A4000DCr CF IDE adapter not booting, activity LED on adapter constantly on

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@tbtorro

Symptoms: IDE activity LED on the CF adapter constantly on, even if the motherboard itself is powered down (with IDE CF powered with external PSU). IDE booting intermittent. After about 30 seconds the IDE activity LED on the CF adapter would go half bright (with motherboard still powered off), at this point if the motherboard is powered on CF IDE devices would boot, but traditional IDE HDDs still would not function and would even prevent motherboard boot (going to KS screen).

Cause: Faulty U311 (7407 open collector buffer chip as LED driver), possibly damaged by plugging in IDE device ribbon cable connector missaligned or reverse.

Explanation:
Possibly internal short on the 7407 chip pulling the IDE activity LED pin low (p39 on the IDE header). Pin 39 according to ATA-1 standard is connected to signal DASP (Drive Active Slave Present), if this signal is constantly pulled low during boot then the CF logic might interpret this as a slave drive (Drive 1) is present, and would wait 31 seconds (following the ATA-1 standard) for valid command from the (non-existent) slave drive. After which the logic would “recover” and Drive 0 would function as normal until the next power cycle on the CF IDE adapter.