• Please review our updated Terms and Rules here

NOT WORKING CBM 3032

Perhaps it wasn't E7 but F7?

However, now you have E7 in a socket - you can remove the RAM device and use some high-valued resistors (4 off 1kOhm ish) and pull-down E7 pins 11, 12, 13 and 14 to 0V/GND with the resistors (one resistor per pin) and then see what happens. The character set should repeat every 16 scharacters across the screen - but the twinkling should have gone (or not).

Dave
 
You're right... It's always good to talk...

OK, plan B...

Remove E7 (244).

Use your pull-down resistors on E7 pins 2, 4, 6 and 8 instead (to 0V/GND which should be pin 10 of E7).

See what that gives on the display instead.

I am going out for a walk now. Just been doing some PDP-11 software development - so I need to clear my head and then I can work on the next bit later...

Dave
 
Ops...i read now your last post...meanwhile i removed E7 2114 ram, i socketed and i replaced the ic!
Now pettester goes in the second screen but i have some confused chars!!
 
So the ROMS are good for BASIC 2...

Line 3 of the display has some errors as well...

Can I suggest (a) checking out the keyboard by pressing the keys during the countdown and ensuring that the 00 bytes have one bit that get set for each keypress somewhere and (b) letting the countdown count down to 0 and let it run the DRAM test.

OK, the display might be a bit 'wonky' but it may give us a bit more confidence in the keyboard and memory sub-systems.

Let's reconvene tomorrow.

Dave
 
daver2 said:
Can I suggest (a) checking out the keyboard by pressing the keys during the countdown and ensuring that the 00 bytes have one bit that get set for each keypress somewhere and (b) letting the countdown count down to 0 and let it run the DRAM test.
Click to expand...
Good morning, unfortunately I don't have any keyboard connected at the moment, I had to disassemble it all to clean it and also I'm missing two keys :(
I will do the full pettest this evening! Tks!
 
No problem with the keyboard.

The memory test would be useful though.

I will have a think about the VDU display. The interesting thing, if the PETTESTER has moved on, is that the correct video memory has been written and read. I suspect, therefore, that it is what is being displayed that is incorrect. That narrows down the fault somewhat.

Dave
 
As I have stated in my post above - the CPU can correctly write and read the correct data - so it is unlikely to be the video RAM I am afraid.

I therefore suspect the fault to be in the DISPLAY part of the logic - not the CPU and VIDEO RAM part of the logic.

Possibly the video address generation or the video latch onwards.

I will have a look at the patterns that are present and see if I can deduce anything from that.

The other thing that you could do is to video the VDU screen with the PETTESTER running - and manually initiate a RESET (by temporarily grounding the /RESET pin of the CPU (pin 40 of the 6502 CPU to GND). This should restart the PETTESTER - but with the VDU monitor warmed up - so we can see the initial screen on the video (in pause mode) and see if anything is awry then. That would give me much more information.

You will be glad to know that PETTESTER V5 has a much longer delay between screens!

Dave
 
So...

Back in post #87 everything seemed OK - apart from video RAM data bit 7.

The problem wasn't the 244 buffer but the high video RAM.

How do we know that the video RAM you have put in as a replacement is OK?

Can you double check your soldering please.

The majority of the erroneous characters are repeats of the codes $20 through $2F. This implies that the correct data has either been written correctly by PETTESTER (but not subsequently erased) or overwritten by PETTESTER writing the initial character display on the top of the screen.

There is also a possibility that the page 0 and 1 DRAM passes the initial (simple) RAM tests but fail when used as part of this test. I am adding a more comprehensive test to V5 incidentally. This is one reason why I would like you to see if the DRAM test passes, fails or crashes...

Dave
 
Memory test is stucked here
 

Attachments

  • 1670873554016..jpg
    1670873554016..jpg
    1.4 MB · Views: 7
I suspect the problem is the lower 16K bank of main memory and NOT the video sub-system.

The reason being given above in post #153:

>>> There is also a possibility that the page 0 and 1 DRAM passes the initial (simple) RAM tests but fail when used as part of the much more comprehensive DRAM test. I am adding a more comprehensive test to V5 incidentally. This is one reason why I would like you to see if the DRAM test passes, fails or crashes...

Dave
 
daver2 said:
I suspect the problem is the lower 16K bank of main memory and NOT the video sub-system.

The reason being given above in post #153:

>>> There is also a possibility that the page 0 and 1 DRAM passes the initial (simple) RAM tests but fail when used as part of the much more comprehensive DRAM test. I am adding a more comprehensive test to V5 incidentally. This is one reason why I would like you to see if the DRAM test passes, fails or crashes...

Dave
Click to expand...
Can i try with piggyback on ram ics?
 
You must log in or register to reply here.
Back
Top