Defender 1C 2C Chip Problem

Jesse69

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I'm stocking up on replacement chips for my Defender boards, but there is a problem. The Later Series Defender drawing set calls chips 1C & 2C as either a 74LS89 or 74LS189 or 74LS289 chip. But I look at my 3 Defender boards and the 1C & 2C chips are marked SN7489N on them, so they're a 7489 chip...

So what chip do I buy? What do your Defender boards have?

Edit - there's also a problem with the 4s & 5s chips - manual says 74LS74 chip but actual chips on a Defender board are marked 7474N.
 
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I just checked 2 of my boards that are easily accessible, and both have 7489's for both chips. FWIW, the full number on all 4 is SN7489N. Also FWIW, I know one of those boards is rev XO, and I think the other is the same.
 
Welcome to the eternal battle of specifications vs reality. The reality is that the engineers made changes on the fly to the boards. Sometimes they updated and republished the sschematics, mostly they didn't. There are a bunch of "field release notes" about these inline mods.

The only answer is, the board wins. What is on the board is the correct chip, unless it is obvious that it has been replaced. That is why when I replace a chip, I socket it. First, because if it went bad once, it may go bad again. Second, that way I know it has been replaced.

I did a quick look at one of my Defender boards and 1C & 2C are SN7489 chips. 4S & 5S are 7474s. Obviously, the LS parts didn't work out.

ken
 
They are all 7489 rams just different manufactuers part numbers. I have these in stock if you need to order some.

"manual says 74LS74 chip but actual chips on a Defender board are marked 7474N"

More than likely either will work. To be on the same side use whats on the board now. If it called for a 7474 and all I had was a LS I would give the LS a try.
 
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If it called for a 7474 and all I had was a LS I would give the LS a try.

There have been a couple of repair threads where people have been able to find LS parts and they didn't work. Remember you are driving some pretty old TTL logic and those LS parts can't alway handle the load.

That being said, if all I had was an LS part and a socket, I'd socket the board and try the LS part. But in this case, Jessie is trying to build up a parts cache, so he might as well buy the right parts.

ken
 
Absolutly but in alot of cases they just used the 74XX part becuase thats what was on hand and the LS part will interchange. I do agree, if your ordering the parts you should get the right one your board needs.
 
I have some Joust PCBs.

5770-09656-00 Rev B
- Two 74S289

5770-09656-00 Rev B
- 1x74S189 and 1x7489 (solder looked original, not a previous repair). The 7489 tested bad and I replaced with a 74S189 from another board. Board works.

5770-09656-00 Rev D
- Two 7489

The 189 is tri-state and the 289 is open-collector. I'm guessing the design doesn't care?

No clue on the LS "didn't work" comment above. Both versions of the Joust drawing sheet note "2" next to the low power Schottky 289. The only reason for listing all 5 to me is to imply any can be used but maybe I'm not thinking in the "Williams way"?

joust.jpg


I'll see what the local surplus dealer has next time I'm in.
 
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