Asteroids Version 6 MPU board

[rhombus]

I been meaning to ask if anyone knows this. I worked on these boards for years and I only ran into 2 or 3 ver6 MPU board in my time. Anyone know what the reason for Atari making the ver6 boards? Seems to me that they had something in mind. It has 4 extra PROM chips at location E8-J8.

 

[andrewb]

The difference is in how the rate multiplier circuit is implemented. On the earlier boards, they did it with 7497's. On later boards, they did it with the PROMs. The Rev6's (and I think Rev5's?) have that gap in the middle of the PCB, where the board can be populated with either. (You'll also see some boards with a separate rate multiplier daughterboard, pic below.)

They did it this way because back at that time, these chips were not an infinite resource. Atari was making so many boards that they could buy up the entire supply of some chips. So many of the PCB revisions you see on Atari stuff were done so alternate chips could be used in some sections of the boards, to accomplish the same functions with different parts that were more available.

That's how badass Atari was at the time. They were outpacing the supply for some of these chips.

 

[ArcadeTechGW]

It might have been cost related as well. If someone drove up prices (we've got Atari over a barrel - they have to pay) Atari was smart enough to say "Engineering - find a different way to do this without this chip."

And then let the wonderboys go to work.

It could be either. I have no evidence to support my speculation.

 

[coinopper]

Atari revised their VCS/2600 board at least 16 times, and each time they did it, it was to reduce cost/save money. Each time they revised it, the performance took a hit, particularly with the audio and picture quality.

 

[Laschek]

Jed Margolin mentions this on his site:
"Part way through the run of Asteroids, we used up the world's supply of 7497s and Texas Instruments (the only manufacturer of 7497s) did not have them on their schedule to make more for several months. Rather than shut down the production of Asteroids, Howard Delman designed a daughter board with small-scale ICs to replace the 7497s. A new layout for the Asteroids PCB was also done using the new circuitry."

The Secret Life of Vector Generators

(Super interesting stuff there, even though I can only understand a fraction of it.)

 

[andrewb]

Yep, that's where the info came from.

Jed's whole site is fascinating, if you do some digging.

 

[coinopper]

That's why the rate multiplier board was created.

 

[andrewb]

That's why the rate multiplier board was created.

See post #2 above.

 

[rhombus]

Good info, thanks. I knew that they made new ver boards to save $$$ but I would have thought that the prom were more money, didn't think about availability to parts at the time. Those guys sure were at the evolution frontline. I found this info somewhere, can't remember were, about replacing the proms with 7497 if you're having problems with the proms:

There is a big difference in the Vector Rate Multiplier Circuitry between
board versions -05 and -06. In a nutshell, the -05 version uses 7497 chips,
and the -06 version uses PROMs.

The -06 version uses four PROMs at locations E8, F8, H8 and J8. Three of
them have the same Atari part number: 35904-01, located at positions F8, H8,
and J8. The PROM at E8 has a different Atari part number: 35905-01. All
four of these PROMs are 82S131. There is a 74LS02 at location C8. There
are 4.7k resistors at locations R159, R160, R161, R162, R163, R164, R165,
R166, R167, R168, and R169. Chip locations F9, H9, J9 and K9 are all empty.

The -05 version uses four 7497 chips (which are easier to find, and you
don't have to program those) at locations F9, H9, J9 and K9. Chip location
C8 is empty; chip locations E8, F8, H8, and J8 are empty; and all of those
resistors R159-R169 are gone.

Therefore, if you think you have a bad PROM on a -06 board, and can't/won't
replace it, you can do the following:

1) Remove the PROMs at E8, F8, H8 and J8. Remove the 74LS02 at C8. Remove
the 4.7k resistors at R159-R169.
2) Install 7497 TTL chips at locations F9, H9, J9 and K9.

This effectively turns a -06 board into a -05 board.

 

[ArcadeTechGW]

Good info, thanks. I knew that they made new ver boards to save $$$ but I would have thought that the prom were more money, didn't think about availability to parts at the time. Those guys sure were at the evolution frontline. I found this info somewhere, can't remember were, about replacing the proms with 7497 if you're having problems with the proms:

There is a big difference in the Vector Rate Multiplier Circuitry between
board versions -05 and -06. In a nutshell, the -05 version uses 7497 chips,
and the -06 version uses PROMs.

The -06 version uses four PROMs at locations E8, F8, H8 and J8. Three of
them have the same Atari part number: 35904-01, located at positions F8, H8,
and J8. The PROM at E8 has a different Atari part number: 35905-01. All
four of these PROMs are 82S131. There is a 74LS02 at location C8. There
are 4.7k resistors at locations R159, R160, R161, R162, R163, R164, R165,
R166, R167, R168, and R169. Chip locations F9, H9, J9 and K9 are all empty.

The -05 version uses four 7497 chips (which are easier to find, and you
don't have to program those) at locations F9, H9, J9 and K9. Chip location
C8 is empty; chip locations E8, F8, H8, and J8 are empty; and all of those
resistors R159-R169 are gone.

Therefore, if you think you have a bad PROM on a -06 board, and can't/won't
replace it, you can do the following:

1) Remove the PROMs at E8, F8, H8 and J8. Remove the 74LS02 at C8. Remove
the 4.7k resistors at R159-R169.
2) Install 7497 TTL chips at locations F9, H9, J9 and K9.

This effectively turns a -06 board into a -05 board.

Nice! A way to fix later model boards if the chips become unobtainum!