I am working on this very old CENCO DC Power Supply (Catalog 79572 or Cenco No. 79572) to fix. It seemed like a relatively simple fix since there was no output voltage. This power supply is very basic but very old and I do not know very much about the older components. I also have also uploaded the manual.



Here was my walk through:

1. Check the fuse, manual called out for 2A fuse, CENCO No: P19923 (I cannot find that exact fuse)
   1. When I received the PS, there was already fuse (that seemed to be not the correct one), 313 3AG 6/10A 125V that I changed out to a 2A 250VAC Slow Blow Fuse.
2. Measured all the resisters and they seemed to be within specifications.
3. Did a continuity check for all the pass-through wiring and connections and everything seemed to connected.
4. All the parts seemed to be original.

This is where things start to get interesting.

1. Started checking the switch and light which seemed to work fine EXCEPT when it gets plugged in and the switch is off, there is a voltage reading of about 44.4 VAC and I am not too sure where it is coming from. When I switch it onto “on” then the regular 120 VAC is being delivered.
2. I measured the resistance of the Powerstat Variable Transformer. I COULD BE WRONG but these values seem to correct. I performs a continuity check on the windings and it seems to be one wire.
   1. 1 - 3:
      1. Min: 0.25 Ohm
      2. Max: 4.90 Ohms
   2. 1 - 2:
      1. OL
3. After the switch is on, I tried to measure the output/input voltages of the Powerstat Variable Transformer type 10B but there is no change
   1. 1-3:
      1. 0.01 VAC (Wiper: Min)
      2. 0.01 VAC (Wiper: Max)

I want to say that the problem is the Powerstat Variable Transformer and that it is bad, I just cannot figure out how and why it is bad. I was looking for a section opinion or if someone might know about this Power Supply, anything helps.

 

Welcome to AAC!

I am working on this very old CENCO DC Power Supply (Catalog 79572 or Cenco No. 79572) to fix. It seemed like a relatively simple fix since there was no output voltage.

This power supply is for hipot testing. What do you plan to do with it?



It looks like it can only deliver a few mA, but it could probably knock you on your *ss.

 

This looks like a problem. It should be 5 ohms fixed, I believe.

1 - 2:

1. OL

 

I am working on this very old CENCO DC Power Supply (Catalog 79572 or Cenco No. 79572) to fix. It seemed like a relatively simple fix since there was no output voltage. This power supply is very basic but very old and I do not know very much about the older components. I also have also uploaded the manual.
This is where things start to get interesting.

1. Started checking the switch and light which seemed to work fine EXCEPT when it gets plugged in and the switch is off, there is a voltage reading of about 44.4 VAC and I am not too sure where it is coming from. When I switch it onto “on” then the regular 120 VAC is being delivered.

At what point in the circuit are you measuring the 44.4 VAC, and are you measuring it with respect to chassis ground? This may be an indication that the Live and Neutral are interchanged in the power plug.

I want to say that the problem is the Powerstat Variable Transformer and that it is bad, I just cannot figure out how and why it is bad. I was looking for a section opinion or if someone might know about this Power Supply, anything helps.

The way to check the Powerstat transformer is, with the power on, measure its output voltage as you turn the control knob. If you get 0 - 110VAC then it is working.

 

Welcome to AAC!
This power supply is for hipot testing. What do you plan to do with it?

View attachment 328642

It looks like it can only deliver a few mA, but it could probably knock you on your *ss.

I am an electronics engineer for a university and one of the professors came by asking if I could fix it. They use it for a demonstration. A lot of professors do not like getting rid of old equipment, especially if it could be fixed.

 

At what point in the circuit are you measuring the 44.4 VAC, and are you measuring it with respect to chassis ground? This may be an indication that the Live and Neutral are interchanged in the power plug.



The way to check the Powerstat transformer is, with the power on, measure its output voltage as you turn the control knob. If you get 0 - 110VAC then it is working.

I measured some more values with respect to ground.
GND - 1 = 53.5 VAC (switch off)
= 0.06 VAC (switch on)

GND - 2 = 122.6 VAC (switch off)
= 122.6 VAC (switch on)

GND - 3 = 53.5 VAC (switch off, wiper min)
= 53.1 VAC (switch off, wiper max)

GND - 3 = 52.7 VAC (switch on, wiper min)
= 52.8 VAC (switch on, wiper max)


When I measured the output voltage, the voltage remained the same at 0.12 VAC (1-GND), and between 1 and 2, its around 0.01-0.12 VAC.

 

View attachment 328671
I measured some more values with respect to ground.
GND - 1 = 53.5 VAC (switch off)
= 0.06 VAC (switch on)

GND - 2 = 122.6 VAC (switch off)
= 122.6 VAC (switch on)

GND - 3 = 53.5 VAC (switch off, wiper min)
= 53.1 VAC (switch off, wiper max)

GND - 3 = 52.7 VAC (switch on, wiper min)
= 52.8 VAC (switch on, wiper max)


When I measured the output voltage, the voltage remained the same at 0.12 VAC (1-GND), and between 1 and 2, its around 0.01-0.12 VAC.

The Powerstat is definitely not doing what it should. Your measurements suggest that the main winding on the Powerstat is not connected to terminal 2. Can you inspect it closely to see if the wire is broken close to the terminal, or there is a bad solder or crimp connection between the wire and terminal?

 

This looks like a problem. It should be 5 ohms fixed, I believe.

1 - 2:

1. OL

Hey Tony!
I found and ordered a used working powerstat and the old powerstat was the issue.

 

The Powerstat is definitely not doing what it should. Your measurements suggest that the main winding on the Powerstat is not connected to terminal 2. Can you inspect it closely to see if the wire is broken close to the terminal, or there is a bad solder or crimp connection between the wire and terminal?

Thank you Keith!
I found and ordered a used working powerstat and the old powerstat was the issue.