The Lab That Must Be Ready in Four Days
At a government senior secondary school, the computer lab has 24 assembled desktops, all about seven years old, and a board practical is scheduled in four days. Three machines failed the pre-check. PC-07 spins its fans and the power LED glows, but there is no display and the cabinet speaker gives a continuous series of short beeps. PC-11 boots into Windows, but every morning the date reads 01-01-2010 and the time 00:00, the boot order has reverted to network boot, and start-up takes several minutes. PC-14 shuts down abruptly, but only when the window air-conditioner compressor starts; that AC, a laser printer and four PCs all draw power from one 16 A socket through a six-way extension strip. The lab gets a technician for one day and has a small consumables budget but no spare PCs. Teachers want all 24 seats working for the practical.
1. For PC-07 and PC-11, identify the most likely cause of each fault and the order of checks. Explain why the beep pattern alone cannot settle the diagnosis.
Read the worked answer
PC-07 - continuous short beeps, fans running, no display. A repeating short-beep pattern at POST most often means the BIOS cannot detect memory; a spinning fan only proves the PSU is producing some output, not that every rail is healthy. Check order, cheapest and most likely first:
- Power off, unplug, hold the power button to drain, reseat the RAM stick in slot 1 and clean the contacts.
- Test one known-good stick at a time in each slot - a dead stick and a dead slot give the same symptom.
- If beeps persist, substitute a known-good PSU, then check CPU seating, and only then suspect the motherboard.
Why the beep code is not decisive: patterns are vendor-specific. AMI, Award and Phoenix assign different meanings to a continuous short beep (commonly memory on one, power supply on another). Without the motherboard manual or a POST card you would be guessing; the beep only tells you where POST stopped.
PC-11 - date/time reset, boot order reverted, slow start. The CMOS cell (CR2032) is flat, so the real-time clock and BIOS settings are lost at every power-off, and the default boot order retries network (PXE) boot first - that explains the extra minutes. Replace the cell, reset date/time and boot order, save with F10, and check for corrosion or leakage. Confirm the fix by leaving the machine unplugged overnight.
2. Is PC-14's shutdown a computer fault or an electrical one? Justify your answer and list what must change before the practical.
Read the worked answer
An electrical supply fault is more likely than a PC fault. Evidence: the shutdown correlates exactly with the compressor starting, and the machine shares a circuit with the AC, the printer and three other PCs. A compressor draws a large inrush current and drops the line voltage for a fraction of a second, so the PSU drops out or the board resets. No component inside PC-14 would 'know' the compressor started.
Do not simply replace the PSU: the same voltage dip will keep resetting the machine, and the real problem is safety. One 16 A socket feeding an air-conditioner, a laser printer (high current while its fuser heats) and four PCs through a six-way strip is overloaded, and daisy-chained strips overheat at loose contacts.
Before the practical: a licensed electrician must give the AC its own circuit, spread the PCs over separate circuits with proper earthing and MCB/RCCB protection, remove the strip chain, and put the PCs behind a UPS or at least a stabiliser. If the electrician cannot come in time, run the practical without the AC rather than with the present wiring, and record that decision.
3. With one technician-day and a small budget, set a priority order for the three machines and say what you would deliberately not do.
Read the worked answer
Priority 1 - PC-14 and the wiring. Safety outranks the exam: an overloaded circuit is an injury and fire risk. This is the one job that cannot be deferred to after the practical. Priority 2 - PC-11. A CMOS cell costs almost nothing and takes five minutes; it fixes date, time and the boot delay, so it gives the greatest benefit per rupee and per technician minute. Priority 3 - PC-07. Reseating and swapping RAM costs nothing and often works; a spare PSU is the only likely purchase. If it still fails, stop chasing it on the last day.
Deliberately not doing: buying a new PC or motherboard the week before a practical (cost, delivery, licensing and driver work); opening the PSU casing (lethal charge in the capacitors, and the technician's day is better spent elsewhere); reinstalling Windows on all 24 machines as 'prevention', which risks breaking working seats.
Contingency: plan for 20 working seats and pair students, and tell the teachers in writing today rather than on exam morning - a known, planned shortfall is manageable; a surprise one is not.