XL194-03...Replaced bulgy caps NO 24v from PSU

[E Parton]

Sounds like the invertor feed (24v) isn't being generated...
Often there is a seperate switch mode supply independant of the rest of the psu ..to generate the 24v ..
You say there is no longer a short on the 24v line after the double diode ..
Does this double diode read as a diode ..or does it read dead short left pin to centre ..and right pin to center ....when removed ...
If so its faulty ...
If it reads ok ..ie ..as A diode should ..
Low resistance one direction ..high resistance the other ...
Then I suspect the switch mode chip driving the transformer ..to generate the invertor supply to be non functional..
Its then a case of sourcing the switch mode surface mount chip ..and repacing ...plus its ascociated power FET ...or ...sourcing a new psu board ...which might be easier..
good luck ..
Evan
 

[scooby-doo]

No there is no short on either diode...good readings from both

I have noticed Andy (Ohm Supplies) has a repair kit for the psu but mentions a short on T2000 or blown IC2000 which is a surface mounted chip on the underside...will have a check on them now.

But thanks again for all your help Evan

[KROB]

This unit is effectively two PSU's on one board. In your picture the top "half" of the board is for the low voltage supplies, the fact that you have "audio" proves that this is working. The bottom "half" in your picture is the 24v supply for the inverters.
The fault is most likely to be the electrolytic capacitor located between the "lower" yellow transformer and the right of the two heatsinks at the bottom. I think that it says C2056??? It is, from memory, 100uF/50v, and sometimes it has been encased in a short length of heatshrink sleeving and is easily missed. It can cause the picture (backlight) to be very slow to appear, sometimes for several hours after the set is switched on!!
You should also replace both of the 47uF electrolytics in the two PSU primary sides, and perhaps the two 680uF's which smooth the output of the 24v supply.

regards

Ken

[scooby-doo]

Cheers Ken
I have replaced 680's...I wish I had 24v to smooth  ...not replaced the one under the heatshrink as yet...nor did I bother with the two 47uf's have got some so will fit them after my cuppa tea.

The kit that Andy sells looks all on standby sides so that wont cure it.

Thanks Ken

[KROB]

I'm pretty confident that replacing the 100uF under the heatshrink will cure it, let me know.

Regards



Ken

[E Parton]

Hi Ken ..
Nice to see you bringing your extensive knowledge here as well ..
Hope your suggestion fixes up S/Ds telly afore he tears his hear out ..
;)
rgds
Evan

[scooby-doo]

Yeahhhhhhhhh!!!!!!!!!!

Thank you thank you thank you....changed the extra three caps you mentioned and hoooorrarrrrr it only bloody works

I did notice the cap with heatshrink around while desoldering the tracks seem very fragile around that area probably because of all the heat off the tx, repaired and now works fine.

Thank you again

[KROB]

Like I said..........

lol


regards

Ken

[scooby-doo]

And dont run off anywhere...A murphy problem coming

[Turnip]

Hi S/D,

What caps replaced ?  have it as C2566 in Quuq files - always curious, but have few 'lol's' noted - due possibly to extreme age - Chris

[scooby-doo]

Hi Chris...Pic on page one of this post will help..cant remember all position numbers

These secondary caps were bulging
2 x 680f x 35v
2 x 1000f x 35v

Change these but looked ok
2 x 220f x 35v

The main culprit was like Ken mentioned the 100f x 50v at position C2056 its not C2566

I also replaced 2 x 47f x 63v...I did get 24v back without changing but didnt want them to feel left out so changed them anyway

[Turnip]

Hi S/D and thanks,

Could appear 'In the know' next time the prob reported - like you, tend to change most every wet cap in the hot area just to be on the safe side - Chris