Sansui LCT32SD not switching on

[Grunder]

Hi guys,

I need help determining the value of two components on the power supply.
I've included a photo of the pcb with the components high lighted.

IC6 = L6599 Hv resonant controller Turquoise square. Vcc is pin 12 (self limiting).
IC3 = opto couple Yellow square.
Trans 5. 2SA1815 (on top of pcb) marked Green. measured okay.
Trans 6. 2SA1015 (on top of pcb) marked Blue. Short/ replaced.
Diode 9. (on top of pcb) marked yellow. okay.
R30. determine value. marked Red. burned beyond recognition.
Zener diode determine value. marked Red. short No inscription.

I tried a 1 ohm (feed resistor?) in position R30. and 5v8 for the Zener.
But set wouldnt switch on and both slowly got hot and burned black.

I tried electro tanya for the diagram, but no luck.

I'm hoping one of the guys on BADCAPS with design knowledge, might be able to determine the values. Thanks.

I forgot to say the 5v stby is there, and the psu-on does appear when pressing standby button, with led going from red to green. I reckon IC 6 isn't getting a supply, so it cant drive the transformer responsible for generating the 9,12 & 24v rails

[Grunder]

Re: Sansui LCT32SD not switching on

Anybody?

[Grunder]

Re: Sansui LCT32SD not switching on

Hi Guys,

Took a chance and done a little experimentation.

Replaced the burned resistor with a 120 ohm 1/4 watt resistor (photo 1)
Replaced the shorted zener with a 12v zener.

Set now switches on (backlights on), and working perfectly! (Photo 2)

I guess the resistor was a limiting resistor, and the first attempt using the 1 ohm allowed too much current through, burning up the zener.

I now get 12v across the zener in standby. 11.3v when the set is running.
I now get 10.7 volts supplied to pin 12 (Vcc) on the Hv resonant ic.

[dick_barton]

Re: Sansui LCT32SD not switching on

What was IC7's part number?

[Grunder]

Re: Sansui LCT32SD not switching on

Hi Dick,

You might not have seen my recent post (3 min before your reply).
I did manage to get the set running.
I didn't identify IC 7, I also suspected IC 7 got damaged. Set has been closed up.
Thanks response.

[dick_barton]

Re: Sansui LCT32SD not switching on

Hi, I did see your post but was thinking that the data sheet for IC7 would give typical component values to check against what you used.

[Grunder]

Re: Sansui LCT32SD not switching on

Hi Dick, quite right, checking the specs on that ic(7) would have given me a better idea of what voltages to expect in that area.

She's running now with no heat or burning of the components fitted, if she comes back (hope not), I will investigate further.

Thanks for the input.

[dick_barton]

Re: Sansui LCT32SD not switching on