Stumped on a repair of an xti4000. Original problem was low output level. Found a shorted cap in the power supply, C47. Replaced and rail voltages looked good. Sounded normal, sent out for use. Came back with low volume report, though initial report was normal operation. Looked deeper, transistors test ok, no major component malfunction apparent. Traced rail voltages to output transisitors and it seems to be lost along the way, on + and - sides. Seeing 30v +/-. That comes from the other power supply tap LR1+/- though so it seems the 140 volts is gone after it enters the power amp section. Got lost going in circles, pretty complicated amp, I am pretty seasoned in repairs but this one is about to be a paperweight if I cant get it figured soon.
Schematic Here, pages 150-154
Crown XTi 4000 file: XTi Series Service Manual original (davidcab) - Audiofanzine
I have a ton of voltage readings, spent hours pouring over the schematics and testing testing to no avail. Any and all advice and help would be so dearly appreciated.
I have a feeling it is some kind of muting circuit or microchip issue?
Thanks, JOSH
Schematic Here, pages 150-154
Crown XTi 4000 file: XTi Series Service Manual original (davidcab) - Audiofanzine
I have a ton of voltage readings, spent hours pouring over the schematics and testing testing to no avail. Any and all advice and help would be so dearly appreciated.
I have a feeling it is some kind of muting circuit or microchip issue?
Thanks, JOSH
So have you checked LOZ_1 and LOZ_2, which control the mute circuits Q10 and Q14. The LOZ control voltages come from U1 which may be broken or unhappy. Maybe there is more trouble in the power supply that is making the uC upset. Did you replace C48 as well as C47?
Note that sheet 7 is a bipolar power supply regulator that reduces the raw +V1 and -V1 to the power amp CH1P, CH1N, CH2P and CH2N
Note that sheet 7 is a bipolar power supply regulator that reduces the raw +V1 and -V1 to the power amp CH1P, CH1N, CH2P and CH2N
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I did replace all power supply caps while I was at it, thanks for the tips I am jumping back in to investigate!
Well, the schematic lists Q13 and 14 as open, as well as the attached resistors. Open they are, there is only empty solder pads on the pcb. The -15v is present on one end of r230 but other than that, well not mush else to report. Any ideas?
Hi sir, I have same problem. My xti4000 is clipping way earlier than usual. It can hold full power for about 1 sec and then comes at aprox. -3dB.
Did you solve the issue? Thanks.
Did you solve the issue? Thanks.
Line voltage sag happens a lot sooner than 1 second. The power supply is probably dialing itself back to stay in safe operation. It’s FAR worse on the Xti1000, which is so stingy it won’t even allow full power operation for a single cycle of 20 Hz.
The power supply is a simple half-bridge with some kind of resonance. There is no feedback at all. If you load just one channel, you'll probably get full power
One can only get so much blood out of a stone. The power supply’s limiting mechanism responds to total loading and is time dependent. If it is limiting “earlier” than it used to, I’d be looking at whatever timing mechanism controls the limiting, or what controls the threshold if I strike out there.
You can always inject low voltage with current limits and see what heats up.
I had repaired a crown xli which had clipping circuit indication error in one channel and lower sound on the same channel. It happens the mosfet and opamp for all these detection had started failing and begun pulling the line towards ground potential. Check all mosfets, transistors, opamps etc between signal and ground and also between rails, ground etc.
I had repaired a crown xli which had clipping circuit indication error in one channel and lower sound on the same channel. It happens the mosfet and opamp for all these detection had started failing and begun pulling the line towards ground potential. Check all mosfets, transistors, opamps etc between signal and ground and also between rails, ground etc.
The LPC2142 controls the limiting if the rail voltage sags too much. To achieve full power, you need 230V at the wall. Alternatively, you can inject 2.5V into the rail-sensing pin on the LPC2142, which prevents limiting and allows it to reach clipping (assuming you haven't programmed the DSP to impose limits).