Jim Strickland
2013-11-25 18:16:54 UTC
Hi. I've done first powerup on my zeta.
Problem #1: When loaded with the 20mhz crystal, it spews a continuous
stream of gibberish out the serial port.
Problem #2: Dropping the clock speed down to 8mhz using the floppy system
clock (no fd installed yet anyway) the gibberish clears up and I get the
startup screen, but can't type back to it.
Problem #3: Sometimes the board starts up halted. Resetting returns me to
problem #2.
My hypotheses right now are that problem #1 is from the 74LS06s that Sergey
mentions in some places as being too slow and that #2 is the result of
deficiencies in my charge pump caps. While they are all .1uF, and the
chip's datasheet specifies these, the disk ceramics I'm using have a huge
tolerance, and if I got one bad one, it would mean one line never goes high
enough to work. I'll be putting new caps in the charge pump lines soon.
Problem #3 has me stumped. It could be a side effect of #1 or #2, I
suppose. Thoughts?
Problem #4 (New development) I just put the cr2032 battery in, and now when
the board is powered up, u25 and x1 get too hot to touch very quickly.
Likewise an area on the board down around r2, d1, and c30 gets very hot. No
changes in operation, however, except that I shut it down very quickly when
I noticed the heating problem
Back to the schematics for me, I guess.
Meantime, some questions:
1. Are full can crystals polarized? I put my 20mhz one in "upside down" at
one point and it very swiftly got too hot to touch. This is in the same
socket where it has run barely warm enough to feel with cold hands most of
the time, and the same socket the 8mhz crystal does the same.
2. Could we have a definite yay or nay whether 74LS06s work at 20mhz,
please? They're what is specified in the BOM.
3. Does anyone see anything obvious wrong with my serial IC selections:
UART: NS16450N
Driver: TRS232ECN (I've read that .1uF caps on these are often
insufficient, so I'll be going to 1.0s when I replace them.)
4. I noted in the discussion about the N8 that it was necessary to put a
450uF cap across power to slow the startup. With all ICs installed, my Zeta
comes up halted at least half the time. With only the bare essentials -
ROM, RAM, UART, Serial, plus all the TTL, the number of halts on startup
drops off dramatically. Was there a revision that I missed when installing
my caps?
-JRS
Problem #1: When loaded with the 20mhz crystal, it spews a continuous
stream of gibberish out the serial port.
Problem #2: Dropping the clock speed down to 8mhz using the floppy system
clock (no fd installed yet anyway) the gibberish clears up and I get the
startup screen, but can't type back to it.
Problem #3: Sometimes the board starts up halted. Resetting returns me to
problem #2.
My hypotheses right now are that problem #1 is from the 74LS06s that Sergey
mentions in some places as being too slow and that #2 is the result of
deficiencies in my charge pump caps. While they are all .1uF, and the
chip's datasheet specifies these, the disk ceramics I'm using have a huge
tolerance, and if I got one bad one, it would mean one line never goes high
enough to work. I'll be putting new caps in the charge pump lines soon.
Problem #3 has me stumped. It could be a side effect of #1 or #2, I
suppose. Thoughts?
Problem #4 (New development) I just put the cr2032 battery in, and now when
the board is powered up, u25 and x1 get too hot to touch very quickly.
Likewise an area on the board down around r2, d1, and c30 gets very hot. No
changes in operation, however, except that I shut it down very quickly when
I noticed the heating problem
Back to the schematics for me, I guess.
Meantime, some questions:
1. Are full can crystals polarized? I put my 20mhz one in "upside down" at
one point and it very swiftly got too hot to touch. This is in the same
socket where it has run barely warm enough to feel with cold hands most of
the time, and the same socket the 8mhz crystal does the same.
2. Could we have a definite yay or nay whether 74LS06s work at 20mhz,
please? They're what is specified in the BOM.
3. Does anyone see anything obvious wrong with my serial IC selections:
UART: NS16450N
Driver: TRS232ECN (I've read that .1uF caps on these are often
insufficient, so I'll be going to 1.0s when I replace them.)
4. I noted in the discussion about the N8 that it was necessary to put a
450uF cap across power to slow the startup. With all ICs installed, my Zeta
comes up halted at least half the time. With only the bare essentials -
ROM, RAM, UART, Serial, plus all the TTL, the number of halts on startup
drops off dramatically. Was there a revision that I missed when installing
my caps?
-JRS
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