LAT printer won't do big files

[Rice Don D]

I have set up a couple of PostScript printers (one QMS, one Apple) on a
terminal server and I can access them from a couple of DS5000s/Ultrix 4.0
just fine for small files.  However, when I have a large (>100K roughly) file
trying to print, the serial data lights on the server flash for many seconds
as the file starts spooling to the printer, then they stop.  At that point,
lpq shows the queue is "waiting for 15 seconds before retrying."  I have a
terminal hooked to the printer's transmit data line to monitor PostScript
messages, but there are none when printing stops.  After the 15 seconds
elapses, it tries sending the file again, gets about to the same point,
and quits...goes to sleep for 30 seconds, retries, etc.
There is no indication of an error from the printer or in the lpd error log.
And, if I use the command
	cp bigfile.ps /dev/tty17
it prints just fine.  This indicates to me that lpd is the problem.  For the
record, the laserwriter line is set up in rc.local by
	lcp -s -h /dev/tty17:SCATTER:ISR_ALW
and its printcap is very simple:
	lsr|ISRnet LaserWriter II:\
		:lp=/dev/tty17:sd=/usr/spool/alw:\
		:br#9600:\
		:fc#0177777:fs#023:\
		:xc#0177777:xs#040:\
		:lf=/usr/adm/alw-errs:mx#0:
The QMS setup is basically identical, using /dev/tty16, and they both have
the same problem.
I'm tempted to just use a background copy to the device since that always
seems to work, but I would like to know what is going on.  Something
degradingly obvious no doubt.

Also, if anyone has a fancier printcap for the laserwriter, I would be happy
to know about it.  I'm using lwf from comp.sources.unix to filter ascii files.
[The files that cause the problems above are bitmap graphics, not that it
matters.]
Thanks,
Don Rice                                  Internet: fnddr at flux.fai.alaska.edu
Geophysical Institute                     E-mail:   fnddr at acad3.fai.alaska.edu
University of Alaska                      Phone:    (907) 474-7569
Fairbanks, AK 99775                       Loran:    64.86N 212.16E