Power Designs PS-2005 (see ABSE for partial Schem)

  • Thread starter Watson A.Name - "Watt Sun
  • Start date
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Watson A.Name - "Watt Sun

Guest
I got two Power Designs PS-2005A Precision sources from two different
sellers on Ebay, and they both work, somewhat. They put out up to
20VDC at a half amp, so they can serve as a power supply. They're
real old, made back in the early '70s so they're an all discrete
design. Essentially they're a linear power supply with a reverence
(yeah right:) diode in an oven. The circuit furnishes a 1 mA
precision current to a series of switched resistances from 0 to 20k,
giving 0 to 20V. I posted half of the schematic on the
alt.binaries.schematis.electronic newsgroup.

The problem seems to be the switches. There are two rotary switches,
each having dual concentric rotors. These are arranged to give 0 to
10k. There is a 10k .01% resistor with a switch shorting it, to add
to the switches to give the 10 to 20V. Another 1 ohm pot called the
vernier is in series to vary the voltage by a millivolt. I can
replace the DPDT switch across the 10k .01% resistor, if I find that
it's so intermittent that it doesn't make good contact. But the
rotary switches are a whole 'nother story. All these switches can be
bypassed by setting them to zero and putting a 0 to 20k resistance
across the terminals on the back. I could put a 20k ten turn pot
there and make it into a power supply, losing the discrete settings
the switches give. But I'd like to fix the switches if I can,
obviously.

I was thinking of giving them a bath in tuner cleaner or some kind of
cleaner to get rid of the intermittent problems. But one switch
doesn't go thru the voltage steps correctly, so I may have to find
that problem. My main question is how to get the rotary switches back
in shape and get rid of the intermittent switch problems. I ran the
switches thru the full ranges quite a number of times to get the
contacts to wipe a lot, hopefully to clean some of the tarnish off
them.

I have some tuner lube, I thought it might be good to lube the switch
contacts after I clean them. One of the units smells of smoke, so I
guess I'll have to clean it up and get rid of the dust and grime in
it. The units are built well, all aluminum with easy access to stuff.
The circuit board is just drilled and eyelets put in for the contacts.
Basically point to point wiring. I have one concern that if I mess
with any of the precision resistors, they probably can't be replaced,
or else I'd have to use lower tolerance parts. So I gotta be careful
about those. Anywqay, thanks for any ideas.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a69092ba2cff0db989b1e@news.dslextreme.com...
I got two Power Designs PS-2005A Precision sources from two different
sellers on Ebay, and they both work, somewhat. They put out up to
20VDC at a half amp, so they can serve as a power supply. They're
real old, made back in the early '70s so they're an all discrete
design. Essentially they're a linear power supply with a reverence
(yeah right:) diode in an oven. The circuit furnishes a 1 mA
precision current to a series of switched resistances from 0 to 20k,
giving 0 to 20V. I posted half of the schematic on the
alt.binaries.schematis.electronic newsgroup.

The problem seems to be the switches. There are two rotary switches,
each having dual concentric rotors. These are arranged to give 0 to
10k. There is a 10k .01% resistor with a switch shorting it, to add
to the switches to give the 10 to 20V. Another 1 ohm pot called the
vernier is in series to vary the voltage by a millivolt. I can
replace the DPDT switch across the 10k .01% resistor, if I find that
it's so intermittent that it doesn't make good contact. But the
rotary switches are a whole 'nother story. All these switches can be
bypassed by setting them to zero and putting a 0 to 20k resistance
across the terminals on the back. I could put a 20k ten turn pot
there and make it into a power supply, losing the discrete settings
the switches give. But I'd like to fix the switches if I can,
obviously.

I was thinking of giving them a bath in tuner cleaner or some kind of
cleaner to get rid of the intermittent problems. But one switch
doesn't go thru the voltage steps correctly, so I may have to find
that problem. My main question is how to get the rotary switches back
in shape and get rid of the intermittent switch problems. I ran the
switches thru the full ranges quite a number of times to get the
contacts to wipe a lot, hopefully to clean some of the tarnish off
them.

I have some tuner lube, I thought it might be good to lube the switch
contacts after I clean them. One of the units smells of smoke, so I
guess I'll have to clean it up and get rid of the dust and grime in
it. The units are built well, all aluminum with easy access to stuff.
The circuit board is just drilled and eyelets put in for the contacts.
Basically point to point wiring. I have one concern that if I mess
with any of the precision resistors, they probably can't be replaced,
or else I'd have to use lower tolerance parts. So I gotta be careful
about those. Anywqay, thanks for any ideas.

--
Click to expand...
Yep, you have a couple of very nice power supplies. I also have one of the
model 2005 supplies, and a model 2005A supply. Basically the same unit with
a more modern front panel. I've never had any problems with my supplies,
but maybe I can offer a bit of help.
When you said that one of the switches doesn't go through the steps
correctly, do you mean that when you increment the switch, the voltage
doesn't change or changes by a large amount? If that is the case, then you
probably have intermittent contacts on the switch or one or more open
resistors on the bad switch. The resistors are in a 1-2-2-5 sequence,
meaning that the switch is making several contacts per wafer at the same
time, placing a short across selected resistor(s) at each position. If one
of the resistors is open, that could cause some very strange voltages at the
output. Check each resistor on the bad switch to find if any are open.
Replacement resistors should be available from distributors such as Mouser
or Digikey. Mouser lists the Vishay/Dale resistor line in their online
catalog, which seem to be available in 0.1% values at 1/2 watts. Those
units should work nicely as replacements if you need them.
Since the resistors are high precision units, cleaning the switches with
tuner cleaner, or any cleaner that leaves a residue may change the
calibration when you get it working. I recommend that you use long wooden
cotton-tipped Q-tips, or similar to clean the contacts. Dip them into a
good deoxidant cleaner such as De-Oxit and clean ONLY the metal contacts.
Stay away from the wafer itself as much as possible while cleaning.
Sometimes the pressure wipers get spread open and fail to provide enough
pressure to make an effective connection. If this is the case, try gently
bending them back into position so that positive contact is made. You
should be able to see the contacts spread when the switch is rotated, and
makes contact at each successive position.
I have had to resort to Tarn-X in extreme tarnish situations, and it works
very well to remove the tarnish. The caveat is that everything must be
cleaned and neutralized after the tarnish is removed. Since Tarn-X is
acidic, use a solution of baking soda to neutralize, followed by a liberal
clean water rinse. Be sure to lubricate the contacts with DeOxit when
you're finished cleaning. Again, only the metal contacts should get the
lube.
It may help to completely remove the switches from the chassis to make
repairs and clean them. Good luck!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
 
In article <AYKLb.7387$6y6.214155@bgtnsc05-news.ops.worldnet.att.net>,
dgmason99@att99.net mentioned...
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a69092ba2cff0db989b1e@news.dslextreme.com...
I got two Power Designs PS-2005A Precision sources from two different
sellers on Ebay, and they both work, somewhat. They put out up to
20VDC at a half amp, so they can serve as a power supply. They're
real old, made back in the early '70s so they're an all discrete
design. Essentially they're a linear power supply with a reverence
(yeah right:) diode in an oven. The circuit furnishes a 1 mA
precision current to a series of switched resistances from 0 to 20k,
giving 0 to 20V. I posted half of the schematic on the
alt.binaries.schematis.electronic newsgroup.

The problem seems to be the switches. There are two rotary switches,
each having dual concentric rotors. These are arranged to give 0 to
10k. There is a 10k .01% resistor with a switch shorting it, to add
to the switches to give the 10 to 20V. Another 1 ohm pot called the
vernier is in series to vary the voltage by a millivolt. I can
replace the DPDT switch across the 10k .01% resistor, if I find that
it's so intermittent that it doesn't make good contact. But the
rotary switches are a whole 'nother story. All these switches can be
bypassed by setting them to zero and putting a 0 to 20k resistance
across the terminals on the back. I could put a 20k ten turn pot
there and make it into a power supply, losing the discrete settings
the switches give. But I'd like to fix the switches if I can,
obviously.

I was thinking of giving them a bath in tuner cleaner or some kind of
cleaner to get rid of the intermittent problems. But one switch
doesn't go thru the voltage steps correctly, so I may have to find
that problem. My main question is how to get the rotary switches back
in shape and get rid of the intermittent switch problems. I ran the
switches thru the full ranges quite a number of times to get the
contacts to wipe a lot, hopefully to clean some of the tarnish off
them.

I have some tuner lube, I thought it might be good to lube the switch
contacts after I clean them. One of the units smells of smoke, so I
guess I'll have to clean it up and get rid of the dust and grime in
it. The units are built well, all aluminum with easy access to stuff.
The circuit board is just drilled and eyelets put in for the contacts.
Basically point to point wiring. I have one concern that if I mess
with any of the precision resistors, they probably can't be replaced,
or else I'd have to use lower tolerance parts. So I gotta be careful
about those. Anywqay, thanks for any ideas.

--

Yep, you have a couple of very nice power supplies. I also have one of the
model 2005 supplies, and a model 2005A supply. Basically the same unit with
a more modern front panel. I've never had any problems with my supplies,
but maybe I can offer a bit of help.
When you said that one of the switches doesn't go through the steps
correctly, do you mean that when you increment the switch, the voltage
doesn't change or changes by a large amount? If that is the case, then you
probably have intermittent contacts on the switch or one or more open
resistors on the bad switch. The resistors are in a 1-2-2-5 sequence,
meaning that the switch is making several contacts per wafer at the same
time, placing a short across selected resistor(s) at each position. If one
of the resistors is open, that could cause some very strange voltages at the
output. Check each resistor on the bad switch to find if any are open.
Replacement resistors should be available from distributors such as Mouser
or Digikey. Mouser lists the Vishay/Dale resistor line in their online
catalog, which seem to be available in 0.1% values at 1/2 watts. Those
units should work nicely as replacements if you need them.
Since the resistors are high precision units, cleaning the switches with
tuner cleaner, or any cleaner that leaves a residue may change the
calibration when you get it working. I recommend that you use long wooden
cotton-tipped Q-tips, or similar to clean the contacts. Dip them into a
good deoxidant cleaner such as De-Oxit and clean ONLY the metal contacts.
Stay away from the wafer itself as much as possible while cleaning.
Sometimes the pressure wipers get spread open and fail to provide enough
pressure to make an effective connection. If this is the case, try gently
bending them back into position so that positive contact is made. You
should be able to see the contacts spread when the switch is rotated, and
makes contact at each successive position.
I have had to resort to Tarn-X in extreme tarnish situations, and it works
very well to remove the tarnish. The caveat is that everything must be
cleaned and neutralized after the tarnish is removed. Since Tarn-X is
acidic, use a solution of baking soda to neutralize, followed by a liberal
clean water rinse. Be sure to lubricate the contacts with DeOxit when
you're finished cleaning. Again, only the metal contacts should get the
lube.
It may help to completely remove the switches from the chassis to make
repairs and clean them. Good luck!!
Click to expand...
Wow, great - I'm gonna try to take the front panel off and see what's
up. I have some tuner lube, I don't know if it's similar to De-oxit.
It's a grease that's used on the old mechanical rotary tuners, and
comes in a tube. I believe it was made by RCA.

I've seen some tarnish cleaners in the shelves along with detergents,
etc, at the market. I'm guessing that this is the same as Tarn-X.
I'll have to check at the store. The one that smells like smoke needs
a good cleaning, I'll have to try to do something about that, too.

I'm hoping that this doesn't turn up any bent or damaged contacts. I
have the schematic so I'm somewhat prepared. Thank you for the help.

BTW, I found the DeoxIT locally, so I'm going to check it out.
--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
In article <MPG.1a69fd6e199d0903989b21@news.dslextreme.com>, Watson
A.Name - "Watt Sun, Dark Remover" <alondra101@hotmail.com>
mentioned...
In article <AYKLb.7387$6y6.214155@bgtnsc05-news.ops.worldnet.att.net>,
dgmason99@att99.net mentioned...
"Watson A.Name - Watt Sun, Dark Remover" <alondra101@hotmail.com> wrote in
message news:MPG.1a69092ba2cff0db989b1e@news.dslextreme.com...
I got two Power Designs PS-2005A Precision sources from two different
sellers on Ebay, and they both work, somewhat. They put out up to
20VDC at a half amp, so they can serve as a power supply. They're
real old, made back in the early '70s so they're an all discrete
design. Essentially they're a linear power supply with a reverence
(yeah right:) diode in an oven. The circuit furnishes a 1 mA
precision current to a series of switched resistances from 0 to 20k,
giving 0 to 20V. I posted half of the schematic on the
alt.binaries.schematis.electronic newsgroup.

The problem seems to be the switches. There are two rotary switches,
each having dual concentric rotors. These are arranged to give 0 to
10k. There is a 10k .01% resistor with a switch shorting it, to add
to the switches to give the 10 to 20V. Another 1 ohm pot called the
vernier is in series to vary the voltage by a millivolt. I can
replace the DPDT switch across the 10k .01% resistor, if I find that
it's so intermittent that it doesn't make good contact. But the
rotary switches are a whole 'nother story. All these switches can be
bypassed by setting them to zero and putting a 0 to 20k resistance
across the terminals on the back. I could put a 20k ten turn pot
there and make it into a power supply, losing the discrete settings
the switches give. But I'd like to fix the switches if I can,
obviously.

I was thinking of giving them a bath in tuner cleaner or some kind of
cleaner to get rid of the intermittent problems. But one switch
doesn't go thru the voltage steps correctly, so I may have to find
that problem. My main question is how to get the rotary switches back
in shape and get rid of the intermittent switch problems. I ran the
switches thru the full ranges quite a number of times to get the
contacts to wipe a lot, hopefully to clean some of the tarnish off
them.

I have some tuner lube, I thought it might be good to lube the switch
contacts after I clean them. One of the units smells of smoke, so I
guess I'll have to clean it up and get rid of the dust and grime in
it. The units are built well, all aluminum with easy access to stuff.
The circuit board is just drilled and eyelets put in for the contacts.
Basically point to point wiring. I have one concern that if I mess
with any of the precision resistors, they probably can't be replaced,
or else I'd have to use lower tolerance parts. So I gotta be careful
about those. Anywqay, thanks for any ideas.

--

Yep, you have a couple of very nice power supplies. I also have one of the
model 2005 supplies, and a model 2005A supply. Basically the same unit with
a more modern front panel. I've never had any problems with my supplies,
but maybe I can offer a bit of help.
When you said that one of the switches doesn't go through the steps
correctly, do you mean that when you increment the switch, the voltage
doesn't change or changes by a large amount? If that is the case, then you
probably have intermittent contacts on the switch or one or more open
resistors on the bad switch. The resistors are in a 1-2-2-5 sequence,
meaning that the switch is making several contacts per wafer at the same
time, placing a short across selected resistor(s) at each position. If one
of the resistors is open, that could cause some very strange voltages at the
output. Check each resistor on the bad switch to find if any are open.
Replacement resistors should be available from distributors such as Mouser
or Digikey. Mouser lists the Vishay/Dale resistor line in their online
catalog, which seem to be available in 0.1% values at 1/2 watts. Those
units should work nicely as replacements if you need them.
Since the resistors are high precision units, cleaning the switches with
tuner cleaner, or any cleaner that leaves a residue may change the
calibration when you get it working. I recommend that you use long wooden
cotton-tipped Q-tips, or similar to clean the contacts. Dip them into a
good deoxidant cleaner such as De-Oxit and clean ONLY the metal contacts.
Stay away from the wafer itself as much as possible while cleaning.
Sometimes the pressure wipers get spread open and fail to provide enough
pressure to make an effective connection. If this is the case, try gently
bending them back into position so that positive contact is made. You
should be able to see the contacts spread when the switch is rotated, and
makes contact at each successive position.
I have had to resort to Tarn-X in extreme tarnish situations, and it works
very well to remove the tarnish. The caveat is that everything must be
cleaned and neutralized after the tarnish is removed. Since Tarn-X is
acidic, use a solution of baking soda to neutralize, followed by a liberal
clean water rinse. Be sure to lubricate the contacts with DeOxit when
you're finished cleaning. Again, only the metal contacts should get the
lube.
It may help to completely remove the switches from the chassis to make
repairs and clean them. Good luck!!

Wow, great - I'm gonna try to take the front panel off and see what's
up. I have some tuner lube, I don't know if it's similar to De-oxit.
It's a grease that's used on the old mechanical rotary tuners, and
comes in a tube. I believe it was made by RCA.

I've seen some tarnish cleaners in the shelves along with detergents,
etc, at the market. I'm guessing that this is the same as Tarn-X.
I'll have to check at the store. The one that smells like smoke needs
a good cleaning, I'll have to try to do something about that, too.

I'm hoping that this doesn't turn up any bent or damaged contacts. I
have the schematic so I'm somewhat prepared. Thank you for the help.

BTW, I found the DeoxIT locally, so I'm going to check it out.
Click to expand...
I bought a can of DeoxIT, I gotta take the PS outside when it's warmer
and give it a bit of cleaning. See what happens tomorrow.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
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