System Clock Trouble!
3 messages in this thread
Don,
Thanks for the information on the jumper. Being an electrical engineer I
needed a reason for the machine to be messed up and you helped me locate
what was wrong. That jumper selects which signal is fed into the 8520 chip
as the TICK signal. If the 8520 is slightly damaged then the system clock
can be off. Sure enough when I pulled it apart I popped in my spare 8520
chip into the U300 position and the system clock got well.
I'm now happy that the clock is working again but I am baffled by a couple
of things. This is a new motherboard and so far it's gone through 2 8520's
in the last 2 months. I'm beginning to think there might be a larger
problem here. The other thing that surprises me is when I first turned on
the system unit to check it I did it without the keyboard attached. The
machine wouldn't even begin to boot! I know the 2000 I used to have would
boot up with or without the keyboard. Have you ever heard of something
like this?
Anyway thanks again for getting me back up and running.
Keith
Keith,
Humm…no idea on the no boot without keyboard. Mine (A2000) boots
just fine without it.
8520's are VERY static sensitive, and also directly attached to
some of the external ports. For example, it generates the keyboard clock,
and read the keyboard data. The external disk connector also has some
lines going to the 8520 as does the mouse ports and parallel ports. The
serial port also has some control lines going thru one of the 8520s, but
they're buffered so are less sensitive to static.
In any event, simply plugging in, or unplugging one of the
connectors can blow one of the 8520s. It depends on how much static is
present, and what steps you take to discharge it prior to making/breaking
the connection.
For me, I keep the rug in my computer room sprayed with anti-static
spray. I made sure the electrical outlets in the room were properly
grounded and polarized. I never make or break a connection without making
sure I'm touching the metal case first. Before I make a connection, I
touch the shell of the connector to the metal case.
In other words, I try to follow proper static precautions. I've
only lost one 8520 in 5 years with the Amiga, and that was due to a
lightning strike on my phone line (fried the modem and came thru one of the
control lines).
Blown 8520s are probably the #1 problem for Amiga owners.
Don
Don,
I knew the 8520's are very static sensitive, that's why I keep my ESD strap
next to the Amiga. It's got a nice stretch band that goes around my wrist
and a long wire with a clip on it so I can keep the static down to a
minimum. The problems I've been having seem to be happening while the
Amiga is just sitting here, no pluggin or unplugging going on.
I've sent a message to Dave Haynie asking him about the booting without the
keyboard. I may have gotten a bad motherboard a couple of months ago, if
so I'll get a new one while it's under warranty. Thanks for the info.
Keith