Cbm 2001 Pet strange boot

[Hugo Holden]

Desperado has an admirable quality......"never give up" Who cares if it is the longest thread in history. I never give up, until the fault is found and fixed.

Of course for the experienced with hardware, the process is shortened. But despite that, even for seasoned fault finding experts, sooner or later a fault comes along that can push the skills to the limit and you wonder; "will it ever be fixed ?". The answer is yes it will be, whether a day , a week a month a year. you will get there if you never give up.

And as Daver2 quite rightly points out, when you find what is wrong, you might kick yourself.

There is an imaginary microscope that works on the principle of hindsight, it is called the "Retrospectoscope". With this tool you look back after you find the correct diagnosis (or cause of a fault) and think; it was all so obvious from the beginning. It is a shame such a tool does not exist in reality and is an abstraction to entertain the mind.

 

[daver2]

This imaginary tool should become experience - so that you retrospectively look at how you should have proceeded with the fault finding and build that into your learning for next time.

Because I document everything in my notebook - I also check that all of the issues I have observed are encompassed by the fault(s) that have been found and fixed - just in case there is something still 'lurking' in there.

Dave

 

[Desperado]

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

 

[daver2]

This manual is awful (and my first language is English)!

So, it looks to me as though setting AUTO means that the oscilloscope operates in 'free run' mode if there is no trigger signal. This appears to be as you have it set (see post #1,674).

The NORM (normal) setting is what I would generally use - and causes the screen to be blank if a valid trigger signal is not being received.

I would suggest repeating monitoring A5/6 and A4/8 and trying the two different settings of the MODE switch (i.e. AUTO and NORM) to see what the effects are. Make sure that the TRIG.ALT switch is OUT (not pressed).

I am expecting that the channel 2 display of the oscilloscope (monitoring BA15) should always look the same (when measuring both A5/6 and A4/8) and not change (as your trace does in post #1,669.

Dave

 

[Desperado]

This manual is awful (and my first language is English)!

So, it looks to me as though setting AUTO means that the oscilloscope operates in 'free run' mode if there is no trigger signal. This appears to be as you have it set (see post #1,674).

The NORM (normal) setting is what I would generally use - and causes the screen to be blank if a valid trigger signal is not being received.

I would suggest repeating monitoring A5/6 and A4/8 and trying the two different settings of the MODE switch (i.e. AUTO and NORM) to see what the effects are. Make sure that the TRIG.ALT switch is OUT (not pressed).

I am expecting that the channel 2 display of the oscilloscope (monitoring BA15) should always look the same (when measuring both A5/6 and A4/8) and not change (as your trace does in post #1,669.

Dave

Ok these is measure on A5/6 and A4/8 with NORM mode and TRIG.ALT Out:

 

[daver2]

Spot on my friend !

Leave the setting at NORM from now on.

Do you see the difference between the pair of traces you have just taken now and the pair of traces you took back in post #1,669?

Now, is the SLOPE button IN (-) or OUT (+)?

Dave

 

[Desperado]

Do you see the difference between the pair of traces you have just taken now and the pair of traces you took back in post #1,669?

Yes now is better!

Now, is the SLOPE button IN (-) or OUT (+)?

IN, pressed!

 

[daver2]

Hmm, so that is not what I am expecting.

It looks like (from the video) that it is triggering on the LOW to HIGH transition of BA15 which (in my book) is (+)...

Can you try again with the SLOPE button OUT instead of IN please?

This is all learning how to use your oscilloscope...

Cheers,

Dave

 

[Desperado]

Hmm, so that is not what I am expecting.

It looks like (from the video) that it is triggering on the LOW to HIGH transition of BA15 which (in my book) is (+)...

Can you try again with the SLOPE button OUT instead of IN please?

This is all learning how to use your oscilloscope...

Cheers,

Dave

Ok, do you need again video or not?

 

[daver2]

Ok, do you need again video or not?

Yes please.

I know it is a pain - but I can easily see what is going on that way.

I am expecting to see the wave go from LOW to HIGH part-way along the screen rather than from HIGH to LOW.

Let's do this and then call it a night - and continue with the real debugging again tomorrow. We next need to have a look at the CPU data bus - but we will have to (again) set the trigger up to see what we want to see... That needs me to think...

Dave

 

[Desperado]

A5/6 and A4/8 with SLOPE OFF:

 

[daver2]

Hmm, nothing appears to have changed...

Why I wonder?

>>> I am expecting to see the wave go from LOW to HIGH part-way along the screen rather than from HIGH to LOW.

This is what I am expecting to observe.

Dave

 

[Desperado]

Hmm, nothing appears to have changed...

Why I wonder?

Dave

I am desperate really now!!!

 

[daver2]

We have no need to be desperate.

Either the oscilloscope is faulty or we are not configuring it properly...

Let's just monitor BA15 for the time being on channel #2 (not bother with channel #1) to simplify the testing.

If you adjust the level potentiometer in the trigger area do you see a change in the BA15 waveform that is displayed or not? No need to post a video this time.

                                              ________
I am expecting to see something like: _______|

Dave

 

[Desperado]

correct now?

 

[daver2]

Now it is. Is this just with adjusting the level potentiometer?

Dave

 

[Desperado]

Now it is. Is this just with adjusting the level potentiometer?

Dave

yes!

 

[daver2]

OK - so the last thing, can you repeat the tests we did previously with Channel #1 to see if we now get what I expect and then we will call it a night.

I think you have done a lot today learning about the oscilloscope. You now see how important the controls and settings are to obtaining the correct readings. Only then can you determine whether something is correct or not.

Dave

 

[Desperado]

OK - so the last thing, can you repeat the tests we did previously with Channel #1 to see if we now get what I expect and then we will call it a night.

I think you have done a lot today learning about the oscilloscope. You now see how important the controls and settings are to obtaining the correct readings. Only then can you determine whether something is correct or not.

Dave

Ok! now i can see A5/6 correct but for to see A4/8 with first low line i had to turn again the level!

 

[daver2]

No, no, no, no, no!

We want BA15 (oscilloscope channel #2) to be initially LOW NOT the signal we are measuring against it (on channel #1)...

A5/6 is fine but you have managed to screw up the measurement of A4/8 I am afraid.

Dave