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- Heathkit 89A<\/li>\n
- Complete set of spare boards from H89A (different mb)<\/li>\n
- H17 Dual hard sectored 5 1\/4\u201d floppy drive<\/li>\n
- H77 Dual soft sectored 5 1\/4\u201d floppy drive<\/li>\n
- Box of hard & soft sectored disks.<\/li>\n<\/ul>\nI was really just after the H17 to go along with my H8, but $30 for all that? No brainer.
\nRay warned me that two caps popped on the main board,\u00a0 and indeed C508 & C515, 2.2u tantalum caps, failed violently.\u00a0 We’ve got to see what other damage they did; tantalum capacitors are like the suicide bombers of the electronics world.<\/div>\n![\"IMG_6388\"](\"https:\/\/paulcarbone.com\/blog\/wp-content\/uploads\/2016\/08\/IMG_6388.jpg\")
<\/a><\/div>\n<\/div>\nThey were replaced with 10u caps I had in inventory (close enough):<\/div>\n![\"IMG_6394\"](\"https:\/\/paulcarbone.com\/blog\/wp-content\/uploads\/2016\/08\/IMG_6394.jpg\")
<\/a><\/div>\n<\/div>\nI found Herb Johnson\u2019s 2016 adventures<\/a> in Heathkit H89 rebuilding while surfing around, and his page is a great reference.\u00a0 As I got a spare set of boards as well, I figured I’d first just swap them out.\u00a0 No go.\u00a0 The boards are slightly different, and that difference includes the power supply connectors.\u00a0 According to Lee Hart,<\/a> the key\u2019d power supply molex connector indicates a late-model H89A. \u00a0That would be the 2549 board<\/div>\n<\/div>\nI\u2019m assuming that also took out U585, a 79M12 and U565, (only have a heath part), as there\u2019s no -12V & +12V on the output of those regulators. \u00a0I also have a spare, earlier model board to compare with (and possibly steal parts from if I\u2019m impatient), but I\u2019m noticing more and more inconsistencies between the two boards, and with the documentation. \u00a0Here\u2019s where it gets (more) annoying:<\/div>\n<\/div>\nU515 is a 71M12C, your run-of-the-mill -12V regulator. \u00a0OK, terrific. \u00a0Same on the old board as well, and consistent in all docs I have.<\/div>\nU567 only has a heath part#, 442-674. \u00a0It\u2019s in parallel with U568, they both feed separate +12V supplies. \u00a0Here\u2019s where it gets squirrelly:<\/div>\n- \n
- In the docs, it\u2019s called out as part 442-663<\/li>\n
- The pinout labeling is different (common pin center, whereas board image & earlier board call common pin as the left one)<\/li>\n<\/ul>\n
Here’s the old board (85-2208-1) incorrectly marked pin-outs, but check out that sexy ceramic ram chip:
\n![\"FullSizeRender(2)\"](\"https:\/\/paulcarbone.com\/blog\/wp-content\/uploads\/2016\/08\/FullSizeRender2.jpg\")
<\/a><\/p>\nHere’s the documentation for the newer board, but the pin-outs are still mis-marked:
\n![\"FullSizeRender\"](\"https:\/\/paulcarbone.com\/blog\/wp-content\/uploads\/2016\/08\/FullSizeRender.jpg\")
\n<\/a><\/p>\nHere\u2019s what I\u2019m left to deduce, and can confirm after some metering:<\/div>\n- \n
- The earlier board silkscreen and artwork in my manual (for the later board) are both wrong for U567 & U568<\/li>\n
- U515, a negative regulator, indeed has it\u2019s common (gnd) on the left; it\u2019s input and output are swapped from positive regulators.<\/li>\n
- U567 & U568 are almost certainly 7812s (+12V regulators), as they are on the earlier board. \u00a0They are only silkscreened correctly on my newer board. \u00a0The new board artwork illustration, and the old board silkscreen are both incorrect.<\/li>\n<\/ul>\nGRRR\u2026.<\/div>\nOK, well U515 seems to be working well out-of-circuit, but there\u2019s almost no resistance between ground and it\u2019s output in the circuit. \u00a0Suspecting C509 & 511 next. \u00a0Lifted both, no dice. I\u2019ve got to be careful with the desoldering gun, the traces are easy to lift.<\/div>\nSo what else is connected to the -12V line? \u00a0Besides the 2 -5V regulators, and the card bus, I\u2019d imagine it\u2019d be the built-in UART used to communicate with the terminal board, since for whatever reason, it\u2019s full blown RS-232 between the two. \u00a0Yep, sure enough there\u2019s a quad EIA-232 driver. Nope, there\u2019s still a short with that removed.<\/div>\nSo it\u2019s the -5V regulators? \u00a0Nope. \u00a0Forgot about C513. \u00a0Yep, it\u2019s shorted. \u00a0It\u2019s always the last place you look…<\/div>\nNext up – replace the regulators and attempt to power up again.<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
I’m just jumping right in – I acquired the following from Ray (WA1FFT) in NJ. Heathkit 89A Complete set of spare boards from H89A (different mb) H17 Dual hard sectored 5 1\/4\u201d floppy drive H77 Dual soft sectored 5 1\/4\u201d … Continue reading
![\"IMG_6388\"](\"http:\/\/paulcarbone.com\/blog\/wp-content\/uploads\/2016\/08\/IMG_6388.jpg\")
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