Protection Blocks; Signal I/O Blocks; Temperature Compression And Shut Down; Miscellaneous Notes For Root Cause And Diagnosis Ideas For Repairs - Crown XTi series Service Manual

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3) Protection blocks

a) DCLF detect Clip_not and Low Vbulk detect
b) Time dependant current limit.with and without Tracker
c) Temperature compression and shut down
d) VI limiter without Tracker..XTI000,DSI1000
e) Power Governor

4) Signal I/O blocks

a) Bias
b) Clip_not
c) Mon1
d) DCLF
e) CH1PDRV, CH1NDRV

Miscellaneous notes for root cause and diagnosis ideas for repairs

1) DCLF, crowbar related; (fully discharge supply before ohmic measurements)
A crowbar event can fall generally into three catagories.
Nondestructive_Normal means nothing wrong, just an unwanted signal or load.
Nondestructive means something is open like a solder connection or resistor but not
In a place where transistors will likely blow up when parts of the protection are defeated.
Destructive means either a device has blown or will if standard root cause methods are
used to defeat a protection (like DCLF reporting) to force the unit on to be able to root cause.
For the latter two, the unit is likely to briefly power up, flash the display on then. Shut down
with no clues, other than the power supply is trying to start and something on its secondary is
loading it down. First, for this case, make sure your loads are removed to see if any unresolved
DC on the output does not flow thru the load and thus pull power supply current uncontrolled thru
a device and load. Remove any loading externally.
a) Nondestructive_normal.One generated by a DCLF > 100ms and then clears if there is no
abnormal load to the power supply, hence the unit will be able to restart normally.
b) Nondestructive. Here, bias is not likely to come on. Remove any load. The following tags
may accompany this; XTI_LED_CHECK_NORM, XTI_Meas_pV1_VBP. Try an ohm reading,
even at neighboring pads the parts are supposed to connect to, at the following that had stopped
bias to enable but did not destroy any other items;
REF CH1; R137, R136, R142, R133, R135, R134.
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C124 is a dc block and thus provides some high pass. R130, R132 (main feedback) and
C104 form the voltage feedback and high pass function for the power stage. D3 is a
clamp function. Using standard long stepped bursts of waveforms will result a normal
high pass step recovery of the at the amplifier output, which may initially look abnormal
to other high passed amplifiers. It is not , only these units are high passed around 10hz,
not the typical 2hz or 5hz like others.
Comparator U103 is used for DCLF and a low +/-Vcc detection. A DCLF = low for a
constant 100ms or more is interpreted as a amplifier fault and the DSP invokes the
crowbar to the power supply. A "not" DCLF with a clip_not = low for 100ms or more
may invoke the "SHORT" command from the DSP and compress the output until the
offending short is removed. Lessor than 100ms clip_not = low may invoke the DSP
compression.
Current limiting is set up with Q110, C115, R151, R798 (2ks,4Ks) R194 and more for
the V term in the 1000s. Q111, R152, C116, R799 (2ks,4ks) R194 and more for the
Vterm in the 1000s.
Temperature compression is driven by any one of the 3 LM75s . Simultaneously
pressing all 3 front panel buttons ques the product into an info mode. The temperatures
of the 3 LM75s and other important information may be obtained by scrolling thru the
menu, including the effective loaded "RAIL" voltage from U17 pin 7.
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