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Cbm pet 8296-d black screen

If you look at the schematic you will see that the pin goes to an arrow (or a ‘signpost’). This contains the ‘name’ of the signal and the number(s) of the other schematic(s) this signal goes to.

Go to the numbered schematic(s) and you should observe similar arrows with a corresponding name (indicating the schematic number the signal comes from).

Dave
 
If you look at the schematic you will see that the pin goes to an arrow (or a ‘signpost’). This contains the ‘name’ of the signal and the number(s) of the other schematic(s) this signal goes to.

Go to the numbered schematic(s) and you should observe similar arrows with a corresponding name (indicating the schematic number the signal comes from).
Great!
I learned a new thing! I didn't know what that number was! Thanks :)
when I get back from work, I will check the continuity .... I was also thinking if maybe it would be better to remove the sockets from the chips that I have changed and solder them directly on the board ...
Maybe in this way I eliminate some danger of non-contact between the pins, what do you think? Have a nice day!
 
I personally wouldn't. The use of a good quality IC socket that is correctly installed shouldn't cause problems for many, many years.

The advantages of having the ICs in sockets at the moment is that we can remove the IC for testing purposes - so (in my opinion) the benefits outweigh any potential disadvantages at this stage.

Removing the sockets to solder the chips in place would involve a further heating cycle of the PCB to remove the socket - and it is this that can damage the PCB tracking.

Now, if you have a faulty socket, that is another matter of course...

Just my thoughts though. It is your machine and you can do with it what you like of course!

Dave
 
Ok i ll follow your suggests!
When i come home, i'll check continuity pins to CRTC and other ics...If CRTC 's socket is bad then i'll change.
 
Good evening Dave, i checked continuity from crtc pin to others pin and seems to be ok!
I I redid the welds on the ics that i changed and now i have same situation like
post #364 actually...as soon as I turn it on, the initial screen seems to be ok and immediately switches to the screen with half screen full of "b" and "g" ... Must i change all dram ics?? :(
 

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First of all, is the picture stable, or does it have ‘flipping’ characters on it still?

No, you don’t need to change ALL of the DRAM. The ‘funny characters’ that are displayed with an associated ‘b’ indicates what data was read from the DRAM. The address within the DRAM is the same as the data value written to the DRAM.

So, by looking up the PETSCII characters and converting them to binary, we can see what the fault is - and thereby which DRAM chip (or chips) are potentially faulty.

Can I suggest reading the documentation for the PETTESTER related to this test and seeing if you can work out what is wrong first? Think of a data bit as being stuck at a ‘0’ or a ‘1’ first...

Dave
 
First of all, is the picture stable, or does it have ‘flipping’ characters on it still?
I have stable picture but I can only see it for a moment because it goes straight to the second part :(
 
Sorry, what I mean is the second part display - the one that you show in post #385. Is that display stable?

Dave
 
If it is stable for a short while - and then you get flipping characters it is most likely something that occurs when a chip starts to warm up. Ideally, you need to look at that first - otherwise the display might lead us astray if it is lying to us... I am thinking of the freezer spray and hair dryer here...

The screen was stable at some point in the past. Is this a true statement? And it only started misbehaving after replacing some parts and doing some soldering. Is this a true statement?

Interestingly, I can see similarities between the data RAM faults and the faults that we saw on the 244 buffers UB9 and UB10. Do you have any knowledge of the history of this machine at all?

I suspect something has happened to it to cause some of the faults we are observing.

Dave
 
The screen was stable at some point in the past. Is this a true statement? And it only started misbehaving after replacing some parts and doing some soldering. Is this a true statement?
Yes, but in the past pettester stay stable in the first screen part...i checked soldering and now seems ok...

Interestingly, I can see similarities between the data RAM faults and the faults that we saw on the 244 buffers UB9 and UB10. Do you have any knowledge of the history of this machine at all?
no...unfortunately i bought this Pet from a private seller and i don't know the story....

Im desperate...we have lost puzzle pieces and i think that this is the end :(
 
We are still working on our 1,000 piece jigsaw - but the end is in sight :)!

So too with this PET, if you stick with it... It is just unfortunate that you have come across one of these potential temperature-dependent issues. It could be with a component that you have replaced of course. Even brand new components exhibit early mortality failures... So you could have replaced a component with a brand new one, it worked OK for a bit, and then has become intermittently faulty. Fortunately, most (all?) of the devices you replaced are in sockets aren't they - so it should be an easy 'swap and check' at some point. BUT, if you go down this route, swap one device out for a replacement. If that doesn't cure the problem, then put the original device back in the board again. If you start swapping things in an uncontrolled manner, you will get in a bigger mess.

Have you read up on my PETTESTER documentation yet and matched that with your photograph in post #385?

Dave
 
You will also need this schematic http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/8032029-05.gif.

What is the first thing you observe on this schematic in the lower left-hand side?

244 buffers!

First things first - use your logic probe on all of the pins of UE8, UE9 and UE10 to see if you have any stuck HIGH, LOW or no signal. All of the signals should be pulsing except for pin 10 (0V = LOW) and pin 20 (+5V = HIGH).

Also, measure the DC voltages (+12V, +5V and -5V) relative to 0V on a few sample DRAM ICs. +12V = pin 8. +5V = pin 9. -5V = pin 1. 0V = pin 16.

Dave
 
You will also need this schematic http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/8032029-05.gif.

What is the first thing you observe on this schematic in the lower left-hand side?

244 buffers!

First things first - use your logic probe on all of the pins of UE8, UE9 and UE10 to see if you have any stuck HIGH, LOW or no signal. All of the signals should be pulsing except for pin 10 (0V = LOW) and pin 20 (+5V = HIGH).

Also, measure the DC voltages (+12V, +5V and -5V) relative to 0V on a few sample DRAM ICs. +12V = pin 8. +5V = pin 9. -5V = pin 1. 0V = pin 16.

Dave
Ok tomorrow I will calmly check all the ls244s and the ram! Thanks for your patience! :)
 
Good evening!
I checked UE8,UE9 and UE10 pins....they all pulse except for:

UE8:

PIN 9=HIGH

PIN 11=NO SIGNAL



UE9:

PIN 9= HIGH

PIN 11= NO SIGNAL



UE10:

PIN 9= HIGH

PIN 11= NO SIGNAL

PIN 13= LOW

PIN 15= LOW

PIN 17= LOW
 
Those signals look ok.

Did you read my documentation to try and work out which DRAMs are potentially faulty to start with?

Dave
 
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