Heath H8 computer

This Web page last updated date Dec 31 2013.


This Web page is about my original H8 Heath computer. I acquired in 2005 an H-8 system and H-19 terminal. The owner originally purchased it in the late 1970's with upgrades in the early 1980's. I also have manuals and software for it, all from Heathkit. In 2009 I did some testing work on it. In 2013 I ran HDOS again.

Check my Heath/Zenith Web page for other Heath computers, and current information about the Heath company. If you have an H8 and a Web site, I'll consider adding a link here to your site. If you have H8 stuff to offer, let me know. For instance, I got in touch with Les Bird in June 2009: he's got some new H8 cards! Follow this link for details.

H8 systems

[Heath H8 system] [H17 floppy drives] The H8 is an interesting machine in many respects. Offered in 1978, it has an OCTAL display and keyboard, not a binary front panel like other 8080 machines. The motherboard is SIDE mounted, not on the bottom, and uses a pin and socket connector and not an edge connector. (The H89 used similar connectors for their I/O cards.) Cards are supported on the far end from the bus with a bracket and brace system. Here's a view of the brace on the end of the card, also a convenient heat sink.

A shorter-length bus than the S-100 means it can run a little faster. Soem people have souped up their H8's to several Megahertz. And, there are Z80 and other upgrade cards which were built for this system. But the original used a cassette board for audio cassette tape file storage, like the early H89.

[H8 cards inside] My machine has, from front to back:
the H8 front panel card
8080 CPU card,
8K static RAM card,
Trionix 48K DRAM card,
H8-4 Multi-port serial I/O card,
H8-17 floppy controller hard sectored board
address board. at the back of the bus.

Not in the machine, is the prior H8-5 I/O card with cassette and serial interface. Additionally, I acquired seperately a Mullen brand extender card - still as a kit!

[H8 test display]2009 Restoration of this H8

I started looking over the system, cleaning the docs up (mold on binders, organizing manuals) on Aug 20th 2009. With a few days work, it appears the H8 system (less floppy drive and boot tests) seems to be operating, with very little repair needed! The AC plug and switch needed to be cleaned, a UART chip was replaced. The displayed image is from a Heath test program entered from the octal keyboard, and displayed on the octal display.

On Sept 4th and 5th 2009, I looked over the H17 dual floppy drive cabinet and Tandon TM100-1 (single sided 40 track) 5.25" drives. Like the H8, the drive cabinet did not need any notible repairs or parts. The AC switch was dirty and needed cleaning to pass AC current. I used a Variac to slowly bring up DC power to the caps - no problem. The notes with the system said the left-hand drive had a loose docr: I pulled parts from another Tandon to fix that.

[H8 boots HDOS] I connected drives, computer and terminal; rooted through the box of diskettes to find an HDOS disk. With a bit of futzing, I got an HDOS prompt! It helped, that I had notes from the prior owner. He wrote up how to start up the system, when he boxed it up and put it away - in January 1989, twenty years ago! But I still had trouble with that other drive; the notes say he had to press the lower edge of the door, to get the drive to "light up". I removed the drive's circuit board, to reveal the head and motor mechanism. THere was not really a "disk detect" switch or sensor, but I figured the index hole sensor was used to confirm a disk was in place. I blew out the sensor and LED, and reassembled the drive. That seemed to solve the problem.

The system seems to work to a point, but crashes often. I need to find more test software! My guess is flaky DRAM, a common problem over decades, as DRAM chips and their driving circuits get "soft".

2013 H8 exhibit

In 2013, I was asked by a local computer club to exhibit an early "homebrew" microcomputer from 1975-1978. Now, I don't like the term "homebrew", it sounds like something amateur and not-quite-serious. But their point was to show early microprocessor-based computers bought by individuals. The H-8 was a great candidate. So I pulled the system out for test and revival. Look on my restoration Web pages for my H-8 work of 2013; and a general description of mid-1970's microcomputing by Heath.

H8 resources

H8 manuals

A computer of the late 1970's had many kinds of documentation, especially a user-assembled or "kit" computer like the H-8. Each board, and the H8 with front panel & power supply & CPU board, had an "assembly" manual and a "operation" manual. There were also software manuals; the H-8 over time had the front-panel software manuals, cassette OS manuals, HDOS manuals and CP/M manuals. Other peripherals, like the H10 paper tape and H9 and H19 terminals, had their own manuals. It adds up!

[H8 box o dox] 595-2014-02 H8 Operation Manual
595-2169-01 H8-17 Software Reference Manual (diskette), 1978: op system, BUG, EDIT, ASM, BASIC
595-2048-02 H8 Software Reference Manual: (cassette), 1977: Op system, PAM-8, BUG-8, TED-8, HASL-8, BASIC
595-2013-02 H8 Assembly, 1977
595-2028-01 H8 4K Static Memory H8-1
595-2033-02 H8 Parallel I/O Interface
595-2032-03 H8 Serial I/O and Cassette
595-1996-04 H9 Video Terminal Assembly
595-2017-03 H9 Video Terminal Operation
595-1970-03 H10 Paper Tape Reader/Punch Assembly
595-2020-02 H10 Paper Tape Reader/Punch
595-2161 H17 Floppy Disk Assembly, 1978
595-2160 H17 Floppy Disk Operation, 1978.

Ask for quote from me for good photocopies of any of these manual - no "scans". Other Heath and Zenith docs are listed on my Heath/Zenith Web page.

SEBHC and Les Bird

In a 2009 private email, Les Bird of the Society of Eight-Bit Heathkit Computerists (SEBHC) archive site alerted me to this organization and this Web archive. There is also a SEBHC Google group. He said: "I have several H-8 computers and H89 computers and a website that is, for now, the home of the SEBHC archive. In addition to many disk images and ROM dumps available on my website I also have several newly designed PCBs for the H8 computer that I offer to those who are interested." The boards are priced near cost plus shipping. The Google group dates from late 2007 and (for a old computer discussion group) is modestly active.

I obtained a board set from Les in June 2009. Many thanks! Here's my image of Les Bird's Z80 H8 cpu board, with his ROM. By August, we acquired the parts needed for them. Construction of those new H8 cards will be on my restoration and repair Web pages.

8080 cross assembler

In Dec 2013 I adapted an 8080/8085 cross assembler, written in C by William Colley, to run under Windows as a 32-bit command line (DOS window) program. Here's a Web page which gives details.

Herb Johnson
New Jersey, USA
follow this link to email @ me

Copyright © 2013 Herb Johnson