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

Thread Starter

mancoast

Joined May 9, 2018
5
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
 

AlbertHall

Joined Jun 4, 2014
12,157
I used to repair Sorensen supplies of many types including this one. If you can post a link to a schematic I can certainly help.
What voltage does it get to?

[EDIT] I found a not well scanned schematic - if you know of a good one please supply a link.
 

Thread Starter

mancoast

Joined May 9, 2018
5
I used to repair Sorensen supplies of many types including this one. If you can post a link to a schematic I can certainly help.
What voltage does it get to?

[EDIT] I found a not well scanned schematic - if you know of a good one please supply a link.
Hello AlbertHall,

Using a DMM I read values less than 190V and I am working from this link, https://www.ntecusa.com/docs/DCR80-33B_data.pdf

Thanks,
Mancoast
 

AlbertHall

Joined Jun 4, 2014
12,157
Make sure the links on the back are correct:
TB3-1 to +ve output
TB3-2 to -ve output
TB3-3 to TB3-4
TB3-5 to TB3-6
TB3-7 to TB3-8
Turn current controls to maximum
Adjust voltage controls from minimum to maximum and report output voltages as indicated on front panel meter and preferably also on an external voltmeter (at this stage the internal meter accuracy is unknown).

Hello AlbertHall,

Using a DMM I read values less than 190V and I am working from this link, https://www.ntecusa.com/docs/DCR80-33B_data.pdf

Thanks,
Mancoast
That link looks much like the one I found - it'll do.
 

AlbertHall

Joined Jun 4, 2014
12,157
Does the voltage adjust down to zero?
Does it get to 190V at the maximum setting or about 1/3 the way up and then stop increasing?
Does it it get to 190V and then suddenly drop to zero?

[EDIT] It's the wee small hours here so I'm off to bed. Back tomorrow.
 

Thread Starter

mancoast

Joined May 9, 2018
5
Hello AlbertHall,

I greatly appreciate the instructions and will test and report immediately when I get back home from travel in a few weeks.

Thanks,
Mancoast
 

Thread Starter

mancoast

Joined May 9, 2018
5
Hello AlbertHall,

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.

What do you suggest to further troubleshoot?

Thanks,
Mancoast

Pictures:












 

AlbertHall

Joined Jun 4, 2014
12,157
You can try adjusting R30 but I expect it will have a fairly small range of adjustment.
Measure the voltages at both ends of R6 referenced to the negative output. You should get -6.2V and -12.4V.
 

Thread Starter

mancoast

Joined May 9, 2018
5
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. (secondhand)

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








 

AlbertHall

Joined Jun 4, 2014
12,157
So the replacement board was for a different supply - that would do it.

A 5.5Ω load resistor at full rated current (4.5A) would give just 24.75V and the resistor would have to disipate over 100W. It is difficult to guess the rating of that resistor but I think it would take 100W at least for a while. This would do for checking the current limiting adjustment but is a long way short of a full power test. That full power test would need a 133Ω resistor rated for 2.7kW. That is not so easy to come by.

I had an assortment of different kinds of load resistors for the various power supplies - I covered from 20V/1000A to 600V/18A.
For the higher voltage supplies I had some 1kW fire bars (UK, 230V - about 4.3A) and I could wire them series/parallel to get the correct load resistance.
 
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