| Electronics > Repair |
| Repair of SMPS for Cambridge Audio x300 subwoofer |
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| xavier60:
--- Quote from: hooverphonique on May 22, 2024, 12:37:40 pm --- --- Quote from: xavier60 on May 22, 2024, 08:20:05 am ---It's unusual that D22 is rectifying the forward half cycle. I'd expect the rail to have poor line regulation. --- End quote --- I guess it has to be that way for the voltage to be above the shared gnd potential. But yes, this circuit probably has poor load and line regulation, but the supplied circuits seem to not care too much about that. --- Quote from: xavier60 on May 22, 2024, 08:20:05 am ---Carefully check R19. A DMM with at least 0.01 ohms resolution is needed. --- End quote --- It measures 2R0 spot on (as is stamped on it) IIRC, but I'll double check. --- Quote from: xavier60 on May 22, 2024, 08:20:05 am ---Try putting some resistance in series with D22. --- End quote --- R54 is already in series with D22 (10R), or did you mean between D22 and C28? --- End quote --- Yes, between D22 and C28. Just to see what happens. |
| xavier60:
I think the 15V isn't meant to supply much continuous current. Is there something else that's supposed to take over powering of the control circuit when the main supply starts? Edit: but then Q2 would not be able to turn off the main supply. |
| hooverphonique:
--- Quote from: xavier60 on May 22, 2024, 12:59:58 pm ---I think the 15V isn't meant to supply much continuous current. Is there something else that's supposed to take over powering of the control circuit when the main supply starts? Edit: but then Q2 would not be able to turn off the main supply. --- End quote --- If I power the 15V circuit with an external power source, it pulls around 35mA, so that's probably ok. No, this flyback psu powers everything low power all the time, including the pwm controller for the high power psu (when STB is pulled to 5V). |
| MathWizard:
The D22 looks more like a low voltage supply tap for the output side. Q2 doesn't look like it's used for regulation, as a series pass element to draw more/less current and load down the windings. But the output side chip could monitor it's voltage and then send info to the primary side chip, I guess over some opto off schematic, to change switching speed or duty cycle, etc. So where's the rest of the schematic ? |
| hooverphonique:
--- Quote from: MathWizard on May 23, 2024, 05:57:03 am ---The D22 looks more like a low voltage supply tap for the output side. Q2 doesn't look like it's used for regulation, as a series pass element to draw more/less current and load down the windings. But the output side chip could monitor it's voltage and then send info to the primary side chip, I guess over some opto off schematic, to change switching speed or duty cycle, etc. So where's the rest of the schematic ? --- End quote --- Q1 and Q2 are only there for the standby function. There's no feedback from secondary to primary side - the flyback uses its primary side controller supply winding also for voltage sensing on pin 4. I've attached the full schematic for your pleasure.. Please note that it says x200, but the psu is the same for the x300. |
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