Low Voltage Dc Power Problems; Hv Supply Problems - ConMed Hyfrecator 2000 Service Manual

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If the resistance reads within 5 and 20 Ω, verify that mains voltage strapping jumpers JP1 - JP5 are properly
installed and soldered in for the rated mains voltage per Figure 5.8, Table 1. If the jumpers are correct and
the resistance reads open circuit, then remove the A2 PWB and test for an open primary in A2T1. This is a
highly unlikely failure, and T1 is both costly and difficult to replace, so it is prudent to confirm the defect
before proceeding.

4.4.8.2 Low Voltage DC Power Problems

There is one bulk source of unregulated Low Voltage (LV) DC power, +24UNREG, used to feed the +12V
regulator A2VR1 and the +5C regulator A1VR2. There are no other loads which use +24UNREG. The
+12V regulator supplies all of the remaining loads, including the High Voltage (HV) controller, A2U2; the
stable reference +5VR output from A2U2 is also used as pullup bias in the tone and PA gate drive circuitry.
Thus, if the +24UNREG supply is nonfunctional, so is the unit.
Check voltage on +24UNREG with A1 disconnected and the AC mains set at rated voltage. It should be
+21 to +27 VDC.
If +24UNREG reads zero, and the mains circuitry checks out properly per 4.4.8.1 above, then check for 18
to 25 VAC on the T1 LV secondary, pins 16 and 18. If the LV AC is acceptable, then most likely BR1 has
opened. If LV AC is also zero, then it is possible that the thermal fuse embedded in the winding has opened.
If so, then A2T1 must be replaced. However, verify the open circuit using an ohmmeter before proceeding
with this difficult and costly replacement.
The T1 thermal fuses open only when the winding temperature becomes dangerously high, probably due to
a short circuit failure. Isolate and correct this fault before installing a new transformer.
If +24UNREG is not zero but well under +21V , verify correct mains strapping per Figure 5.8, Table 1. If
correct, suspect a fault in BR1 or C1 or on either of the +24UNREG or +12V lines, detectable by
ohmmeter. Disconnecting the ribbon harness can help isolate the fault to A1 or A2. If +24UNREG is low
only with A1 connected, check A1TP4 (+5C) and A1TP5 (+5M); both should be +4.9 to +5.1 VDC.
If +24UNREG is well above +27V , recheck AC mains voltage and verify mains voltage strapping per Figure
5.8, Table 1.
If +24UNREG is acceptable, check +12V from +11.4 to +12.6 VDC. If it is high and within a few volts
of +24UNREG, verify GND on VR1-2 (center pin) before removing VR1 for replacement. While VR1 is
removed, verify no shorts between +24UNREG and +12V with A1 connected. If confirmed, then replace
VR1 and recheck +12V and A1 +5M, since A1VR1 may have been damaged by excessive power
dissipation.
If +12V is low or zero, isolate by disconnecting A1 and then checking for shorts. A short on +5M will
cause A1VR1 to enter current limit or thermal shutdown, but if A1VR1 is shorted, damaged components
powered by +5M may also cause an overload on +12V .

4.4.8.3 HV Supply Problems

Most HV Supply problems will first appear during POST or in operation as Fault Code "-1" or "-2". Note
that failure of HVENA to shut down HV during one of the first three steps of POST will also yield a "-2"
Fault.
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