The Workbench

Re: LX2802N can not start

yachadm — Tue, 24 Mar 2009 06:42:27 GMT

Catn,

Perhaps I should have mentioned this at the start:

When a Horizontal Deflection Transistor (also called a HOT - Horizontal Output transistor) fails, there is usually a good cause for that.

These transistors are not in the habit of just failing off the bat, one day.

The normal causes are as follows and I would suggest that you check these out, before replacing your transistors, otherwise they'll just fail again.

1. Dry joints in nearby area - in the HOT leads, flyback transformer, horizontal driver circuits could cause HOT to blow.

2. Shorted flyback primary winding.

3. Shorted or open internal capacitor in flyback transformer.

4. Too high B+ voltage- A higher than normal B+ voltage will kill the HOT instantly. Make sure the B+ is supplying the right voltage to the primary winding of flyback transformer.

5. Running at wrong frequency - the horizontal driver circuit area running at a different frequency - a too low frequency will kill the HOT after “ON” for a few hours!

6. Bad electrolytic capacitor in the supply line to horizontal driver transformer- If you found a HOT shorted, make sure you check on this capacitor which usually developed high ESR value that destroys the HOT in few hours time.

7. Shorted horizontal yoke coils- A shorted horizontal yoke coil could instantly kill the HOT.

I always use the Smith flyback tester (now sold by Anatek) to confirm first that the yoke coil is good before the replacement of a new HOT.

8. Safety capacitor value out - If this safety (holddown) capacitor value drops to zero, the high voltage produced at the anode could shoot up to over 30KV thus killing the HOT in a split-second.

9. Wrong replacement - someone else had fitted a different specification of HOT thus making the HOT breakdown after some time.

10. Nearby components - There are some possibilities too that bad components nearby the HOT could cause the HOT to blow. Check the surrounding components before you switch “On”.

Thanks to Jestine Yong for these tips.

Menahem

Re: LX2802N can not start

catn — Fri, 20 Mar 2009 07:30:58 GMT

the originally transistor is marked on the flatside with c369 and the row below W17, unfortunly I did check how it was mounted, I just removed it , my transistor tester could't stabilize around any value so assumed it was broken.

/C atn

Re: LX2802N can not start

yachadm — Tue, 17 Mar 2009 12:21:36 GMT

To tell the truth, I'm loathe to recommend anything, unless I can see the PCB close-up and clearly, to see where those pins (and their traces) are going, that it's not a misprint. I've come across plenty of B&O PCB's with incorrect component markings on them.

At a start, if it is in fact correct, it suggests to me that the BC369 which you found there was actually not the original transistor from the factory, but a substitute, which some repairer put in at some time.

I'd like to know what was there.

Based on the the pin configuration, it may have been a BC212B, which B&O liked to use in those years, and that would suit the pin configuration and the little orientation picture.

If that was so, then a modern BC546B would be a perfect CBE replacement (but a BC546 has only an Ic of 0.1A)

But if you want to put in a BC640 (Ic 1.0A), you'd need to twist the left leg (E) around to make it the 3rd leg on the right side. Then you'd have a CBE arrangement.

Re: LX2802N can not start

catn — Tue, 17 Mar 2009 07:49:09 GMT

Hi Menahem,

If you check the picture I've published 6/3, the TR15's print on board is

so how shall I mount the BC369?

anyone out there having service manual for this tv set.

next quest: since it can't start, shall there be power on this board in standby mode?

/C atn

Re: LX2802N can not start

yachadm — Tue, 17 Mar 2009 03:23:59 GMT

Hi Catn

BU508 is a Horizontal Deflection BiPolar Power Transistor (3 pins - Base, Collector, and Emitter), not a FET (3 pins - Gate, Drain, and Source).

Here are 2 perfectly good substitutes for it:

1. Sanyo 2SC5763

2. Fairchild KSC5030F, or the FJAF6810 which is specifically a Horizontal Deflection Transistor.

The Fairchild unit is probably more available, and would be my first choice.

You cannot just put transistors in Willy-Nilly in any pin position, and expect them to work. You could also cause damage to the rest of the circuit.

BC369 is a PNP, with a BCE configuration, I would try a Fairchild BC640 ECB, but mounted front-to-back.

For a Transistor checker, I have the Peak Electronics DCA55

http://www.peakelec.co.uk/acatalog/jz_dca55.html

Regards

Menahem

Re: LX2802N can not start

catn — Mon, 16 Mar 2009 16:41:15 GMT

Soory, could't see any sparks, after some trials the silent puff is now replaced with a dong followed by a 1 sec bzzzz, both FET(BU508) seems to be broken, do you have any suggestions?

Re: LX2802N can not start

Die_Bogener — Sat, 07 Mar 2009 13:43:01 GMT

Exactly what it means... you can see the sparks!

Switch off the light and watch the mainboard around the transformer. You will see the light...

Re: LX2802N can not start

catn — Sat, 07 Mar 2009 05:19:25 GMT

what did you mean with the sentence...

Usually you should see the problem in the dark ;)

in post: 11-08-2008 2:27 PM

/ T

Re: LX2802N can not start

catn — Fri, 06 Mar 2009 04:21:42 GMT

c369 mystery: if I asume it's a bc369 then the pin order missmatch it's ebc on the board...

so either it's a print error on the board or the c369(which i can't find any data sheet for) shape(flatside position) differs from the replace part nte123ap http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm

c369: TR 15 top left CBE (left to right)

bu508: bottom left

solderside:

c369: middle left.

bu508: bottom right

I've tried to start the TV with the c369 it in both positions, just the red stadby indicator, goes off for a second with one silent puff then it becomes red again.

I tried to measure the voltage on c369's C and E in standby mode, but no voltage found on either pin. (actually no voltage found on the board anywhere in standby mode)

I've retested the replace part nte123ap after my trials and it's still alive with the correct vce(260) value according the data sheets.

The bu508 is harder to test, but my broken one indicated near 0 with the diode tester and the new one doesn't it's around 500(is there any power transistor testers availible on any multimeters availibe on the market today)

Re: LX2802N can not start

Die_Bogener — Thu, 05 Mar 2009 12:31:04 GMT

Hmmm, i dont have the manual for the LX2802... but C369 means probably BC369, this is a common PNP transistor.

Look at www.segor.de

http://www.segor.de/bilder/00001607.jpg

Re: LX2802N can not start

catn — Thu, 05 Mar 2009 06:16:16 GMT

Hi, I'm into fixing the startup problem with this TV,

I've replaced the bu508, but it's also another transistor called c369 that seems to be broken, I found a replace part called nte123 NPN type.

My concerns is the print on the board, if put the transistor in according to the print(the flatside in a specific direction) on the board, the pin configuration(also printed on the board) doesn't match!!

was really the c369 a NPN type??

I can't find any datasheet for c369 with google, so my question is, can I turn the replace part around(flat side in wrong direction) so the pin configuration match?

Re: LX2802N can not start

Die_Bogener — Sat, 08 Nov 2008 14:27:54 GMT

No, if you have a BZZZZZZ, then this transistor ist still alive, otherwise you hear nothing than a "ding". That was the fuse...

BZZZZ is typical for bad solderings around the transformer and the high voltage plastic capacitors. Resolder them carefully.

Usually you should see the problem in the dark ;)

LX2802N can not start

nrhalne — Sat, 08 Nov 2008 09:15:54 GMT

I have a problem with my Beovision LX2802N, when I tryed to start it up (push the button "step" on the tv) it just says BZZZZZZZ for about 1 or 2 seconds, can anyone help what to do, and I can use a soldring iron.

I had asked in the old Beoworld.co.uk but forgot the anserw, it was something with a power transistor there had to be changed out.

Thanks

Per