Is their a difference in a SN74LS86N and a 74LS 86

SaminVA

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Is their a difference in a SN74LS86N and a 74LS 86
I guess I could have a bad batch. The second Pac man board that was in the bottom of my Pac man cabinet when I bought it works but it was missing the Fruit. I tracked it down to a problem on the V-Ram Addresser aux board. Swap the board between boards and the missing Fruit moves with V-Ram Addresser aux board. So I figured it's a bad chip on the aux board and it only has 10 IC chips so I ordered 5 of each chip from Bob Roberts. I got out my logic probe and started poking around thought I had found the problem twice and replaced both chips with no change. Then I noticed if you put the probe on one pin on one of the SN74LS86N the fruit would appear so I took one of the new 74LS 86 and piggy backed that chip and the fruit appeared and the game played fine. I remove the chip ,put in a socket and the new 74LS 86 and I still have no fruit and I lost my Pacman and ghosts but he still chomps the dots.
I put the original SN74LS86N back in the socket and it works but I am missing the fruit. Piggy back the new 74LS 86 on the old chip in the new socket and the game works. It's strange. Could the new chip be bad or just isn't the same as the original chip?
 

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The prefix is just the manufactuer. SN=Motorola.
That being said, I recently encountered a strange issue on three different boards and all were caused by the same defective IC. When a TI chip was used the problem stayed, using an ST chip fixed the issue on all three boards. Its the only time I ever encountered this on a pac board but you read alot about it on other pcbs. If in doubt replace the IC with one from the same manufactuer.
Did you carefully inspect the traces on the bottom of that pcb? I see them alot where the traces get broke from people prying the sockets off with a screwdriver. Sometimes its just solder smeared across to another pad, sometimes you can hardly see the broke trace so look carefully.
 
Yea, I looked at all the solder joints and traces and everything looks fine. The strange thing is it works when I piggy back the new chip on top of the old chip. The old chip works except for the missing fruit but if I put the new chip in I am missing the fruit , Pacman and the ghosts. In attract mode the dots just disappear. I believe the new 74LS 86 chips must be bad.
 
just for giggles, try piggybacking 2 new 74ls86's. If that fixes it, you've got something down the line drawing more current than the single 86 can supply.
 
just for giggles, try piggybacking 2 new 74ls86's. If that fixes it, you've got something down the line drawing more current than the single 86 can supply.
Yeah, that's what I'm thinking. Something down the line is overloading the '86.
 
Yea, I looked at all the solder joints and traces and everything looks fine. The strange thing is it works when I piggy back the new chip on top of the old chip. The old chip works except for the missing fruit but if I put the new chip in I am missing the fruit , Pacman and the ghosts. In attract mode the dots just disappear. I believe the new 74LS 86 chips must be bad.


The 'N' in the suffix on the original part only means plastic DIP package.
But, actually, the SN prefix = Texas Instruments.
However, during the 1980's, most assembly manufacturers used entire part numbers on their parts list including the manufacturer specific prefixes and suffixes. Texas Instruments pretty much had a lock on parts lists because everybody called out SN74xxxxN parts. Buyers would go out and specifically buy that part and not cross them to other vendors. To get more parts into the market, Motorola also released SN prefixed parts. They weren't the only ones to do this. Motorola usually prefixed their parts with variations beginning with "M".

If I remember right, the "74LS 86" part shown in the pictures is an old Eastern European version. If you need to go with specific variations of 74LS86's then you either have a speed problem or an overloaded output problem. If you can, try a 74F86 and see what happens - this kills two birds with one stone - faster and higher current drive (at the cost of higher power consumption). There probably isn't anything wrong with the new 74LS86's that you are trying. They may be just a little slower than the previous Moto's.... or may have less current drive than the Moto's.

-- Ed
 
I agree with ED. I have bought a few batches of LS out of europe and they all look like those. I havent run into any issues with them.
 
Well problem solved and Pacman board # 2 is fully working again. So here's a recap of what I did.
I first replaced U10 (74LS02) with no change. Next I replaced U2 (74LS257) with no change. Then I replaced U9 (74LS86) because when I piggy backed a new 74LS86 the missing fruit started working but when I replaced the old chip with a new one not only was my fruit missing again but Pacman and the ghosts were missing too. I tried piggy backing 2 new 74LS86 chips but it didn't work so I put the old SN74LS86N back in and started checking again with my logic probe. I noticed by applying the probes tip to certain chip pins it would make the fruit appear. I did this testing with the game froze on a screen that should have the missing fruit displayed buy switching dip switch 8. I then probed all the pins and wrote down all the chip and pin numbers that made the fruit appear. Turns out I got the most active pins on chip U5 (74LS157) and a couple of pins would produce part of the fruit so I de soldered it and put in a socket and put a new 74LS157 and now I had my fruit back. I then decided to put one of the new 74LS86 chips back in U9 and it still worked so their was nothing wrong with the 74LS86 chip so I guess the bad U5 (74LS157) was causing it to appear like it was bad.
So if anyone wants to add this to their Pacman repair logs Here ya go.
If your game is missing the Fruit in both attract mode and game play and the large Pac man chasing the ghost in the first intermission is missing his bottom Jaw then U5 a 74LS157 is bad. That's the chip in the middle of the V-RAM Addresser board.
One more board fixed so many more to go. I guess Frogger is next. :D
 

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