DeskJet / DeskJet+ / Atari ST Powerup Sequence Problem -- SOLVED AGAIN!! ------------------------------------------------------------------------ By Rob L. I was interested in finding out how to solve the problem of printing to the DeskJet when it is powered up AFTER my ST, when I ran across an article in ST REPORT, which described a method using a PNP transistor. Well, to make a long story short, I DIDN'T HAVE a PNP transistor, and I started wondering: "Hey, what do you need a transistor for, if all you want to do is prevent a powered-off DeskJet from pulling down the STROBE line?" It didn't take long to figure out the answer, and HERE IT IS! Just use a DIODE! The part costs 10 cents or less, and you only have to solder 2 connections instead of three (I hate soldering -- smoke messes up my contact lenses :-). The DeskJet, when powered up, provides a 5v signal on pin 1. The ST likes to see that, because it has the SAME signal on its own pin 1 when it comes on. When the ST strobes that line, it grounds the line for a split second, taking BOTH signals with it, then returning to 5v. But, when the DeskJet is turned OFF, its pin 1 no longer has the 5v signal, and as a matter of fact, it acts as a "2000 ohm to ground" load (or thereabouts) on pin 1. So, when the ST powers up (and the DeskJet is OFF), the 5v signal the ST puts on its pin 1 gets SHUNTED to ground (through the DJ's 2000 ohms), and the ST doesn't like that one bit, so it decides to screw up the printer port so you won't be able to print even when you DO finally turn on your DeskJet! WELL, THE NERVE OF SOME COMPUTERS! :-) Not to worry, we'll fix that problem for good. The diode mod is like this: The anode (positive end) of the diode, is marked by a black band (I know, black usually means negative, but diodes are strange :-) on the 1N914 small signal switching diode (a very common type). That black end should point TOWARD the ST's pin 1, leaving the cathode pointing away-> to the DeskJet's pin 1. The easiest place to put this diode is inside the DB-25 connector at your ST's printer port (so you don't have to dig under your DeskJet to get to the Centronics connector). 1.) Unsolder the wire at pin 1 of the DB-25 connector. 2.) Clip the leads of the diode to about 1/4" on each side. 3.) Solder the BLACK end to the DB-25 pin 1 4.) Solder the other end to the wire. -- THAT'S IT! [Be careful when re-assembling, so you don't short anything on the hood] The diode allows the ST's STROBE line to sink the current on the line when in use, but if the DeskJet is NOT turned on, it will present a VERY HIGH impedance on its pin 1, so it will not load the ST's STROBE line, and the ST won't get mad! You can turn on your printer when you're ready to print, and your ST will be able to send printer data as if the DeskJet had been on since bootup! AMAZIN! Simply AMAZIN! :-) Here's a simple diagram so you know roughly what the 1N914 diode looks like, and how to hook it up: From DJ's Centronics port >>> ------===##------ To ST's printer port >>> Pin 1 Diode (1N914) Pin 1 Happy Jetting! Rob