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Model 4D Gate Array - Screen characters missing first bit

Tibs is offering to test my Gate Arrays. I'm going to send them to him and see how that goes.
More later!
 
Yeah sorry that is the one that is bad. Had a real bad night didn't follow up after I tested.

Other two didn't cause the issue. 4.3 is bad.
 
I'm glad that it's actually the IC (U17) the schematics pointed me to.

Now, who in the world has a stock of these parts? It's possible Ian has a couple spares or a Donor Motherboard.


Larry
 
I've got a board with a bad GA for the serial on it. I might let the GA fall out in his package back.
 
"*Oops* Now where did that GA go? :) "

That's very kind if it happens to find its way back to me...
are they reprogrammable? I guess so. Perhaps my original one
has just become stale? Does that happen with GAs?
I barely had contact with this technology back in the day. Colleagues programmed 22V10s I recall
in stuff I did software for. That was about the closest I came.

Its great to get a conformation of the bad part. Did your video look the same as mine?
 
Well here's the rub then, if you got essentially the same results with my GA in your machine,
then I'll assume that is IC was the ONLY issue with my board for now and find a replacement U17.

Thanks!
 
I'm curious what was the wire soldered on the small chip for?
 
It was there when I opened it up. My somewhat educated guess is that
this particular board benefited from a thick sturdy ground directly to the chip.
I might scope it without the connection and see just how bad it is.
Perhaps the trace is bad, this was a way to fix it topside without having to unmount the board.
 
Ah, haven't seen that, but then I have never seen a 4D in person, even in Radio Shack back in the day.

Since these are all interchangeable on the gate array and very few changes were made with the 4D, my late model 4 doesn't have that jumper. Anyway, you should have the tracking number, glad I could help you out.

What it looked like on my end when you booted and left a floppy in, you can easily see what it was doing with the word Diskette? The D and k really showed it fast for me. Once I knew that was the chip, I was able to emulate what you had.

It was less obvious in 64x16 mode, but still visible.
 
Excellent.
Yes I never mentioned I booted off a Model III disk and also saw similar flaws to the pixel generation.
Thanks for the extra details.
 
Least I could do. Your blog was very helpful when I had to fix my Model I.
 
Nice to hear that was helpful! It gratifying that a few people have gleaned some useful knowledge from that one.
And I boldly went into this repair thinking it was going to proceed just like that Model I repair...
until I ran into the pesky Gate Arrays.
 
Doug,
I don't know if you already reset that Jumper J11 Back to J12 for the Adder, but in case you didn't, you should move it back to the original position.

GOOD JOB!

Thanks.

Larry
 
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