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From: hull@hao.UCAR.EDU (Howard Hull)
Newsgroups: comp.dcom.modems
Subject: Re: Capetronic 2400bps external modem review
Message-ID: <920@hao.UCAR.EDU>
Date: Sat, 3-Oct-87 12:21:00 EDT
Article-I.D.: hao.920
Posted: Sat Oct  3 12:21:00 1987
Date-Received: Wed, 7-Oct-87 01:18:15 EDT
References: <975@julian.UWO.CDN> <502@esunix.UUCP>
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 37
Summary: mitac modem tab regulator

In article <502@esunix.UUCP>, blgardne@esunix.UUCP (Blaine Gardner) writes:
> in article <975@julian.UWO.CDN>, peter@julian.UWO.CDN (Peter Marshall) says:
> > ...
> > this to the modem being very new.  The power adapter seemed to be
> > rather hot though.  The manual told me not to worry about heat since
> > high powered LSI components were in use!
> 
> This sounds much like the manual that came with the Desktalk II 2400
> baud modem. I opened the case, and their "high power VLSI" turned out to
> be a 5 volt tab regulator and it's heatsink. They were using the
> Rockwell 2400 baud chipset though.
Yeah.  I got a mitac 2400BD (ril cheap).  It didn't seem to generate large
amounts of heat, though it was tolerably warm on top.  But naturally, I wanted
to see what technology they used, so I opened it up.  Like you, I found a
Rockwell 2400 baud chipset.  Also like you, I found a 7805 tab regulator,
but with an ~4-inch on a side sheet aluminum heat sink projecting to the
right, up, and then over about 1/3 of the other IC's.  Wanting to see who
they were torturing under the shadow of this heatsink, I pulled up slightly
on it - and discovered that there was nothing to prevent it from rotating
(with far less force).  I also discovered that the speaker was held in
place with a piece of _masking tape_.  I removed that and substituted a
butyl rubber o-ring I happened to have handy (you know what masking tape
does after a long time in a hot place...).  When I put it back together,
none of the lights would come on.  Ok, I sez, musta dinged it.  Back apart,
I removed the heat sink mounting nut and discovered a small square of paper
cemented over a 10-mil land under the sink, and another land with a via
that was not protected at all.  The usual via solder bump was squashed
flat and wiped a little.  I had expected (perhaps) to find a mica spacer.
Not so.  Anyway, I followed the spirit of things and stuck another piece
of paper over the munged land and via, put it all back together, and was
back in business.  Thank God for overcurrent protect that's in the 7805.
As for the mitac, well, talk about cheap... any other nominations anybody?
								Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
                 ...Then only the deranged will discuss yet unproven concepts]
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