Electronics > Repair

What more i can do?

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m k:
Yes.
Afterwards Harry can do his trick and then we'll see how data has changed.

Harry, if second data is E9 check also to where it is actually jumping.
Previous data indicates that address will be F8E9.

68k CPU has a special 8 bit write cycle, it doubles one side of 16 bit data.
Controller chip can have a mode something like that.

But it also means that OE is not activated.
Or something is forcing that other side of data bus.
Or there is a latch.
Or something else.

asis:
Hello,

@222Lab_Test222

I analyzed the content of this thread and out of more than 450 replies, as it turned out, 25% directly or indirectly boiled down to an attempt to understand the behavior of IC23 (NEC uPD4990A) CMOS.

All those participating in the discussion sometimes came very close to understanding the truth.

All the possibilities were determined only by the presence of a two-channel scope.
But, believe me, it is very difficult to perceive the processes occurring in the product from the pictures on the scope screen, with so many components and, let's say, turning the scope into a signature analyzer or Curve Tracer.
-
I would like to offer you an idea.
-
As you can see, there are six quartz generators on the PCB, servicing various nodes.
All together they must interact - as a single organism.
Figuratively speaking, - all hearts must beat in a single rhythm.
-
Now to the point.
I want to draw your attention to the Clock 32768kHz (X1 - IC7 74ACT08).
Or, more precisely, to C10.
I doubt that it is installed for time correction (in the sense of GLOBAL/UTC).
As a rule, the accuracy is sufficient wherever the 32768kHz quartz is used.
I suspect that the C10 adjustment determines some kind of "global synchronization" that optimizes timings in conjunction with other nodes, including  IC23 (NEC uPD4990A) CMOS.
The presence of checkpoints TP1, TP2 convinces me of this even more.
-
I offer you - such a scenario:

On a non-working board, you find a pin on IC7 (74ACT08), measure and write down the original frequency so that you can return to the original state ( check TP1, TP2).
And start adjusting C10, carry out the delta F deviation to a larger, and then (!), to a smaller value, fixing it all together.
That is, I suggest you find a range of acceptable values, in which IC23 (NEC uPD4990A) will work stably.
Perhaps, this will be facilitated by the LED indication and the buzzer reaction.
If everything works out, set C10 to the average frequency value in a certain interval.
You will probably have to turn the device on/off several times.
But, if we go back in time, all old PCs had a priority of devices, starting with KBD and ending with CD / HDD, etc.
If you have KBD, then the easiest way to create NMI is Ctrl - Alt - Del.
You may have a different combination.
But it should be.

Good luck.

222Lab_Test222:
@Harry_22
@fzabkar

Here are the EPROS Datas
4 Datas are there.
Working High, Working Low, Non Working High and Non Working Low

222Lab_Test222:

--- Quote from: asis on December 14, 2024, 04:29:43 am ---On a non-working board, you find a pin on IC7 (74ACT08), measure and write down the original frequency so that you can return to the original state ( check TP1, TP2)

--- End quote ---
TP1 is shorted with PIN 11 of IC23 uD49.
TP2 is shorted with GND.

I still couldn't find the PIN on IC7 for frequency. Those IC7 Pins are either connected to IC6 or IC3 or Flash Memory.
Did i miss something?

squadchannel:
interleaved at single byte. (attached)
no difference in comparison. probably a hardware failure.  :-BROKE

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