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Bush ws6671sil - 11AK19Pro chassis - Help needed!
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Mon May 30, 2005 7:07 pm    Post subject: Bush ws6671sil - 11AK19Pro chassis - Help needed! Reply with quote

Hello!
First off, this site is probably the most useful electronic repair site I have come across. Well done to everyone involved! Smile

Ok, now onto my problem.

This Bush tv set (11ak19pro, widescreen) was found in a skip, broken but untouched by a soldering iron. Wink

TV turns onto standby when switched on.

When the set is first switched on via P+, the standby light turns green and a 50hz buzz is audible (at a low volume) through the speakers. When switched off and on again, the PSU emits a fairly loud chirp repeatedly while the led flashes from green to red. So something's shorted...

Checked, substituted known good SMPSU rectifier diodes for D814/D815/D816. No joy.

Replaced LOPTr 2SD2579 with BU2508DF. Still no joy.

Removed audio chip IC100 and vertical output chip IC701. Switched on, no change in symptoms. No shorts between legs and case GND on either chip (except GND of course).. Soldered em back in.

Removed the RGB driver chip IC901. This time no chirp from PSU - when switched on green light switches on briefly, buzz from speakers, then goes red. No cycling - have to press P+ each time. Sometimes may stay green with buzz. (I always switched it off at this point anyway.) Soldered it back in. Realised that disconnecting the plugs from the CRT board resulted in the same effect!

Checked mains smoothing capacitor (220uF) with capacitance meter - over 200uF (limit of meter). Retains its charge well - when in circuit takes a good 5 minutes to discharge (to 40V) through the discharge resistor. Checked C848 (220uF) electrolytic on primary side - measured above 200uF so apparently ok.

Removed LOPTr and D611 (BY299), D612 (BY228) in flyback circuit, hoping that any hidden shorts in D611, D612 would show up. Switched on, same symptoms. Components measured ok. Unplugged scan coils, same problem. Realised that doing this group of actions may have opened a coil in the FBT. Doh! Embarassed

Checked FBT with mutimeter. Coil between 150V and E/W open. Pretty sure it was closed when last measured, can't bloody remember. Should be a coil there in the circuit diagram!

Put back in LOPTr and D611, D612. Plugged CRT board connectors back in.

Desoldered the 150V pin on FBT. PSU switches on, speakers buzz, trips with no tweet (have not used a dummy load). No cycling, have to press P+ each time.

Reconnected 150V pin. Back to original symptoms, PSU cycling, tweeting.

When the PSU decided to not trip occasionally, I measured the SMPSU voltages. 150V line at 152V, ok. +-14V audio power lines both a little low at +-12.1V, but since they were both the same probably ok.

Haylp!

What is the FBT part number? Did I f**k up the FBT by removing LOPTr and D611/D612 and switching on? Have I missed anything obvious? I would be extremely grateful for any help on this one 'cos its a fairly nice TV set and I don't want to chuck it back in the skip!
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adamij
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PostPosted: Tue May 31, 2005 5:05 pm    Post subject: 11AK19PRO4 Reply with quote

Check R866=0R33 and remaining :R865=0R33,R802=0R33
Good luck !
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Wed Jun 01, 2005 9:56 am    Post subject: Reply with quote

Thanks for reply, adamij.
Will check these components when I get home!
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Wed Jun 01, 2005 3:19 pm    Post subject: Reply with quote

R866, R865 are wire links. Can't find R802. Sad

I have ordered a new LOPT for it.
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Sat Jun 04, 2005 9:25 am    Post subject: Reply with quote

OK, fitted a new LOPT and arrrrrrrggh same problem. Lol well at least I've got a spare bush LOPT now.

Hmm. I've replaced the LOPT and HOT. I've double checked the 3 main SMPSU secondary rectifiers. All those fusible resistors in this chassis have mostly been replaced with wire linksby the manufacturer.

Tweeting and cycling.

Unplug PL901 and switch on I get two green pulses from front LED then back to standby. This may be the correct behaviour since dead IC901s give these symptoms and removing PL901 takes IC901 out of circuit by removing the GND connection.

The 50Hz buzz I am experiencing through the speakers might point to overloading of the primary side of the SMPSU. I cant find anything thats shorting out the secondary side anyway. But then again the PSU starts up into standby, so it must be working. Bah.

Anyone got any ideas?
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Tue Jun 07, 2005 4:11 pm    Post subject: Reply with quote

OK Narrowing down the problem now.
Disconnected 150V line to FBT. Put in a 60W bulb dummy load over the supply. Turned on. 150V line still cycling so something is lurking in the PSU.

(Should have done this before ordering that FBT! Lol well I don't do this everyday, so you live n learn!)

Next I am going to lift the anodes of all those recifiying diodes (except the 150V of course!!). A question first though. I am correct in saying NOT the 150V diode? This is the supply that is fully regulated by the PSU. Lifting the anode may destroy the SMPSU because of the feedback circuit? I know the SMPSU controller protects the switching transistor from excessive pulse width, really I just want to be sure.

Any help appreciated! I have a good grounding in electronics and repair - just not the experience you would get in a repair shop fixing TV after TV.
I AM GONNA FIX THIS BUGGER OF A TV SET. Twisted Evil
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Wed Jun 08, 2005 6:08 pm    Post subject: Reply with quote

Right, lifted the anode of D812 of the +14V line that also goes to a 7808 regulator for the +8V supply.

150V supply comes up on dummy load for a few seconds then goes off. No tweeting of supply so this seems to have cleared the short. Smile

Replaced D812, back comes the tweeting.

Removed 7808 - no tweeting. Seem to be getting somewhere now...
Regulator doesn't appear to be shorted will test it tomorrow probably.
Are there any common problems/shorts that affect the +8V supply in this set?
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Thu Jun 09, 2005 9:19 am    Post subject: Reply with quote

Found the leaky diode!!! Cool
It was D817, rectifier for the circuit with C813 (4700uF 16V) in, which is in the circuit diagram but the number was left out. Substituting D187 and putting back in the 8V regulator did the trick!! The duff diode tested ok.

Now the 150V comes up solid, and doesn't switch off.

Wicked. Now I've gotta hope and pray that my changes to the horizontal output doesn't f**k the TV up. I have replaced the LOPT/FBT with a HR8029 and the HOT with a BU2508DF. The original HOT was a 2SD2579.

Can someone with the knowledge confirm this for me? I don't want to switch this set on and find it blown up, especially after all this effort!

The chassis is an 11ak19pro.

I could replace the new LOPT with the old LOPT and put back in the original HOT. What do you guys think?
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Thu Jun 09, 2005 11:32 am    Post subject: Reply with quote

I powered up the set with the new LOPT in and changed the BU2508DF for an AF version because quite a few repair tips have done this substitution. PSU comes on good, horizontal circuit is oscillating but there's a fairly loud hissing+squealing sound coming from the horizontal output circuit. There is EHT, but appears to be no heater voltage or anything.

Changed the new LOPT back to the old one and put back in the old HOT, to make sure i hadn't made a boo-boo ordering the LOPT. Set comes on with same symptoms. Well at least I've got the old, but now known to be good parts in (Exactly how much soldamop have I used recently??!! Shocked )

Does this mean there's more duff rectifier diodes in the flyback circuit? What are these symptoms typical of?

I measured the 200V output because it was easy to get at and it measures 179V .. low - indicating crappy diodes in other parts of the flyback PSU circuit? I suspect D605 or D606.
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absorbentgnome



Joined: 30 May 2005
Posts: 51
Location: Cardiff, UK

PostPosted: Thu Jun 09, 2005 12:08 pm    Post subject: Reply with quote

Right checked the rectifier diodes by substitution with known good ones, no difference.

Realised that once the TV was on for more that around 10 seconds, scanlines came up on the screen!!!!!!!! It looks like there is horizontal field collapse (as the size is wrong and all over the place), but the vertical 'size' is ok.

There must be some TV engineers out there that know why this is! The 200V supply is low at 179V, the other supplies including heater are ok.
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