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Apple //e picture issue


Tony359

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As I said before, you are unlikely to get a proper signal on an LCD. They are designed to demodulate video in an entirely digital manner, with very little wiggle room for nonstandard signals. The Apple II PAL signal is what Apple dubbed 'International NTSC @50Hz'. You can try a C1084 PAL monitor with it, and you should get decent results. 

 

The Apple II was the only system where we used NTSC machines to write and test software, before using PAL systems, in that era. Part of that was marketing, as the software would primarily be sold for NTSC markets, but part of it was that we needed to get it to look right on NTSC, then see if it had problems on the PAL systems. (Let's not even think of ITT 2020 compatibility.)

Edited by GameGeezer
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Looking at the schematic, the 4 adjustments I see are 2 resistors (R63 and R64), a variable capacitor (C112) and a variable inductor (L7).

 

R63 and R64 adjust the strength of the Red/Green (R63) and the Blue/Yellow (R64).  If outputting white, you should of course have them adjusted so that you see white at a decent brightness.  I would guess that you start each one halfway between up and down, then rotate each about the same amount in opposite directions if the tint is off.

 

C112 is the color burst frequency fine tune.  If you have an oscilloscope or frequency counter, you should be able to watch pin 1 on the TCA650 and tune it to 4.43MHz.

 

L7 is a trap for 3.58MHz (the NTSC color burst).  The PAL circuitry is like a kludge here.  There's an NTSC color burst that the NTSC circuitry adds in, so here it has to shut that up and replace it with the PAL color burst.  So they added a trap to remove the 3.58MHz burst.  I think what you need to do (with a scope) is to trigger on Q3 base high, and have the probe watching the junction of R7, R46, and C111.  Tune this trap to minimize the signal at that point (but only while Q3 is high).

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GameGeezer

I appreciate what you say but I see youtube videos where people are using LCD successfully (such as in the below video) so I'd like to try to get to that point too. 

 

ChildOfCv

C112 seems to change the amplitude of that clock, not the frequency. I found a partial explanation on the video below and I could confirm the same behaviour on my machine. 

 

 

R63 and R64 are for Colour balance? Interesting! 

 

I'll test what you recommend on L7 - thanks for taking the time to look at the schematics for me!

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5 hours ago, Tony359 said:

C112 seems to change the amplitude of that clock, not the frequency. I found a partial explanation on the video below and I could confirm the same behaviour on my machine. 

Now that I think about it, crystal circuits typically have a couple of loading capacitors on them to keep them from jumping to harmonic frequencies.  So adjusting for max amplitude (at 4.43MHz) makes sense because that likely means the capacitors are keeping it tuned to its primary frequency.

 

Also, the capacitor probably does attempt to tune the oscillator circuit itself.  But if it's not at the same frequency as the crystal, they're going to fight, and reduced output is the result.

 

It's also a shame that he didn't try out the video capture device again after fixing it though.  Would be interesting to see if it still jumps around like yours does.

 

But ultimately, the success of working with LCD may depend on the decoding hardware of the device, as you notice that each device he tested reacted differently.

Edited by ChildOfCv
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Hi

 

I went ahead and did some more tweaking and tests.

I maxed out the crystal amplitude - that required more than a small adjustment. It went from 400 to 600mV p/p. 

 

As you said, colours would change when tweaking R63 and R64. But the easiest way to balance them is to look at the black background while in colour mode as tweaking the trimmers would give a colour cast to it and the idea is to eliminate it. In B/W this is less evident as there are no colours so you see some kind of noise patterns appearing on the black and - again - the idea is to make the black more black possible. 

 

Regarding the inductor, I believe I understood what had to be done but then again it required more than a small adjustment and I basically reached the end of it and the burst was still slowly decreasing. Are we talking of the area circled in the picture - which is basically going to be replaced by the 4.33Mhz PAL colour burst? (apologies for the notification text on top, the stupid oscilloscope recorded that too!!). As you said, the burst is there only when Q3 is high - which happens when the system switches to colour mode.

 

Despite all of this, unfortunately I still have the same issues I mentioned before. 

 

And with 30C in the room, the HAL becomes uncomfortable to touch...

 

 

 

SDS00002_LI.jpg

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16 hours ago, Tony359 said:

GameGeezer

I appreciate what you say but I see youtube videos where people are using LCD successfully (such as in the below video) so I'd like to try to get to that point too. 

 

ChildOfCv

C112 seems to change the amplitude of that clock, not the frequency. I found a partial explanation on the video below and I could confirm the same behaviour on my machine. 

 

 

R63 and R64 are for Colour balance? Interesting! 

 

I'll test what you recommend on L7 - thanks for taking the time to look at the schematics for me!

Keep in mind what he says at this time index:

 

It is a matter of the display being able to interpret the signal, which is a hybrid format. Some LCDs will, most won't, and you will still have distortion of the image perspective, and the intended output. 

 

I have to ask here: Are you are doing this out of technical curiosity to make something new, or do you simply want a proper display with relatively-appropriate colour data?

 

FWIW, I had to deal with these issues when the ][europlus, and //e were new products. It was hellish then, but now, with digital sync involved, f'ek that. I do applaud you if you find a solution, bearing in mind that video signal generation was not my department--Christopher was in charge of that--and I always appreciate new ideas. Hell, I built a composite video amplifier and converter for vintage systems out of vac tubes. 

 

In closing, it is easier to hack the //e to produce a better PAL signal, than to get modern displays, designed to decode PAL signals to decode the //e signals. I hope that this helps you in some manner. 

 

Edited by GameGeezer
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I'm just tinkering with the Apple//. I like learning new things - this new project is teaching me something about TV signals I didn't know etc. Now, IF I could have a stable signal on my Dell monitor - in a way or another - that would be great too. Don't get me wrong, I understand the way the Apple outputs video signal is unconventional and "tricks" CRT analogue electronics in order to display a picture. I get that. I am just making sure the video circuit is properly calibrated (see the "learning attitude" above) and if that does not fix it... I don't know, I'll think about it. 

 

Same attitude on the missing vertical line: rather than swapping chips around at random (which I don't have anyways!) I wanted to try to try to find the fault myself - that has taught me a lot about how this machine works and also how to better use my scope!! Again, this is a hobby fun project, I am not doing this for a living so time is not a concern.

 

Regarding the timecode of the video, he says "the apple is not outputting a correct PAL signal" but that refers to his machine which has a faulty flip-flop chip. But I get your point.

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So, looking closer at the schematic, I need to retract some of what I said.

 

On NTSC systems, there's a NOR gate that generates color burst.  It has the CLRGATE as one input and the 3.58MHz clock as the other.  When CLRGATE is high, the NOR gate stays low.  Otherwise it follows the clock.  But that's only how NTSC works.  The PAL version does not have this NOR gate, so there is no color burst to remove or replace.

 

What we do have is a circuit that routes these bits directly to the output, but has a trap door along the way.  When not in GR mode, the 74LS175 is held in clear mode, so the color circuits never move, and the dots are sent unfiltered straight through the video circuit just like with NTSC.  The trap is not active for this, so there is no pixel filtering going on.

 

When in GR mode, the color circuits are allowed to run.  Every 4th pixel tick, the 74LS175 loads the upcoming 4 bits into its translation buffer, the LS175.  Each bit still goes through that bypass line I just talked about, but now the trap is active.  Its purpose seems to be to smooth the pixels into a single brightness smear rather than individual on/off bits.  This trap is turned on or off at the beginning of a line, probably to facilitate the mixed GR modes.  The CLRGATE signal goes to Q8, so when inactive (high), Q8 is on, which in turn activates Q9.  This places a roughly equal bias on both the R and B lines.  When CLRGATE goes low (active), Q9 shuts off.  This adds high bias to the red line and low bias to the blue line, for that roughly 45 degree color burst.  The flip-flop that the guy replaced in the video causes it to switch that to the 90 degree shifted phase on alternating lines.

 

So based on this new understanding of how it works, I think the proper adjustment procedure for the trap should be to fill the screen in graphics mode with a color that alternates the bits (like 5 or 10) and then adjust the trap to remove as much ripple from the line at that junction as you can.

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Sorry this has taken a while - I wanted to learn how to display a full colour screen first!

 

So first I plotted a 5 or 10 colour on screen and then I zoomed into the actual video signal with my scope. The result is below: while I was filming I was moving the adjustment from one end to the other or so. I could see something happening on screen but not much. The amplitude jumping at some point is me removing my metal hex key from the socket - sorry I do not have a plastic one right now. 

Have I correctly understood your advice? What you see on screen is the video field, triggered and magnified. 

 

 

Then I had an idea: I put Frogger's welcome screen on and played with the adjustment to see if I could see any visible effects. The effect was obvious: on green colour you can clearly see some vertical bar appearing while adjusting which can be minimised by rotating the adjustment. The final adjustment for the most smooth colour is indeed half way through the range. The pictures below should clearly show what I am talking about and I feel it's compatible with your idea of smoothing pixels? I could also see the same effect on Blue but I feel on Green it was more obvious.

 

Thanks!

frogger2.jpg

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Yeah I wondered if it might be better to look at a visual while adjusting.  Apparently Frogger was just the ticket.  That color bars program that the guy in the video ran probably would be useful too.

 

Anyway, it looks like you did find what that adjustment was made for--or at least something that it's useful for ;)

 

Definitely would be better with a plastic tool, since the metal one had such an effect that it must have greatly affected the inductance.  But while adjusting, it appears to have made the sine wave more or less symmetrical, possibly even sinusoidal.

 

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I'll check again with a colour bar. 

I'm not sure how to correlate what I see on video with the scope trace: when the trace looks nice and symmetrical, that's one end of the adjustment and the picture won't look right when that happens. I'll see if I can find out - for posterity! :)

 

And indeed I must replace the plastic tool I can't find anymore!

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  • 2 weeks later...

Just a quick follow up for future reference: I put up a colour bar and the behaviour is the same on all colours and it happens simultaneously. So frogger is ok to adjust :) 

That said, this is using an LCD monitor: I do not own an Apple colour monitor nor a normal CRT TV. So hopefully this is not just a weird behaviour caused by modern electronics reacting to weird PAL signal.

 

I'd like to run some tests with my monochrome Apple monitor as I kind of see vertical stripes on inverted text or on solid backgrounds and wondering if it's just the way it's supposed to look or maybe the adjustment can have some role in it.

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