27 Apr
2002
27 Apr
'02
4:57 p.m.
From: Bill Pechter <pechter(a)pechter.dyndns.org>
As far as I know that's as far as it got inside DEC
as well.
I once wondered where was the base DOS/Batch box left inside DEC
to build the XXDP stuff and DECX/11... I figure they just hacked it on
a DEC10 or RSTS/E box... maybe later on a VAX under PDP11 emulators.
Used to be in building 21 fieldservice diagnostic engineering. I always
wondered what the internal structure of it was.
Allison
27 Apr
27 Apr
6:07 p.m.
New subject: Old Power Supplies, revisited
I am putting my SWTPc 6800 back together, after complete disassembly
for cleaning. So, on to testing the power supply.
It works! But here's the question, which I know has been discussed
before with respect to S-100 machines.
The power supply is a big transformer with one really big (91,000 ufd)
capacitor, and the usual rectifier stuff, etc. The documents call for
7-8 volts unregulated, along with + and - 12V.
I am getting something like 9.3 V, and + and - 14.3 V. Are these
voltages too high? Of course, on the SS-50 and SS-30 cards there are
voltage regulators, but I don't want to cause any damage. This thing
probably hasn't been powered up in 25 years.
How can I check the capacitor function without an oscilloscope or other
fancy equipment? Should I worry about "reforming" the capacitor?
Thoughts appreciated.
Louis
6:40 p.m.
New subject: Old Power Supplies, revisited
Louis Schulman wrote:
I am putting my SWTPc 6800 back together, after complete disassembly
for cleaning. So, on to testing the power supply.
It works! But here's the question, which I know has been discussed
before with respect to S-100 machines.
The power supply is a big transformer with one really big (91,000 ufd)
capacitor, and the usual rectifier stuff, etc. The documents call for
7-8 volts unregulated, along with + and - 12V.
I am getting something like 9.3 V, and + and - 14.3 V. Are these
voltages too high? Of course, on the SS-50 and SS-30 cards there are
voltage regulators, but I don't want to cause any damage. This thing
probably hasn't been powered up in 25 years.
How can I check the capacitor function without an oscilloscope or other
fancy equipment? Should I worry about "reforming" the capacitor?
Thoughts appreciated.
Louis
Shouldn't be a problem, as S100 cards have onboard regulators to get +5,
and +/-12. Only problem there is that the regulator transistor will be
dissapating a bit more power, so have a fan on the card cage if
possible. The heatsink should run warm to the touch, and if it it is
too hot to comfortablly hold for several seconds, then you may be in
trouble. Any excess heat means a premature death for solid state
electronics.
You might look at the cards and inspect the regulator circuitry. a
darkening of the pcb underneat the heatskink is normal, but if the
traces seemed to be crispy crittered, ya got problems, or will have
probs very soon.
Gary Hildebrand
ST. Joseph, MO
8 p.m.
New subject: Old Power Supplies, revisited
At 11:07 PM 4/27/02 -0400, you wrote:
I am putting my SWTPc 6800 back together, after
complete disassembly
for cleaning. So, on to testing the power supply.
It works! But here's the question, which I know has been discussed
before with respect to S-100 machines.
The power supply is a big transformer with one really big (91,000 ufd)
capacitor, and the usual rectifier stuff, etc. The documents call for
7-8 volts unregulated, along with + and - 12V.
I am getting something like 9.3 V, and + and - 14.3 V. Are these
voltages too high?
Those readings sound about right for a PS with no load. You have to remember that this
is a totally unregulated circuit and that the caps will charge to the PEAK voltage instead
of the average (RMS) voltage since there's no load to draw their voltage down.
Of course, on the SS-50 and SS-30 cards there are
voltage regulators, but I don't want to cause any
damage. This thing
probably hasn't been powered up in 25 years.
Assuming that the PS still puts out the same voltage under load, your regulators should
handle 9.3 and 14.3 volts, at least for a time. The problem with excessive voltage in a
situation like this is that the regulators will have to drop more voltage (9.3v -5v) vs
(8v -5v) and to do that they convert it to heat. So they have more of a tendency to
overheat. But my guess is that once you put a load on it you'll find that the PS
voltages are nearer to normal and the regulators will handle it just fine.
How can I check the capacitor function without an oscilloscope or other
fancy equipment?
Connect a dummy load and check the PS voltage with any decent meter. If the caps are
shorted the voltage will be zero. If the caps have little or no capacity then the voltage
will be low. How low depends on the current capacity of the PS, how much capacity that the
caps have and how much of a load is applied so it's MOL guess work. You can use just
about anything for a dummy load. Light bulbs would be a good choice but I've used old
disk drives and all sorts of things that were disposable. I'd start with something
that would draw about 1/10 of the rated current and work up to perhaps 1/2 of the rated
current.
Should I worry about "reforming" the capacitor?
If you're already powered it up then the capacitor has already been
"reformed". If they were bad you'd have almost certainly known it by now
(blown fuses, zero voltage output, etc).
Joe
Thoughts appreciated.
Louis
28 Apr
28 Apr
9:41 a.m.
New subject: Old Power Supplies, revisited
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27 Apr
27 Apr
8:15 p.m.
New subject: Old Power Supplies, revisited
These voltages are OK for an unloaded system. Put in four or five 2102
memory boards and it drops to 7.5 volts. If you want to replace that big
capacitor you can find a new replacement at Mouser Electronics.
www.mouser.com
The Mouser part number is 539-CGS16V110000 and they cost about $22. This is
the right size, 2.5 x 4.125 inches.
Michael Holley
www.swtpc.com/mholley
----- Original Message -----
From: "Louis Schulman" <louiss(a)gate.net>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, April 27, 2002 8:07 PM
Subject: Old Power Supplies, revisited
I am putting my SWTPc 6800 back together, after
complete disassembly
for cleaning. So, on to testing the power supply.
It works! But here's the question, which I know has been discussed
before with respect to S-100 machines.
The power supply is a big transformer with one really big (91,000 ufd)
capacitor, and the usual rectifier stuff, etc. The documents call for
7-8 volts unregulated, along with + and - 12V.
I am getting something like 9.3 V, and + and - 14.3 V. Are these
voltages too high? Of course, on the SS-50 and SS-30 cards there are
voltage regulators, but I don't want to cause any damage. This thing
probably hasn't been powered up in 25 years.
How can I check the capacitor function without an oscilloscope or other
fancy equipment? Should I worry about "reforming" the capacitor?
Thoughts appreciated.
Louis
28 Apr
28 Apr
7:16 a.m.
New subject: Old Power Supplies, revisited
At that low voltage and low capacititance, I'd say you needn't worry about
"reforming" the capacitors. Many of my commercial S-100 supplies put out over
12 volts, at no load, on the so-called +8V supply, and over 20 volts on the
bipolar 16 volt supplies. They come down by 10% or more as they're loaded but
none of them come down below 8 or 16 volts even when loaded somewhat beyond
their specified current. It's nice to have the regulators dissipate as little
power as possible, but it's also necessary to avoid ripple voltage
"valleys"
that drop below the 2.2-volt margin recommended by the regulator vendors.
You can check the unregulated output of your filters by loading the supplies
and measuring the output voltage in both DC and AC mode. The DC level will
reject (averaging it out) the AC component. The AC reading will reject the
DC. If the AC voltage is sufficient that it, when centered about (therefore
subtracted from) the DC level is lower at its minimum than the required
minimum input for your regulators, then you may have a problem.
Adding/substituting a larger capacitor may help, but if there's no resistor
between the cap and the diodes, it might be well to add one, to limit the
current from the diodes to the cap at power-up. Knowing the rating of your
diodes will help you decide whether this is desirable, and what value resistor
is needed.
Dick
----- Original Message -----
From: "Louis Schulman" <louiss(a)gate.net>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, April 27, 2002 9:07 PM
Subject: Old Power Supplies, revisited
I am putting my SWTPc 6800 back together, after
complete disassembly
for cleaning. So, on to testing the power supply.
It works! But here's the question, which I know has been discussed
before with respect to S-100 machines.
The power supply is a big transformer with one really big (91,000 ufd)
capacitor, and the usual rectifier stuff, etc. The documents call for
7-8 volts unregulated, along with + and - 12V.
I am getting something like 9.3 V, and + and - 14.3 V. Are these
voltages too high? Of course, on the SS-50 and SS-30 cards there are
voltage regulators, but I don't want to cause any damage. This thing
probably hasn't been powered up in 25 years.
How can I check the capacitor function without an oscilloscope or other
fancy equipment? Should I worry about "reforming" the capacitor?
Thoughts appreciated.
Louis
9:36 a.m.
New subject: Old Power Supplies, revisited
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8095
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8096
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7 comments
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participants (7)
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ajp166＠bellatlantic.net -
ard＠p850ug1.demon.co.uk -
edick＠idcomm.com -
ghldbrd＠ccp.com -
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swtpc6800＠attbi.com