Heathkit/Zenith H/Z-100

Heathkit/Zenith H/Z-100 system

H-100 low profile. Dual half height, 5 MHz cpu, 763 KB memory, color 64 KB video.

H-100 low profile backside.

H-120 All-In-One. Dual half heigh floppies, 5MHz cpu, amber monitor, 763 KB memory, monochrome 32 KB video.

H-120 All-In-One backside.

H/Z-100 description from the Christmas 1985 catalog.

Heathkit H-100/Z-100 Boards

This is the H/Z-100 motherboard first revision 85-2653-1. It is highly modified for 256K chips, 8 MHz, 8087 math coprosessor.

Backside of the highly modified 85-2653-1.

This is the newer revision of the H/Z-100 board. It is 85-2806-1 with 64K memory chips and 5MHz clock.

This is the newer revision of the H/Z-100 board. It is 85-2806-1 with 256K memory chips and 8 MHz clock.

Heath/Zenith H/Z-100 64K video controller.

Video controller backside.

Dallas clock chip under the EPROM. This was sold by Zenith as the Smart Watch. See manual list for it.

Another view of the clock chip.

The highly modified motherboard uses the CDR Incorporated Z100 Speed Module, ZFM memory modification and Easy87 module. It is interesting to note that the ZMF memory upgrade was done without the aide of a new PAL in U111A or elsewhere. The Heathkit modification kit HA-108 used new PALs in several spots. I have included all relevant speed and memory upgrade articles from several issues of REMark in PDF format including the HA-108 upgrade.

The 85-2806-1 came in 2 versions. The first was a 5 MHz motherboard using 64K chips for a total of 192K while the second version was 8 MHz using 256K chips for a total of 768K. You can easily convert the new style board to 256K chips by changing the PALs at U110, U111A and U173. The problem, of course, is that these PALs are no longer available. I am working on this problem and as soon as I have a supply of N82S137N chips I will make extra PALs for U111A. Converting to 8 MHz takes a little more effort. I have a comparison PDF file showing the chips used on all 3 versions of the motherboard.

Heathkit/Zenith S-100 Boards

Heathkit Winchester disk controller 85-2819-1.

Heathkit data sepearator. This must be used with the 85-2819-1 S-100 board.

Cabling configuration.

Another view of the cabling configuration.

Heath/Zenith 8" & 51/4" floppy disk controller.

Heath/Zenith 8" & 51/4" floppy disk controller backside.

	Software Wizardry 8 MHz upgrade manual
	"The Z-100 Survival Kit" a collection of 13 articles from REMark magazines, 37.5 meg PDF file.
	REMark articles on installing and using the NEC V20 chip, 5.5 meg PDF file.
	H/Z-100 Manuals