NOT WORKING CBM 3032

[Desperado]

This is F9 pin 12:

 

[daver2]

Another good video!

That is completely wrong and is where your twinklies are coming from! Now we have to play "hunt the faulty component"...

Right, with the oscilloscope on exactly the same settings, can you probe and post a video of the following two (2) pins please: E7 pin 8 and E7 pin 11.

Dave

 

[Desperado]

E7 pin 8:

 

[Desperado]

E7 pin 11:

 

[daver2]

Excellent.

So, the problem appears to be before the data bus buffer feeding the video RAM.

It's lunch time here, so I will check the schematic after lunch for the next point to probe.

Dave

 

[Desperado]

Excellent.

So, the problem appears to be before the data bus buffer feeding the video RAM.

It's lunch time here, so I will check the schematic after lunch for the next point to probe.

Dave

Have a good lunch sir!

 

[daver2]

OK, I would suggest the following pins next (for comparison purposes).

E7 pins 6 and 13.

Followed by E10 pins 11 and 8 and E10 pins 13 and 6.

Just to confirm - this is with my PETTESTER ROM running isn't it?

Dave

 

[Desperado]

OK, I would suggest the following pins next (for comparison purposes).

E7 pins 6 and 13.

Followed by E10 pins 11 and 8 and E10 pins 13 and 6.

Just to confirm - this is with my PETTESTER ROM running isn't it?

Dave

Do you need always video?

Yes is your pettester!

 

[Desperado]

E7 pins 6 and 13.

These are same to E7 pin 8 and 11

 

[Desperado]

Followed by E10 pins 11 and 8 and E10 pins 13 and 6.

Also these pins are like previously pins

 

[daver2]

I think you had better post videos please.

They may look the same to you - but they will probably look different to me...

Dave

 

[Desperado]

E7 PIN 6 AND 13:

 

[Desperado]

E10 PIN 11 AND 8

 

[Desperado]

E10 PIN 13 AND 6

 

[daver2]

Unfortunately, I see what the problem is. The buffers from the CPU data bus through to the buffers on the VIDEO RAM are permanently enabled when the VIDEO RAM is not being read from. As a result, you are seeing all of the activity on the data bus.

The problem is either E7, F7 or F9.

I am less inclined to think it is F9 (the 373 octal latch).

It is more likely to be E7 (244 buffer) or the VIDEO RAM itself at F7.

Is it worth trying our low-value resistor trick to 0V/GND on E7 pin 8 first?

Dave

 

[Desperado]

Unfortunately, I see what the problem is. The buffers from the CPU data bus through to the buffers on the VIDEO RAM are permanently enabled when the VIDEO RAM is not being read from. As a result, you are seeing all of the activity on the data bus.

The problem is either E7, F7 or F9.

I am less inclined to think it is F9 (the 373 octal latch).

It is more likely to be E7 (244 buffer) or the VIDEO RAM itself at F7.

Is it worth trying our low-value resistor trick to 0V/GND on E7 pin 8 first?

Dave

Thanks Dave! I try now!

 

[Desperado]

Is it worth trying our low-value resistor trick to 0V/GND on E7 pin 8 first?

If i connect E7 pin 8 to Gnd i see correct pettester screen but is stucked on the first page!

 

[daver2]

I don't think you will see the correct PETTESTER screen - as you will have no inverse characters on display!

This implies that F9 is potentially OK (it is not generating the twinkles itself).

Toss a coin on replacing E7 or F7 (depending what you have got in your spares box).

Having a device in a socket will mean that we can perform further tests by removing the device.

Dave

 

[Desperado]

I don't think you will see the correct PETTESTER screen - as you will have no inverse characters on display!

Yes sorry, i don't see flickering chars and i don't see inverse chars!

i ll try to remove E7 first and i ll socket this. Tks!

 

[Desperado]

I am desperate! I changed E7 but i have same problem