Model 4 just began displaying a screen full of 09090909

[Dokken]

I've been working on a model 4 trying to get the floppy drives working. the computer has worked fine, booted fine until this afternoon. I turned it on and the screen was full of 09090909.

Any thoughts on where to look?

 

[TXNathan]

My model 3 did a very similar thing and it was a bad ram chip. I replaced the set with some from Mav but I tested after each and ultimately found that it was one

 

[ldkraemer]

Here is where I'd start looking. On Startup the SPACE is written to the Display to CLEAR it.

SPACE = 0x20 = 0010 0000

09 Displayed and repeated, which is 0x30 0x39

0x20    0010 0000
0x30    0011 0000
           ^
    Which is Bit 4 or Ram IC 04 (Starting from Right to left RAMIC{0..7})

 
0x20    0010 0000
0x39    0011 1001
           ^ ^  ^
    Which is Bit 0, Bit 3, and Bit 4 or Ram IC's 0,3 & 4 (Starting from Right to left RAMIC{0..7})

You might try carefully removing those RAM IC's and Re-Inserting them in the IC Sockets.
If you get the same results, try replacing them, or maybe swapping Ram IC 4 with RAM IC 1,
in which case you will likely get 0x2B = +

+++++++++++++++++++++++
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Do you have Private Messages turned OFF? I can't PM you???
Larry

 

[Dokken]

thank you both!! I read last night on Ira's site that garbage on the screen could be RAM or the Z80. I have a chip tester, and all the RAM chips passed. I tested the Z80 and it failed. I had a spare, put it in the model 4, and the computer works again!

 

[Robbbert]

That was quick. I was dreaming up all kinds of reasons for the failure, but you've fixed it already. Well done!

 

[Eudimorphodon]

Way back in the late 1990's I was in the middle of playing with my Model 4P when it just froze and henceforth was dead. I didn't have much in the way of diagnostic tools at the time but as a shot in the dark I pulled the Z80 out of a Timex Sinclair 1000 that was literally a doorstop and swapped it in, and the 4P lived again. Apparently Z80s just die sometimes.

 

[Dokken]

Finally, my fully working Model 4 with 2 working disk drives.



And my spare to continue working on. Something is up with the floppy control. Machine boots fine, but can't get a floppy or gotek to be recognized. Pretty sure it's not the FDC card as I have a spare.

 

[Quagmire]

Question: Did you repaint the case? Looks great - good job.

 

[tradde]

Nice looking machine.

 

[Dokken]

thanks. no paint, just cleaned it.