Auto Delay Your Boot Time

 

I too have recently been struck by this bug after a recent graphics card upgrade. My once rock steady KT7aR/1400 T'bird system has started failing to boot. Requiring a hard reset after power up to correctly boot. The upgrade was only a minor GF2 to GF2 Ti. but this was enough to cause the problem. Although this doesn't prevent the PC from working, it is irritating if you forget to press the RESET.

The problem appears to be caused by a failure of the PSU to cope with the current surge demand of the system when powering up from cold. Although I have not investigated the exact cause thoroughly, my guess is the motherboard is starting its initialisation before the PSU rails have settled within spec, and thus not correctly initialising. Symptoms I have seen first hand on different systems are a total failure to boot, booting through the BIOS but freezing as Windows starts and also appearing to boot and then locking up or rebooting as Windows loads the video drivers. If you suffer from any of these symptoms and yet pressing the RESET button for several seconds after powering up the system, the PC boots and runs normally then this mod is for you. If pressing RESET does not enable the system to boot and run properly then either the PSU is not up to the job of running or system or you have a problem elsewhere and this circuit will not fix it. Actually there is a second possible cause, that of running an XP CPU on an older motherboard such as the KT7a which was not designed for XPs. In this case the problem is due to the XP having different timing requirements from previous Athlons. Again, this circuit should cure the problem.

I was somewhat hesitant to release this mod since I do not consider it to be a really valid solution to the problem, merely a workaround, and then I thought, if I don't someone else will and it might help a few people, so here it is. I have tried to make this mod as simple, cheap and effective for as many systems as possible and as such should be considered somewhat experimental. The approximate cost of this project is L2-3, which although small, arguably you should not have to bear since your "adequately" rated supply is not really up to the job. For many electronics hobbyists the circuit can be made from parts out the "junk box".

The circuit works by basically simulating the pressing of the RESET button at power up for a few seconds to give the PSU time to settle before allowing the system to start initialising. The circuit uses a CMOS quad NOR gate package type 4001B although almost any CMOS quad gate type could be used AND, NAND etc. The circuit operates a relay whose normally closed contacts are connected across the RESET switch, holding the system in a state of RESET. After a delay the relay is energised causing the contacts to open and thus allowing the system to initialise and boot normally. At switch on, gates a and b generate a relatively clean stepped input to the R1,C1 network which produces a delay before gates c and d switch. When the output of gate d switches high, transistor T1 conducts causing the relay to operate which opens the contacts allowing the boot sequence to begin. Capacitor C2 helps prevent false triggering due to supply voltage fluctuations and diode D1 protects the circuit from reverse voltages when the relay is de-energised. The gates are used in pairs as shown to enable inverting or non-inverting gate arrays to be substituted. It also ensures all inputs are used and not left unconnected which could cause false triggering. The resistor R1 can be replaced with a 100K variable preset to allow the time delay to be adjusted to a minimum whilst still allowing the PSU time to settle. Note this circuit leaves the RESET button fully functional.