My first Apple-1 build / Video scrambled

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My first Apple-1 build / Video scrambled

Hello there,

 

I have completed my first Apple-1 board (using "Uncle" Bernie's kit and fixes). Unfortunately, I do not have a proper NTSC-Monitor at hand, so I though I check it using an RCA to HDMI-Converter and hook that one up to my TV.

 

I see a distorted picture (similar to what you get when you try to watch an NTSC signal on a PAL tv), but I can see the typical underscore/at-character blinking pattern. It looks like this:

 

If I do not have a "pure" NTSC monitor at hand – does anybody have a suggestions how to test the video?

Best

 

Armin

 

 

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HDMI converters and flat screen monitors/TVs ...

... used with an Apple-1 are a hit-and-miss exercise. Some work, but most don't. This is caused by the Apple-1 having a non-conforming video signal. There is a remedy which often helps but it should be used only if everything else fails:

 

https://www.applefritter.com/content/how-fix-nonstandard-apple-1-video

 

Before trying the above fix, try this:

 

The first thing to do is to turn off the termination resistor many "professional grade" monitors have. There usually is a switch on the back side. Put it into the "Hi Z" position or whatever turns the termination resistor off.

 

The second step is to make sure the video level is high enough. I recommend to set the VIDEO LEVEL trim pot on the Apple-1  to the middle position of the trim range, or, if you have an oscilloscope, adjust it to 1.5Vpp.

 

Then, you should be able to see a picture. If it rolls up or down, adjust V-HOLD on the monitor. If you can't do that due to the 50Hz/60Hz conundrum, look if there is a black horizontal bar visible (even if picture still rolls). No black bar = something wrong in the circuit, it has no sync (a sync pulse is blacker-than-black). This rule does only apply to real CRT monitors. For those tender of age, CRT = Cathode Ray Tube. On all flatscreen TVs you can't see any sync even if it's there. Some even make black bars that have nothing to do with the actual sync pulse. Another reason to hate them. Too much digital skullduggery and deceit lurking in them.

 

If you can see the sync bar (on a real CRT based monitor), and you run out of adjustment range of V-HOLD, try first to crank up VIDEO LEVEL, but not too much. This might help. If it doesn't, you need to modify the inner circuit of the monitor. Find the V-HOLD trim pot and follow its wires to another resistor in series with the trim pot. Solder a parallel resistor to it to reduce its resistance by 10% from its original value.

 

Once you have achieved vertical synchronisation, and the picture has wiggly lines, adjusting H-HOLD may help. If it does not, again, increase VIDEO LEVEL a bit. If that does not help, apply the video fix circuit of the link above.

 

Always keep in mind that all CRT monitors you can find today are old. Actually, they are so old that they may be dangerous and comprise an electical hazard or a fire hazard. Their electrolytic capacitors in the signal path may be "dull" and may need replacement.  If you replace them you will have cracked the lousy quality, aged, and brittle phenolic PCB found in the cheaper monitors and even if you can't see the cracks, most likely there will be numerous hairline cracks. Trying to find and fix the hairline cracks will drive you so mad at the poor monitor that you want to shoot it with your pistol right on the lab bench or , if living outside the USA, and not having a gun, take a hammer to it to smash it into bits and pieces. DON'T DO THIS ! The CRTs are high vacuum devices and an implosion can send high velocity shrapnel around and into your body. Very nasty, as most of it are glass shards which surgeons can't see under an X-ray screen, so they are very hard to find and if one can't be removed, you will suffer from it for the rest of your miserable life.

 

OK, these are the dangers. How to avoid them ? Easy: find a CRT monitor which is known to work with an Apple-1 or Apple-II. All original Apple brand monitors sold for the Apple-II should work with the Apple-1. Even the B&W monitor of the Apple IIc can be adjusted to work with it. So even if you can't buy or steal such a monitor, try at least to borrow it for the bring-up phase of your newborn Apple-1. Once you know your build works, you can try find a HDMI converter or a flatscreen monitor which works with the Apple-1. It's worth to look at Apple-II forums, too. If a given flatscreen solution works with an Apple-II, it also can be made to work with an Apple-1. Maybe with the above fix, maybe without it. But it can be made to work.

 

All this trouble with monitors for the Apple-1 drove me into a new and possibly futile project: designing a new, CRT based, B&W monitor from scratch, with new electronics, and a new epoxy PCB. Only the CRT and the flyback transformer must be salvaged from a donor monitor or TV (these two parts are long obsolete now and nobody makes them anymore).

 

If this succeeds, such a "new" monitor will probably last for 50 years, and then you replace the electrolytics and it will last for another 50 years.

 

Sounds much better than having half a dozen "vintage" monitors around which always tend to die when you need them, or make nasty smells that will frighten you too much to keep them powered on, isn't it ?

 

Comments invited !

 

 

 

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Hi Uncle Bernie!

Uncle Bernie why on all monitors (CRT or LCD) the Apple-1 image is slightly shifted to the right?

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Reason for Apple-1 character field shifted to the right.

In post #3, macintosh_nik asked:

 

"Uncle Bernie why on all monitors (CRT or LCD) the Apple-1 image is slightly shifted to the right?"

 

Uncle Bernie answers:

 

The reason for this is the nonstandard Apple-1 video signal, which has several issues. This causes monitors to do weird things.

 

The issue causing the right shift of the character field is twofold:

 

a) the HSYNC pulse comes too early

b) the HSYNC pulse is twice as wide as it should be

 

My little one transistor trick circuit in this thread fixes this by delaying and shortening the HSYNC pulse. It also adds serrations to the VSYNC:

 

https://www.applefritter.com/content/how-fix-nonstandard-apple-1-video

 

What actually happens in the monitor/TV is that the "early" HSYNC turns off the horizontal power transistor too soon, so the flyback pulse happens too soon. Since the horizontal oscillator in analog TV sets / analog monitors has no start / stop capability but rather is a sort of phase locked loop (PLL), the electron beam starts too soon in the next line, and is already 1/7th into the visible screen area when the first character comes along.

 

The reason why that oscillator has no start/stop function also is interesting: the horizontal deflection coil, together with the flyback transformer, form a high powered resonant circuit. In larger CRT based TV, there may be more than a kilowatt of power sloshing around in this "tank" circuit. You can't suddenly turn the oscillator off ... bad things would happen and overloaded  components could explode. This is why the flyback transformer in a typical TV actually is part of a switching power supply which generates various voltages, including the one which powers the horizontal oscillator itself and the horizontal output stage. This is why you see that shrinking picture when you turn off these TVs or monitors, or pull the mains plug. The whole deflection system continues to run from the power available in the horizontal resonant tank. Only when all  the energy stored in the tank circuit has been consumed, over a second or so, the whole circuit shuts down into a safe state.

 

How the chicken-and-egg problem of starting up that contraption is solved, depends on the manufacturer.

 

So far for true analog TVs or monitors having a CRT. For the first few generations of LCD monitors/TVs, those with a video input, the IC designers tried to replicate the behaviour of real analog monitors/TVs as closely as possible, and so guess what - they implemented the horizontal oscillator again as a PLL, but is was digital, of course. This was largely driven by the justified fear that lots of different TV game consoles etc. are lurking in the world which all have quirky and non-standard video signals. I remember a disaster with so-called "digital comb filters" for NTSC color decoding which gives excellent picture quality but only works when the video signal is true NTSC ... and most video game consoles and the early home computers (like Atari 400/800, C64, Apple II, ...) did not generate true NTSC signals. So, sorry, no color with these devices if used with a comb filter. Our digital design team had to add a classic quadrature demodulator based NTSC decoder in the chips to get the color back if the LCD TV/monitor is used with these non-standard signals. The next issue was how to properly detect true NTSC and switch the comb filter in and out automatically. Somewhere in the early 2000's  all the design of new video chips was moved to Asia / China and since then it went downhill because a lot of know-how was lost in the process. So the more modern a LCD TV/monitor is, the more trouble it might make if used with nonstandard video signals from long obsolete devices. The grizzled, old designers in the West knew about these issues and how do design around it. The newbie Taiwanese and Chinese IC designers did not know. They fell into every pitfall in the video jungle known to man. Because they did not know nothing. There is a reason why some TV ICs are called "jungle circuits" ;-)

 

I have fond memories how TV progressed from tube based TV sets, to transistors, to ICs, and then everything was digitized.

The TVs I loved most were those with lots of tubes inside:

 

Ahhh, these were the good old times of tube based TVs ... the 1950s and 1960s! Even under normal operating conditions they ran so hot that you could almost smell a fire. And when things went wrong, and you were unlucky, they failed in a most spectacular way, like fireworks in the living room, and this could have set your house on fire ! And the MTBF of these TV sets full of tubes (no transistors !) was so bad that armies of TV repairmen could make a living just by driving from house to house and replace tubes. Which were socketed for a reason ! And yours truly, at tender age of 10, already had figured out which type of tube caused which failure symptom and I had a huge stock of tubes salvaged from old TVs I found in the dumpsters. So I became the "little TV repairman" in my neighborhood and I could fix most TVs in a matter of 5 minutes or so. As long as I had only to pull a dead tube and replace it. Anything else was beyond my skills at the time. I had no oscilloscope. But I was successful often enough to be recommended from family to family and I made good money with it ... a fraction of what a real TV repairman would charge. It was this money which allowed me to jump on the microcomputer bandwagon early, as soon as the first ones came out in the mid 1970s.

 

How much progress did we make since then ! Amazing ... now all these tubes are gone, and we have replaced the 5 Transistor radio to play music with a thing called "Smart Phone" (despite it ain't smart) needing some hundreds of millions (!) of transistors to play the very same music. This is called "progress" !

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Hi Uncle Bernie!

Great story and so much information... Have you ever thought of putting all these stories and technical information together in one book? 

Thanks Uncle Bernie from the bottom of my heart!

By the way, retroplace_1 got everything working on his CRT TV.

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One can not thank Bernie

One can not thank Bernie enough for his incredible work and willingness to share his knowledge. 

 

Yes, everything indeed works on a 70ies CRT but I would love to hook it up on my regular TV sometimes. In this video by Aaron, you can see at this timecode that they managed to hook the newly build apple (Bernie Kit) to a modern flat screen. I am waiting on Aaron's answer if he remember how they did that i.e. what kind of converter/adapter they have used.

 

Here is what my setup looks like now (the cables have been shortened meanwhile and the soldered in header for the keyboard (D'OH!) has been replaced by a socket):

 

 

All works well. Now waiting on the keyboard to arrive – I am going with an Apple-2 keyboard and – because I want to try more options, a PS/2 keyboard using Macintosh_nik's adapter. I am waiting on Claudio's "Software Jukebox/Expansion", too.

 

Also on the list of upcoming projects: Building a power supply using the Mean Well PT-65b (if I recall the name correctly) and boxing it into a proper 3D-printed case. 

 

Once that's all done and tested, I want to complete a few more Apple-1 eventually offering complete sets including fully populated board, keyboard and manuals. Only the power supply will not be included (but available probably seperately) to avoid risks with liability. After all, people can potentially kill themselves if the power supply is not handled with care.

 

Best

 

Armin

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