Video Signal troubleshooting

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Video Signal troubleshooting

Hi,

not sure whether this topic has been already discussed here....

I was wondering why I am struggling to get a picture when connecting  my Newton Replica to any monitor or TV other than my monochrome Apple II monitor. I tried already many different kind of displays and composite video adapters but without success. Sometimes I get an on / off picture sometimes the selected display struggles to sync. More often there is no picture at all. I tried to adjust the adjustable resistor R12 in all directions — no luck.  

But again — on my old Apple II monitor there is a crystal clear picture without no problem. Therefore I always thought this is related to this difficult non standard video out of our Apple—1.

 

Today I looked in this issue again and found something strange. In the schematic this adjustable resistor R12 is rated with 100 (Ohm?). Having this unit adjusted so I get a nice picture on my AII monitor I measure 1100 Ohms!

I received that part from another Apple—1 owner here in Germany and was told that's the right one. I am not so sure anymore. I can adjust that thing from 0 up to 1200 Ohms and just at the very end of that scale I am getting a picture on the selected display if any.

 

What is your opinion? Did I install the wrong type? What adjustable resistor types you are using?

 

thank you

best regards

Denis

 

 

 

 

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The video level trimmer on the Apple-1 must be 100 Ohms ...

... so unless your measurements are botched, you have a wrong trim pot.

 

If you don't have a correct 100 Ohms trim pot you can use a voltage divider made out of two 47 Ohm or 51 Ohm resistors until you get the right trim pot.

 

It would be helpful to know what inscription your trim pot has. Some show a type number which can be looked up in the datasheet of the trim pot family, some show the resistance in plain text ("100", "1K", ...) and some encode it like resistors but with digits instead of color rings: the last digit is the number of zeros:

 

101 = 10 with 1 zero = 100 Ohms

102 = 10 with 2 zeros = 1000 Ohms

 

... so you can see a lot of things can go wrong in terms of interpretation.

 

With the proposed divider, the video signal of the Apple-1 should work with Apple made monitors such as the monitor for the IIc.

 

With other monitors, you may get a rolling picture (adjust V-HOLD) or wiggly lines (adjust H-HOLD) but if this does not help despite the monitor itself is known good, the proposed remedy is in this thread:

 

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

 

regards,

Uncle Bernie

 

 

 

 

 

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Hi Uncle Bernie thank you for

Hi Uncle Bernie

 

thank you for your clarification. It turns out its a Spectrol Model 62-1-1-102

So obviously a 1000 Ohms Pot as you stated. Also found the data sheet of that thing.

 

Will now look for a proper 100 Ohms Pot :-)

 

thanks 

best regards

Denis

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Hi Denis1973!

You can use the Bourns 3329H-1-101LF - it's 100% proven.

 

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Hi Macintosh_nik thanks for

Hi Macintosh_nik

 

thanks for your suggestion. I am sure this unit will work properly. But looking to the photos of the original Apple-1 in the registry it seems to me almost all got the yellow round trim pot installed and not a metallic one. Maybe I am wrong but I already checked a lot of units.

 

I found at least a nice yellow Spectrol Model 62 with 200 Ohms at Jameco. Maybe this one will do the job?

 

 

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In post #5, Denis1973 wrote:

In post #5, Denis1973 wrote:

 

I found at least a nice yellow Spectrol Model 62 with 200 Ohms at Jameco. Maybe this one will do the job?

 

Uncle Bernie answers:

 

I think it's worth a try as it looks nice. They have two, a BI brand 200 Ohm and a Spectrol brand 250 Ohm. But be aware that depending on the input impedance of your monitor the adjustment setting you need may be in the last quarter of the range available.

 

Tell us if it works ! You suggested it, you try !

 

(Note to the nit-pickers: before you start about wrong impedance matching, calculate if this matters for a 2 ft long video cable).

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Yes - I will do :-) I hope it

Yes - I will do :-) I hope it does not take too long with USPS - I have just ordered...

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It took me a while for being

It took me a while for being able to test the part I got from Jameco. Unfortunately they did not send the yellow one I found on their shop. It actually looks like the one on the photo from Macintosh_nik.

 

I was searching hours to find a suitable "original" looking yellow one and ordered only from Jameco because it was the ONLY source having the yellow type with low Ohm value. Aarrgh! I could save a lot of money for shipping and customs ordering here in EU :-(

 

Anyway - I was curios to try out that thing to see whether it brings any improvement compared to the 1000 Ohm one. With the 200 Ohm trim pot installed I get at least something on the screen on my cheap LCD TV. Tried also on my Retrotink 2x which converts the composite signal into HDMI. Now I get a black screen there. With the 1k unit there was nothing. And I can see on my LCD TV the range of getting anything became wider. It seemed to me that this TV gets the signal somehow but cannot properly sync.

 

Today I tried a 100 Ohm trim pot. Far away from looking "original" and having the wrong shape (standing part and not flat lying). But I was curios to see whether that fixes my Video issue. It did not. On my LCD TV the picture gets more clearer now but it is definitly not syncing horizontally.

 

I wonder now whether my Apple Clone has another issue or I am just using the wrong displays. What is strange - with all 3 different kind of trim pots I was able to get a cristal clear picture on the screen of my Apple Monochrome Monitor. Just the range of adjustment differs which makes totally sense to me.

 

Does anybody know the answer about that mystery? What LCD Displays you are using if any?

 

best regards

Denis

 

 

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More hints on fixing Apple-1 video and using 200 Ohm trim pots:

In post #8, Denis1973 wrote:

 

"Unfortunately they did not send the yellow one I found on their shop."

 

Uncle Bernie comments:

 

Oh, I see you fell into the same trap as I did. After you pointed me to them, I ordered the "spectrol looking" 200 Ohm and 250 Ohm trim pots from Jameco and only the 250 Ohm one was yellow with the black adjustment screw. The 200 Ohm had a metal ring much like the 100 Ohm I furnish with my kits. As I needed these trim pots anyways to replenish the empty drawers on my lab, no money wasted. Had they not run out, I could have answered your first question about the suitability of such a pot earlier. 

 

Alas, I did not try these trim pots in an Apple-1 yet since all available units are running 24/7 to produce more of my famous IC kits.

 

I think you still can make your video work. The screenshot on the Apple monitor in your post #8 proves that there is no bad component in your Apple-1. Which resistance works and which does not depends on the input impedance of the monitor used. But you can always add a small resistor between the wiper and the ground pin of the 200 Ohm trim pot to get much the same impedance conditions as with a 100 Ohm pot, and still have enough adjustment range left. For a 200 Ohm trim pot, you would set it to 50 Ohms between the emitter of the video transistor Q5 and the wiper,  and you would have 150 Ohms left between the wiper and the ground. Add a small 75 Ohm fixed resistor (1/8W is strong enough by far) between the wiper and ground pins. 150 Ohms and 75 Ohms in parallel circuit are 50 Ohms - bingo, you got the same impedance levels as with a 100 Ohm pot.

 

But the problems you see with your modern TVs or monitors are most likely the timing issues in the nonstandard Apple-1 video signal.

 

The fix is here:

 

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

 

As you can see in that thread, many people were able to get video on more modern monitors by adding this little trick circuit, but some experimentation with the component values may be required.

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