bstnguy
Well-known member
Board #1
No acid damage.
Boots up on bench w/ATX switcher & adapter , Self Test fails various 2116 RAM.
Fluke 9010a passes Bus Test, correctly reads ROMs, correctly reads other RAM, doesn't see
2116 RAM.
Test ATX PS and no -5VDC. (2116 needs -5VDC to work)
Switched to Switcher w/adapter. 100% passes Self Test.
Board #2
Slight acid damage to 4 traces, cleaned up.
Blew tantulum cap clean off the board. Replaced with electrolytic.
Blew next tantulum cap clean off the board. Replaced with electrolytic.
Switcher now shuts down.
Scratched head. Hmmmmm.....
Ohmed GND to +5VDC, high ohms, okay.
Ohmed GND to -5VDC, high ohms, okay.
Ohmed GND to 12VDC, zero ohms. Not good.
Ohmed tantulum caps on 12VDC rail and found one dead shorted.
Replaced with electrolytic.
100% passes Self Test
Board #3 (in process)
No acid damage.
Locks up on bench w/switcher & adapter. All voltages good. Won't enter Self Test.
Fluke 9010a passes Bus Test, incorrectly reads ROMs, all RAM failed RAM Test 0000-7FFF, 8000-83FF, 9000-93FF, 8400-87FF.
Replaced socketed 74LS245 U69. Now correctly reads RAM 0000-7FFF, 8000-83FF, 9000-93FF. 8400-87FF failes RAM Test.
Both chips are good, all the traces are buzzing out correctly from the IC leg to it's destination IC leg. The 8400-85FF isn't writing anything and reading FE for all locations, and the 8600-87FF is writing 55 and reading back 54 (dropping the last bit).
Will post when I figure this one out. I'm leaning towards a bad data buffer someplace.
No acid damage.
Boots up on bench w/ATX switcher & adapter , Self Test fails various 2116 RAM.
Fluke 9010a passes Bus Test, correctly reads ROMs, correctly reads other RAM, doesn't see
2116 RAM.
Test ATX PS and no -5VDC. (2116 needs -5VDC to work)
Switched to Switcher w/adapter. 100% passes Self Test.
Board #2
Slight acid damage to 4 traces, cleaned up.
Blew tantulum cap clean off the board. Replaced with electrolytic.
Blew next tantulum cap clean off the board. Replaced with electrolytic.
Switcher now shuts down.
Scratched head. Hmmmmm.....
Ohmed GND to +5VDC, high ohms, okay.
Ohmed GND to -5VDC, high ohms, okay.
Ohmed GND to 12VDC, zero ohms. Not good.
Ohmed tantulum caps on 12VDC rail and found one dead shorted.
Replaced with electrolytic.
100% passes Self Test
Board #3 (in process)
No acid damage.
Locks up on bench w/switcher & adapter. All voltages good. Won't enter Self Test.
Fluke 9010a passes Bus Test, incorrectly reads ROMs, all RAM failed RAM Test 0000-7FFF, 8000-83FF, 9000-93FF, 8400-87FF.
Replaced socketed 74LS245 U69. Now correctly reads RAM 0000-7FFF, 8000-83FF, 9000-93FF. 8400-87FF failes RAM Test.
Both chips are good, all the traces are buzzing out correctly from the IC leg to it's destination IC leg. The 8400-85FF isn't writing anything and reading FE for all locations, and the 8600-87FF is writing 55 and reading back 54 (dropping the last bit).
Will post when I figure this one out. I'm leaning towards a bad data buffer someplace.
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