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NOT WORKING CBM 3032

Desperado said:
I tried piggyback also on other video ram and seems to be better but some chars aree wrong...
Click to expand...

Actually, that is interesting...

I wonder if you do have a faulty high video RAM seeing that photograph?

It might be worth repeating that test again and see if you get the same result.

Is it just possible that you were accidentally shorting two pins together when you tried the piggy-pack test before I wonder?

Dave
 
Ah sorry, I am thinking backwards...

It was the higher video RAM we replaced last time wasn't it (data bit 7 = inverse video) and you are now piggy-backing the lower video RAM.

It is difficult to see how this would be a problem if the PETTESTER saw the video RAM as working. It must have been working correctly when it performed the video RAM test... So that has to rule it out.

I can't see what I want to see from the video you posted of the manual reset. You need to get a good shot of the PET screen. I can't see the individual characters too well on that video I am afraid.

Dave
 
daver2 said:
Ah sorry, I am thinking backwards...

It was the higher video RAM we replaced last time wasn't it (data bit 7 = inverse video) and you are now piggy-backing the lower video RAM.

It is difficult to see how this would be a problem if the PETTESTER saw the video RAM as working. It must have been working correctly when it performed the video RAM test... So that has to rule it out.

I can't see what I want to see from the video you posted of the manual reset. You need to get a good shot of the PET screen. I can't see the individual characters too well on that video I am afraid.

Dave
Click to expand...
Ok, can you see something now?
 
Yep, spot on.

There is no problem with the video memory test, but the page 0 and page 1 memory tests are showing some anomalies. I suspect they are transient in nature and, as the PETTESTER continuously tests the memory, eventually it all works.

However, when it then comes to the later tests, because there are some transient RAM issues it causes the code to fail in unpredictable ways.

Please forget the video RAM and concentrate on the main RAM.

There is a way to swap over the two 16K RAM banks. You may have a working upper bank but a problematic lower bank. I will explain how to do that tomorrow.

Dave
 
daver2 said:
Yep, spot on.

There is no problem with the video memory test, but the page 0 and page 1 memory tests are showing some anomalies. I suspect they are transient in nature and, as the PETTESTER continuously tests the memory, eventually it all works.

However, when it then comes to the later tests, because there are some transient RAM issues it causes the code to fail in unpredictable ways.

Please forget the video RAM and concentrate on the main RAM.

There is a way to swap over the two 16K RAM banks. You may have a working upper bank but a problematic lower bank. I will explain how to do that tomorrow.

Dave
Click to expand...
Hi Dave, did you take the time to look at how to swap ram? Tks!! ;)
 
Follow the /CAS0 and /CAS1 signals back from the two banks of RAM. They should go to two (2) resistors.

/CAS0 drives the low 16K bank of RAM.

/CAS1 drives the high 16K bank of RAM.

Desolder one leg of each of the resistors that the /CAS lines go to and swap them over so that each resistor drives the opposite/CAS line that it was originally driving.

Dave
 
daver2 said:
Follow the /CAS0 and /CAS1 signals back from the two banks of RAM. They should go to two (2) resistors.

/CAS0 drives the low 16K bank of RAM.

/CAS1 drives the high 16K bank of RAM.

Desolder one leg of each of the resistors that the /CAS lines go to and swap them over so that each resistor drives the opposite/CAS line that it was originally driving.

Dave
Click to expand...
ok thanks so much!
 
Dave on schematic i can't see resistor between cas0 and cas1 signal :(
 

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Yes,

Desolder the ends of the resistors you have circled in red in post #173.

Then, wire the desoldered lead of R42 to signal /CAS0.

Then, wire the desoldered lead of R41 to signal /CAS1.

This swaps over the two banks of RAM.

I thought this is what I stated back in post #168?

Dave
 
daver2 said:
Yes,

Desolder the ends of the resistors you have circled in red in post #173.

Then, wire the desoldered lead of R42 to signal /CAS0.

Then, wire the desoldered lead of R41 to signal /CAS1.

This swaps over the two banks of RAM.

I thought this is what I stated back in post #168?

Dave
Click to expand...
Sorry Dave are these sides?
 

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I can't tell from looking at your picture. Use your multimeter (resistance) to find out which end of the resistors are wired to G7 and which end is wired to the RAM...

I see that the red circle on resistor R42 is connected to G7 pin 6, so R42 is the other end...

Look at the PCB for R41 to see which end is wired to G7 pin 12, and it is not that one.

Dave
 
daver2 said:
Look at the PCB for R41 to see which end is wired to G7 pin 12, and it is not that one.
Click to expand...
i ma desperate because both R41 sides is wired to G7 PIN 12!! My multimeter sounds beep for every side of this R41 between G7 pin :(
 
The resistor is only 27 Ohms. Stop using the 'beep' function of your multimeter!

Use a low resistance setting - or just follow the PCB track from G7 pin 12 to the resistor. It is the other end you want!

Dave
 
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