Hi
The typical rail voltage is around 18 volts some place. This
should be on the order of 1/3 watt someplace for the resistor.
The 1/4W resistor is way too small. I'd tend to think that
you might be better with the 220 ohm resistor. The diode of
1W is a maximum of 83 ma. I'd suspect that you only need about
1/10 that much to get reasonable regulation. Even at 15V
input, a 1.8K would be enough. One would need to figure
how much current the video chip needed, before selecting the
right value resistor.
Since you have one board with a three terminal regulator,
you might add a 10 ohm resistor to the input lead of the
regulator to work as a temporary current sensor. The regulator
draws some current but it is usually small. Add about 50%
to this value and then add 8ma for the diode. From this
you should be able to calculate a reasonable dropping
resistor. Figure a minimum supply of about 15 volts and then
figure the wattage with the 22 volt level.
Or, as was suggested, go to a 3 terminal regulator for all.
I've seen a number of negative regulators fail, when used
under minimum load. I suspect this is actually caused
by back current when the supply is turned off. Any filtering
capacitors after the regulator may hold longer than the
input filter capacitors. This causes significant back current.
When using a 3 terminal regulators under a minimum load, as
you'll be doing, I suggest that you add a 1N4001, back biased,
>from the input to the output lead ( for a positive regulator,
band on the input lead ).
When working for a company doing embedded machines, we saw
this problem and we had no more returns after adding the
diode.
Dwight
>From: "Cini, Richard" <Richard.Cini at wachovia.com>
>
>All:
>
>
>
> I'm playing around with the SSM V1B video board in my Altair,
>and I have a question about errata and board modifications, specifically
>with regards to the +12v power supply.
>
>
>
>I have three boards. One is "condition unknown" and two are working. The
>+12v regulated supply consists of a small-value series resistor, a zener
>diode and a cap. One of the boards has a 100 ohm, 1/4w resistor which is
>charred and when operated, continues to smell. The other working board has a
>220 ohm resistor and the same zener diode and appears to work fine with no
>smell. The manual specifies a 100 ohm resistor and a 1N4742 diode.
>
>
>
>The "condition unknown" board has a 7812 regulator soldered to the pads
>replacing the resistor and the diode. From what I can tell from the
>schematic, the +12v is used only for the character generator chip. When
>turned on, I get a display full of well-formed garbage, which is probably
>just that it's displaying the random data in buffer memory.
>
>
>
>Does anyone have a view on what the best kind of repair might be?
>
>
>
> Thanks.
>
>
>
>Rich
>
>
>
>
>
>Subject: Solid State Music V1B question
> From: "Cini, Richard" <Richard.Cini at wachovia.com>
> Date: Fri, 15 Jul 2005 08:39:42 -0400
> To: "'General Discussion: On-Topic and Off-Topic Posts'"
> <cctalk at classiccmp.org>
>
>All:
>
>
>
> I'm playing around with the SSM V1B video board in my Altair,
>and I have a question about errata and board modifications, specifically
>with regards to the +12v power supply.
>
>
>
>I have three boards. One is "condition unknown" and two are working. The
>+12v regulated supply consists of a small-value series resistor, a zener
>diode and a cap. One of the boards has a 100 ohm, 1/4w resistor which is
>charred and when operated, continues to smell. The other working board has a
>220 ohm resistor and the same zener diode and appears to work fine with no
>smell. The manual specifies a 100 ohm resistor and a 1N4742 diode.
>
>
>
>The "condition unknown" board has a 7812 regulator soldered to the pads
>replacing the resistor and the diode. From what I can tell from the
>schematic, the +12v is used only for the character generator chip. When
>turned on, I get a display full of well-formed garbage, which is probably
>just that it's displaying the random data in buffer memory.
>
>
>
>Does anyone have a view on what the best kind of repair might be?
>
>
>
> Thanks.
>
Rich,
The best fix is the three terminal regulator. The resistor and zener
diode works well but the correct value of resistor is dependent on the
raw 12+ volt power on the S100 buss. Since I've seen that bus run from
barely 15V (marginal for three terminal regulator) to as high as 22V
the right resistor varies greatly. I'd speculate (I don't know which
character rom) on the required 12V power needs that the 100ohm is
plainly too low and maybe 220 is right. If the resistor is too low
the Zener diode will overheat and if too high the regulation is poor.
Zener diodes have power ratings like many parts and if exceeded they
fail. Using a three terminal regulator eliminates a lot of guessing.
Allison
I may have posted this request...plea...on cctech some
time ago. I've been looking for an early Microsoft
Fortran compiler for eons. Vanilla DOS version would
be fine, but for something exotic like the Tandy 2000
or Zenith Z-100 would be exquisite. I was fortunate to
obtain, oo, MS-COBOL recently, and to my amazement I
managed to WinImage the disks. Version 2.0 or
something.
If any of you weren't aware, the earliest versions of
Turbo Pascal and Turbo C are available for download on
the Borland Museum.
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
I'd posted here a while ago looking for info on a Tally 420PR tape
punch
--
I just put three different 420 manuals up at
http://www.bitsavers.org/pdf/tally
> D-10632-01 Data Channel Linc Tape, CO3000N Option 008
Jay West is probably the only person on the planet that would have a
use for that.
Tom Jennings is nearby, and may want the other boards.
I am looking for a good picture of the 1975 Motorola MC6800 design package.
This has the MC6800 IC family mounted in foam covered with plastic.. (The
MC6800, MC6810, MC6820, MC6850, and MIKBUG ROM.) This came with data books
but I just want a picture of the chips on the card.
One of these was sold on eBay a year or so ago and someone on this list got
it.
Michael Holley
www.swtpc.com/mholley
I haven't tried using an IDE drive with a real IBM AT, but I suspect it
will not be plug and play! The original BIOS supports 15 predefined
drive types and I don't remember any user defined settings. You might
try something like "Disk Manager" or other such utilities. IIRC, they
can allow larger than the 32 MB partition sizes and I *think* will allow
settings other than what IBM provided.
> I have two "true-blue" IBM ATs, both the early motherboard revision.
> I have the following questions:
>
> - Is it possible to use an IDE hard drive instead of MFM? I have
> tried several different drive/controller combos, and nothing works so
> far :-( . The drives are small ( < 100 MB), so it's not a geometry
> issue (at least, I don't think so :-) )
>Yep, one of my local recyclers is like that. I think they assume that
>anyone who appears to be knowledgeable about what they have is
>immediately going to take their junk and make a fortune selling it. Tell
>them that it's worthless in financial terms and they think you're lying;
>tell them that you absolutely will not sell it on and they still think
>you're lying. I haven't figured out a way of dealing with that class of
>people yet :-(
Bring your SO along, pretend to spot the item and say "Oh look honey,
this is just like the <insert item here> we were using when we met". Then
have your SO say "Oh, we simply MUST buy it"
Then offer the guy 50% of what you really are willing to pay for it.
Watch the dollar signs roll in his eyes as you haggle your way up to the
amount you were willing to pay.
-chris
<http://www.mythtech.net>
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5217360547&
category=51046&ssPageName=WDVW&rd=1
>
> Somewhat interesting. It's basically a computer recycler
> that has decided to dump it's entire collection of Apple
> stuff, including Lisa's, ]['s, and it seems a lot of recent
> stuff like iMac, G3's, etc.
>
> Located in "Northeast USA". Shipping is $750.
Yeah, I think I know who this is. I'm a little pissed as I've bugged
them for the vintage stuff before and they act like it's gold, don't
want to talk about it, yet sometimes scrap it. Tried to deal on an
Octane and it was weeks of "we're not sure what we're doing with it" and
then it vanished.
I think I'll drive out there tomorrow.
