Re: Assistance please...

> << I'm now completely baffled. Does anyone have any suggestions as to
> where/how to start debugging this problem? I have all the parts I need to
> continue my vector hack and I'd like to get it going again. >>
> I'd socket & replace the 74LS245 @ F1 first.

I think you meant the 74LS245 @ P1. F1 Is an EPROM socket.

Man, I just don't know what the problem is. I wound up writing a program
that just bangs 0ffh/00h to the entirety of vector RAM repeatedly. I've
troubleshot for the last couple of hours and have done the following:

* Swapped out all 2114s again just to make sure
* Replaced the AMD 8304B with a 74LS245 (and yes, I soldered the socket
down in the proper row of leads)
* Verified that the DB lines were all toggling as expected (at the 245,
the EPROM sockets, and the 2114s)
* Verified that the AMxx lines were all toggling as expected (at all of
the LS157s and both EPROM and 2214s)
* Verified R/!W is reaching the 245 and is toggling
* Verified !VMEM is present at every LS157
* Verified that all of the AB0-AB12 lines were toggling out the side of
all LS157s
* Verified that the LS139 @ L2 keeps !VRAM low (since that's all my test
does)
* Verified that !VROM1/!VROM2 are always high (it's supposed to since I'm
not accessing them)
* Verified the 74LS32 @ M4 is giving toggled results as expected on both
inputs and outputs
* Verified the LS04 @ L4 is inverting as it should
* Verified that !VRAM and M10 are making it to the 74LS32 and 74LS04
respectively

I did have one bad 2114 that stuck DB6 low, and another that stuck DB5
low. Now that none stick, I've hooked back up the EPROMs and I still get
the 2 high/1 low beep. ;-(

Any suggestions at all? I'm not sure where to turn next!

-->Neil

-------------------------------------------------------------------------------
Neil Bradley Play a song wrong once and it's a mistake.
Synthcom Systems, Inc. Play a song wrong twice and it's Jazz.
ICQ #29402898

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Received on Tue May 1 01:55:13 2001