the science & technology of Commodore 8 bit computers and circuits

Disk drives, Monitors, SuperCPU etc.
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

Gyro Gearloose wrote:You got it, the voltage on those big caps goes up. It doesn't matter what switcher you use.
You're worried about something not worrysome at all!

From what I saw, when you reduce power consumption by virtue of replacing the linear regulator with a switcher, the voltage from the transformer does increase a little because the load lightens but mostly, the voltage simply does not ripple as intensely at each voltage cycle. It just says high a greater portion of the time.

You don't need to have capacitors rated for a higher voltage. In the 1541, the voltage at the leads of the large cap rated for 16V is 10.8V at it's peak - increase it by 20% and you get 13V which is still perfectly safe.

Same for the other big cap rated for 25V, same for the VIC-20...

No drama here...


Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

If I am to go on chronologically about my discoveries of the technology inside Commodore computers, back around 1985, my first attempt at making a power supply for my VIC-20 (which I would later learn is known by techs as the VIC-20cr) ended in a lot of noise, a blown capacitor and incredibly bad smell.

I used a 18V transformer with center tap. I should have used 2 isolated 9 Vac sources... The 2200uF capacitor inside the VIC exploded.

The interesting and bewildering part of that story is that I could still see the VIC's display on the TV with the cursor flashing right after the cap blew up. Of course, I immediately slammed the switch off.

That's about when I learned to make power supplies the right way.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
User avatar
Gyro Gearloose
Member
Member
Posts: 471
Joined: Sun Nov 15, 2015 5:20 am
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

"You're worried about something not worrysome at all!"

Maybe you're right. I always used the "50% voltage derating" rule for sizing power supply decoupling caps, without really knowing why. It's just something I always use.

From what I do know, the real enemy of Al electrolytic caps is heat, either from self-heating or just the other stuff around. Even then, the big old caps in my tube gear sit right next to giant triodes, no problems as long as the small Rotax engine keeps blowing in fresh hair.

My 1541 has both linears replaced by my module. Seems fine so far.

So you want a TO-3 switcher? I have one bare PCB left, it is best for 5V.
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
User avatar
Gyro Gearloose
Member
Member
Posts: 471
Joined: Sun Nov 15, 2015 5:20 am
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

Oh, and most of my discoveries about the insides of Commodore computers did come from the VIC-20, but mostly just reading about it.

I built my first C64 from a 4064 board from Addison, I guess that's where I first got into repairing/taking apart/building.

I also got a very low cost 256k REU upgraded to 512k for free. There was a Microserv computer store a few streets down from my place. One day I was walking by and saw a bunch of DIP chips in the bushes. I lunged to pick up this treasure and it was a bunch of 41256 DRAMs! They must have been desoldered from a Mac or something. Naturally I picked them all up and soldered 8 of them into the 1764.

I think about that time I also had to build a bigger supply for the REU, that's when I built a metal-cased monster that I still have.

When I was in college I brought in my VIC-20, painted in zebra stripes, to the various labs since it was much easier to use and program than the PC/XTs they offered. The VIC-20 was an early Arduino in a way!

I created an "arbitrary waveform generator" in the ADC/DAC lab, using BASIC to create lookup tables with complex equations, and a simple ML loop to push out the data from the user port. Quite nice to see weird waves on the scope from a simple VIC-20. It wasn't very fast though.

The next simple thing I did was to use the 1408 DAC and a LM317 to create a "digital power supply". Super awesome, just enter the voltage and there you had it! I was quite happy.
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

Gyro Gearloose wrote:So you want a TO-3 switcher? I have one bare PCB left, it is best for 5V.
That's what I'd use it for in the VIC-20 with PSK.

BTW, this old fellow I got from Jean-Claude Lachapelle back in 2006 has serial number 7829.. very early machine. All chips inside are dated 1981.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

If I go on with my tech and science ramblings, in 2003, i was accepted at Ecole de Technologie Supérieur as a student to get a bachelor's degree in electrical engineering.

The first year, I got an A+ in elementary digital design, the same with fundamental analog electronics. This gave me a whole different perspective on all my old computers.

In the summer of 2003, I acquired a TDS-1002, created my own 11 MHz function generator and built a 32k RAM expander for my VIC which was based on a single 32k x 8 SRAM chip. It became the design basis for the Ultimate Expander.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
User avatar
Gyro Gearloose
Member
Member
Posts: 471
Joined: Sun Nov 15, 2015 5:20 am
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by Gyro Gearloose »

Behold my Vicduino. I used this to plow through the digital lab work stuff in school, like the DAC stuff.

Image

What was fun was that not only did I get the labs done much faster, but the technical library had a dozen or so books about the VIC-20, which I bought for 1$ each when they decided to clean up the place.
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

@Gyro
When I began studying at ETS, I did expect the knowledge I acquired about logic circuits, power supplies and small analog electronics to help me out a bit. What I didn't anticipate was how broad the acquired basics would give me an advantage and this was reflected in the grades I got during my first 2 years there.

Of course, the VIC-20 and the 64 did not show me anything about wireless communications, AM, FM modulations and high power electrical lines so I lost this advantage as things progressed.

Nonetheless, I now have good enough grades to go for a master's degree thanks in part to what I learned on these 2 machines.

I also owe a part of my knowledge about the PLA to the access I had to large and powerful Tektronix logic analysers in the logic design labs.
Last edited by eslapion on Sun Feb 07, 2016 12:48 am, edited 1 time in total.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
User avatar
motrucker
Member
Member
Posts: 191
Joined: Tue Jul 21, 2015 6:11 pm
Location: Maryland, U.S.
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by motrucker »

This might make you feel like pulling out some hair. This is title of a post over at the other 64 forum. THis is real, I did not make this up.
"What on earth is -5 volts anyway?".
I had to walk away from the computer, then come back to make sure I wasn't seeing things.

I studied at NRI, which is a correspondence school, but since they are based in Washington D.C., I could attend classes there. I had the best of both worlds. These guys from that other forum could easily study there. It's as close the U.S.Mail, or your computer, and isn't all that expensive. I guess it's too much trouble. And gets in the way of playing games.
C-64, C-128, and Amiga A2000 user
User avatar
eslapion
Active Member
Active Member
Posts: 1215
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: the science & technology of Commodore 8 bit computers and circuits

Post by eslapion »

As I said, I feel left out... and I'm glad!
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
Post Reply Previous topicNext topic

Who is online

Users browsing this forum: Ahrefs [Bot] and 5 guests