KBIC SIMPLIFIED TROUBLESHOOTING GUIDE
KBIC SIMPLIFIED TROUBLESHOOTING GUIDE
Upon receiving a returned control from a customer, please follow the next few
steps in order to determine if the control is in warranty.
EQUIPMENT NEEDED: Digital voltmeter (VOM) with diode test, alignment tool,
potentiometer, line cord, 100 watt bulb
Visually inspect the KBIC control for broken components. burn and/or smoke
marks, or blown devices. These observations should be made known to the
Broken Components are caused by mishandling of the control.
Burned or Smoke Marks are caused by miss wiring of the control.
Blown Devices such as SCR’s or flat pack diodes are caused by shorted or
possibly grounded armature leads. Blown devices, such as MOV’s, are usually
caused by an over line voltage condition or line surges greater than the MOV can
If you receive the control and it has none of the obvious defects above, proceed
to Step 2.
Set scale of VOM to diode scale. Remove Plug-In-Horsepower ® Resistor.
Check resistance across Li and L2. Reading should show infinite or open circuit.
Be sure to reverse leads across Li and L2. Reading should still be infinite.
Measurement values shown below are approximate only and reflect measurements
made with a Beckman 310 digital VOM. Other meters will have different results. I
suggest you use a known good control as your guide and compare its readings with
the suspect control.
You may also substitute my readings with those of your meter. lf ”0” ohms is
observed, check field diodes D4 and D7. With (+) lead on L2 and (-) lead on Li,
if .66 ohms (( I your reading here) is observed, replace diode D7; if .56 ohms (
1 your reading here) is observed, replace diode D2. With (+) lead on Li and (-)
lead on L2. if .66 ohms ( ] your reading here) is observed, replace diode D4: if
.56 ohms ( J) your reading here) is observed, replace power diode Dl.
Check resistance across Fi- and F-. With (±) lead on F— and (-) lead on F-.
reading should be infinite. With reversed leads, reading should be 1.2 ohms (
your reading here If reading is less, check diodes D4 and D7.
Check resistance across A+ arid L2. Reading should be infinite. If reading is
less than infinite, check SCR2.
Check resistance across A+ and Li. Reading should be infinite. If reading is
less than infinite, check SCRI.
Check resistance from A+ to F-. With (+) lead on F- and (-) lead on A+,
reading should be .55 ohms (11 ] your reading here). With leads reversed,
reading should be infinite. If readings are “0” ohms, check power diode D3.
Change resistance scale to 10K or nearest selection. Check resistance from P3
to P1. Set MAX trim pot to 50% rotation. Resistance should read about 5,000
ohms. If resistance is infinite, MAX pot must be replaced.
Check resistance from P1 to 12. Set MIN trim pot to 50% rotation. Reading
should be about 1200 ohms. If reading is “0” or infinite. MIN pot must be
Change scale back to diode scale. Check resistance across zener diode Z1.
With (+) lead on stripped end and (-) lead on plain end, reading should be
infinite. With reversed leads, resistance should be .7 ohms ([ ]) you’re reading
here). If reading is “0” or infinite with leads this way, replace Z1.
Repeat Step (H) across Zener diode Z2.
Check the resistance across the Plug-In-Horsepower® Resistor. It should equal
the value printed on the resistor, or at least indicate continuity, not an open.
On-Line Test. Connect 5K pot to P1, P2, P3. Connect 100W lamp to A+, A-. If
testing a 120V control, be sure to use a 120V lamp. Likewise, use a 240V lamp
for 240V controls or two 120V lamps in series. A 240V lamp may be used for 120V
controls. However, the lamp brightness will be reduced.
In order to avoid any unnecessary damage to controls, I strongly recommend that
you add a 100W lamp in series with the AC line,. This will protect the control
from shorting in case any steps were overlooked. Also, add a simple SPST toggle
switch in parallel with the lamp. This will allow you to put direct line voltage
on the control. (See Fig. 1)
Be sure SPST switch is in OPEN position and 5K pot is set fully CCW. Be sure to
replace plug-in-resistor. Apply line voltage. If control is good, lamps 1 and 2
should be dim or off. If lamp 1 is at full brightness, then there is a short
circuit in the Power Bridge of the KBIC control. Remove control from test and
repeat Step 2 (A)-(E).
If lamp 1 is dim or off, slowly rotate 5K pot. Lamps 1 and 2 should increase in
brightness. If this is not the case, some voltage checks should be made.
Using the digital VOM, select the proper AC scale to measure the incoming AC
voltage across Li and L2. This will verify that AC voltage is present at the
control terminals. Next, change scales from AC to DC 250V range. Check voltage
from F+ to F-. On 120V controls the reading should be approximately 1 O6VDC.
Double that for 240V controls. On 240V controls the field voltage may vary
depending on the actual line voltage. If field voltage is not present, or Y2 the
required voltage, check diode D4 or D7. Next, measure the voltage from A+ to A-.
Be sure to rotate 5K pot fully CW. Readings should be 90 or 1 8OVDC, depending
on input line voltage. If voltage reading is low, adjust MAX trim pot to proper
setting. If output is not adjustable either with MAX trim pot or with 5K pot,
then check the following test points.
Reset scale on digital VOM to nearest range above 2OVDC. With (-) lead on F-,
measure voltage at junction of R17 and Z2. Reading should be 18+ volts. If
reading is below 20 (such as 15 or 12), then zener diode Z2 is wrong value
and/or defective. It should be replaced with 22 volt, 1 watt device. If reading
is “0”, then Z2 or Q3 may be shorted. Check resistance of Z2 with AC power off.
If normal (infinite and .7), then with the power off clip out Q3 and retest.
If voltage is 1 8V, observe reading while removing AC power. Voltage should drop
instantly to I .2V, then to “0” in 1 sec. This will confirm that the auto
inhibit circuit (consisting of Q3 and Q2) is working.
If voltage is 20V, then check voltage on left terminal of MAX trim pot. It
should read 12-15VDC.
If reading is less than or greater than this voltage, then Z 1 is defective.
Next, measure voltage on P3, while varying the MAX trim pot. Voltage should vary
from 12-15 to 7- 9VDC. If no reading is observed, MAX pot is open.
Next, adjust MIN pot to full CCW position. Measure voltage on P2 while varying
the 5K pot. It should vary from 0 to 7+. The MAX voltage depends on where the
MAX pot is set. If the voltage does not vary over this range, the MIN pot is
open. While measuring the voltage on P2, vary the MIN pot. The voltage on P2
should increase smoothly. If it suddenly jumps to a higher value then the MIN
pot is open.
Next, measure the voltage on Ii. Increase the 5K pot from 0 to full CW. The
voltage on Ii should increase smoothly as a result of our controlled
acceleration circuit (R5 & C101). Decreasing the 5K pot from full CW to 0 should
cause the voltage to drop very quickly. This will confirm that diode Dl01 is OK.
This completes the simplified testing procedure that should help resolve 99%
of all problems encountered.