Power to the Model 4P

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And another TRS-80 roars to life!


Like the Model III I resuscitated last summer (see “Power to the Model III”), I was able to bring up a Model 4P by swapping out a bad power supply. This particular unit was purchased on eBay for $11 before shipping, with the understanding it had some sort of power issue. As a nice bonus, it arrived with an extensive cache of diskettes which were not mentioned in the auction description.

The unit itself is in good shape; there are the typical minor scuffs, scrapes and yellowed plastics you’d expect to see on a 25+ year old machine, but nothing outright broken or missing. The keyboard’s feel is fantastic, probably the best out of the TRS-80 series.


The Tandy power supply was replaced with a new, old stock Antec 65 watt unit from computernews80. This is a drop-in replacement, and takes only a few minutes to install.

Once everything was buttoned back up, the unit booted without complaint, requesting a ROM diskette in multiple languages. I was able to bring up TRSDOS 1.3 and its Model III ROM and then softboot (using the reset button to keep the soft ROM in memory) the Model III versions of MultiDOS, LDOS, etc. This soft-ROM (Kickstart?) arrangement allows the Model 4P to run CP/M, as a physical Model III ROM isn’t intruding on address space.


After playing around with this machine a bit, I can certainly see passing my Model III on to another hobbyist - this little guy should fit the bill for any Model I/III/4/4P software I come across, and do so in a smaller footprint. My next step is to upgrade the RAM to the full 128K which looks pretty easy to do. More fun to come!

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This page contains a single entry by nekonoko published on March 13, 2009 5:48 PM.

A Short Break was the previous entry in this blog.

eBay and Zip Chips is the next entry in this blog.

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