Apple 1 Power Supply - Accpetable Noise Level on -5 Volt DC Line

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Apple 1 Power Supply - Accpetable Noise Level on -5 Volt DC Line

I read this post:https://www.applefritter.com/content/about-apple-1-transformers-and-fuses

 

I've added the fuses as suggested, with LED indictors as to the state of the fuse, proved very helpful.I was not too comformable about the design of the Apple 1 power supply, so build one on veroboard (strip board) to check how it operated.  All good.

 

Testing the AC noise levels on my Apple 1 mainboard, I see that the -5V is very noisy, when viewing with an oscilloscope.  I'm guessing this is due to the design on the Apple 1 circuit board layout.Any advise is gratefully received.Russ.

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On -5V noise and the Apple-1 PCB in general

In post #1, RussellSpeight1967 wrote:

 

" I see that the -5V is very noisy, when viewing with an oscilloscope.  I'm guessing this is due to the design on the Apple 1 circuit board layout."

 

Uncle Bernie says:

 

You can ignore that issue on the -5V line. You are right that it's the poor PCB  layout. Which was made by a true "artist" and I don't mean that to mock him (don't know if he's still among us). The Apple-1 PCB layout is a true work of art - as in "artist" - because it looks   beautiful   and well thought out.

 

But RF wise it is thoroughly wrong and rotten. To be fair, we cannot demand that a PCB layout technician has any insight in transmission line theory or even Maxwell's equations (the "evil math" used to calculate antenna designs, and every trace in a PCB is such an antenna).

 

What happend is that APPLE (the corporation) ran afoul of the FCC regulations and they had to redesign the layout of the Apple II motherboard several times. And this was not done by said "artist" but by real electronics engineers.  Who are supposed to know what they are doing. Still, they needed several design iterations.

 

This said, the Apple-1 motherboard layout is rotten RF wise and has very poor ground and power rail performance but it is at least  beautiful   - in the sense of "piece of art". Which may contribute to the value of the Apple-1. It just has the right 1970s "look".

 

To be honest, it is not worse RF/EMI wise than most other contemporary PCB layouts for early microcomputers. Most arcade machines had worse layouts. Ugly and a mess, and still spitting RF/EMI all over the place. But what counts is the  money  collected by these machines. The number of quarters sucked in per hour is their metric of performance, and nothing else.

 

Here is a personal anecdote: being a private pilot, I often listen to the radio traffic between commercial airliners and COS municipal airport approach control, using a handheld walkie talkie I have bought because I don't trust the 50 year old electronics  in the junk airplanes I have to fly sometimes. This helps me to stay current on the lingo. Well, the point here is that while I was running a bunch of burn-in rigs for my Apple-1 IC kits, it was hopeless to receive anything from my house (about 10 miles away from the ILS glide path). With the rigs turned off, I could receive everything loud and clear. So the EMI/RF issue is real. But nothing bad did happen, no airliner misunderstood the EMI from my Apple-1 burn-in rigs as being the ILS glide path. Otherwise I may have found a free jet engine in my backyard, along with lots of aircraft grade aluminum in place of where my house was before the impact ;-)

 

This said, EMI is bitch, and may have bad effects on radio reception over all frequencies. But what can I say. The utter morons ("affirmative action" low IQ individuals in charge ?) in the government have authorized 5G cell tower operation despite it interferes with certain radar altimeters used in commercial aircraft. This may really kill people, folks. (The Apple-1 won't, its EMI signals are too weak at a few 100 yards distance).

 

- Uncle Bernie

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Thank you for the insight.I

Thank you for the insight.

I will park this issue, and move on.Russ.

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