Re: Red Alert help needed (6502 CPU question too)

Franklin Bowen wrote:

> I posted something similar on RGVAC and got no response so I though I
> would try it here.
>
> Does anyone have a different manual than the one on-line (my board is
> about 20% different, mostly parts not populated, than this manual)?
> If so, can I borrow, buy, or get a scan of it?
> If not, does anyone have better scans of the Main Logic pages or
> schematics I can borrow/buy?
>
> The voltages on the board are perfect. The thing I can't figure out
> is why the CPU address lines are all low! I have placed my logic
> probe on them at power up and I never notice the high light activate
> or the tone change. But maybe it happens too quickly for it to be
> noticeable? I swapped the CPU with another (neither verified good)
> and got the same results. Stable picture of garbage with no
> noticeable activity.
>
> So here is what is happening at the CPU:
> /RESET starts low, then stays high
> Clock in (pin 37) is 733.2 KHz. Supposed to be 1MHz according to MAME.
> Clock outs both 733.2 KHz.
> A15-A0 are all stuck low.
> D7-D0 all pulse.
> R/_W is high
> SYNC is low
> /NMI is high
> /IRQ is low (I pulled the driving chip and tied the signal high. No
> change)
> RDY is low

RDY (pin 2) is stopping the processor, but according to the schematic
there is nothing to pull it high. I would think there should be a
pullup resistor in there somewhere, probably from +5 to the collector of
TR9. Something in the 1K to 4.7 K range should work.

>

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Received on Sun May 2 15:00:03 2004