[Techtoolslist] Fluke 9010 bus test address tied message confusion

[David Shoemaker]

Ok so I got one of my SI boards working. And that let me figure out what was
going on here.

The pod (twisted pair cable) would always show this error when doing bus
test and ram reads / writes were flakey.  Any of my 3 boards.

I have 3 of the 8080 pods (two flat cable and this one twisted pair).  But
the flat cable pods have never been able to work reliably with the midway
8080 boards for me.  Read 2000 loop would toggle values.  Obvious the
address drivers were having trouble.

So I did some substitutions between pods.  Swapped the twisted pair cable
over to one of the flat cable pods and WONDER of WONDERS.  The pod now will
do a RUN UUT, and everything is golden, read / writes are fine now.  (Same
board that is giving the A13 error).

So I swapped the CPU boards (and noticed something odd, the twisted pair pod
has a different rom part number than the two flat cable pods).  No change,
still A13.

OK so must be in the IO board.  Looked at the schematic and found A13 goes
through the protection chip (praying that is not bad).  And from there to a
245.  Well those go bad, and there is another one on the board so I swapped
them.

No more A13 error.  And looking at the schematic that buffer gate isn't used
in the other location so it is "Fixed" for now.  Will look at getting some
replacements for these in (not standard LS family).

I tried the flat cables with the clock resistors jumped and it didn't make
any difference.  The twisted pair doesn't need them jumped.

At the end of the day all 3 pods work with the twisted pair cable.  But ONLY
with that cable.

So where do I get new twisted pair cables for these?  Anyone?

David

-----Original Message-----
From: Techtoolslist [mailto:techtoolslist-bounces at flippers.com] On Behalf Of
John Robertson
Sent: Wednesday, July 10, 2019 6:41 AM
To: techtoolslist at flippers.com
Subject: Re: [Techtoolslist] Fluke 9010 bus test address tied message
confusion

On 2019/07/10 12:10 a.m., David Shoemaker wrote:
> Working on a space invaders board.
>
> 8080 pod, passes self-test.
>
> Put it onto UUT and hit auto.  Getting an error that does make sense.
>
> ADDR bits 13 tied-Loop?
>
> Thought at first that was bits 1 & 3 tied.  But probing around didn't find
> anything.  So I tried tying them together myself to see what happens.
>
> ADDR Bits 1 and 3 tied - loop?
>
> Uh, ok so they are explicit on the two bits tied.  That's good to know.
But
> why is it only telling me one bit?
>
> So I pulled out the manual and from the bus test error messages table
there
> should never be a "bits" message without two bits.  But I am only getting
> one (and no MORE led, and more button does nothing).
>
> The only single bit error should be if bit tied low or high. But that is
not
> the message (and it says "bit" not "bits").
>
> I tried exercising bit 13, did a write @ 2000 = 0, probe set on address
and
> can see the line being driven high.  And no other bits are being driven
when
> I check.
>
> Thoughts?
>
>   
>
> Thanks,
>
> David
>
>
When I get these errors (not specific about what it is tied too) I 
search the entire line and usually find it is shorted to something the 
CPU has no connection to. For example on the SI board - do you have the 
sub-board unplugged? Take a look in the socket for junk/bent pin 
shorting A13 to some other line (if A13 goes to that socket). This error 
simply means that the Fluke can't exercise A13 easily and it assumes it 
is stuck to some other line that the pod can't 'see'.

Have you done a Diode Test to compare A13/Vcc/GND results with A12 or 
A14? They should be the same with the Fluke pod disconnected.

John :-#)#

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