Suddenly there was a Big Bang

Although software problems represent the most common Computer faults there are also hardware items that fail. Amongst them are Monitors, Hard Drives and Power Supplies. A recent request for a service call to investigate a Computer which would not start turned into a nightmare for the owner. I was informed that whilst she was reading her email suddenly everything just went off and the Computer would not restart. There can be various reasons why this may happen however a faulty power supply seemed very likely although someone’s definition of not starting may be different from mine.

Upon arrival I saw a typical 4 to 5 year old Pentium 2 with the usual attachments including an internal modem and 17” Monitor. A press of the start button caused the power supply to start as evidenced by the noise of the fan. No lights were displayed on the front panel however and a faint smell of burning was evident. I removed the mains plug and proceeded to open the case. There was no evidence of anything physically wrong inside the case and even though the owner had purchased the complete Computer in Turkey the components were very much the same brands and models available here in Australia.

I pushed the start button again and observed what appeared to be a fine smoke emitting from the power supply via the fan… Before I could remove the power cord from the rear of the machine there was an extremely loud bang and a discharge flash of electricity at the power connector for the CD ROM drive. It is the job of the power supply to transform the 240 volt AC into lower DC voltages. The voltages are: 3.3 volts 5 volts 12 volts. The 3.3 and 5 volts are typically used by digital circuits, while the 12 volt is used to run motors in disk drives, CD ROM’s and fans. Certainly the 5 and 12 volts supplied to the CD ROM drive could not cause such a huge electrical arc. As a related issue the important specification of a power supply is its output watts with 300 watts being the minimum acceptable today considering the many devices connected internally including CDRW drives.

I told my client that the machine would have to go back to the workshop for a complete checkout and to prepare her a little I mentioned that repairs could be extremely costly if in fact 240 volts AC had found its way into the lower voltage DC circuits.

Back in the workshop I removed and disconnected everything. With new RAM, Video Card and Power supply connected to the existing Motherboard and Processor I tried to power up the very basic system. Incidentally this is all you need to test the basic components of the Processor and Motherboard. Although the start button would cause the power supply to start there was no video display and not error codes emitted from the internal speaker. Holding down the start button for the usual minimum of 4 seconds would not turn off the power supply either. There was therefore a fault with either the Processor or the Motherboard but which one was irrelevant as both components were years out of date and no replacement would be able to be sourced except from a junk bin. The client had also expressed some urgency in getting back onto the Internet.

I then set about checking the other components in my workshop test PC. The Hard Disk drive would not rotate but the small LED mounted on the circuit board was lit. The Sound card and the Video card stopped the test PC from booting up as did the diskette drive. The CD ROM drive was dead as was the RAM module. Everything had been hit by this surge of 240 volts and damaged. The only device that could be installed into my Workshop unit was the internal modem but without software at this point I was unable to test its full operation.

I decided the only course of action was to rebuild the Computer using a Gigabyte GA 6VEM Motherboard which includes on-board Video and Sound chips. This would help to keep the costs down and with 256MB of SDRAM there would be plenty of RAM to allocate to the Video. Assembling this into the existing case along with the new Power Supply and CD ROM, Diskette Drive, Hard Disk and RAM plus a Intel Celeron 1.1 GHZ Processor was quick and easy and within 30 minutes I had Windows 98SE loaded and the latest updates installed. My client could not locate the software for the modem. It was a typical internal modem in that it was completely unbranded and a quick search on the Internet failed to get any match for any of the numbers on the circuit board or Integrated circuits. Devoting anymore than 10 to 15 minutes or so on such a search is in my view a waste of time as a new internal modem is less than $45.00 installed.

Although my client now faced a large bill she had in fact got a complete upgrade of her computer with the only original device being the case. She was happy to be back on-line within 24 hours and even happier that she only used Hotmail for all her email because if she had used an normal program such as Outlook Express all her messages and contacts would have been lost due to the damages Hard Disk drive. Hotmail messages are stored on a Computer controlled by Microsoft and possibly situated in the USA.

The question is how and why did such a catastrophe occur? My guess is that like most tower and mini tower cases that sit on carpeted floors a certain amount of dust is drawn into the case by the action of the fan. Maybe in this case the dust contained some conductive particles which ultimately led to some sort of flash over within the unit causing 240 volts to be flashed over to the lower voltage areas. Most modern Power supplies are “short circuit” proof and can withstand all sorts of problems at their output connectors but nothing of that manner can prevent the insulation of a unit braking down and putting high voltage where it is not desired. This job was certainly the most destructive I have ever experienced. As a side note, when upgrading any Computer in my workshop I always use a small vacuum cleaner to remove the accumulated dusk, something readers should also consider every few years or so.