Need schematic for TURBOSOUND SIENA TSP122_AN

[Rajan Paliwale]

Every time smps powered monitors come to me for high voltage input,one of them is very easy to repair.Find out burnt tracks,mosfets, smd resistances, driver ics,replace new ones & the monitor is on.But the other board will have big problems. IN this case also it found to be true. Output voltages are becoming high after few seconds,damaging output pairs of mosfets. Can anybody share some knowledge. I don't have schematic. IF someone has it kindly share it please.

[J M Fahey]

No schematic but just some thinking aloud:

Most (not all) SMPS have "fixed" input voltage: 300 something Volts, whatever rectified Mains peaks reach if nominal 240V or same DC Volts if 120V mains but using a doubler, so that is not the source of your rising voltages.

Now, to allow for regulation which is always downwards, not upwards, typically ferrite transformers are wound to provide an *excess* of secondary voltage, a lot of it, then measure secondary voltage (generally using a Zener as reference, might also use a TL431) and tell switcher to turn down , generally using an optocoupler for isolation.

IF that down regulating system fails or path opens, untamed secondary voltages can shoot up sky high.

Find which switcher/controller IC was used and get datasheet, circuit often is that shown as an application, or very close to it.

[doctor]

Usually, MOSFETs in a digital amplifier burn out for other reasons. The used transistors have an allowable voltage of 200V. And the working voltage is only ±70V. But if you suspect that the voltage is changing, do a check. Lift (unsolder from the pad) pin 03 of the IC4. After that connect together the two pins of the IC1 (pins 10 and 12). Now turn mains on and monitor the supply voltages.

[Rajan Paliwale]

Today I tried as per suggestions. 1) lift pin no3 of ic4 NE555,short pins10&12 of ic1SG3525.But still the voltage output is +140 -140.Any more suggestions. & if you are having schematic for this,Kindly share it.I will be very much obliged.

[doctor]

If so, return everything to its original state. Check if R48 and C96 are connected correctly. If ok, replace C96 (470pF 0.1% 25V minimum). If that doesn't work, replace IC1 (KA3525).