|
Subject: PALs,jumpers and expansion on the Amiga 1000.
Keywords: C Ltd.,TI,MMI,bunk,bull
As many of you are aware, a company called C Ltd. produces memory and hard
disk products. They acknowledge that some of their products (and products
from some other manufactures) will act unreliably on some Amiga 1000's, and
that if you chain two or more of those (*unbuffered*) devices you run a
greater risk of failure. Symptoms range from total refusal to work, to
intermittent crashes to intermittent loss of Kickstart (machine crashes all
the way to Kickstart). They recommend as a solution replacing two PAL chips
inside the machine. My repair person friend, Bruce Takahasi, does not
subscribe to this belief. Replacing the PALs has not produced any fantastic
improvement in any of the cases that he has tracked. He does have an
alternate solution...
First, though, here is what C Ltd. has to say::
> ...This problem stems from the speed of the PAL chips used by Commodore in
> the manufacture of the Amiga. Early Amigas used PALs manufactured by MMI,
> and these chips seemed to work well in almost every case, but at some point
> Commodore started using PALs made by Texas Instruments. The TI PALs,
> though having the same rating as the MMI parts, simply do not perform as
> well causing the problems as stated above. Replacing the parts with the
> much faster 16L8B part (any manufacturer's "B" versions are fast enough)
> solves the problem. We have researched this problem to 'death' and are
> confidant both from analysis of the system with the Texas Instrument PALs
> and from experimental analysis of the system with the faster 16L8B PALs
> that we know what the problem is and how to fix it...
>
> ...So in conclusion, the best solution to the problem is replace the PALs.
> By the way, if there is blame in this matter it is probably on the
> shoulders of Texas Instruments and their PAL chips.
>
> E.J. Lippert II C Ltd. Wichita, KS (316) 267-6321
Bruce's explorations lead to a different solution. The key clue was noise.
A high speed 'scope revealed that the ground pins of two of the four PALs
on the RAM/ROM daughterboard had a very high 90 milivolts of noise. This
is at the very least a potential cause of problems... and one that would
not be solved directly by swapping PALs. (Swapping PALs may fix the
symptoms, but would not cure the cause).
The RAM/ROM daughterboard has 4 layers with one each for ground and +5.
One might assume that all four grounds would be securely tied together.
This turns out not to be the case. Under a bright light it is revealed
that the two PALs with high noise are isolated from the main internal
ground layer. The classic reason for isolating grounds is to isolate noise.
In this case it appears that these isolated PALs have an insufficient
ground.
The solution that has worked in several cases is to improve the grounds for
these PALs. The ground pins of each of the four PALs are connected, and a
clip extends from the last PAL (U6J) down to the motherboard. Here's a
diagram:
^ clip
|
| J K L N
---X---O X---O X---O X---O
O---O O---O O---O O---O
..........................
The X's indicate pins to be connected. The clip connects to ground on the
motherboard at a point just to the left of the power supply connector
(There is a row of 8 capacitors with ground on the side nearer the
connector).
One other modification is made in certain cases. A ground is extended from
the negative end of a capacitor at the "diving board" end of the
daughterboard to a capacitor in the chip ram array. Newer Amiga 1000's
already have this modification from the factory and thus don't need it.
|\ /| . Ack! (NAK, SOH, EOT)
{o O} . bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce
(")
U "Fanitic: One who can't change his mind, and won't change the
subject."
Newsgroups: comp.sys.amiga
Path: decwrl!ucbvax!hoser.berkeley.edu!bryce
Subject: Re: PAL Chip Mod Questions
Posted: 14 Nov 87 21:30:30 GMT
Organization: University of California at Berkeley
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
|
|
OK , here is the latest on my A1000 .
I was lucky enough to have a friend that was very knowledgeable
with the A1000 grounding of the PALs. He did add the grounding
you did describe and I still have the same problem occuring. The
next step I'll do prior to bringing it to the store will be to have
my memory board tested on another A1000. I Had Guru code that said
something like (illegal instruction or address error) .
For the people capable of reading Guru i'll give it to you :
00000004.00200DF2
00000003.0020AEB0
00000003.0020AD88
Thanks for the previous help and I will let you know of the
outcome .
See ya ,
Jean_Denis
|
| I have been trying to get hold of a new PAL chip for my 2000 modelA.
I'm assured by every dealer that this will allow me to actually
use more than the one expansion card on the Amiga side that I presently
have. Until I have it my new hard drive is unuseable. I've had the
chip on order since February, and I've tried dealers and distributors
in Holland, Germany and UK. The part I'm after is 380715-02. This
replaces 380715-01 which is what I have.
So,
1) Can anyone tell me the telephone no. of Spirit Technologies (re.1)
2) Anybody know if this (new) chip is the same as in later 1000's.
Maybe I could cannibalise one.... A shot in the dark, but any
help GRATEFULLY received.
You might imagine I'm getting kind of frustrated using my new Quantum
as a door stop. I'm also frustrated that you have to chase a part
half way round the world to fix your machine to do something it
was always supposed to do.
Thanks
Colin
|