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Desperado said:
i suspect bad UC3 or UB3 :(
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So put the NOP generator in and test the buffered address lines (the outputs of UB3 and UC3) to the ROM sockets...

If you suspect them - test them. This will also test the continuity of the CPU and ROM sockets - but for these signals only.

Dave
 
I changed also pettester socket and now if i turn on with ue9 and ue10 in socket, i see this screen... In first line i can see abcdefghij etc
 

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I find this little capacitor C31.... It s very very hot!!!
 

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Good troubleshooting. I’m sure you Changed the cap.
Sometimes a bad socket will trick your continuity test. With sockets only use a light pressure with the test lead.
Daver2 will know how to interpret that test result.
 
Good detective work.

C31 is a decoupling capacitor. If it is getting hot it is faulty. It would be dragging one of the voltage rails down. Remember what I said about your senses - sight, sound, smell and touch?

I assume you replaced buffers E9 and E10?

Going back, I assume you now get consistent pulses on CPU pin 7?

What are you now getting on the pins of UD2?

Remember, we have a procedure to follow... Is the CPU executing instructions (CPU pin 7 pulsing) and does the operation of the signals on UD2 indicate that the PETTESTER ROM is executing correctly?

I suspect things are working correctly (that is where the letters are coming from) but we need confirmation of this by measurement.

I suspect we are now having problems with the video RAM, video RAM buffers or video RAM address multiplexers. This will be where we go next.

Dave
 
daver2 said:
C31 is a decoupling capacitor. If it is getting hot it is faulty. It would be dragging one of the voltage rails down. Remember what I said about your senses - sight, sound, smell and touch?
Click to expand...
Tomorrow i'll desold this but i don't know if i have one spare like this.... :(
daver2 said:
I assume you replaced buffers E9 and E10?
Click to expand...
I haven't replaced because these are good....i tested with logic tester!
daver2 said:
Going back, I assume you now get consistent pulses on CPU pin 7?
Click to expand...
at moment i have again low signal :(
 
If you don't have a spare C31 just remove it for now. Do not leave it in the PCB if it is getting hot!

By 'replaced' I meant plugged the devices back into the sockets you installed.

If you have no pulse on CPU pin 7 we are not out of the woods yet I am afraid...

Dave
 
I changed also Pettester socket but nothing changes....
I'm looking for a wall to crush my head :(
Time to headache pill???
 
So, now i have verified PETTESTER eprom and verified UD9 eprom on socket....and i have new sockets for these ic...
I tried three cpu but i have always low signal on pin 7....
Maybe bad ud2????
 
Test it then...

Use the NOP generator and look at the output pins.

We have done this before. Use UD2 pin 20 as the trigger on channel 1 and measure the /0 through /15 outputs with channel 2 to observe a low pulse moving across the oscilloscope screen with each pin measured.

Set channel 1 for a LOW to High trigger and set the timebase to get 3 (stable) cycles on the screen before you start measuring.

Dave
 
daver2 said:
Test it then...

Use the NOP generator and look at the output pins.

We have done this before. Use UD2 pin 20 as the trigger on channel 1 and measure the /0 through /15 outputs with channel 2 to observe a low pulse moving across the oscilloscope screen with each pin measured.

Set channel 1 for a LOW to High trigger and set the timebase to get 3 (stable) cycles on the screen before you start measuring.

Dave
Click to expand...
Can i test Ud2 outputs without ch1 for trigger pleasE?
 
Desperado said:
Can i test Ud2 outputs without ch1 for trigger pleasE?
Click to expand...
Not really (if you want to do it properly). Otherwise all you see is a pulse - but you don't know where that pulse is occurring in time relative to the other outputs.

Setting the trigger up means you can see that.

The other way of doing it is to use channel 1 to measure the /0 output and channel 2 to measure the /1 output. Channel 2's pulse should occur after channel 1.

You then move on to test the /1 output on channel 1 and /2 output on channel 2 and so forth.

Dave
 
Just another thought... Did you plug the two buffers E9 and E10 back in their sockets? If so, I would remove them for now.

Dave
 
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