I had an eMac with an 820-1798a board, which worked great...until the flyback blew. It was a good board, and overclocked well.
I had it booting as a headless eMac following lbodnar's site. Note that later developments meant that the downconverter isn't strictly required, but I had it set up with downcoverter, providing 12v, 5v and ground through the blind mate connector and grounding the DCO line.
At some point, while trying to configure the VGA out, I accidentally budged the blind-mate connector, there was a spark. I believe the firewire "19v" (actually 12v in the above configuration) hit the 5v line, as I'd assume ground would arc but not cause big problems. From that point, the board would still power up, but not startup chime. The CPU does get warm, and I verified voltages supplied to the board are correct. There is no visible damage to any component, and a somewhat random check of transistors and mosfets attached to the 5v blind-mate lines doesn't show anything shorted. All board fuses and fusible links are intact.
I have another eMac (call it eMac B), which boots but has swollen caps. I swapped the above (Emac A) board into this otherwise working eMac B, the folowing things happen: the power light comes on and the CRT is energized. Still no chime, but the light is on solid (it will blink if I remove the ram). The fan does not spin, and drives do not spin-up. The power button works as expected, holding it will shut the board down, including the LED.
I don't have a schematic, but it seems similar enough to other schematics I've seen around the PMU and boot up logic. I suspect the PMU is unable or unwilling to power up the rest of the board, including sending the signal to the downcoverter to enable the ATA power. I am not 100% sure of this, but it's my best guess, possibly the PWR_FAIL or similar circuit is broken?
Looking for recommendations or schematics, I suspect this will require component level repair, but I do have another eMac motherboard here as a donor if necessary. I am comfortable doing board-level work at this size. Interested to see if the above symptoms might indicate specific components to check next.
I had it booting as a headless eMac following lbodnar's site. Note that later developments meant that the downconverter isn't strictly required, but I had it set up with downcoverter, providing 12v, 5v and ground through the blind mate connector and grounding the DCO line.
At some point, while trying to configure the VGA out, I accidentally budged the blind-mate connector, there was a spark. I believe the firewire "19v" (actually 12v in the above configuration) hit the 5v line, as I'd assume ground would arc but not cause big problems. From that point, the board would still power up, but not startup chime. The CPU does get warm, and I verified voltages supplied to the board are correct. There is no visible damage to any component, and a somewhat random check of transistors and mosfets attached to the 5v blind-mate lines doesn't show anything shorted. All board fuses and fusible links are intact.
I have another eMac (call it eMac B), which boots but has swollen caps. I swapped the above (Emac A) board into this otherwise working eMac B, the folowing things happen: the power light comes on and the CRT is energized. Still no chime, but the light is on solid (it will blink if I remove the ram). The fan does not spin, and drives do not spin-up. The power button works as expected, holding it will shut the board down, including the LED.
I don't have a schematic, but it seems similar enough to other schematics I've seen around the PMU and boot up logic. I suspect the PMU is unable or unwilling to power up the rest of the board, including sending the signal to the downcoverter to enable the ATA power. I am not 100% sure of this, but it's my best guess, possibly the PWR_FAIL or similar circuit is broken?
Looking for recommendations or schematics, I suspect this will require component level repair, but I do have another eMac motherboard here as a donor if necessary. I am comfortable doing board-level work at this size. Interested to see if the above symptoms might indicate specific components to check next.