robinson@renoir.Berkeley.EDU (Michael Robinson) (08/03/87)
In an article in a recent Amazing Computing (V.2 #7), Oran Sands III asserts
that the inferior quality of Amiga composite output (compared to other
composite output) is due, in part, to a poorly chosen resistor in the
composite conversion circuitry which does not conform to the Motorola
specification for the MC1377P composite encoder chip. He provides rather
extensive and impressive documentation of his claims, however, before I
open up my Amiga and start flailing about with my soldering iron, I would
like to solicit comment from Commodore representatives, ex-Commodore
personnel, or anyone else who knows an R-Y axis from a sync pulse.
Also, in the article he makes a distinction between two flavors of Amiga
1000, each of which requires a different fix. However, he is unable to
describe which computers are which flavor beyond those which are
pre-June '86 and those which aren't. As I bought my Amiga around June '86,
I was wondering if someone at Commodore could provide a more detailed
distinction between the two.
Thank you.
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Mike Robinson USENET: ucbvax!ernie!robinson
ARPA: robinson@ernie.berkeley.edugrr@cbmvax.UUCP (George Robbins) (08/05/87)
In article <19939@ucbvax.BERKELEY.EDU> robinson@renoir.Berkeley.EDU (Michael Robinson) writes: > In an article in a recent Amazing Computing (V.2 #7), Oran Sands III asserts > that the inferior quality of Amiga composite output (compared to other > composite output) is due, in part, to a poorly chosen resistor in the > composite conversion circuitry which does not conform to the Motorola > specification for the MC1377P composite encoder chip. He provides rather > extensive and impressive documentation of his claims, however, before I > open up my Amiga and start flailing about with my soldering iron, I would > like to solicit comment from Commodore representatives, ex-Commodore > personnel, or anyone else who knows an R-Y axis from a sync pulse. His article seems pretty reasonable. The R140 resistor he makes an issue of is the sort of thing were either you have to provide an adjustment, trim at system test time, or select a compromise value the seems to provide acceptable results in most systems. The MC1377 video encoder is a nice, but not magic chip, and if the chip or circuit characteristics change, then there might well be a better value for many systems. Lowering the output level may also improve results with some video equipment. Some devices can accommodate quite a range of video levels, others are less flexible. > Also, in the article he makes a distinction between two flavors of Amiga > 1000, each of which requires a different fix. However, he is unable to > describe which computers are which flavor beyond those which are > pre-June '86 and those which aren't. As I bought my Amiga around June '86, > I was wondering if someone at Commodore could provide a more detailed > distinction between the two. This makes no obvious sense. As far as I know the same main board was used in all NTSC amiga systems. Later revisions of Agnus and Denise were used on newer boards, but these have no direct connection with the analog or composite video levels or characteristics. Resistors are cheap, I'd try it either way and take whatever seems best. Disclaimer: Yes, it voids the warranty and all that. If you desire this sort of fine tuning, this might not be a big issue... -- George Robbins - now working for, uucp: {ihnp4|seismo|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@seismo.css.GOV Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)