Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

[mancoast]

Greetings,

I seek relevant forums and communities to document my issue and to formulate structured dialogs. With respect to the repair and restoration of a vintage DC power supply from the early 1980's, I need advice and direction. Majority of my experience exists on the computer designing systems, but this project sparks a new curiosity with vintage electronics restoration.

The Sorensen DCR 600-4.5B DC Power Supply, 0-600V, 0-4.5A, 2700W rests on my workbench with the system input voltage supplied from 208V 3-phase 20A because the Sorensen factory default M1 configuration needs 208 VAC for DCR-B series 2700-Watt models. The manual for this vintage Sorensen power supply exists on the internet (Document No. 165042 Rev F), however I am not sure if we can post external links here. Additionally, I have concurrently formed similar threads across a plurality of electronics forums, so know that there exists cross-posting.

When initially getting the device, the system's chassis fan activated with a flip of the main breaker, however little else occurred in the 7" high chassis. Troubleshooting at the component-level initialized by tracing the supply line voltages. The schematic reflects line voltage to a large transformer, so I verified voltage at those nodes. However, at this point I seek advice and directions. The service manual states, “DCR-B series supplies are phase controlled type with SCR's (Silicon Controlled Rectifiers) or Triacs at the input to the transformer, followed by a passive LC filter … Low dissipation transistors and diodes are located on a single printed circuit board while high dissipation devices are heat sinked to aluminum brackets and heatsinks.”

Replacement of the single printed circuit board (DCR control board P/N 586955-1) returned some progress. Now, the system generates variable voltage output when the main breaker activates, however I cannot reach the required 600V specified by the manual. What are your thoughts and advice?

Sincerely,
Mancoast

[goontron]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

Have you tested the Diodes? if a pair is open then voltage will be low. Along those lines, you will be able to see said noise with a 'scope.

[mancoast]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

Have you tested the Diodes? if a pair is open then voltage will be low. Along those lines, you will be able to see said noise with a 'scope.

Hello goontron,

What are the instructions to test the diodes? By diodes are you referring to the SCR's? Do you suggest inspection of the DC output with an o'scope for noise analysis?

Thanks,
Mancoast

[goontron]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

^Nevermind. I misread your post. I read "low dissipation Diodes" as low loss.

Im actually having a hard time visualizing how in the world this thing works.... Can you post pictures?

[mancoast]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

^Nevermind. I misread your post. I read "low dissipation Diodes" as low loss.

Im actually having a hard time visualizing how in the world this thing works.... Can you post pictures?

At this time I am traveling and haven't taken any pictures yet. When I get back home in a few weeks I will post plenty of photos. Am I allowed to post the external link to the repair manual with the factory drawings and schematics on these forums?

[goontron]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

^Yes.

[eccerr0r]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

You should be able to post links or at least you should be able to trick the interpreter to post links - this was added to prevent bots and possibly people from spamming the forums with advertisement links. Seeing the actual service guide would be helpful, if not the actual pictures of the innards would be nice.

As this is an thyristor controlled, the thyristors not completely turning on or shorted would be a bad thing. I suspect the short case can be ruled out if the power supply isn't heating up and self-immolating or its fuse. You probably will need to remove or have access to the thyristors to test them. I'm not sure whether your device is a TRIAC or SCR based, suspecting the former due to the voltage range, which means there should be normal diodes on the secondary as well.

Also this is a line-frequency based power supply, so the supply probably has fairly large HV capacitors (>=8mF at >=600WVDC ?) If they at least sort of still work like a capacitor, they may be good enough to at least get it to 600V output. But the small ones on the control board, all bets are off.

Be careful with an oscilloscope, don't fry it or yourself...

[mancoast]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

Hello,

Service manual located here: https://cdn.badcaps-static.com/pdfs/...19b5565efe.pdf

The chassis holds some huge capacitors, aluminum heat sinks with some components and large transformer. Any thoughts on how to proceed?

Thanks,
Mancoast

[eccerr0r]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

So what are and you aren't seeing? When the voltage is set to 600V, you get what out?

Also note as this is regulated by TRIAC (SCRs, actually) the slew rate is really slow on downslope compared to upslope. Though it should still shoot the setpoint within a second with no load.

Do you have a 600-V safe multimeter? Also, do you have a load resistor that can draw that much power? I'd say getting five 100W incandescent light bulbs in series should be sufficient for now though will not test the full load. You can substitute five 60W incandescents if you wish, but don't use LED or CFL.

Do you have an isolation transformer? Likely the testing you will come across will be dangerous without one, especially if you need an oscilloscope.

Are you getting the full 600V across the primary filter capacitors, schematic accurate, it would be C5's + to C4's - would be the full voltage (half will show up on each capacitor). This should be the setpoint voltage as well.

[mancoast]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

Hello eccerr0r,

I see the voltage will adjust down to zero and up to about 190V over the full range of the knob. It does not suddenly drop to zero. This was verified using an external multi-meter. I do not have a load resistor that can support this wattage, for now I would like to defer the load testing.

I will test voltage across the primary filter capacitors and report the voltage.

Do you have any other suggestions to further troubleshoot this power supply?

Thanks,
Mancoast

Pictures:

[eccerr0r]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

So you're saying you can get 0-190V and then past ~half turn, you stay at 190V?
Likely you're not hitting OVP as it should drop to ~0V right away.

You will need the load at some point, some load is better than no load.

The isolation transformer is important otherwise it will be hard to test the phase control.

For now without additional information, you should check that both SCR control circuits are intact. Make sure CR8, CR9, R9, R10 aren't burned out on the PCB. Ensure that at least the gate to cathode connections on the two SCRs behave like diodes and aren't open; at least if you can't fully test them.

[mancoast]

Re: Repair Vintage DC Power Supply, Sorensen DCR-B series 2700-Watt 600-4.5B

Greetings,

Thank you very much for the pointers and direction. Reconfiguration of the resistors on the control PCB enabled an output voltage of 600V. This required removing the (4) 150k resistors from the old board and populating them on the "new" board.

Now I would like to perform a load test. Below are pictures of a very large 5.5 OHM resistor. What is the recommended procedure for load testing this PSU. What size wires are required from the terminal block to the resistor?

Thanks,
Coast