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Cbm 2001 Pet strange boot

Nivag did suggest reducing the sweep speed (timebase) to get at least one full cycle of BA15 displayed on the channel #2 trace. Please do this. We may (otherwise) miss detail.

I would suggest measuring A3/11 with channel #1 as a test.

Dave
 
Nivag did suggest reducing the sweep speed (timebase) to get at least one full cycle of BA15 displayed on the channel #2 trace. Please do this. We may (otherwise) miss detail.

I would suggest measuring A3/11 with channel #1 as a test.

Dave
I am desperate!!! This is the best setting to see a stable waveforms :(((
This scope is a sh.. !!!

Maybe bad ls244???
 
>>> Maybe bad ls244???

Or maybe a bad CPU!!!

Will you please stop just throwing random ICs out that you think could be faulty. This doesn't help at all. It is likely that a data bus buffer could be to blame. But, equally likely, it could be part of the decoding logic. Replacing the 244 buffers could then be a waste of time and you will still be desperate as a result! We are trying to approach this is a logical manner rather than guessing. If we guess, we miss something - and then we all get desperate!

>>> This scope is a sh.. !!!

Why? That video appears to show a beautifully stable and well-formed /SEL8 signal on A3/11 :)!

I assume you can slow down the timebase a bit more can't you? The possibility is that the stable wave may become difficult for the human to see because the phosphor is not retaining its glow for long enough to indicate a complete, solid trace. We are dealing with quite sloooooow signals here at 7ish Hz... The only way to solve this is to buy a long-persistence phosphor oscilloscope (or a storage oscilloscope) or a digital oscilloscope. All of which costs mucho money! If that timebase setting is the best that can be achieved, then let's go with that.

With this set-up you need to repeat the pins I asked for back in post #1,626 i.e.:

B2/6.
A3/11.
A4/1.
A3/10.
A4/3.
A4/6.
A3/3.
A3/4.

Remember, we are using BA15 as our trigger point and everything is timed relative to the HIGH to LOW transition of BA15.

Dave
 
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>>> I can see this on UB2 pin 6.

I am glad you can. This is correct!

If you look at the name of the signal on the schematic it is called X8XX. This signal goes HIGH every time the address matches X8XX. So there should be 16 high-going pulses for every complete cycle of BA15. we can't quite see the full cycle of BA15 due to the timebase setting - but it looks pretty good nonetheless.

Carry on...

Dave
 
Those traces look fine to me.

It is not too easy to view the videos however (from my perspective). If I freeze the video, I only get part of a frame. I would have to 'rip' the YouTube video and import it into my video editing software and 'single frame' it.

It would be of more help (to you at any rate) if you can work out for yourself (from the simple logic gates of the schematic) that what you are observing on the oscilloscope screen looks correct to the logic. Do you think you can do that?

The next points to look at are:

A5/6 and A4/8 with the oscilloscope. Post the videos.

Also check the following IC pins as well. Don't get desperate (!) they should all be DC levels...

A10/3 and A10/4.
A3/13 and A3/12.
A3/9 and A3/8.

These are all inverter gates on the R/W CPU signal - so the gate output should be the inverse logic state of the gate input. The CPU R/W line (pin 34) should be logic HIGH - so you should be able to now work out whether what you observe is correct or not. Please see if you can work this all out from the schematic. Print the schematic out and write down on the schematic what you would expect to observe.

Dave
 
Those traces look fine to me.

It is not too easy to view the videos however (from my perspective). If I freeze the video, I only get part of a frame. I would have to 'rip' the YouTube video and import it into my video editing software and 'single frame' it.

It would be of more help (to you at any rate) if you can work out for yourself (from the simple logic gates of the schematic) that what you are observing on the oscilloscope screen looks correct to the logic. Do you think you can do that?

The next points to look at are:

A5/6 and A4/8 with the oscilloscope. Post the videos.

Also check the following IC pins as well. Don't get desperate (!) they should all be DC levels...

A10/3 and A10/4.
A3/13 and A3/12.
A3/9 and A3/8.

These are all inverter gates on the R/W CPU signal - so the gate output should be the inverse logic state of the gate input. The CPU R/W line (pin 34) should be logic HIGH - so you should be able to now work out whether what you observe is correct or not. Please see if you can work this all out from the schematic. Print the schematic out and write down on the schematic what you would expect to observe.

Dave
A10/3 3,94V
A10/4 5,1V
A3/12 0,5V
A3/13 5,1V
A3/8 4,1V
A3/9. 0,5V
 
Those traces look OK to me. It took me a while (with my video editing software) to extract the traces for A5/6 and A4/8 - but I got there in the end.

There is something not quite right with the triggering though. The two traces for A5/6 and A4/8 should have exactly the same waveform for channel #2 (BA15) - but they don't. This implies to me that the oscilloscope is not 100% configured correctly and it may be triggering on channel #1 rather than channel #2 (or something like that).

Can you post a photograph looking directly in front of the oscilloscope to see where all of the controls are set to please.

Also, can you double-check the setting of the ALT/CHOP button please. It should be pushed IN (CHOP mode).

If I can get this tonight and see if we can sort out why the configuration is not correct we can make some more progress tomorrow. I will need to think of the next step. The oscilloscope configuration will not change the results though...

Incidentally, the double line for A3/8 is nothing to worry about. The signal is well and truly HIGH. It is just picking up some slight deviations in the voltage level each time the trace sweeps across the screen. There will be some (minor) crosstalk between signals. This is a 'real' circuit as opposed to a theoretical circuit on paper - so you will come across imperfections like this.

The 'trick' or 'knowledge' is to know when something is OK and when it isn't. This is experience - and you need to build up your level of competence with the oscilloscope as a measurement tool.

You are starting to improve in that area - so the more measurements you take the better.

However, you need to also start to develop your own relationship between what the circuit should be doing, how we configure the oscilloscope to take the measurements to ascertain whether it is working or not, and then how to interpret the results. Remember, the oscilloscope is a tool - no more no less...

Dave
 
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Yes Dave, CHOP button is pusched IN!
 

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Yes Dave, CHOP button is pusched IN!

Fair enough...

It might be something to do with the LEVEL adjustment?

It is interesting that both CH 1 and CH 2 waveforms transition simultaneously from HIGH to LOW when measuring A5/6 whereas both signals have no transition at the trigger point when measuring A4/8.

Can you scan and post the manual description for the TRIG.ALT and MODE controls. These are the only two controls that I don't know what they do - and they are on the timebase section. I always want to know what all of the adjustments do - this is why I like to read the manuals...

Dave
 
I am desperate!!!
 

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>>> I am desperate!!!

Why? We know an awful lot about what it isn't now!

Ah, that explains a lot now - make sure TRIG.ALT is NOT engaged. The button should be out and not pressed in.

I also now see there are two (2) switches labelled MODE. I should have been more specific shouldn't I?! I meant the MODE switch in the TRIGGER section rather than the VERTICAL section. The switch is marked AUTO, NORM, TV-V and TV-H. I understand what the TV-V and TV-H settings are, but not AUTO and NORM.

Dave
 
Can you get me a scan of the outstanding documentation that I requested when you get back from work please - and I will work on the next step.

This is a pretty interesting fault isn't it :)...

Look at it this way - you are (hopefully) learning a lot in the process - and other faults with other machines can't be as complicated as this! We will all kick ourselves when we do find out what it is!

Dave
 
Yes Dave, when i back from work ;)
This is the worst fault that i have found in these Cbm :(
This is the most longest thread of this forum!
your patience is now over I guess.... :(
 
>>> This is the most longest thread of this forum!

There is a longer one...

>>> your patience is now over I guess....

Not at all. We just have to be meticulous and take "small steps" otherwise we make mistakes and will overlook the culprit!

Dave
 
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