(Topic ID: 210511)

F-14 U25 Error


By CadillacMusic

1 year ago



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  • 12 posts
  • 5 Pinsiders participating
  • Latest reply 1 year ago by CadillacMusic
  • Topic is favorited by 2 Pinsiders

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#1 1 year ago

Getting a u25 RAM error when booting up my F-14 Tomcat. I socketed and replaced the RAM with a 6116 chip. Still having problems. The strange thing is that if I powercycle the machine quickly, it works fine. It also remembers settings correctly. It's pretty clearly something on the CPU board. What exactly are the steps it goes through to self test that RAM?

#2 1 year ago
Quoted from CadillacMusic:

What exactly are the steps it goes through to self test that RAM?

Just a basic read/write test, but other problems can cause the same error. Basically the cpu can't consistently communicate with RAM. Could be corrosion on the board (post some close-up, in-focus photos) or a bad chip socket or cold solder joint.

#3 1 year ago

Try a different brand 6116?

#4 1 year ago
Quoted from terryb:

Could be corrosion on the board (post some close-up, in-focus photos)

+1

#5 1 year ago

Not really seeing corrosion here, but I don't like this chip for some reason. The last one in the box always makes me wonder if someone put it back because it didn't work. No other 6116 chips, so I'm gonna jumper for a 64.

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#6 1 year ago
Quoted from CadillacMusic:

Not really seeing corrosion here, but I don't like this chip for some reason. The last one in the box always makes me wonder if someone put it back because it didn't work. No other 6116 chips, so I'm gonna jumper for a 64.

You can't jumper for a 6264. U25 is only 24 pins. No additional pads/thru-holes for a 28 pin chip on that board. You're stuck with a 24 pin RAM (6116).

U25 errors are often caused by low 5V/marginal power supply.

--
Rob Anthony
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#7 1 year ago

Oh, duh. Well, poop. Gonna check that voltage then.

#8 1 year ago

Hmm. 4.94 at cpu board. Not spectacular, but is that really enough to cause problems?

#9 1 year ago
Quoted from CadillacMusic:

Hmm. 4.94 at cpu board. Not spectacular, but is that really enough to cause problems?

That should be enough. Board looks good and the socket looks good, but if you're a good solderer I would probably replace it along with the new RAM chip.

Any previous work done to the board?

#10 1 year ago

There's a hack to the switch area that honestly makes me laugh, but is functional. Some past guy didn't have a resistor array, so he just made one out of a bunch of resistors. Otherwise, no previous work. That is a new socket. I'm beep testing lines as we speak. Looks like the processor goes through u16 for the data lines, and u11 and u13 for the address bus. Doing some beep testing to make sure there's no broken traces, but those are my next targets.

#11 1 year ago

And, neither of those are in stock. I guess this is tabled until I get some chips in. Always tempted to pull from old boards, but that just complicates things.

#12 1 year ago

Update: Was a bad U16. All fixed!

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