Voltages Of Interest; Scr Malfunction Instructions - Hobart 6T28-600CL Operation And Maintenance Manual

OM-2244 / Operation and Maintenance Manual
DCS-600/ Series 500082 / Solid State Transformer-Rectifiers

4) Voltages of Interest

a) Across the secondary on all 3 phases - 66 VAC ± 10% *
b) To secondary coil center tap on all phases - 33 VAC ± 10% *
* The ± 10% refers to the possibility of input voltage being out of balance or not at the nominal value.
c) Across the 115 VAC receptacle - 115 VAC (230 VAC on 50hz units) ± 10% *
d) Between X1 and X3 on Fuse Block - 37 VAC ± 10% *
e) Test Point Values for PC board
A control board malfunction will probably result in one or more of the following symptoms:

loss of output voltage

inability to produce full load current

output voltage too high or too low
Section 2-2 shows the circuit board test points and provides standard voltages at those points.
NOTE: The circuit board potentiometers are preset at the factory and should not have to be reset in
the field. If a need arises that would indicate the need for field adjustments, please contact the
factory. The only exception is R109, which adjusts the 28 V output level. If necessary, use this control
to increase the output voltage slightly to compensate for the voltage drop in a long output cable.

5) SCR Malfunction Instructions

a) SCR Failure Symptoms
SCR failure is not common. When they do fail, they generally do so either by shorting or by failing to
turn on.

Shorted SCRs will generally result in tripping the circuit breaker at the power source. However, a
shorted fly-back diode (on the filter choke input or across the output contactor coil) may also trip
the breaker. This is a severe malfunction.

If an SCR does not turn on, it may be because it is open or because the gate signal from the
control board is not reaching the SCR.
o
If one SCR does not turn on, a very small change will occur at the output, which will be
difficult to notice. The ripple voltage at the output will increase.
If two SCR's do not turn on, the ripple current will increase and can cause other problems.
o
(consult troubleshooting procedure).
December 15, 2014 Chapter 2-1
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