The Cellar - I need some help

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Originally Posted by Clodfobble

That's nice, but you left out the part where for the second and third computers we bought high-end, non-Asian-market surge protectors, and they also didn't work. Or perhaps you were speaking hypothetically?

First every shunt mode plug-in protector is or is same as the "Asian-market surge protector". There is no magic in these devices. They all use same circuits discussed in that 1970 GE Varistor Manual. Furthermore, most every MOV is now manufactured in Asia.

Shunt mode plug-in protectors - cheap or expensive - are same if they have same joules rating. However many love to be scammed. They may pay $100 for the Monster Cable model that is electrically same as a $20 model from others.

Why did a protector not work? From previous posts:

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Grossly overpriced plug-in protectors forget to mention that effective protection is already inside that computer.
Plug-in protectors also forget to mention that an adjacent protector provides typically destructive transients with more paths into and through a computer.
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So what do plug-in UPSes and power strip protectors completely avoid mentioning? Earth ground. Why? Ineffective protectors are sold mostly on myths. They avoid the most essential component of a protection 'system' - earth ground.
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How to identify an ineffective protector: 1) Protector has no dedicated connection to earth ground, and 2) Manufacturer avoids discussing earth ground. Plug-in protectors from APC, Belkin, and Tripplite violate both points.

One final point. How typically is a modem damaged. Remember, the phone line already has a 'whole house' protector provided by Verizon, SBC, Qwest, et al.

Lightning strikes an 'antenna like' device - AC electric lines above the street. Incoming through breaker box seeking earth ground. Incoming on computer's AC wires. Bypasses power supply to connect to motherboard ground plane. Through modem, out phone line, and to earth ground via the telco 'whole house' protector.

Part most often damaged on modem is its DAA section - section adjacent to phone line. In particular, the PNP transistor that drives an off-hook relay. A small transient will leave the PNP transistor shorted. When computer is powered, then phone line is always connected through modem. Phone line acts like a phone has been left off hook.

A large transient opens that PNP transistor. Therefore computer complains about "No Dialtone Detected" because off-hook relay never connects modem to phone line.

Some are quick to assume rather than first learn underlying theory. They assume this transient entered on phone line because only modem was damaged. But notice an essential requirement. To have an electrical transient, both an incoming and outgoing path must exist. Incoming on AC mains. Outgoing on phone line. Only after transient is passing through everything in that circuit does a part somewhere in that circuit fail. Besides, why would the transient enter on phone line when phone lines already have a 'whole house' protector.

The above example demonstrates why transients on AC electric so often damage modems, fax machines, answering machines, and portable phone base stations.