10 Feb
2011
10 Feb
'11
5:32 p.m.
On Friday 20 August 2010 03:10:24 pm JP Hindin wrote:
On Fri, 20 Aug 2010, Tony Duell wrote:
Further on this, you can also power the '64 up with only the +5VDC. The
9VAC (as has been mentioned in past) is used primarily for TOD and
cassette port power. If the OP is needing precise timing, this probably
isn't a long-term solution - but if it comes up correctly under +5VDC
(which presumbly can be sourced with relative ease) then you know it's the
brick also.
For what it is worth.
- JP
Coming in *way* late on this, but I worked on a heck of a lot of C64s. The 9VAC is what
eventually leads to both +5V and +12V regulators internal to the 64, 9V in the last
revision or two -- if it's not there you won't have proper operation of the VIC
chip, and no video. Or sound.
What I did with these when seeing that kind of symptom was first off to check those two
supplies, easy enough at the regulators, and the +5 coming out of the brick. Then check
the 3 or four pins on either side of the PLA at the end furthest from the notch with a
scope -- this would be 10, 11, 12, 13, and 15, 16, 17, 18. Pin 14 is ground if I'm
remembering right. I've often seen bad outputs here, that wouldn't present a
valid high logic level. Or no activity at all where there should have been some.
Subsequent to that check I scope the data bus at each of the RAM chips. Usually one of
those two things will point to the problem. Occasionally I've run into RAM that was
so hot you didn't want to touch it, I suspect that finding this would go hand-in-hand
with loading down a power supply rail as well.
PLA chips were the single most common failure part with those machines, giving a variety
of symptoms. Blank screen was one of them.
We also had quite a pile of those bricks, all bad, and sold a lot of aftermarket
supplies back in those days as well.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
The C64
that I want to use is 27 years old and worked just fine when I last
fired it up about 10 years ago. Anyone have any experience with this type
of behavior? Is it worthwhile to replace the internal power supply
electrolytics or should I build a new power supply for it? Have lots of 5
VDC supplies but don't seem to have a 9 V transformer in my junk box.
If you think it's the power brick (and it might be), you could test
things by using the 9V AC otuput from that 'brick' (that is unlikely to
fail in an odd way, it's just the secondary wining of a transformer),
along with a separate 5V supply connected in placeof the 5V output from
the brick (in other words, desolder the 5V wire at the C64 conenctor and
connect a 5V PSU to the C64). If it works, then you know ehre the problem
lies.