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From: joost@neabbs.UUCP (JOOST BOERHOUT)
Newsgroups: comp.sys.amiga.hardware
Subject: Problems with LUCAS&FRANCES (was 2.0 in FRANCES)
Message-ID: <449417@neabbs.UUCP>
Date: 15 Sep 90 16:12:04 GMT
Organization: NEABBS multi-line BBS +31-20-5733533 (13x), Amsterdam, Holland.
Lines: 37

In article 446008@neabbs.UUCP Steve Warren wrote:

>In article <444299@neabbs.UUCP> joost@neabbs.UUCP (JOOST BOERHOUT) writes:
>>I can't explain why FRANCES needs the warming up except the darn thing
>>is working on the edge of the (timing) specs. A heated chip will have
>>a shift in the timing specs so this seems to be the case.

>Yes, a common failure on higher-speed systems is the "cold" failure.
>Some technicians debug a board like this with a can of freon:

Hmm, yes I did this 'freeze' test. I went all over LUCAS and FRANCES with
the freon nozzle (one chip at the time) but could not find anything.

I looked at the power and ground lines of the 74ls245 drivers using a
20 MHz scoop. This showed a lot of high frequency junk going on
(peaks of 1 Volt !) which seemed to be related to the /DATABUSEN signal.
There is no way I can get rid of these peaks (I use 1uF tant parallel
to 100n ceramic for decouple caps).

Another thing is the infamous U9 flip-flop (it's more a flop then a
flip :-). The only chip which worked for LUCAS is a 74HC74 and I have
to solder a jumper from the GND pin to the expansion port GND.

I checked several GND points at the two boards with a volt meter (one
terminal to the pin, one to the expansion GND). The meter read 2.5mV
at most in all cases.
It makes no difference if I use a 16MHz or 20MHz oscillator. All
'features' stay on.
What I haven't tried yet is to change the PALs on the piggy back board.
However, I must say I don't expect much from such a change.

The system works, however, after a short warming up time. And when it
chrashes it mostly happens with the same programs. BLink for example
chrashes 1 in 3 times !

Ideas anyone ??

- joost -