sony kdl-22ex320 fuse blows after 10 mins

[KountZERO]

Hiya, long time away due to ill health, anyway..

Picked up titled set and when plugged in, it runs for about 10 minutes then blows the plug fuse. There are no artifacts on screen or sound issues.
Pulled the board and there dont seem to be any physical defects, rubycon caps all look good and no scorching on the board near the hot components.

Will a short lightbulb rig reveal anything useful before i start desoldering? Ive been told it could either be condesation or cold solder joints (would that case a surge when the joint fails when warm and if so which component?) I thought a bad joint would just give an open short?

[Andrew F. Ali]

Re: sony kdl-22ex320 fuse blows after 10 mins

I can't see the labels on the connectors clearly from you picture. However, I think you may have an inverter or Hi-voltage transformer problem, at first glances.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Will grab a better pic with camera soon, in the mean time i pinched another image of a replacement board. Sorry, pevious is not much betterbthan a thumbnail.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Been missinformed, its not blowing the fuse. Just had it on the bench and it ran for a good hour, left it to grab a firmware update as it was out of date and not conecting to bravia network, came back to it and it was dead. Checked the fuses, all good, unplugged it for a few minutes whilst doing this obviously but when plugged in it fired up again for a few seconds then died again.

Sounds like something is collapsing when it gets hot, thermal fuse by the main winding?

The person i got it off must have been confused by the fact that it cooled down while the fuse was being changed.

[budm]

Re: sony kdl-22ex320 fuse blows after 10 mins

When you said it dies again, what does it really mean? Do you have no DC outputs from the power supply board at all to run the main board when it is DEAD, or no backlights, etc? What kind of test have you done when it is not working?
That power supply is an always on power supply with some of the outputs that are switched ON when PS-ON is present.

[Andrew F. Ali]

Re: sony kdl-22ex320 fuse blows after 10 mins

Well with this new information it puts a different spin on things. Answer the questions asked by budm.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Makes sense,. After a brief check getting 24v on one of the MOSFETs, the single one on far left. It goes completely off, no standby lights. Getting high voltage as far as the transformer with a couple of quick probes. The thermo fuse is still good.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

I'll run the power board solo later and get some values proper. I was expecting the bridge rec to be the problem or a cap short when I got it but its deeper dish than that it seems.

[Andrew F. Ali]

Re: sony kdl-22ex320 fuse blows after 10 mins

Perhaps if you post clear, focused, close up Pictures of the PSU so that we can see the labels on the connectors clearly we could tell you better where your problem lies. We need to know if PS-ON, STDBY, BL-ON, etc voltages are still present at shutdown. Those voltage readings you took is with reference to Hot GND or Chassis GND and to me they are of no use for me.

[budm]

Re: sony kdl-22ex320 fuse blows after 10 mins

What thermo fuse? There is no thermo fuse.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Test pics

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Is there not one next to the main transformer, to the left in the 1st pic? FB303

Sorry, been a couple of years since i got the test gear out so im out of practice. Ill put some high res pics on as soon as i sort the lighting out. Was too dark just now for close ups and too much glare with the flash.

[budm]

Re: sony kdl-22ex320 fuse blows after 10 mins

FB = Ferrite Bead which is installed on the leg of resistor R301 to form a very small inductor on that resistor leg.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

FB = Ferrite Bead which is installed on the leg of resistor R301 to form a very small inductor on that resistor leg.

Ahha ithought it was one of these, bad eyes.

https://www.jaycar.co.uk/192oc-thermal-fuse/p/ST3810

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

No standby voltage at pin 10 on the connector when the shut down happens. Seems to occur faster when there is More residual charge in the caps. Fully discharged, the TV can stay on for nearly an hour, just turning off for a few minutes results in a shut down just after the snow of analogue appears.

Few pics of the reverse side attached.

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Further to the last post, when working the readings match those of the attached schematic. They read zero when it fails.

[budm]

Re: sony kdl-22ex320 fuse blows after 10 mins

Please upload the service manual so I can easily see what is going on.
Never mind, I found the service manual, no schematic of course.

[budm]

Re: sony kdl-22ex320 fuse blows after 10 mins

Further to the last post, when working the readings match those of the attached schematic. They read zero when it fails.

So there is NO (0 Volt) DC Voltages on any one of those pins of the power supply when it is not working, correct?

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

That's right, although I have not run through them on the millivolt range. All the pins that registered 12, 5 and 3.3v when it was operating showed no significant charge. I did notice however that the 12v lines seemed to creep up to 12.8/9 when working after a while which seems odd. Perhaps this is a symptom worth chasing?

[KountZERO]

Re: sony kdl-22ex320 fuse blows after 10 mins

Please upload the service manual so I can easily see what is going on.
Never mind, I found the service manual, no schematic of course.

You beat me to it, thanks dude.
.