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So that now looks correct.

I hope the oscilloscope timebase was set the same fir both videos...

Can you see what the difference between the two videos posted in #208 (bad) and #221 (good)?

Make sure all the remaining data bus lines look like the video in #221!

We will work out why the video in #208 appears to be incorrect later...

Dave
 
daver2 said:
Can you see what the difference between the two videos posted in #208 (bad) and #221 (good)?
Click to expand...
Ok ok now i see that signal in post 221 is more stable and definited!
I have same signal on Ue9 and Ue10 ic pins 2-3-4-5-6-7-8-9.... except for both pins 19...
 
Ok,

Can you remove the NOP generator and make sure the Kernal and PETTESTER ROMs are fitted to UD9 and UD8 respectively.

Leave UE9 and UE10 out of the sockets.

Don't get desparate, but the screen will probably contain cr*p. This is expected behaviour because buffers UE9 and UE10 are not fitted!

What we want to check is pulsing activity on CPU pin 7 and (if this is the case) what pulsing activity is on the pins of UD2.

We are going to check if we can get the PETTESTER to work now, but we won't be able to see anything on the screen! However, if we fit the missing buffers, then the PETTESTER ROM may not work again until we find the fault!

Dave
 
daver2 said:
Ok,

Can you remove the NOP generator and make sure the Kernal and PETTESTER ROMs are fitted to UD9 and UD8 respectively.

Leave UE9 and UE10 out of the sockets.

Don't get desparate, but the screen will probably contain cr*p. This is expected behaviour because buffers UE9 and UE10 are not fitted!

What we want to check is pulsing activity on CPU pin 7 and (if this is the case) what pulsing activity is on the pins of UD2.

We are going to check if we can get the PETTESTER to work now, but we won't be able to see anything on the screen! However, if we fit the missing buffers, then the PETTESTER ROM may not work again until we find the fault!

Dave
Click to expand...
I have always LOW signal on CPU pin 7 :(
 
Somehow, then, either you have missed something or one (or both) EPROMs are not working correctly in the PET.

Dave
 
That is why you did all of the continuity testing that you did...

Now, if you didn't do it properly - this comes under the heading of you missed something...

Dave
 
daver2 said:
That is why you did all of the continuity testing that you did...

Now, if you didn't do it properly - this comes under the heading of you missed something...

Dave
Click to expand...
I seem to have run the test correctly...maybe there is some logic broken?
 
Desperado,
Are both D8 and D9 on sockets? Sometimes when measuring continuity, pressing hard with probe will give positive result, but there is still intermittent when pressure removed. At least spray some contact cleaner into the sockets.
We are running out of options.
 
Desperado said:
I seem to have run the test correctly...maybe there is some logic broken?
Click to expand...
The point is that we have removed all of the logic from the data bus other than the two (2) ROMs and the CPU... The only other logic device that is present is the 74154 address decoder...

That is why I went to the trouble of asking you to remove the VIA, PIAs and the E9 and E10 buffers.

Dave
 
daver2 said:
The point is that we have removed all of the logic from the data bus other than the two (2) ROMs and the CPU... The only other logic device that is present is the 74154 address decoder...

That is why I went to the trouble of asking you to remove the VIA, PIAs and the E9 and E10 buffers.

Dave
Click to expand...
So now what can i do? :(
 
dave_m said:
Desperado,
Are both D8 and D9 on sockets? Sometimes when measuring continuity, pressing hard with probe will give positive result, but there is still intermittent when pressure removed. At least spray some contact cleaner into the sockets.
We are running out of options.
Click to expand...
yes these roms are in socket and i already used contact cleaner in socket :(
 
The first thing is to repeat the continuity tests from the ROMs back to the data bus of the 6502 CPU (with the NOP generator removed), the address buffers and the pin 20 chip select lines to the 74154.

Look CRITICALLY at all of the soldering and PCB tracking.

After that:

Is the Kernal ROM the one that came with the machine? If so, can you temporarily swap it for one that you know works? This is with the PETTESTER ROM IN and the NOP generator OUT. We are, of course, checking for CPU pin 7 pulses. Also worth double-checking CPU pin 40 to make sure that the CPU is being RESET on power-up or reset (if you still have the pushbutton).

Do you know for a fact whether the PETTESTER ROM you are using in the machine actually works. In fact, try the PETTESTER and Kernal ROMs in a working PET to see if they really do work.

Dave
 
daver2 said:
Is the Kernal ROM the one that came with the machine?
Click to expand...
yes but i burned another eprom but doesn't works again :(
daver2 said:
Also worth double-checking CPU pin 40 to make sure that the CPU is being RESET on power-up or reset (if you still have the pushbutton).
Click to expand...
i have a good reset signal!
Pettester works in another Pet.....i am really desperate now!!!! maybe bad video ram :(
 
It can't possibly be bad video RAM can it?

The video RAM has been disconnected from the data bus (so there is no interaction there) and our current problem (that we are trying to resolve) is that the CPU is not correctly executing instructions out of the ROM.

Until you can get the CPU to run reliably please FORGET everything else!

What I suspect we need is a test Kernal ROM image that just does something simple. I am sure we have posted something already in another PET thread that will do the trick somewhere.

Dave
 
It could be - but you should have tested it with the continuity tests that you did...

Go back and repeat the continuity tests... Be careful this time how you take the continuity measurements. I would put the probe on horizontally to the ROM pin so that I don't push down on the ROM device and potentially affect the measurement.

I have given you everything to check (post #234) I can think of I am afraid.

Dave
 
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