13 Nov
2007
13 Nov
'07
10:56 p.m.
Date: Tue, 13 Nov 2007 11:17:41 -0600 (CST)
From: "Jeff Walther" <trag at io.com>
Subject: Re: How not to fix a classic mac (or: fried logic boards)
To: cctech at classiccmp.org
Message-ID: <12318.209.163.133.242.1194974261.squirrel at webmail.io.com>
Content-Type: text/plain;charset=iso-8859-1
> Date: Mon, 12 Nov 2007 22:45:09 -0800
> From: Josh Dersch <derschjo at msu.edu>
> First point of business, I discharged the CRT.
> To the main chassis. This, as I have now discovered, is not what you
> are supposed to do to discharge the CRT unless you want to destroy the
> logic board.
That particular failure is documented in Larry
Pina's "Macintosh Repair
and Upgrade Secrets" and probably in "The Dead Mac Scrolls" as well.
I'd
look it up for you, but I don't have my books with me here.
Okay, I'm home, I have my books. It says on page 98 that
discharging the CRT without a big honking resistor may blow a 74LS38N
(U2) on the analog board and the LAG chip on the logic board. The
former sounds like it might be fairly standard. The latter sounds
like it may be one of the custom programmed PALs or GALs or whatever
that Tony was writing about.
I wouldn't be surprised if folks had already figured out all the
internal logic for the various Mac 128/512/Plus chips though.
Finding it might be a bit of a challenge.
OTOH, the LAG chip may be fine and it could be U2 on the analog board
that has the problem.
Jeff Walther
14 Nov
14 Nov
1:26 a.m.
Excellent -- thanks. I'm guessing it's probably the LAG chip -- I've
swapped a Mac Plus board into the 512k and it runs fine, and running the
512k in the Plus exhibits the same fault, so it's not the analog board.
The LAG is labeled "HAL16R8CN 8440 / 342-0251-A" so it does look like a
custom ("HAL") chip such as what Tony was mentioning. Guess that would
be tough to replace, unless someone out there has the means to make a
dupilicate. Bah. That'll teach me to think twice next time I think I
know what I'm doing :).
Thanks,
Josh
Jeff Walther wrote:
Date: Tue, 13
Nov 2007 11:17:41 -0600 (CST)
From: "Jeff Walther" <trag at io.com>
Subject: Re: How not to fix a classic mac (or: fried logic boards)
To: cctech at classiccmp.org
Message-ID: <12318.209.163.133.242.1194974261.squirrel at webmail.io.com>
Content-Type: text/plain;charset=iso-8859-1
> Date: Mon, 12 Nov 2007 22:45:09 -0800
> From: Josh Dersch <derschjo at msu.edu>
> First point of business, I discharged the
CRT.
> To the main chassis. This, as I have now discovered, is not what you
> are supposed to do to discharge the CRT unless you want to destroy the
> logic board.
That particular failure is documented in Larry
Pina's "Macintosh Repair
and Upgrade Secrets" and probably in "The Dead Mac Scrolls" as well.
I'd
look it up for you, but I don't have my books with me here.
Okay, I'm home, I have my books. It says on page 98 that discharging
the CRT without a big honking resistor may blow a 74LS38N (U2) on the
analog board and the LAG chip on the logic board. The former sounds
like it might be fairly standard. The latter sounds like it may be
one of the custom programmed PALs or GALs or whatever that Tony was
writing about.
I wouldn't be surprised if folks had already figured out all the
internal logic for the various Mac 128/512/Plus chips though. Finding
it might be a bit of a challenge.
OTOH, the LAG chip may be fine and it could be U2 on the analog board
that has the problem.
Jeff Walther
3:30 a.m.
On Tue, 2007-11-13 at 22:26 -0800, Josh Dersch wrote:
The LAG is labeled "HAL16R8CN 8440 /
342-0251-A" so it does look like a
custom ("HAL") chip such as what Tony was mentioning. Guess that would
be tough to replace, unless someone out there has the means to make a
dupilicate. Bah. That'll teach me to think twice next time I think I
know what I'm doing :).
http://www.latticesemi.com/dynamic/view_document.cfm?document_id=102
There's not much to those chips. I'd be surprised if you couldn't suss
out what it was doing fairly easily - assuming you had a working one!
I *might* still have a Mac Classic board or two kicking about. I'll let
you know if I find one.
Gordon
7:17 p.m.
The LAG is labeled "HAL16R8CN 8440 /
342-0251-A" so it does look like a
custom ("HAL") chip such as what Tony was mentioning. Guess that would
It is. The important part of the number is the '16R8' bit. That implies
it's got 8 registered ouptuts and a total of 16 inputs to the AND array
(8 serpate inputs and 8 feedback terms from the output pins). That, of
course, accounts for 16 pins on the 20 pin package, the others are +5V,
ground, a common clock input to all the flip-flops, and a common output
enable signal to all the outputs).
It's the same architecture as a PAL16R8, and could be replaced by a
suitably-programemd GAL16V8. Not that that is any help at all without the
PAL equations.
I will try to find all my notes on the Mac+ (but not tonight!). I know I
never figured out the PAL equations, but I might have something of use.
-tony
8:34 p.m.
At 03:17 PM 11/14/2007, you wrote:
There are equations for the PALs on my website:
http://www.stockly.com/forums/showthread.php?t=6
The LAG is
labeled "HAL16R8CN 8440 / 342-0251-A" so it does look like a
custom ("HAL") chip such as what Tony was mentioning. Guess that would
It is. The important part of the number is the '16R8' bit. That implies
it's got 8 registered ouptuts and a total of 16 inputs to the AND array
(8 serpate inputs and 8 feedback terms from the output pins). That, of
course, accounts for 16 pins on the 20 pin package, the others are +5V,
ground, a common clock input to all the flip-flops, and a common output
enable signal to all the outputs).
It's the same architecture as a PAL16R8, and could be replaced by a
suitably-programemd GAL16V8. Not that that is any help at all without the
PAL equations.
I will try to find all my notes on the Mac+ (but not tonight!). I know I
never figured out the PAL equations, but I might have something of use.
15 Nov
15 Nov
1:10 a.m.
Cool.
So, two things spring immediately to mind:
1) Does anyone know if the LAG from a Mac Plus is the same as (or
equivalent to) the LAG from a 512k? If so, I can take the one out of my
Plus and put it in the 512k for testing purposes. If this succeeds,
then we proceed to point 2:
2) Can anyone, given the logic equations that Grant's so kindly
provided, program a GAL16V8 for me? (For which I will gladly compensate
time & effort & parts)
Thanks!
Josh
Grant Stockly wrote:
At 03:17 PM 11/14/2007, you wrote:
There are equations for the PALs on my website:
http://www.stockly.com/forums/showthread.php?t=6
The LAG
is labeled "HAL16R8CN 8440 / 342-0251-A" so it does look
like a
custom ("HAL") chip such as what Tony
was mentioning. Guess that
would
It is. The important part of the number is the '16R8' bit. That implies
it's got 8 registered ouptuts and a total of 16 inputs to the AND array
(8 serpate inputs and 8 feedback terms from the output pins). That, of
course, accounts for 16 pins on the 20 pin package, the others are +5V,
ground, a common clock input to all the flip-flops, and a common output
enable signal to all the outputs).
It's the same architecture as a PAL16R8, and could be replaced by a
suitably-programemd GAL16V8. Not that that is any help at all without
the
PAL equations.
I will try to find all my notes on the Mac+ (but not tonight!). I know I
never figured out the PAL equations, but I might have something of use.
4:21 p.m.
So, two things spring immediately to mind:
1) Does anyone know if the LAG from a Mac Plus is the same as (or
equivalent to) the LAG from a 512k? If so, I can take the one out of my
Plus and put it in the 512k for testing purposes. If this succeeds,
then we proceed to point 2:
Look at the Apple part number on the chip (i.e. anything apart from a
date code and the HAL16R8 bit). If that part number is the same, then
I'll wager quite a lot that it's the same prgoramming.
In my experience Apple PCBs of this vintage are not nice to work on,
though. The holes are small, the traces lift if you're not cable. it is
not easy to desolder and remove parts. It is possible, but take care.
-tony
22 Nov
22 Nov
11:35 p.m.
The LAG is labeled "HAL16R8CN 8440 /
342-0251-A" so it does look like a
custom ("HAL") chip such as what Tony was mentioning. Guess that would be
tough to replace, unless someone out there has the means to make a
dupilicate. Bah. That'll teach me to think twice next time I think I
know what I'm doing :).
I remember reading somewhere that a guy from an old repair shop reverse
engineered these equations and put it online. Google is your friend :o)
14 Nov
14 Nov
7:13 p.m.
Okay, I'm home, I have my books. It says on page
98 that
discharging the CRT without a big honking resistor may blow a 74LS38N
(U2) on the analog board and the LAG chip on the logic board. The
IIRC that '38 is part of the vidro drive circuit (at least it is in the
Mac+). I can't rememebr what the LAG chip does, it's one of the PALs I think.
My first thought, though is 'why those 2 particular chips only?' My
_guess_ is that the author of said book has had to repair a couple of
Macs danaged by incorrect CRT discharging, and those where the chips he
found had failed. Next time it might be something else.
former sounds like it might be fairly standard. The
latter sounds
The 74LS38 is a standard TTL part, a quad 2-input NAND with open collector
outputs. It's a very common IC.
like it may be one of the custom programmed PALs or
GALs or whatever
that Tony was writing about.
It is.
-tony
5 Feb
5 Feb
1:01 a.m.
Just to follow up on a very old thread -- I finally got a replacement
LAG for my 512k Mac (thanks to a very helpful list member with a GAL
programmer) and after replacing it, the Mac is once again functioning.
So if you do accidentally do what I did (discharge the CRT to the main
chassis) and you end up with a very long, drawn out boot beep, the LAG
is quite possibly the culprit.
Thanks once again to all you helpful folks. You've been, well, helpful :).
- Josh
That particular failure is documented in Larry
Pina's "Macintosh Repair
and Upgrade Secrets" and probably in "The Dead Mac Scrolls" as well.
I'd
look it up for you, but I don't have my books with me here.
Okay, I'm home, I have my books. It says on page 98 that discharging
the CRT without a big honking resistor may blow a 74LS38N (U2) on the
analog board and the LAG chip on the logic board. The former sounds
like it might be fairly standard. The latter sounds like it may be
one of the custom programmed PALs or GALs or whatever that Tony was
writing about.
I wouldn't be surprised if folks had already figured out all the
internal logic for the various Mac 128/512/Plus chips though. Finding
it might be a bit of a challenge.
OTOH, the LAG chip may be fine and it could be U2 on the analog board
that has the problem.
Jeff Walther
6096
days inactive
6179
days old
9 comments
6 participants
participants (6)
-
alexandre-listas＠e-secure.com.br -
ard＠p850ug1.demon.co.uk -
derschjo＠msu.edu -
gordonjcp＠gjcp.net -
grant＠stockly.com -
trag＠io.com