RE: 68000 Pod Query

Hmm... I would probably be at the point where I'd carefully snip just
the pin (for whatever data line) until I found the culprit. How many
374s are you talking about? 4 or 5? That's not too bad and not too much
of a hack if you're careful and have good snips.

I've never found the bus check on the Fluke to be helpful... ever :-)

I take it when you read a given address, you always have this bit set to
1. (I always like to confirm with the Fluke probe sync'ed to data ...
makes it very easy to catch a problem when the bit is stuck on the
output of a buffer chip, but that doesn't seem to be your problem.)
Before snipping, I'd just double-double check. I hate cutting things
without knowing for sure that I'm on the right track. But if you're
always seeing this bit set at 1, then you're probably right... I've
never found a great technique for isolating these types of problems.
When you throw your scope on that node, is it always 1 as well?

JB

--James Bright
www.QuarterArcade.com
Restored Arcade Games for your Home

> -----Original Message-----
> From: owner-techtoolslist@flippers.com [mailto:owner-
> techtoolslist@flippers.com] On Behalf Of Phillip Eaton
> Sent: Saturday, June 05, 2004 4:16 PM
> To: techtoolslist@flippers.com
> Subject: 68000 Pod Query
>
> I have a broken pinball motherboard here that I'm trying to fix. I'm
using
> a
> Fluke to spy on the data bus because it has a line stuck high.
>
> Connected to the data bus there appears to be:
> 1 EPROM
> 1 RAM
> 1 Resistor pack
> A couple of 74HC244's bringing in the switches matrix data
> A load of 74AC374's driving the transistor-controlled outputs
>
> I've isolated the EPROM, RAM and 244's from the circuit and it makes
no
> difference.
>
> I don't really fancy removing all the 374's so I thought I'd ask if
anyone
> knows whether the 374 IC would ever fail in a state where it would
drive a
> bus line high from an input to that IC? I could understand an output
from
> a
> 244 doing it but they have all been isolated.
>
> Do resistor packs die very often?
>
> Is there a better way of testing for a stuck bit other than snipping
the
> pins of the ICs :-(
>
> The processor on the PCB is a 68000 and when I use the Fluke and 68000
pod
> to check the bus, it says it's OK, but every manual read from the
databus
> gives a stuck bit. Has anyone ever seen the 68000 pod do this?
>
> TIA!
> Phillip Eaton
>
>
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Received on Sat Jun 5 16:57:14 2004