Re: Tempest resetting problem

When the RAM fails on those atari games you can get some pretty strange results,
especially if the RAM that is used during the RAM test is bad or the 74LS245 for the
RAM is flaky.
  On your roomates idea that the CPU will not see the RAM since it is resetting... the
CPU is actually running quite a while between those resets. One of the first things
the program does is set up the RAM and test it.
  These types of problems would be much easier to fix with the fluke unless you want to
just start swapping RAM chips. Since you have a Fluke this is a good time to learn how
to use it (then you can show me! ;-) I would see if you can write a 0x55 and 0xAA to the
RAM locations and make sure they are all okay. Also, maybe you have some address decoding
problems?? Do rule out the 74LS245 RAM buffer either, I had one with a bad bit output
depending on the data it was buffering.

  One weird thing tho is that the CPU RAM is not being addressed while the Vector RAM is.
The program should be checking out and using the program RAM right away. Check the address
decoders maybe.

Matt Rossiter - Verio Southern California wrote:
>
> Well, I've ruled out the Power Reset and Watchdog counter along with the
> clock circuit. I used a logic comparator and tested every chip in that
> circuit and they all test out fine.
>
> My roomate seems to disagree with my "it's a ram problem" theory because
> if the CPU keeps resetting it will never see the ram.
>
> I do have a question though. There are 4 2114 ram chips which make up the
> program ram and about 6 which make up the vector ram. Right? Well, I
> tried pulling out the roms as suggested below and looked at the chip
> select pins on the ram chips. All the program ram chips stayed high while
> all the vector ram chips were pulsing on the chip select line. In fact,
> they pulsed at about the same frequency as the reset line pulsed. Could
> there be a clue here? hmmm....
>
> By the way - I ordered some of those Braemar tapes for the Fluke 9010a
> troubleshooter and they are $16 bucks a piece (yes I also know how to use
> the RS232 interface) and they only sell them in packs of 10. I got them
> anyway - don't ask me why. Well, whoever can give me a solution that
> works for this tempest problem will get a free blank tape on me! Oooh
> Ahhh! You don't even have to pay for shipping.
>
> Matt
>
> _____________________________________________________________________
>
> On Mon, 18 Oct 1999, Chris Loggans wrote:
>
> > > ...
> > >2) I'm not so sure of the ram. My fluke 9010a can't do a read/Write to
> > >anything in the ram address space (both program ram and color vector
> > >ram) - so either one of the buffers is bad or a ram chip is bad.
> >
> > I think this is your best guess right here. If the Fluke cannot reach the
> > RAM, then the CPU can't reach the RAM and nothing will work. As you
> > mentioned, it could be a buffer issue. It could also be a chip select
> > issue. If this is the case, then either the chip select lines are not
> > functioning or there is a chip that is stuck "on", regardless of whether or
> > not is is selected. Even though you know the ROM's are OK, I would remove
> > all of the ROM's and then try to do the RAM test. If the RAM can now be
> > reached, then put the ROM's back in one at a time and see when the problem
> > re-occurs. You should be able to narrow it down from there.
> >
> > Good luck,
> > -Chris
> >
Received on Tue Oct 19 09:53:47 1999