1541 won't work with VIC-20

[Boray]

Hmmm..... I think I will buy a better multimeter. It doesn't seem very accurate.... Or the power outlet is varying quite much... But I think I will buy a new one anyway. A digital one....

/Anders

[Boray]

It won't, 9VAC will need to be replaced by a 12V DC (RMS VAC * root 2).

Lee.

> "It won't, 9VAC will need to be replaced by a 12V DC (RMS VAC * root
> 2)." Any idea what he talks about?

Anders,
I might agree if I had not had a look at the schematic of that
particular VIC20. After the rectifier, the only thing there is a 5 volt
regulator and a pass through to the cassette regulator circuit (six
volts). A conventional regulator needs an input about three volts
higher than its output to regulate (not drop out). A 9 volt DC input
meets that requirement. The AC input does provide a higher DC input
voltage, but the excess is just converted to waste heat.

Ray

> I have now done some measuring... My Vic-20 PSU delivers 10.5V AC.
> So 10.5V goes into the rectifyer, and out comes 11V DC...!?
> Can this be because they have increased the voltage of the
> power outlets from 220 when the vic20 was built into
> more like 225-230V today?

Good questions, and you've got it right. The voltage is "nominal"
9VAC, but what you actually measure will indeed be higher (or lower)
depending on how you measure it, whether the transformer is loaded or
not(computer connected), the line voltage (which varies a lot from place
to place and even in the same location at different times of the day).
With 9VAC input to the bridge recfifier and filter capacitor, the
unloaded output will be somewhere in the neighborhood of 12.7 volts DC.
That's because it's the peak to peak (RMS times 1.414) excursions of the
line that are actually being measured. On one half cycle, the AC voltage
goes above zero about six volts, then crosses zero and goes below zero
about six volts. Loading has a lot to do with what the actual voltage is
at that point. Note that there is not a lot of energy in those peaks, so
when you load down a capacitor input filter (what they call a standard
rectifier and filter cap circuit), the running voltage is something less
than the peak reading. The "effective" voltage (loaded) is something
they call RMS (ratio means square). It has to do with how much actual
power is available (expressed in Watts or Volts times Amps).

> Could this be the cause of the heat problems I have had?
> (I have moved the rectifyer out of the vic20 case etc...)

The rectifier and regulator in the early VICs do run pretty hot.
That's why the later design uses the "split" supply like a C64... the
regulator is in the supply to keep the heat away from the computer.
Waste heat is a consequence of linear regulation. That's why switchers
are the supply of choice nowadays... greater efficiency means less waste
heat.

> Would it be more healthy for my vic-20 if I bought one
> of those DC power packs we talked about to use 9V DC instead?

Probably not. The regulator in the VIC is where most of the heat
comes from. Notice the enormous heat sink. Using DC instead of AC as an
input still requires the internal regulator that converts the input (AC
or DC) to +5VDC for all the chips.

> If you remember, I have a vic-1020 expansion box (which I sent
> you the scematics for once). The power goes from the PSU into the
> vic-1020 to power it, through a "master" on/off switch and then into the
> vic-20 (which always has the power switch on). Would it work to
> use 9V DC for it all? To just replace the original PSU with it so
> to say...? If you don't still have the scematics, then I can send
> it to you.

I do, and I put them up on my schematics site for all to use. I
did notice something odd however. The 1020 power supply diagram seems to
be incorrect. They show what is called a full wave rectifier (two
diodes) instead of a bridge arrangement (four diodes). Their full wave
circuit has no ground return. Such a circuit usually has a center tapped
transformer, but a standard VIC supply has none. So, I suspect the
schematic is incorrect and the actual circuit is a bridge. I can't
verify that without seeing the unit. But, to answer your question, I
think a DC supply would power the 1020 OK too.

I would like my vic20 to live as long as it can, and
> running it on 11.5V instead of 9V seems a bit unhealhty, don't
> you think?

Well, the higher the input voltage, the harder a regulator has to
work to drop the excess voltage. However, it's made to work that way
unless you're ready to modify it to make it more efficient. That would
mean getting the 5 volt regulator out of the box. Then you would feed a
regulated +5VDC to the computer directly. 5 volt supplies are even
easier to find, but this mod would require a bit of work to implement.

Ray

[Boray]

Sorry for this double post with the buy&Sell forum, but this concerns this thread too...

---

I just bought a better multimeter and made some measurements. And
Lee is absolutely right: 2A is clearly enough.
My vic-20 uses 1.64A while running and more like 1.75A at startup.
Vic-20 + vic1020 uses 1.79A while running and something like 1.95A
at startup. These ampere measurements has an accuracy of
+-(2.5% +5). I don't know what the +5 means (maybe someone can
explain), but if it's just the percent, then the real value for a
vic-20 should be in between 1.60A and 1.68A.



Some more measurements:

The power outlet varies in between 228V and 231V.

The vic20 PSU without load: 11.4VAC (49.9Hz)

Over the rectifier while the computer is running:
in: 10.3 VAC, out: 10.9 VDC

Over my old rectifier without load (I have replaced it):
in: 11.4 VAC, out: 9.73 VDC

(AC accuracy +-1.2% +3)
(DC accuracy +-0.8% +3)

Interesting?

/Anders

[Boray]

Woops... The c64 PSU can only deliver 1A of 9V (right?) so maybe I was right anyway.... it's not enough!

/Anders

[ChristopherT]

Woops... The c64 PSU can only deliver 1A of 9V (right?) so maybe I was right anyway.... it's not enough!

/Anders

I swap my C-64 PSU between my C-64 and my VIC-20 just fine. I don't
think that would be a problem. I think the problem is wether or not you
are getting good clean AC to the PSU. I just used my DVM on my outlet,
I got a good 122.0 volts and it never varied. Try eliminating anything
between the wall outlet and the PSU, maybe you have a surge suppressor
that's getting old and flaky?

Christopher

[carlsson]

I think you may have a VIC-20CR, the newer one with a 3 or 5-pin DIN connector providing both 9VAC~ and 5VDC=. It draws equal power as the contemporary C64 does, so it is not an issue here. We're speaking the first generation VIC-20 with its two-prong connector, which only gets 9VAC~ input.

[Boray]

Yes... and it's not me having the trouble either.... But it seems idrouge (the original poster) isn't reading this forum anymore or he would probably had replied...

Btw, running the tape takes futher 0.1A (playing) to 0.2A (rewinding). Anyway, a total of 2A should be enough for a normal 2-prong vic20...

/Anders

[carlsson]

Phew. Did you measure if different colour combinations or size of writable screen draws more power too? What about with and without a cartridge plugged in, or for that matter a joystick, disk drive (which the thread originally was about) or with Shift Lock depressed?

[ChristopherT]

I think you may have a VIC-20CR, the newer one with a 3 or 5-pin DIN connector providing both 9VAC~ and 5VDC=. It draws equal power as the contemporary C64 does, so it is not an issue here. We're speaking the first generation VIC-20 with its two-prong connector, which only gets 9VAC~ input.

You're right, my VIC does have the DIN style power connector. I'll have to go through my stuff and see if I have any schematics pertaining to the
older 2-pin series of VIC-20's. It would be interesting to see how much power a VIC-20 draws during normal operations.

Christopher

[carlsson]

The sticker on the bottom should give you a hint about maximum effect, 25W for the old model and 15W for the new IIRC.

Actually, the DIN-style PSU appeared in a few variations too. My old, broken brown brick is rated to 9VAC 1A + 5VDC 1.5A. Then I had some similar brown bricks but with a power switch, rated to 9VAC 1A + 5VDC 1.7A IIRC (I can't check, as it sent them away to someone.. Zeela?). The white rectangular PSU to the newer C64C is also rated 1.7A on the 5V.

[Boray]

Phew. Did you measure if different colour combinations or size of writable screen draws more power too? What about with and without a cartridge plugged in, or for that matter a joystick, disk drive (which the thread originally was about) or with Shift Lock depressed?

Joke on, but as the tape motor uses the vic's power, I thought it would be good to measure... Running the diskdrive does not use any of the vic's power but that doesn't mean that the problem isn't too weak power anyway, because it could be the chips used for disk access that are more sensitive to low power...

About carts... Well, I had my vic connected to the vic1020 all the time and measured between it and the vic, so I thought it was to much work

/ANders

[Boray]

It would be interesting to see how much power a VIC-20 draws during normal operations.

Christopher

My vic-20 draws exactly 17.3W idle and 18.5W while rewinding the tape.

/Anders

[carlsson]

Now you can start keeping a diary on when you use your computer, sum the Wh and compare to your electricity bill.

[Boray]

Now you can start keeping a diary on when you use your computer, sum the Wh and compare to your electricity bill.

Except for that I haven't measured how much is lost in the PSU!

[idrougge]

idrougge, Did your friend come so you could test with the original PSU?

Yes, he did. Sorry for being absent, but I was quite fed up with the VIC and have been spending some time with my new toy, a flash cartridge for the 8-bit Sega. =)

My friend, who bought the stock of a Commodore repair shop some years ago, did bring both an old, black, two-pin trafo and some VIA chips. We swapped the VIAs and ran the VIC off the correct PSU, but the machine just misbehaved as usual.
That's when I was fed up with the machine. It does everything right, it just won't communicate with the 1541.
I see no other solution than getting another VIC-20, and then possibly swapping bits and pieces back and forth in order to find the culprit.