Electronic equipment repair and service manual search discussion :: Topic review

Guest · Posted: Thu Aug 21, 2008 4:46 am Post subject:

Voltage in hot line is 135 V. And bulb burn. So power supply is OK.
So there have to be shorted in hot line. I have tested all capasitors and resistors. Everything seems OK. If it possible that flyback transformer could cause that fault?

Guest · Posted: Tue Aug 19, 2008 5:05 pm Post subject:

I tested power supply using bulb (150 v diode and chopper transistor are taken off). The bulb burn but when I measure the voltage there is only 0,5 - 1 v across the bulb. Is my power supply OK?

torbjorn · Posted: Tue Aug 19, 2008 7:33 am Post subject:

Have you checked that the entire voltage control circuit works properly?

Try the following:
1) Don't connect the tv to the electrical mains.
2) Connect +5V from a lab power supply to USS (TPS 31, the output from NO04), return to the ground pin of NO04.
3) Connect about +10-11 V from another lab power supply to NO01's VCC (pin 14), return to pin 12 of NO01.
4) Connect a variable voltage to U1 (cathode of VO30) and measure the voltage between pin 5 and pin 12 of NO01. This voltage should change from high to low when U1 crosses about 150 V. If not, you have a problem around VO12 - NO03. It is possible that you also have to connect +12V to the point RO106 - LO31 - CO37 to get the circuit to work, i wonder what the circuit RO106 - VO13 is there for.

Guest · Posted: Mon Aug 18, 2008 6:32 pm Post subject:

Diode V030 has 1000 Vrms. It is possible that high voltage across the diode cause the fault? Can I measure voltage without load by voltage meter?

Guest · Posted: Mon Aug 18, 2008 5:08 am Post subject:

How I can measure TDA16846? What will be happen if NO01 is broken?

Guest · Posted: Sat Aug 16, 2008 10:44 am Post subject:

Any other ideas? Where the fault can be find?

Guest · Posted: Fri Aug 15, 2008 3:40 pm Post subject:

I check all the components and any of them was not open circuit.

torbjorn · Posted: Fri Aug 15, 2008 9:04 am Post subject:

I don't think the power supply can deliver so much current that just the current would damage the VO30. It is more likely that it is too high voltage across the diode that causes it to fail.

Check the snubber network across the diode, RO107 and CO074. Also, it can be a good idea to check the snubber components on the primary side of the switching transformer, VO07, VO08, CO14, CO21.

The voltage control circuitry is around VO12 and NO03. For example, if one of the resistors RO026 or RO030 goes open circuit or if the photocoupler NO03 is bad, the power supply will get out of regulation. Also, you will get no voltage control if the supply voltage for the photocoupler, that seems to be 5 V and come from the NO04, is lacking.

Guest · Posted: Fri Aug 15, 2008 6:13 am Post subject:

I dont't have variac so I have to try isolate. How I isolate all the places U1? What is the component that regulate the system?

vtech · Posted: Fri Aug 15, 2008 5:39 am Post subject: