Quote:
Originally Posted by SiriusHardware
I don't think the video waveform should be a square wave, if you think about what is actually being displayed at the startup prompt it is a few characters on an otherwise dark screen, so what you will see on the video output will be a few thin positive spikes on a largely zero-volt level.
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The thought had crossed my mind but I was going by the Technical Ref document. It’s possible that the square wave applies under certain test conditions not described in the document although it may just be that I haven’t spotted the relevant reference.
Quote:
Originally Posted by SiriusHardware
Quote:
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It still looks like you have no vertical drive.
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Not sure that's true, if you go back to pud's earlier post with 5 images the one for the vert drive clearly shows two levels with a bit of bright line at the bottom of the screen.
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I’m not convinced the vertical drive signal is missing either. The timebase needs to be set to 5mS
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Quote:
Originally Posted by SiriusHardware
Pudwink, see if you can turn the second channel on your scope off so there is only one trace on the screen and then scope the horizontal drive and vertical drive signals for us again.
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Looking at the first image of post #48 I don’t think there’s a problem with the horizontal drive.
Quote:
Originally Posted by SiriusHardware
Would it be possible (anyone?) to mark up the track layout diagram with the places Pud needs to scope as asked earlier?
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These are the waveform test points for the vertical drive signal:
4-Base of Q611
5-Collector of Q611
6-Base of Q601
7-Base of Q621
8-Base of Q651
9-Base of Q652
10-Other end of R656 from the emitter of Q651
11-Junction of R622, C652 (+ve end) and R658
12-Junction of R663, R657 and C652 (-ve end)
These are the waveform test points for the horizontal drive up to and including the LOPT driver transistor:
14-Base of Q701
15-Base of Q711
16-Collector of Q711
17-Base of Q721
18-Collector of Q721
These are all easy to find on the layout diagram and the correct timebase plus vertical sensitivity settings are given on the waveform diagrams. Beware of the high voltages in the vicinity of these test points! Number 18 itself should peak at around 400V. The others are low voltage. Please note what I said in post #61 about using test clips and not releasing the monitor’s PCB.
Alan