Fix for a resetting Com21 cable modem
If you have a Com21 modem with a 15V@1A power supply (mine says it's made by AULT INC.), you might benefit from swapping it out for one from a laptop computer. The power supply from many P3-era Thinkpads are rated at 16V@4.5A with same polarity (center positive) and the plugs are the same. It fixed my intermittent resetting problems on my modem, maybe others are having a similar issue.
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I became keenly aware of this problem recently after I bought an old HP Laserjet 5 printer. Going by the ratings, the printer can apparently draw about 1000W at max. Every time I turn it on it causes a momentary brownout and the modem resets. These power hiccups don't seem to bother my computers or routers, but it consistently kills the modem. This repeats every time the printer cycles power to the fuser, which happens about as often as the length of time it takes for the modem to login to the ISP. So basically I had no connection as long as the printer was running.
I hooked the modem up to my UPS, and to my surprise it didn't help. The modem was still resetting. Damn it's picky.
So I looked at the modem's AC/DC transformer. It was very warm, and rated at 15V@1A. The power adapter for my IBM Thinkpad A20m is 16V@4.5A, same polarity. Negligible voltage increase, way more load rating, and it's a brand I've heard of (Astec). I tried it - and it works perfectly. No more resets even with the printer at it's worst.
I imagine the weak power adapter was a problem for a long time, before the printer made it more obvious what was going on.
Laptop power adapters are better quality than the cheap bricks on most smaller devices, so if you've got any laying around they deserve to be used for something. They can also be bought used for decent prices, but make sure you get a real one, not a knockoff (I could write another story about that).
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I became keenly aware of this problem recently after I bought an old HP Laserjet 5 printer. Going by the ratings, the printer can apparently draw about 1000W at max. Every time I turn it on it causes a momentary brownout and the modem resets. These power hiccups don't seem to bother my computers or routers, but it consistently kills the modem. This repeats every time the printer cycles power to the fuser, which happens about as often as the length of time it takes for the modem to login to the ISP. So basically I had no connection as long as the printer was running.
I hooked the modem up to my UPS, and to my surprise it didn't help. The modem was still resetting. Damn it's picky.
So I looked at the modem's AC/DC transformer. It was very warm, and rated at 15V@1A. The power adapter for my IBM Thinkpad A20m is 16V@4.5A, same polarity. Negligible voltage increase, way more load rating, and it's a brand I've heard of (Astec). I tried it - and it works perfectly. No more resets even with the printer at it's worst.
I imagine the weak power adapter was a problem for a long time, before the printer made it more obvious what was going on.
Laptop power adapters are better quality than the cheap bricks on most smaller devices, so if you've got any laying around they deserve to be used for something. They can also be bought used for decent prices, but make sure you get a real one, not a knockoff (I could write another story about that).
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