Cbm pet 8296-d black screen

[daver2]

Post #356 - replace 244 buffer UB10...

Dave

 

[Desperado]

Post #356 - replace 244 buffer UB10...

Dave

Ah ok sorry!
as soon as I get back from work i ll replace it! Thanks!

 

[Desperado]

Good evening Sir,
im desperate (((
I changes UB10 but nothing changes ((

This is new video:

 

[Desperado]

If i try to insert PETTESTER V4 the situation is worse than before

 

[daver2]

On the assumption that all you have done is to replace UB10 then one (or more) of the following situation(s) applies:

1. The buffer you have replaced UB10 with is faulty.
2. There is a problem with the IC socket, the PCB or the soldering of the UB10 socket.
3. Another (unrelated) fault (or faults) has happened between the other day and now.

Can you post a close-up photograph of the top and underside of UB10 please?

EDIT: The fact that the PETTESTER V4 display is all completely screwed up indicates that something else has gone faulty between taking my test version of the firmware out and putting V4 in!

EDIT: Actually, the video in post #363 does show that the reason for changing UB10 has actually worked. We now don't have '@ a @ a @ a @ a ...' we now at least see characters that we are vaguely expecting. For some reason we have the initial characters on the screen in inverse video - which is something I wasn't expecting? Strange about the 'flipping' characters. Does it get worse when the machine heats up I wonder?

Dave

 

[Desperado]

On the assumption that all you have done is to replace UB10 then one (or more) of the following situation(s) applies:

1. The buffer you have replaced UB10 with is faulty.
2. There is a problem with the IC socket, the PCB or the soldering of the UB10 socket.
3. Another (unrelated) fault (or faults) has happened between the other day and now.

Can you post a close-up photograph of the top and underside of UB10 please?

Dave

Yes i changed only ls244 on ub10....
Ok do you wanna photograph of socket ub10 or ls244??

 

[daver2]

The socket of UB10 - from top and bottom please.

Dave

 

[Desperado]

Ok! I tryied different ls244 on ub10 but it's the same....

 

[daver2]

My suggestions are:

1. Clean off the flux after you have finished soldering. I use isopropyl alcohol.
2. I can see what I think are 'gaps' between a couple of the IC pins and the copper pads. I shouldn't be able to see any gaps.
3. Can you check that pin 10 of the UB10 IC itself is actually connected to 0V (test for continuity between the physical IC pin 10 of UB10 and pin 10 of another 244 buffer).

If you have other soldering that looks the same, you ought to repeat this with the other devices (just to rule this out as a failure mode).

Dave

 

[Desperado]

I cleaned flux anche i checked continuity between ub10 pin10 and and un9 pin10 and this is ok!
If in insert your pettester v9, i have this situation:

 

[Desperado]

Update:
i removed gaps with new solder and now (with v9 pettester) i can see this screen:

 

[daver2]

So, I can partially see what is going on.

The PETTESTER V4 in post #364 actually PASSED the VDU test and then moved on to test page 0 and 1 RAM - where it failed. Read the manual... A 'g' indicates a good memory byte and a 'b' indicates a bad memory byte.

Post #370 appears to also move on from the VDU test to the RAM test - and then also fails - but the display is corrupt (both the initial VDU display and the RAM display). This sort of indicates to me that the issue is either on the VDU display side of things (not the CPU/VDU memory side) or it is intermittent - and will sometimes PASS the VDU test and other times not.

Post #371 is worse - it is not passing the VDU test anymore AND there is serious flipping of display characters.

I suspect you have an intermittent solder joint, bad socket or something similar occurring - and we need to fix this otherwise we will get nowhere. Have you cleaned up the flux from the other ICs you have replaced? If not, can you do that now please. The next thing would be to continuity test from the leg of each of the ICs you have replaced to a connected point on a pin of an IC that you haven't replaced.

You could also have a device that is temperature sensitive (i.e. it works better when it is cold than when it warms up). To detect this you can use a hairdryer (to heat a small portion of the board up at a time) and a freezer spray (to cool down an IC at a time) to see if this has any effect on the observed display pattern.

I am afraid this is 'slog' rather than detective work...

Dave

 

[Desperado]

So, I can partially see what is going on.

The PETTESTER V4 in post #364 actually PASSED the VDU test and then moved on to test page 0 and 1 RAM - where it failed. Read the manual... A 'g' indicates a good memory byte and a 'b' indicates a bad memory byte.

Post #370 appears to also move on from the VDU test to the RAM test - and then also fails - but the display is corrupt (both the initial VDU display and the RAM display). This sort of indicates to me that the issue is either on the VDU display side of things (not the CPU/VDU memory side) or it is intermittent - and will sometimes PASS the VDU test and other times not.

Post #371 is worse - it is not passing the VDU test anymore AND there is serious flipping of display characters.

I suspect you have an intermittent solder joint, bad socket or something similar occurring - and we need to fix this otherwise we will get nowhere. Have you cleaned up the flux from the other ICs you have replaced? If not, can you do that now please. The next thing would be to continuity test from the leg of each of the ICs you have replaced to a connected point on a pin of an IC that you haven't replaced.

I am afraid this is 'slog' rather than detective work...

Dave

Ok Dave i understand, i ll check all ic that i have change and i ll check continuity! Thanks so much, i ll update you very soon.... I hope

 

[daver2]

I have just noticed on the schematics that pin 16 of the CRTC (UB13) can invert the video signal. Pins 17 and 18 also drive signals such as the CHARACTER SET OPTION and the DISPLAY ENABLE. It is not a bad connection again on some other pins of UB13 is it!?

Dave

 

[Desperado]

But now must i use v4 or v9 pettester version?

 

[Desperado]

I have just noticed on the schematics that pin 16 of the CRTC (UB13) can invert the video signal. Pins 17 and 18 also drive signals such as the CHARACTER SET OPTION and the DISPLAY ENABLE. It is not a bad connection again on some other pins of UB13 is it!?

Dave

Can i try change ub13 socket.... We Have already had some troubles in this socket..

 

[daver2]

But now must i use v4 or v9 pettester version?

It depends.

Do you have two (2) EPROMs (one with V4 and the other with V9) or not?

I would suggest using V9 for the time being... Everything (apart from the VDU test) is the same in V9 as it is in V4 - but the VDU test gives us some extra information.

Dave

 

[daver2]

Can i try change ub13 socket.... We Have already had some troubles in this socket..

I wouldn't for now. Just perform a continuity test and make sure the pins are making good contact with the PCB tracks. Let's try not to introduce more variables.

Of course, I can't stop you if you want to change it can I?

Dave

 

[Desperado]

I wouldn't for now. Just perform a continuity test and make sure the pins are making good contact with the PCB tracks. Let's try not to introduce more variables.

Of course, I can't stop you if you want to change it can I?

Dave

Ok tomorrow i ll check continuity on ub13 pins!

 

[Desperado]

I have just noticed on the schematics that pin 16 of the CRTC (UB13) can invert the video signal. Pins 17 and 18 also drive signals such as the CHARACTER SET OPTION and the DISPLAY ENABLE. It is not a bad connection again on some other pins of UB13 is it!?

Dave

If i look schematic i can t see where check continuity from pin 16,17 and 18 of UB13....