How to convert a 50 Hz TV (Europe) to 60 Hz (Apple-1)

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How to convert a 50 Hz TV (Europe) to 60 Hz (Apple-1)

People ask me this question all the time, so I decided to post an answer in this public forum:


Q: Can I modify the Apple-1 to produce a 50 Hz frame rate ?

A: No, you can't.


(At least not without major surgery on the motherboard which would lead to an unsightly result).


But the alternate solution is simple. Unlike the horizontal deflection circuits in a CRT TV/monitor, which are tricky and dangerous to modify, the vertical deflection circuits are simple enough to work with 50 Hz and 60 Hz frame rate (actually, you can push the same circuit farther than that as 50, 60, 70 Hz is incredibly slow for any form of electronics --- you could drive the deflection coils with your Stereo set ;-). The only question is if the range of the "V-HOLD" adjustment knob is wide enough to set the 50 Hz TV/monitor to 60 Hz frame rate. If so, you will initally get a "rolling" picture with the Apple-1, and then you simply adjust the V-HOLD until the rolling stops and the picture is stable. Job done.


But if you can't do this, the controls for the V-HOLD don't have enough adjustment range, and a small circuit mod is necessary. Which is very trivial, you don't even need a schematic for the TV/monitor.

Any electronics hobbyist can do that mod. Just disconnect the TV/monitor from the line voltage (to be safe) and open the enclosure to get at the electronic guts of the TV/monitor. Keep in mind that there are some hazards: some capacitors - including the picture tube - can hold some truly shocking - potentially lethal - charge for a long time. And if you hit the picture tube with an impact, it might implode and send glass shrapnel all over the place. So be safe, don't finger around near any big capacitors and the picture tube, don't hit the picture tube with a hammer, and always wear safety goggles to protect your eyes.


Then find the V-HOLD setting potentiometer. It might be on the front panel or somewhere near the back of the TV. On very cheap TVs it might be just a regular trim pot on the printed circuit board with a corresponding hole in the enclosure so it could be adjusted by means of a screwdriver from the outside.


Once you found that trim pot, follow its connections to the next resistor which is connected in series with the pot. To avoid a screwup, inspect that node carefully - only the one leg of that resistor shall be connected to the trim pot, and to no other component. If you can find the resistor following that rule, you can do the mod. Otherwise it may get a bit more complicated and requires circuit diagram reading skills beyond a typical hobbyist. So if you can't find that resistor, let it be, lest you may damage the TV/monitor if you start to experiment.


But if you have found the resistor, determine its value. Either by reading its color rings, or by measuring it, but note that you need to desolder and lift up one leg of the resistor to get a correct measurement. Solder that leg back when you know the value, say R.


And here comes the mod: solder another resistor of four times that value (4R) across it. Round down to the next lower value in the series.


That's all ! Mod done !


Now you should have a TV/monitor that was 50 Hz but can be adjusted to 60 Hz frame rate.


Easy peasy.


The only issue you might occasionally get with this mod in terms of picture quality is somewhat darker horizontal "hum bar" which slowly scrolls through the picture. This points to a lousy black level clamping circuit in the TV. Or to a bad, ripply internal power supply due to inadequate (or aged) electrolytic filter capacitors. But this is a rarely seen issue. Most TV/monitors will work just fine.


Note there is another known issue with the Apple-1 video signal, and that is its non-standard horizontal sync pulse width. This may lead to slanted pictures, wiggly lines aka horizontal PLL lock-in effects, and loss of horizontal synchronisation. Not to be confused with vertical sync / frame rate issues --- these are distinct, with vertical sync issues the picture is fine, except that it rolls vertically (up or down). Do not confuse the two effects. The remedy for horizontal sync problems with the Apple-1 is here:


So don't fear. With a little bit of mods you can get any CRT based TV or monitor running with the Apple-1.Except maybe those old, vacuum tube based, terrible and dangerous monsters from the 1950s and 1960s. Stay away from them ... don't use them. They are notorious for failure modes which have set many living rooms (and houses) on fire. Those also usually are the "hot chassis" type where all the electronics inside are galvanically connected to the "hot" wire on the line cord. So a fatal electrical shock hazard is lurking everywhere in those. Avoid them like the plague !


The safest TVs and monitors to experiment with are those fully transistorized ones which came out of Japan since the late 1960s (and later, Korea) which can be run with batteries or on the cigarette lighter outlet of a car. If they have a line cord, they typically have a transformer inside which galvanically isolates their electronics from the line voltage. If in doubt, look inside and follow the line cord wiring inside the TV/monitor. It should only go to a transformer primary, and nowhere else. The possible exception being a line side ON/OFF switch and maybe a fuse, and / or a power on indicator neon bulb. But all the electronics must be only on the transformer secondary side. If in doubt, don't use this thing as a monitor for your Apple-1. Note that more modern TVs / monitors often have a switchmode power supply which does have some electronics on the line voltage side. Unless you mess with those, this TV/monitor also should be safe to use as a monitor for the Apple-1. There is a transformer in them, but it's for higher frequencies. But beware of that innocent looking input filter capacitor in the switchmode power supply . . . is has enough charge to kill a horse. Do get near that. No curious fingers there and no licking with your tongue !


As always, follow these recipes at your own risk and peril. The author does not assume any liability for incidental or consequential damages (including injury and death) arising from your messing around with line voltages and potentially dangerous guts of TVs or monitors. Don't try anything exceeding your skill and knowledge level. Keep in mind that electronics professionals undergo safety training before they are allowed to work in an electronics lab, and in industrial labs it is prohibited to work alone: there always must be a second person in the lab to push one of the red power cutoff mushroom switches which are everywhere in reach. Safety rules. As Morpheus so aptly explains to Neo, "Some rules can be bent. Others can be broken." --- but always remember, the characters in a movie are fictional and even when getting shot up and blown into pieces, the actor playing them stays unharmed and alive. The real world is different and many hobbyists (and professionals) have electrocuted themselves by doing stupid things. "Play stupid games, win stupid prices". Shortly, don't be stupid. Instead, stay safe.


Hope this post completes everything I have to say about TVs and monitors used with the Apple-1, and all the monitor related open questions for prospective Apple-1 builders have been answered now. Have no fear, you will be able to find / beg /borrow /steal and, if needed, modify a TV or monitor to work with your Apple-1.


- Uncle Bernie