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Repairing Old School Power Supply?

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  • Repairing Old School Power Supply?

    I have an old, probably 60s or 70s vintage Gesswein plating power supply that has been stored in my damp cellar. I have a need for such a thing now but I can't get any volts out of it, even when its plugged in! I've searched for repair power supply videos but all I can find are videos for more current models and nothing for such a basic unit as this. It has a analog voltmeter and a 0-xx ammeter and rheostat type thing to control it. And it is very ugly being heavily freckled from the dampness. I will also add that I am electrically challenged and while adept at changing batteries, light bulbs and fuses, I know little more. Can anybody point me to a very basic tutorial on how I might go about trouble shooting this? I do have a DVM and an old Triplett meter and I can't imagine I would need anything more to trouble shoot and repair this, if I only knew how. Thanks for any help!
    You may only view thumbnails in this gallery. This gallery has 1 photos.

  • #2
    You're going to have to take the cover off and get some good pics of the innards so someone can point to a few likely trouble spots. If the voltage control is wire-wound it (the rheostat) might be unsalvageable judging from the exterior condition.
    Last edited by chipmaker4130; 05-19-2022, 03:06 PM.
    Southwest Utah

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    • #3
      Well the first thing you should have done is tell us WHERE you are. So some local old electronic engineer could look at it and tell you what is wrong or fix it for you.
      ...lew...

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      • #4
        Originally posted by chipmaker4130 View Post
        You're going to have to take the cover off and get some good pics of the innards so someone can point to a few likely trouble spots. If the voltage control is wire-wound it (the rheostat) might be unsalvageable judging from the exterior condition.
        Concur. The basic technology used is not known for sure (it can be guessed at) from seeing the outside. I'd give it a 15% to 30% chance of being sensibly fixable from what I see, but the inside might be clean, we just don't know what the inside condition or technology used is..
        CNC machines only go through the motions

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        • #5
          It's most likely a Variac or Powerstat, which is a variable autotransformer, and it would also have a 200 watt (10V 20A) transformer and a rectifier (possibly an old school selenium type with cooling fins and stacked rectifier plates).

          Click image for larger version

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          Last edited by PStechPaul; 05-19-2022, 06:36 PM.
          http://pauleschoen.com/pix/PM08_P76_P54.png
          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030

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          • #6
            I have had the cover off looking for disconnected wires and to clean any contacts that might be in there. That was a while ago so I don't remember exactly what I did but do recall fussing with one of the meters. When I get a moment, I'll take the cover off. Also if I remember correctly, the inside did not look like the outside and was much cleaner.

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            • #7
              Originally posted by Gazz View Post
              I have had the cover off looking for disconnected wires and to clean any contacts that might be in there. That was a while ago so I don't remember exactly what I did but do recall fussing with one of the meters. When I get a moment, I'll take the cover off. Also if I remember correctly, the inside did not look like the outside and was much cleaner.
              In that case, it may be that the case has few, or no, vents. That would tend to suggest a variac type supply, as they have less heat output than other types. But a view of the inside would make things clear..

              Since the model name appears to be "Electro-plater Model D" (possibly "P", or "B", etc), it is not likely to be very precision as far as it's voltage, you adjust to what you want to see for what you are doing. It may have no filtering of the DC, as that is generally not required for plating, as far as I have seen.
              CNC machines only go through the motions

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              • #8
                Power supplies, particularly old ones, are/were fairly simple. The circuit probably has only a few items in it and you can follow the power path through it with your VOM.

                First, when power is applied with the covers off, lethal Voltages/currents will be exposed. So DO BE CAREFUL. If you are at all unfamiliar with working with live equipment I would suggest that you have it UNPLUGGED while setting up a test/measurement. Then plug it in and turn it on to observe the readings. Then OFF and unplugged before you start to set up the next test/measurement, etc.

                Observe where the power cord comes into the unit. It probably goes to the power switch, possibly a fuse (it should have one), and then to the transformer or auto-transformer. You can set your VOM for AC Voltage and a high Voltage range setting; 200 VAC or higher. 400 VAC if you have 230 Volt house power sockets. (This is part of why your location is important.) The black lead from the meter is connected to the common side of the power cord (the one that does not go to a switch or fuse). And the red lead from the meter to the input connection on the transformer. This skips over the switch and any fuse, but It divides the AC circuit into two pieces. If you have Voltage (115 or 230 VAC) at the input of the transformer, then the AC side of things is probably OK. If not, then possibly a bad switch or fuse.

                The next check would be after the transformer. The wiper, that is the moving contact of the transformer should have a lower Voltage when measured to the common connection on the secondary or output side of the transformer. And in an auto-transformer the input and output sides can and probably will shard the same common terminal. So your black meter lead goes to the transformer's output common and the red meter lead to the wiper or moving contact. For the present, the meter settings can be the same. It is always best to start with a high Voltage setting and switch to lower ones only after confirming that the Voltage is, indeed low. Now the meter should read around 10 Volts AC or less, depending on where the wiper is set. I got that 10 from the meter scale in your photo. But if there is a range switch for that meter, then the reading could be higher. If you had AC Voltage at the input to the transformer and none at the output, then the transformer is probably bad. If you do get a Voltage at the output then the transformer is probably OK. You should move the wiper across it's full range and observe that some AC Voltage is present at all settings.

                From the transformer the lower AC Voltage should go to a rectifier. This could be one, two, or even four diodes which could be in a number of physical packages. It could also be a selenium rectifier which looks like a stack of square metal plates with spacers between them and some terminals at the ends and in the middle.

                https://www.google.com/search?client...nium+rectifier

                At the output of the rectifier you should have a pulsating DC Voltage. Now the meter should be switched to DC measure and a Voltage range that is at least two times the AC Voltage measured at the transformer output. The meter leads would be on the + and - rectifier output terminals. If you have an AC Voltage at the input of the rectifier and no DC at the output then the rectifier is likely bad. If you have a bad selenium rectifier, do not look for a direct replacement. Just use a solid state (silicon) rectifier with the same ratings (Voltage and current).

                From the rectifier the pulsating DC can go to one of several types of components. In modern power supplies it would go straight to a filter capacitor (electrolytic) and old electrolytic capacitors frequently go bad. Again you do not need to use an exact replacement, just one with the correct Voltage and capacitance ratings.

                Some high current power supplies had a series choke (inductor or coil) to smooth out the ripple in the DC before the filter capacitor. This may look like a transformer but with only two terminals, input and output. They may not be labeled and are interchangeable. Again, check for DC at the input and output terminals.

                Some manufacturers took a cheaper choice of a series resistor instead of a choke inductor. Same test as the choke but expect a slightly lower Voltage at the output.

                That should take you to the output terminals on the front panel.

                Of course, check all the wires along the way. With that much corrosion on the outside, a bit on the inside would not be a surprise.

                If this does not help please do post some photos. And tell us your location, at least a general one like country and region.
                Paul A.
                SE Texas

                And if you look REAL close at an analog signal,
                You will find that it has discrete steps.

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                • #9
                  Send it to Mr. Carlson (youtube) if it's bad enough to go to the dumpster, he'll likely be able to rescue it.

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                  • #10
                    I’ve never seen one stored underwater before, however it’s fixable, worst case you end up replacing all the components, might as well buy a new case too,
                    I’ve only had one brush in 30 years it’s had 5 new handles and 18 new heads ( can’t remember the amounts, 2 Ronnies sketch very funny, of fork handles fame)
                    https://youtu.be/pV1IP4N9ajg
                    I’d hazard a rotted variac wire myself,
                    mark

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                    • #11
                      As it is apparently for plating, it is likely extremely simple.

                      Fuse bottom left of panel, pilot light above that, switch to the right of the fuse, then adjustment knob, and outputs at the right.

                      Bolt pattern is not correct for the usual variac, but that proves nothing. Could be variac, could be multi-tapped transformer, might even be an adjustable resistor.

                      Pic of inside makes all as clear as the pic is.
                      CNC machines only go through the motions

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                      • #12
                        "Heavily freckled"... I like that!

                        If it is indeed a Variac (other makes are available), and given that the unit's output is high-current and low-voltage, I would expect to see a step-down transformer between the Variac's output and the panel terminals. This enables the use of a low-current Variac, and also gives isolation of the output from the mains.

                        I have seen the reverse arrangement with a step-down transformer and a low-voltage Variac, but it's less common.

                        George

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                        • #13
                          Hammer and block of wood .. Bump on all 8 corners . That doesnt work then repeat more intensely without block of wood.

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                          • #14
                            Well, the Op has not responded yet with his inside pics.
                            Here is what a plating power supply looks like inside FYI
                            This is a Selectron supply from 1968 and most likely cleaner than the Op's
                            I believe it goes to 60 Volts at 25 Amps Max, but most plating is done around 2-4 volts
                            Rich

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                            Last edited by Rich Carlstedt; 05-20-2022, 03:53 PM.
                            Green Bay, WI

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                            • #15
                              Wow a selenium smoke generator!

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