I have tried to position it that way for all of my pictures (at least where it was relevant, and I wasn't trying to show other things, like a zoomed in view) - for instance all of my shots in #646 you can see the falling edge.
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Cromemco dazzler replica project
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I have tried to position it that way for all of my pictures (at least where it was relevant, and I wasn't trying to show other things, like a zoomed in view) - for instance all of my shots in #646 you can see the falling edge.
daver2
10k Member
Exactly,
So in post #667 onwards I am expecting to see the blue trigger trace (test point 'T') to be the same as post #646.
Dave
So in post #667 onwards I am expecting to see the blue trigger trace (test point 'T') to be the same as post #646.
Dave
In 667 the first shot is zoomed out, was intentional to show the pulses were in sync, the 2nd shot is zoomed in (i guess just slightly off-center) so not showing the falling edge of T but I wanted to clearly show the timing of both rising edges.
In 675 I was repeating test 22, which puts T back on channel 2. I was zoomed out for both shots because I wanted to show the pulse frequency.
Is there anything in particular you want to see?
In 675 I was repeating test 22, which puts T back on channel 2. I was zoomed out for both shots because I wanted to show the pulse frequency.
Is there anything in particular you want to see?
daver2
10k Member
No, I think people were just getting confused by the differing timebases and what was being shown. I know I was...
I will power up my laptop shortly and see if I can come up with some inspiration for step 30...
Dave
I will power up my laptop shortly and see if I can come up with some inspiration for step 30...
Dave
daver2
10k Member
OK, this is what I have come up with.
Use RDOS to place some 'random' data into memory addresses from 0000 to 001F (say). Let's make sure there is some data in video memory to work with.
Run my test program and set the data bits D7 to D0 of port 0Fh to '00011001' (normal resolution, picture in 512 bytes). D5=0.
Test point 'T' as a trigger at the correct timebase setting (5 us/div).
Measure and post IC46 pin 15. (/G).
Measure and post IC46 pin 1. (S).
Check (just post one of the pins as a short video) IC46 pins 3, 6, 10, 13, 2, 5, 11 and 14 for random data. IC46 inputs.
Check (just post one of the pins as a short video) IC46 pins 4, 7, 9 and 12. IC46 outputs.
If the outputs from IC46 are either permanently HIGH or permanently LOW, I would be inclined to remove IC34 and perform this test again. Don't bother to post anything other than the outcome of the test.
The outputs of IC46 drive the inputs of IC34. I want to check that the inputs of IC34 are not faulty.
Reinsert IC34 afterwards (if you removed it)...
Dave
Use RDOS to place some 'random' data into memory addresses from 0000 to 001F (say). Let's make sure there is some data in video memory to work with.
Run my test program and set the data bits D7 to D0 of port 0Fh to '00011001' (normal resolution, picture in 512 bytes). D5=0.
Test point 'T' as a trigger at the correct timebase setting (5 us/div).
Measure and post IC46 pin 15. (/G).
Measure and post IC46 pin 1. (S).
Check (just post one of the pins as a short video) IC46 pins 3, 6, 10, 13, 2, 5, 11 and 14 for random data. IC46 inputs.
Check (just post one of the pins as a short video) IC46 pins 4, 7, 9 and 12. IC46 outputs.
If the outputs from IC46 are either permanently HIGH or permanently LOW, I would be inclined to remove IC34 and perform this test again. Don't bother to post anything other than the outcome of the test.
The outputs of IC46 drive the inputs of IC34. I want to check that the inputs of IC34 are not faulty.
Reinsert IC34 afterwards (if you removed it)...
Dave
Gary C
Veteran Member
Does the 74157 test ok in a logic tester
daver2
10k Member
According to post #661 they do.
But there are logic testers and logic testers...
IC46 has also been replaced with the same results. However, the batch of ICs does look suspicious...
Dave
But there are logic testers and logic testers...
IC46 has also been replaced with the same results. However, the batch of ICs does look suspicious...
Dave
pin 3:
also pin 3, I have zoomed out to 100us to show more of the random data
pin 6: random
pin 10: random
pin 13: random
pin 2: random
pin 5: random
pin 11: random
pin 14: random
pin 4:
pin 7: same
pin 9: same
pin 12: same
None are permanently high/low but I performed these tests anyways....Removed IC34.
pin 15: same as above
pin 1: no clock/wave here
pin 3: random
pin 6: random
pin 10: random
pin 13: random
pin 2: random
pin 5: random
pin 11: random
pin 14: random
pin 4: same as above
pin 7: same
pin 9: same
pin 12: same
Attachments
Granted, I'm just using the Logic IC test function of a TL866-II.
Gary C
Veteran Member
If its suspect, I would either second source one or get another tester (or both)
I have already ordered some NOS replacements, should have it early next week.
Anyone have a good tester they can recommend?
daver2
10k Member
Cheers,
I can't think of any logical reason why IC46 pin 1 should disappear when you remove IC34.
Can you post a short video of IC47 pin 9 for completeness.
It looks to me as though whatever data is being latched in, the result us always FFh!
Again, the fault seems to support the display of a white screen.
I can then have a think...
Dave
I can't think of any logical reason why IC46 pin 1 should disappear when you remove IC34.
Can you post a short video of IC47 pin 9 for completeness.
It looks to me as though whatever data is being latched in, the result us always FFh!
Again, the fault seems to support the display of a white screen.
I can then have a think...
Dave
Oh my god, I'm dsylexic or something. I wrote 34, but I removed IC43! will retry that 2nd part of the tests!
daver2
10k Member
No problem!
Dave
Dave
daver2
10k Member
Ah, a missing 0V!
Dave
Dave
Dang I was really hoping that was it, I replaced IC34 and I just retried GDEMO and still no color. And these tests all still look the same. It's possible that pin was actually making contact with the socket.
So I pulled IC34 (for sure this time).
pin 15: same as above
pin 1: clock @ 446KHz
pin 3: random
pin 6: random
pin 10: random
pin 13: random
pin 2: random
pin 5: random
pin 11: random
pin 14: random
pin 4: same as above
pin 7: same
pin 9: same
pin 12: same
So essentially no change when removing IC34?
So I pulled IC34 (for sure this time).
pin 15: same as above
pin 1: clock @ 446KHz
pin 3: random
pin 6: random
pin 10: random
pin 13: random
pin 2: random
pin 5: random
pin 11: random
pin 14: random
pin 4: same as above
pin 7: same
pin 9: same
pin 12: same
So essentially no change when removing IC34?
BTW I still don't know what I'm supposed to be seeing when running your test app?
daver2
10k Member
I didn't think IC34 was the problem, but it would have been the next thing we fell over!
When running my test app you may see anything on the screen. At this point we don't care! All we are interested in is following the troubleshooting guide...
And signal IC47 pin 9?
Dave
When running my test app you may see anything on the screen. At this point we don't care! All we are interested in is following the troubleshooting guide...
And signal IC47 pin 9?
Dave