A3640 - Adress line A1 and U213

mortenkjerulff · 29 April 2020, 22:08

I have been struggling with the stability of my poor A4000, and may have narrowed the problem down to U213 on the A3640.

I noticed the pin 2 (CLK) did not have a clear signal on the oscilloscope (like pin 2 on the other GAL-chips). It is connected to the A1 adress-line, as far as I can tell.
It is neither high nor low, but maybe 200 mv with lots of noise.

When I measure A1 on Buster or Alice on the mother board, it is the same.

But if I remove the A3640, A1 on Buster or Alice is high.

So I think something is wrong on the A3640.
Unfortunately I have a hard time following the trace for A1 on the A3640, and I have a very limited understanding of the workings of the A3640.

Another reason for suspecting U213, is that the computer worked for hours after spraying U213 with a freeze-spray to hunt for problems, until I assembled the computer with zorro-boards and everything. Then it worked for a few minutes and then black screen.

I have reflowed U213 without any results.

Any ideas?

Cheers
Morten

torsti76 · 29 April 2020, 23:32

Perhaps ask John "Chucky" Hertell for help. He designed the A3660 and should know the A3640 inside and out.

dalek · 30 April 2020, 00:49

Why not just replace U213?

mortenkjerulff · 13 May 2020, 17:06

Just an update.

I think this was a dead end.

I tried swapping the A3640 with a new A3660, and the symptoms are the same, so I guess the problem is somewhere on the motherboard.

29 April 2020, 22:08	#1
mortenkjerulff Registered User Join Date: Apr 2020 Location: Marstal Posts: 19	A3640 - Adress line A1 and U213 I have been struggling with the stability of my poor A4000, and may have narrowed the problem down to U213 on the A3640. I noticed the pin 2 (CLK) did not have a clear signal on the oscilloscope (like pin 2 on the other GAL-chips). It is connected to the A1 adress-line, as far as I can tell. It is neither high nor low, but maybe 200 mv with lots of noise. When I measure A1 on Buster or Alice on the mother board, it is the same. But if I remove the A3640, A1 on Buster or Alice is high. So I think something is wrong on the A3640. Unfortunately I have a hard time following the trace for A1 on the A3640, and I have a very limited understanding of the workings of the A3640. Another reason for suspecting U213, is that the computer worked for hours after spraying U213 with a freeze-spray to hunt for problems, until I assembled the computer with zorro-boards and everything. Then it worked for a few minutes and then black screen. I have reflowed U213 without any results. Any ideas? Cheers Morten

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29 April 2020, 23:32	#2
torsti76 Registered User Join Date: May 2018 Location: Germany, Baden-Wuerttemberg Posts: 387	Perhaps ask John "Chucky" Hertell for help. He designed the A3660 and should know the A3640 inside and out.

30 April 2020, 00:49	#3
dalek Registered User Join Date: Nov 2014 Location: NSW/Australia Posts: 462	Why not just replace U213?

13 May 2020, 17:06	#4
mortenkjerulff Registered User Join Date: Apr 2020 Location: Marstal Posts: 19	Just an update. I think this was a dead end. I tried swapping the A3640 with a new A3660, and the symptoms are the same, so I guess the problem is somewhere on the motherboard.

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