At 01:18 pm 20/08/2001 +0200, you wrote:
>Adrian Vickers wrote:
>> Then there's the 3016 (not 4016, as I wrote in c.s.cbm). That switches on,
>> and displays a picture, but it's full of garbage.
>
>Clear evidence of video logic which hasn't been initialized. Could be a
>number of things, like a blasted ROM, faulty RAM, a broken CPU and even
>the power supply.
I shall try the PSU first, as that is the easiest thing to check with
nothing more than a multimeter. WRT ROMs, the 3016 is the only early PET
I've got; the others are both 8032-based; I'm assuming that I can't swap an
awful lot with these. CPU perhaps, but the ROM surely not? Also, since the
RAM is not socketed (he assumed, without looking), how can I test that - or
is that the likely place for the fault if ROM/CPU/PSU are ruled out?
>I once got a "slim" 4032 (which is basicly the same as a 3016 with more RAM
>and upgraded ROMs, no CRTC in this case) which had exactly the same symptoms
>on arrival. It worked before I shipped it. It turned out that the power
>supply *was* broken. The video logic is powered independantly from the
>rest of the logic. It has two 7805's, one of them powering the video, the
>other one the rest. (That's not entirely true, but it does boil down to
>that). In my case, the lower 7805 had died, the upper one still worked,
>giving exactly the things you described.
Um - so, there's a 7805 on the lower board, and a 7805 on the board inside
the CRT box? Am I reading that right?
>
>I'd measure the supply across the processor, and see if *that* one is
>at 5V too.
>
Will do.
>> There's some photos of that one too; the display is different each time you
>> power it up.
>
>That's because the video memory isn't initialized yet. It's containing
>random data.
I see.
Unfortunately, I'ts been many years since I did any electronics, and I
never really got above using a 555 timer... Can anyone recommend any
bedside reading which would teach me the basics of IC-type elecronics (esp.
microprocessor stuff)?
Cheers!
Ade.
--
B-Racing: B where it's at :-)
http://www.b-racing.co.uk
Message was sent through the cbm-hackers mailing list
Archive generated by hypermail 2.1.1.