[techtoolslist] Fluke 6800 POD resets when testing UUT...

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I don't know if anyone else has had this happen, but I was fixing an Atari
pinball MPU and my 6800 pod would give timeout errors and reboot the pod to
the default display of "Fluke 9000 Ready".

Found a number of interesting causes - first the 6800 uses both phase 1 & 2
clocks, and phase 2 was noisy. Fixed that...

So far so good...still got the pod rebooting itself...strange. Unplugged
the interconnect cable between the MPU and the Lamp/Audio AUX board and the
pod worked perfectly (found additional faults on MPU RAM). Plugged the AUX
cable back in - down went the pod. Even gave messages of self test etc
flickeringly fast as the base would then reset. None of the lines connect
directly to the address or data bus to the AUX board, but there is a
filtered A1 and A2 that feed back to the CPU - weird, check the schematic!
However if I put the AUX cable on sideways so not all contacts engage the
board will work until I get near the A/1 end (the A1/2 are at the K end of
the plug - long since connected) at which point the pod craps out again.
Pull out scope. Check Audio output lines - they are noisy...find bad latch
IC for one Address line for the Audio PROM. Now the board works fine with
the AUX cable plugged in.

I believe the noisy Audio lines were cross-talking with the two address
lines and this was enough to load down the CPU and shut it down.

Moral of the story? Don't assume that just because something isn't
connected to the Address/DATA bus that it can't take the UUT down!

(UUT = Unit Under Test)

John :-#)#

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Received on Thu Aug 14 21:00:19 2003