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From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.sys.mac.misc,comp.periphs.printers
Subject: JetLink Express 1.2 vs HP DeskJet 500
Message-ID: <83840@coherent.coherent.com>
Date: 31 Oct 90 22:00:18 GMT
Followup-To: comp.sys.mac.misc
Distribution: comp
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 49

I've discovered that a bug in GDT Softworks' JetLink Express 1.2
printer-driver can cause serious problems when printing to a
Hewlett-Packard DeskJet 500 printer.  The problem doesn't occur when
printing to a DeskJet, DeskJet Plus, or DeskWriter.

Symptoms: when printing a document at 300 dpi, the DeskJet 500 prints a
portion of a page, halts for 30 seconds or more with the "Busy" light on
steadily, prints several lines of garbage, and resumes printing.  A
large fraction of a page's output will have been omitted or garbled.  If
the problem occurs on the last page of a print job, the printer will
never finish printing the page, and it'll be necessary to press the
"Reset" button to clear the printer.

Analysis: under conditions which are somewhat difficult to identify,
JetLink Express 1.2 will output an illegal sequence of PCL (Printer
Control Language) to the printer.  The DeskJet and DeskJet Plus detect
and ignore the illegal sequence.  The DeskJet 500 apparently tries to
interpret it, becomes seriously confused, and ends up discarding a large
fraction of the data intended for the current page.

Workarounds: making even subtle changes to the data on the page may
enable you to evade the problem... try changing the margins slightly, or
printing in a different font.  Or, try changing the amount of memory
allocated to your application (if you're running under MultiFinder).
Or, print at 75, 100, or 150 dpi rather than 300 dpi... I haven't seen
this problem at any of those densities.

I phoned GDT Softworks' tech-support line yesterday afternoon and
discussed this with them.  They had heard reports of the problem, but
had been unable to reproduce it in-house.  Apparently, even slight
differences in a Mac's setup can alter the driver's rasterization
behavior enough to make the problem appear and disappear.  They had been
"banging their heads" against this problem for several weeks (their
words) and were quite happy to receive an analysis.

I've faxed them a partial dump of the driver's output, showing the
illegal code sequence, and have mailed them a diskette with the complete
driver-output dump, a test-case file, and further information.  With a
bit of luck, their programmers should be able to identify and correct
the faulty logic in the driver without too much waving-of-dead-
chickens.

I haven't yet received my copy of the new JetLink Express 2.0 driver
package, so I don't know whether the problem will occur in this
version... but I suspect it will.

Many thanks and a big "Attaboy!" to Dave Neff of Hewlett-Packard, who
found the illegal code sequence in the dump-file I mailed to him and
explained why it's causing problems.