Author Topic: What more i can do?  (Read 36908 times)

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Offline m k

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Re: What more i can do?
« Reply #525 on: December 26, 2024, 06:05:51 pm »
Here are the Address and Data pictures of the first 20us for the working machine.
The first address is 3FFF8h.
The comparison for non-working machine I will make next.

My guess is that your address is one off.
A0 is actually A1 and real A0 is not present.
So ROM address for boot goes to correct address 7FFF0.

A bit after first jump is IN 35h.
Pictured A4 is dropping down after a jump and single high is 35h.

Jump address is F800, so A11 stays up.
35h has A5 and A4 up and A0 is missing.
« Last Edit: December 26, 2024, 06:58:26 pm by m k »
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Offline m k

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Re: What more i can do?
« Reply #526 on: December 26, 2024, 06:06:59 pm »
Working Board Address Inputs Wa0-Wa9

If you like you can check that A4 of all faulty boards.
If shape is the same you have functioning connection between CPU and program ROM.

If that single high is not there you have a similar fault that the original test subject has.
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Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #527 on: December 26, 2024, 11:07:42 pm »

Why did you scope only half of the data?
Half the data mean?
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #528 on: December 26, 2024, 11:16:17 pm »

If you like you can check that A4 of all faulty boards.
If shape is the same you have functioning connection between CPU and program ROM.

If that single high is not there you have a similar fault that the original test subject has.
If I do not get similar signals then that hints CPU is faulty?
Or is there any way to know CPU is ok or not.
 

Offline asis

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Re: What more i can do?
« Reply #529 on: December 27, 2024, 12:48:32 am »
Hi,

If you have time, check the circuit by ringing the connections.
Please.
-
Next step will be - FRAM/ DRAM SIMM72.
 

Online Shock

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Re: What more i can do?
« Reply #530 on: December 27, 2024, 01:34:16 am »
I read this and I thought hmm beep only on a working board and I immediately thought a case opened tamper switch. I'd laugh if they are all working but a few aren't.
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Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #531 on: December 27, 2024, 04:16:15 am »
Hi,

If you have time, check the circuit by ringing the connections.
Please.
-
Next step will be - FRAM/ DRAM SIMM72.
There is no direct connection between CPU and BIOS. there seems to buffer IC between them.
Please check Reply #283 and #275.
If you do not understand the connection let me know.

Note: here looks like IC 10 11 12 13 acts as a bridge between data pins of BIOS and CPU.
 

Offline asis

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Re: What more i can do?
« Reply #532 on: December 27, 2024, 04:55:24 am »
Ok
I got that, but I don't see the type 10,11,12,13.
74LS245L x 4pcs?
-
I'll fix it.
Tnx.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #533 on: December 27, 2024, 05:38:10 am »
Ok
I got that, but I don't see the type 10,11,12,13.
74LS245L x 4pcs?
-
I'll fix it.
Tnx.
They are on back side of PCB. Here is the image.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #534 on: December 27, 2024, 07:42:05 am »
Time for New Year Break

be back again in a week

Happy New Year All
 
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Offline Swake

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Re: What more i can do?
« Reply #535 on: December 27, 2024, 08:13:47 am »
You too, and also for everyone here, have a perfect 2025 !
When it fits stop using the hammer
 

Offline m k

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Re: What more i can do?
« Reply #536 on: December 27, 2024, 11:41:02 am »

Why did you scope only half of the data?
Half the data mean?


D0 to D7 only once.
So it was like #382?

First bigger interference of #477 means the start.
So first D0 is up, so 0d0d.
76543210
00001101

But the end part is very different than #382.
So one more time, with three sets you can start voting.



If you like you can check that A4 of all faulty boards.
If shape is the same you have functioning connection between CPU and program ROM.

If that single high is not there you have a similar fault that the original test subject has.
If I do not get similar signals then that hints CPU is faulty?
Or is there any way to know CPU is ok or not.

You can't prove negative.
CPU is also so complex that you can have a faulty section even when the thing seems to be ok.
One example is memory test, back in the day it was doomed to be inaccurate and only accurate thing being an operating system.
And even then it was still like which end or something in between.

Internal CPU errors are rare, like one day adding doesn't go anymore.
Usual problem area is external world interfacing part.
New processors with embedded extras are different.

So in practice you must diagnose enough faulty pins by judging them as not right, so comparing them with known good state.
But your CPU is regular and it is socketed, so "just" find an old regular computer and test them.
Digging the chip out is not necessary easy, check few videos.

In this case you can also use measurements, since that earlier wrong data was 0d0d and other ROM content is 0d, you can make an educated guess.
You swap ROMs and do the same measurement again.
But since you don't know what you don't know there are no short cuts, partial measurement doesn't tell much, you must do it all again.
Don't hassle either, be sure that chips are correctly inserted and legs are straight.

With old and new measurement you can do a comparison.
If the data is still 0d0d you can guess that it is not from a ROM at all.
If it is e9e9 you can guess that it is from the swapped ROM, and this can affect CPU operation in measurable way.
Since e9 is a jump you must have addresses measured also, so that you can check how that jump is executed.
If that jumped address then correlates to next data bytes you can say that the CPU is actually seeing what you have measured.
If jump address is something else you can do the next educated guess.
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Offline asis

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Re: What more i can do?
« Reply #537 on: December 27, 2024, 02:00:48 pm »
next...
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #538 on: January 06, 2025, 04:32:17 am »
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #539 on: January 06, 2025, 04:33:39 am »

Why did you scope only half of the data?
Half the data mean?


D0 to D7 only once.
So it was like #382?

First bigger interference of #477 means the start.
So first D0 is up, so 0d0d.
76543210
00001101

But the end part is very different than #382.
So one more time, with three sets you can start voting.



If you like you can check that A4 of all faulty boards.
If shape is the same you have functioning connection between CPU and program ROM.

If that single high is not there you have a similar fault that the original test subject has.
If I do not get similar signals then that hints CPU is faulty?
Or is there any way to know CPU is ok or not.

You can't prove negative.
CPU is also so complex that you can have a faulty section even when the thing seems to be ok.
One example is memory test, back in the day it was doomed to be inaccurate and only accurate thing being an operating system.
And even then it was still like which end or something in between.

Internal CPU errors are rare, like one day adding doesn't go anymore.
Usual problem area is external world interfacing part.
New processors with embedded extras are different.

So in practice you must diagnose enough faulty pins by judging them as not right, so comparing them with known good state.
But your CPU is regular and it is socketed, so "just" find an old regular computer and test them.
Digging the chip out is not necessary easy, check few videos.

In this case you can also use measurements, since that earlier wrong data was 0d0d and other ROM content is 0d, you can make an educated guess.
You swap ROMs and do the same measurement again.
But since you don't know what you don't know there are no short cuts, partial measurement doesn't tell much, you must do it all again.
Don't hassle either, be sure that chips are correctly inserted and legs are straight.

With old and new measurement you can do a comparison.
If the data is still 0d0d you can guess that it is not from a ROM at all.
If it is e9e9 you can guess that it is from the swapped ROM, and this can affect CPU operation in measurable way.
Since e9 is a jump you must have addresses measured also, so that you can check how that jump is executed.
If that jumped address then correlates to next data bytes you can say that the CPU is actually seeing what you have measured.
If jump address is something else you can do the next educated guess.
Seems more complicated than I expected.
 

Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #540 on: January 06, 2025, 04:35:29 am »

We can also be pretty sure that Harry didn't do any mistakes.


@222Lab_Test222, when the time permits check our measurements.
Measure directly on the chip pin. Start with non-working board IC16 data.
The datas are same, no change at all
 

Offline m k

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Re: What more i can do?
« Reply #541 on: January 06, 2025, 09:02:12 am »
Earlier data width and low address decode signals were rational.
Data signals of swapped ROMs compared to original position ones were not.

Change your approach.
For now you are concentrated to diagnose, change to repair mode.
Your goal is to repair, any board, not the board.

Check all faulty boards.
Swapped ROMs and data lines is one possibility.
That earlier A4 also.

If operation is similar to original faulty board change both ROM sockets, three chips inside them and DIP switch pack.
Logic chips are easier if sockets are off, DIP switches and sockets are general suspects, all are cheap.

Don't hassle, be sloppy or how ever you like to call a robot like function that is very easily happening when you do same things over and over again.
You can be fast all but that fraction of time when you must be slow, one of those moments is when you reseat components.

Don't operate simultaneously more boards than you have a good space for.
Tag everything so that you can be sure what is what, Roman numerals are good if space is not tall.
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Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #542 on: January 06, 2025, 01:17:39 pm »
Looks like i need to again start from zero BUT keeping all the infos i get in mind.
 

Offline asis

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Re: What more i can do?
« Reply #543 on: January 06, 2025, 02:45:43 pm »
Hi,

I would suggest you to hook on a more reliable synchronization source than IC1 MB3771 pin8 (Reset).
Which one?
Until there is a fragment of the circuit - I don't know.
-
Maybe you shouldn't overload the forum with pictures, maybe it's enough to write down in BIN or HEX form, those values ​​on the pins that you will take from the buses during the measurement, i.e. get a data stream in the form of a virtual logic analyzer?
-
There will be a number of questions about the circuit...
 

Offline m k

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Re: What more i can do?
« Reply #544 on: January 06, 2025, 05:24:26 pm »
Looks like i need to again start from zero BUT keeping all the infos i get in mind.

No, you just change the mode for a moment.

Your ROM data measurements indicate that the CPU has no ROM access at all.
CPU is socketed and ROMs also, the environment of use is possibly hostile.
It's an educated guess that some socket contacts are or have been bad and have possibly taken some logic gates with them.
Diagnosing that is difficult without proper tools.
So the short cut is to change all easy targets, changing few bits too much is not an issue.

But first you must check how common problem this no ROM access is.
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Offline 222Lab_Test222Topic starter

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Re: What more i can do?
« Reply #545 on: January 07, 2025, 02:21:28 am »
Looks like i need to again start from zero BUT keeping all the infos i get in mind.

No, you just change the mode for a moment.

Your ROM data measurements indicate that the CPU has no ROM access at all.
CPU is socketed and ROMs also, the environment of use is possibly hostile.
It's an educated guess that some socket contacts are or have been bad and have possibly taken some logic gates with them.
Diagnosing that is difficult without proper tools.
So the short cut is to change all easy targets, changing few bits too much is not an issue.

But first you must check how common problem this no ROM access is.
There is IC between CPU and ROM, does that somehow indicates the IC is the problem?
 

Offline asis

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Re: What more i can do?
« Reply #546 on: January 07, 2025, 03:07:55 am »
Hi,

The problem may not be in IC11; IC12, but in what it is controlled by (pin's: 1,19).
Only they determine the directions of request/service ROM,FRAM,DIM, etc.
For this reason, I ask to check the connections (CPU)IC8: P1, L3, D1,F3 on (74LS245)IC11: 11,18 (&) IC12: 11,18.
This will allow us to check whether we are developing correctly.
 

Offline m k

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Re: What more i can do?
« Reply #547 on: January 07, 2025, 10:01:53 am »
There is IC between CPU and ROM, does that somehow indicates the IC is the problem?

Rope has two ends, so either way.
Those low address CPU signals, combined with logic chips, are the thing for one direction.

There are also possible middle chips for other direction.
That is why you must measure same thing from different locations.

There are also possible connection problems, like inadequate socket contact.
That can be also so that multimeter measurement is fine, but live situation is not.

So ROM data you must measure from CPU pins, but its control, like address, from ROM pins, first.
If it's fine then fine, if not then you check the other end.
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Offline asis

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Re: What more i can do?
« Reply #548 on: January 07, 2025, 11:19:22 am »
@mk

Let's first define what is connected with what and check it.
Only after that we will take measurements.
-
We have already gone through 547 different proposals, but the productivity from this is negligible.
 

Offline m k

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Re: What more i can do?
« Reply #549 on: January 07, 2025, 08:08:32 pm »
Power, reset, boot.
I don't understand how that took so long, even without the actual code, it must still jump before address flips.

But I still don't know either how those data measurements are done exactly.
So maybe better do something possible advancing before next 500 replies.
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