated

In June 2024 I had an opportunity to buy another MP-A board at a low price. It needed many chips and had old-school sockets, even Molex-pins. But the price was good and I obtained it. Now I'm populating it with all the odd TTL and 6830-substitute I can scrounge.

sockets and ICs: So the board itself looked OK, the sockets in OK shape. I removed the Molex IC pins and decided to use other old IC sockets for consistency. On replacing the IC's, I'd forgotten how many of them were not ordinary 7400 series chips: some are 74L. Here's the parts list from the manual, and here's a typical MP-A board (not mine).

tristate buffer substitutes: Checking these non-7400 parts against the list, they generally match. But a set of tristate chips don't match. The list says "IC-5, IC-6, IC-7 DM8097 Hex Tri-State Buffer". The photo shows "SN74367". I turned to the schematic, and some old IC data books, for guidance. I found a variety of tristate hex buffers would work. Why? Because the MP-A ties together the pair of enables for the (2 X 3) non-inverting buffers. So an 8097 or 8095 would work. The corresponding 7436X parts are 74367 and 74365. I had some 74367's on hand, so I used those.

Other odd parts I had on hand, were the 74H00, 74H08, 74L04 (I used LS04), 74366 (I used a 74LS366, some 74366's are on order), 7420 (I used 5420, a ceramic version). The 8835's (quad transceiver) I have from old stock or pulls. Also I had a stock of the Motorola parts, the 6800 and 6810 and 14411 (baud rate generator). Here's a layout (negative) photo of my repopulated MP-A to show the part numbers. A true-color photo of my "new" MP-A is here, and the back is shown here.

The 6830 ROM is a special part. These are custom Motorola ROM chips from the factory. The original 6830 for the MP-A was a 512 byte MIKBUG ROM modified to use the MP-C serial board. But later, SWTPC offered a 1K byte SWTBUG ROM. Here's the update document. That called for a wire mod on the MP-A to enable the extra address bit. Look at the back of this MP-A near the SS-50 connector. See the soldered wire? That's the mod.

I thought "I'm not gonna find a SWTBUG ROM." Holley's Web pages suggest building a 6830 to 2716 ROM adapter board. I thought I'd go that route and update this Web page. Well, my good friend and colleague Jon Chapman offered me a STWBUG ROM when I mentioned this work! by mid-July 2024 it was in my hands! - Herb Johnson

MP-A board no chips

Sometime ago, I acquired a SWTPC MP-A card, chips all pulled. The sockets are the usual old TI and other brand low-profile sockets. As they don't look particularly damaged, least effort suggests I try to use the old sockets. As I am working on another MP-A card in mid-2024, I'll put this one aside. - Herb, July 2024

Other SS-50 SS-30 cards that need review & work

Several years before 2024, I obtained a box of some SS-50 circuit boards. "In for a penny, in for a pound." So I've at now, at least, photographed and documented them as follows.

Here's the back of the DSD 16K card. It came with the simplest of manuals, and here's the PDF of that. I have six or so of these cards. They use 2114's which are very common, most of the other chips are common (not all).

DSD made a number of SS-50 SS-30 products. Here's their catalog.

A SWTPC MP-S serial card, bare board. SouthWest sold bare boards so these appear from time to time. I have only one bare board. This I may rebuild sooner.

A NewTech audio card for SS-30. Looks complete. Here's a back view and a closeup of the back legend which says "Model 68 REY B P-4001 / copyright 1977 / NewTech Computer Systems / All rights reserved". I'll see about getting docs for it.

NewTech Computer Systems of Brooklyn NY, made a number of microcomputer products for S-100 and SS-50. I believe they had a board like this one for the S-100. Here's an archive of NewTech documents. the July 1978 newsletter dewscribes use of the "model 68" music board. Otrher documents on site are about the S-100 version.

I was pleased to find, my late colleague Bob Armstrong of Corsham Tech, recreated the NewTech music board. Details (Eagle PCB files) on his github site. I processed his Eagle files into this schematic and parts list.

Another person breadboarded the music circuit on "long branch never" Youtube channel to demonstrate his SWTPC 6800 system.

Here's the component side of the card and and the back of the card. Brand is not clear. It seems to be a +5 and +12 power supply with simple circuits. I'll draw them out later. More likely this is useful for small 5.25 inch floppy drives.

In Sept 2024 I acquired a SSB Smoke Signal (Broadcasting) 16K RAM board. I see it uses MM5257 4KX1 SRAMs. The TI equivalent is the TMS404. It's a simple 1-bit in, one-bit out static RAM with chip-enable and write-enable controls. Here's the SSB manual. More news when I work on it. - Herb

Copyright © 2024 Herb Johnson