bilbo@pnet02.cts.com (Bill Daggett) (11/14/87)
Can we work this out? There seems to be disagreement among the "hacker"
Commodore ranks.
I believe I have been experiencing gurus resulting from a PAL chip problem. I
replaced the two affected PALs with their faster "better" variety when I
installed Kickstart in ROM. After that I continued to experience gurus -
though I was running Word Imperfect at least some of the time. There are two
methods now developed to "ground" pin 10 of the PAL chips:
1. "Hacker" method: Ground all pin 10s to the daughterboard capacitor and
then down to the motherboard.
2. Commodore: You don't really need to because the PALs are already grounded
in the fashion they were designed to be grounded BUT if you really want to
jumper between U6J and U6K; and a second jumper between U6L and U6N.
I'd really like to KNOW what the heck is going on here. I think there is
still some mystery going on here that has been untold. But I really don't
want to experiment if facts can prove one method correct. Can anyone help?
Bill Daggett -- a.k.a.
*Bilbo Baggins* Recombinant Hobbit
* Sometimes The Dragon Wins! *
INTERNET: bilbo@pnet02.CTS.COM
UUCP: {hplabs!hp-sdd!crash, ihnp4!scgvaxd }!gryphon!pnet02!bilbo
WHAT?:bryce@hoser.berkeley.edu (Bryce Nesbitt) (11/15/87)
In article <2282@gryphon.CTS.COM> bilbo@pnet02.cts.com (Bill Daggett) writes: >Can we work this out? There seems to be disagreement among the "hacker" >and Commodore ranks... > >1. "Hacker" method: Ground all pin 10s to the daughterboard capacitor and >then down to the motherboard. >2. Commodore: You don't really need to because the PALs are already grounded >in the fashion they were designed to be grounded BUT if you really want to >jumper between U6J and U6K; and a second jumper between U6L and U6N. > >I'd really like to KNOW what the heck is going on here. You are a bit confused. What you outline as the "Commodore" method is nearly electrically identical to the "Hacker" method I posted a while back (Search backwards if you want a copy... I'm not reposting again). Here's the story and reasoning: The two PALs that were "lifted" from the motherboard kept the same grounds they had before. These ground paths are long and torturous. (These are PALs U6N and U6K) The two PALs that are new to the daughterboard have a nice clean ground from the 4 layer board. (These are U6L and U6J) The two "lifted" PALs grounds have a very high 70mv or so of noise on some machines. Improving the grounds turns some non-working situations into working ones (even some non-working "illegal" combinations, but lets not flame that point any more). This statement is based on experience with many machines... actual mileage may vary. There are at least three ways to think about doing this: 1> Daisy chain a *heavy* wire between pin 10 of all four PALs (U6J U6K U6L U6N) 2> Same as above except add a wire diving down to the motherboard. 3> Don't connect all four, instead just connect the U6J and U6K pair and the U6L and U6N pair. The last puts a little bit of isolation between the two "lifted" PALs. The second is probably overkill. All are close enough to equal to make the difference ignorable in your case. I'll continue to use #1 because I know it works. >I think there is >still some mystery going on here that has been untold. Nope, I think it is all on the table at this point. |\ /| . Ack! (NAK, SOH, EOT) {o O} . bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce (") U