Re: Battlezone

It's very common for the address and data buffers (74LS244 and 74LS245)
to go bad,. If the self test doesn't even come up or make a beep - then I
assume it's one of those or a bad vector generator ROM. I prefer going
through with a signature analyzer to avoid using the hit and miss method.

Matt

> Thanks Chris, I'll give it a try. First, I went to school for electronics.
> I have a basic understanding, but really no practical experience. I have
> an ocilloscope and a logic probe.
>
> When I turn the game on, there is no attract mode. Also in test mode,
> there is no picture, except some artifacts. I put the scope on X or Y out
> and got what I thought was a valid signal, but there was nothing on Z out
> except some very small spikes. I went to Q7 and I got a signal. Q8 was
> turned on thereby blanking the screen, always. I traced the signal back to
> H10 and found "statclk" and "latch1" were always high. "statclk" comes
> from K10 (vector timer control) which has an input from "strobe2". I found
> that J7 provided these signals among others and all were high, always. I
> thought the vector state prom was bad so I got one from Eldorado Games. It
> made no difference. I checked the three inputs, OP0, OP1, OP2 to the state
> prom and they were stuck too. As a side bar, I could not figure how this
> thing got started if the inputs to the prom were from outputs based on the
> prom. Anyway, I have an asteroids schematic and in the circuit description
> for the state machine, it says the state machine gets its instructions
> from the MPU to access the VG ROM. I put the scope on the processor's
> address lines and got some square waves and got some fuzzy lines I could
> not resolve. Part of the problem is I don't know what waveforms to expect.
> So I replaced the processor with one I know works, but nothing. I am not
> able to do a checksum on the ROMs. I am getting stuck.
> I am not even sure my approach is correct. Btw, all the voltages are
> correct. I cleaned and reseated all the chips. I visually inspected the
> board and components. I checked the soldier on the board interconnect. All
> of the basic stuff seems to be as it should be. Also, I am getting all the
> clock signals. In regular mode, the game keeps resetting, but that is
> understandable since there is no activity on the address lines("wdclr"
> from the address decoder is always high). As an example of my
> inexperience, the X and Y out that I thought was a good signal in test
> mode, when I put it on the scope in XY mode there was something but it was
> not the test screen.
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Received on Sun Oct 10 13:09:31 2004