Voltage Gain Related, Ch1 Ref; Power Supply / Amplifier Related; Tracker / Amplifier Related; Mft Tags - Crown XTi series Service Manual

找资料学技术，故障求助
Other suspects; Q116,Q134 leakey? Try REPAIRnotes.txt 1
c) Destructive. Discharge power caps. TP26 to TP27. Remove any load. Measure the
following;
1) TO-220 to TO-220 sink...should be >90 ohms. If not,
D180, D181, D182, D191 are shorted.
2) Q114 (TO-220 sink) to HS1 amp + sink...should be >>1K....suspect Q114 device
3) Q115 (TO-220 sink) to HS2 amp – sink...should be >>1K.....suspect Q115 device
4) For a pulled Q114, or Q115 measure R147 and R148 if open.
5) Measure Q112, Q113 collector to emitter while TO-220 part is out...>1K
6) Measure HS1 to CH1 red post....>>1K...suspect HS1
7) Measure HS2 to CH1 red post....>>1K...suspect HS2
8) Turn over PWA and check the soldered base pins of each TO-3 device. Check for
missing pin or not soldered well.

2) Voltage gain related, CH1 REF

Check R132 value.
Check disc caps C228 and C240 (15pf) vs C290 and C299 (220pf) for not swapped.
Check for soldered end of C124, C13, C38, C20 well or not.

3) Power supply / amplifier related.

THD1 is the heat sink to foil connection

4) Tracker / amplifier related

THD1 is the heat sink to foil connection

5) MFT tags

One tag XTI_nVcc_cur_Draw was a bent openTO-3 PNP base pin, lightly hitting the
Amplifier heat sink.
NOTES;
1) Q116 or Q134, if leaky the bases may read -17v or so.
2) Q108, Q106, R135, R142, R137. a possible open 0603, no bias.
3) R133. One end is the error amp output. Check for non-intermittent solder at pad.
4) Bias is not sensitive, set wiper to center should be 0.8 about.
5) R147,R148. If a TO-220 driver was shorted chances are that one of these resistors were also
opened on the process and an opposite polarity device like a TO-92 pre-driver or TO-3 went too.
A shorted To-220 can mask the 340 resistor or TO-92 transistor measurement as good or not.
6) If the TO220 sink to sink is not about <<100ohms then the diodes are shorted across R150.
7) the amplifier will still work if the low side low passed feedback resistor R87 wasn't there, only
damping factor, crosstalk and an indicator of > +/-100mv of DC offset will result.
8) Amp sinks HS1,2,5,6 are tied to the Vbulk for the 1000s, and +/-30v at idle for the tracker
based units. In an amplifier "mute=bias off" mode the + amplifier sinks (CH1P,CH2P) in a tracker
based unit may float up to +90vdc. This is normal. When bias is on they come back down to the
30v.
( refer to REPAIRnotes.txt for heat sink replacement)
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page with "power off".