12 Sep
2004
12 Sep
'04
2:21 a.m.
[If it is a
2114, it will be the second one I've found dead in PET hardware
over the past month - other was was video RAM in a 4032]
FWIW, I've had _lots_ of 2114s fail. I had to replace all of them in my
8050 (IIRC, if you hvave multiple RAM errors, you get the flash code for
the lowest bank first, then when you've replaced those you get the code
for the next bank, and so on...). I had to replace the video RAMs in my
TRS-80 Model 3. And the RAM in my HP82163 video interface. And more...
In my experiece the 2114 is one of the least reliable chips ever... 
12 Sep
12 Sep
9:24 a.m.
Btw, it is an 8050, and replacing those two chips did fix it. [Naturally,
the one I pulled first was not the defective one]
Excellent. If you need any more help, just ask. I've got the 8050 service
manual (little more than schematics and parts lists, actually) here.
-tony
4:45 p.m.
New subject: 2114 Static RAMs...
Dave Dunfield wrote:
Tony Duell wrote:
I've seen a few other ones fail as well - funny, I used a LOT
of 2114s in my early building (at 4 bits each - way less
wire-wrapping than 2102s). Never had any trouble with them at
the time, however they do not seem to age well...
Another data point plus an "Arg!"...
Ohio Scientific was quite fond of 2114s (Arg!). It looks like
the cause of the power supply failure in my C4P is that one of
the 24K memory cards (48 2114s) was drawing well over spec, even
though it appeared to be providing reliable memory operation. It
was populated with the LC (low power CMOS) 2114 chip. According
to specs on the web, these should draw 40 milliamps max. I pulled
10 at random. Not one pulled less than 70. Now, I tested them
with all pins floating other than power and ground and I wonder
how much difference that makes, but totaling up an average of 75
per chip gives about what the card as a whole draws when in
operation. The other card, populated with another vendors 2114s,
draws over 1/2 amp less when in operation, reflecting about 42
milliamps per chip.
[If it is
a 2114, it will be the second one I've found
dead in PET hardware over the past month - other was
was video RAM in a 4032]
FWIW, I've had _lots_ of 2114s fail. I had to replace all
of them in my 8050 (IIRC, if you hvave multiple RAM errors,
you get the flash code for the lowest bank first, then when
you've replaced those you get the code for the next bank,
and so on...). I had to replace the video RAMs in my TRS-80
Model 3. And the RAM in my HP82163 video interface. And more...
In my experiece the 2114 is one of the least reliable chips
ever... 
13 Sep
13 Sep
noon
New subject: 2114 Static RAMs...
Bill Sudbrink may have written:
Another data point plus an "Arg!"...
Ohio Scientific was quite fond of 2114s (Arg!). It looks like
the cause of the power supply failure in my C4P is that one of
the 24K memory cards (48 2114s) was drawing well over spec, even
though it appeared to be providing reliable memory operation. It
was populated with the LC (low power CMOS) 2114 chip. According
to specs on the web, these should draw 40 milliamps max. I pulled
10 at random. Not one pulled less than 70. Now, I tested them
with all pins floating other than power and ground and I wonder
how much difference that makes, but totaling up an average of 75
per chip gives about what the card as a whole draws when in
operation. The other card, populated with another vendors 2114s,
draws over 1/2 amp less when in operation, reflecting about 42
milliamps per chip.
When I was designing I/O boards for spaceborne computers I once saw
what happens when most inputs are left floating on CMOS designs. This
was a design full of (~30) 54HCxx ICs. When powered up, the boards
power consumption varied wildly from almost nothing to way above
spec. You could play the power consumption by waving your hands
above the board.
Thim makes me conclude that in order to correctly measure stand
by current consumption on any CMOS circuit, you _must_ tie all
unused inputs to either Vdd or Vss, whichever makes most sense.
If the input of a CMOS inverter is left floating, there is a good
chance it will stay somewhere in the middle between high and low and
both transistors will be half open for current to flow all the way
from Vdd to Vss. If the input is tied to Vdd or Vss,
then at least
one of the transistors will be shut off, and very little current
will flow. This is all there is to CMOS low static current con-
sumption.
Thank you for listening.
/Ulf Andersson
Veteran computerist in spe.
15 Sep
15 Sep
8:40 a.m.
New subject: 2114 Static RAMs...
>>
>> Thim makes me conclude that in order to correctly measure
>> stand by current consumption on any CMOS circuit, you
>> _must_ tie all unused inputs to either Vdd or Vss,
>> whichever makes most sense.
>>
>> If the input of a CMOS inverter is left floating, there is
>> a good chance it will stay somewhere in the middle between
>> high and low and both transistors will be half open for
>> current to flow all the way from Vdd to Vss. If the input
>> is tied to Vdd or Vss, then at least one of the transistors
>> will be shut off, and very little current will flow. This
>> is all there is to CMOS low static current con- sumption.
>>
The above is quite correct. Over current is merely one of the effects of
Leaving CMOS inputs floating. What gets real interesting are the
bi-directional pins which
Need to be terminated when they are inputs, but not HARD tied when they are
outputs.
This offten requires some "scaffolding" curcuitry to power up a board
"outside of its native habitat".
9:16 a.m.
New subject: 2114 Static RAMs...
At 05:00 PM 9/13/2004, you wrote:
When I was designing I/O boards for spaceborne
computers I once saw
what happens when most inputs are left floating on CMOS designs. This
was a design full of (~30) 54HCxx ICs.
<snip>
Thank you for listening.
gak! 54xx IC's -- No wonder the space program cost so much!
Ed K.
17 Sep
17 Sep
12:20 p.m.
New subject: 2114 Static RAMs...
On Wed, 2004-09-15 at 11:16, Ed Kelleher wrote:
At 05:00 PM 9/13/2004, you wrote:
>When I was designing I/O boards for spaceborne computers I once saw
>what happens when most inputs are left floating on CMOS designs. This
>was a design full of (~30) 54HCxx ICs.
gak! 54xx IC's -- No wonder the space program
cost so much!
And running TTL off batteries! Ouch!
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