Technika L22/14A-GB-TCDUK PSU

[Andyd1970]

Hi Guys, My sons TV is dead

I have checked the PSU output that is listed as +12v but only a few mv on the two pins. I noticed that the main large cap's top is slightly domed (pictures attached) most likely cause?? as a new PSU is £20.00 and not really worth it on such a small TV but worth it for a few cap replacements.

Or any other tips voltages to check on PSU.

kind regards
Andy

[tom66]

Re: Technika L22/14A-GB-TCDUK PSU

Check output diodes on PSU - near the large group of caps - for shorts.
Check fuse, in plug and on PSU.
Check for 320V~350V across large cap.
Listen carefully do you hear slight ticking sound from PSU when plugged in? Look for shorts or bad startup cap.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi Tom,

Check output diodes on PSU:
Used my meter on the diode range across the left and middle pin and then the right and middle pin, no shorts. But across the left and right pin I get a short.

Check fuse, in plug and on PSU:
Had checked them and they are both fine.

Check for 320V~350V across large cap:
Across the two legs I read approx 220volts.

Listen carefully do you hear slight ticking sound from PSU when plugged in:
No ticking just a very low hum.

Look for shorts or bad startup cap:
Only bad cap I can see is the large cap which has a slight bulge.

So I guess its the large cap at fault?

[tom66]

Re: Technika L22/14A-GB-TCDUK PSU

220V DC? That capacitor may be the cause, then.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi, Yes 220v DC, I will order a cap and let you know

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi Tom,

The 400v cap arrived just fitted it, I am reading 320v ish across it but still no red light! I have measured the two pins that should be +12v and I have no where near that approx 90mv.

I have checked the large bank of caps and none of them are S/C.

Any suggestions? was I testing the output diodes correctly?

[budm]

Re: Technika L22/14A-GB-TCDUK PSU

Pictures of the bottom side of the board and also check that start Up cap E2 next to D1.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi Budm,

See attached image of the back of the PCB, I have a Chauvin Arnoux C.C 5220 Multimeter.

It has V, Velec, Hz, Ohms, diode, cap, mA, 10A ranges. So I put the probes across the pins of cap E2 and it cycled and then gave me a reading of 22uf, the rating on the cap, when I use the same mode on the large bank of caps, it cycles and then displays O/C reading and beeps. So I guess not sure if that is the meter not handling the cap or it means the cap is dead? I guess I need a ESR meter in the future.

[budm]

Re: Technika L22/14A-GB-TCDUK PSU

See attached image?

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Ops!

[tom66]

Re: Technika L22/14A-GB-TCDUK PSU

What is part # of IC1 - small surface mount 8 pin black chip?

[budm]

Re: Technika L22/14A-GB-TCDUK PSU

OK, I would try replacing that cap E2, you can try heating that cap with hair dryer to see if the power supply will start up. D1 is the rectifier for the AUX winding of the transformer to supply the VCC to the IC after the circuit starts up. Once we get the IC number, we can start checking the VCC pin also.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

IC1 Part Number: LD7575PS 082317

[budm]

Re: Technika L22/14A-GB-TCDUK PSU

Here is the spec sheet. Check the voltage between the VCC pin and the Ground pin, be careful, do not touch any thing with your hands since you are working in the hot side of the circuits.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi Guys,

Just checked it was a stable 11.9v

[tom66]

Re: Technika L22/14A-GB-TCDUK PSU

That is not really high enough to work (minimum START voltage is 16V), so I would replace E2 and if that does not work, the LD7575.

[Andyd1970]

Re: Technika L22/14A-GB-TCDUK PSU

Hi Tom,

I have replaced E2 and no different I then replaced LD7575 and still no life, I measure across VCC and ground pin and get 12v.

[tom66]

Re: Technika L22/14A-GB-TCDUK PSU

OK, also check the diode and resistor circuit which goes into the E2 capacitor, it should go from Vcc pin to transformer. If there is a zener diode near VCC try checking that too.