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Philips tv with no picture or disapearing picture or slow picture startup but good sound??

Hi all

I have a Philips 28ml8805 (FL1.6 or near) with a strange and hard to find problem. The unit is a slow starter which mean that it takes up to

20min to get picture while the sound is comming on after 5s. Sometimes the picture comes after 15s but goes away again after som sec and then it takes several minutes to reappear. The picture is real good (when on) and no mechanical respons from all circuitbords.

No problems with the 200v, 141v, 5v, 8v, 13v, 16.5v, the only voltage thats diff a little is 17.5v is 19.5v. I have changed the tda4680 in an atempt to se if it was the cause of the fault but no diff. I think i have checked all resistors around this circuit and found no fault in them, i have resoldered all components in the HOT area and some outside it also, no reaction on the fault.

I have seen some that have this problems also on the net but no answer to what it is. I suspect the CRT but thats no option to change, the odd thing is that the picture is WERY good on this unit when working so this would oppose the theori that it is the CRT that are the fault.

Is there some that have a clue to whats wrong with this unit?

Janne G

Reply to
Janne G
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ESR the filter caps around the Flyback and in SMPS or just replace them.

kip

Reply to
john

While I've never worked on a Philips TV, I do have some suggestions.

Check your voltages that go to the tube, i.e. G2, etc. See if the filments are lit up, see if the tube is getting what it needs to work in other words.

How does the pic come on, does it fade in or just pop on with full brightness and good color?

If you have the voltages, then you're going to need to trace the video/deflection path and see where it goes awry. I said deflection because you could also have vertical collapse, although many sets will turn off if they detect that problem.

Reply to
Matthew P. Cummings

How is the picture with a vcr connected by a scartcable.

If the picture is there right away, suspect the tunerpart. If so the tuner has possible some electrolytic capacitors inside which are leaking. Check the pcb traces for interrupts made by the leakage.

Greetings Peter

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Reply to
eddumweer

A few ideas:

I've seen this symptom on a cp110 chassis - had to replace the 22uF

250v caps in the high voltage line from the power supply - if you already have done, you might want to try doing it again to be sure, as you could have a duff cap.

Remove the neckboard from the tube and clean all the contacts there. In the past, philips had some bad sockets.

I assume you have resoldered the CRT heater leads on the mainboard and neckboard?

check: RGB blanking circuit and associated RGB cap?

Sorry can't be more precise with your model!

-B

Reply to
b

I had some sleepless nights over this but i find a way to get to the "kern"(bottom) of the problem with a plastic pin that insulated me from the high voltage of the CRT and "friends".

It was a "jumper" (SMD shortcut) that was loose near the horisontal powercircuit tda3654 or someting (the one thats get really hot) that had poor soldering. I did not see anything in the microscope when examine it but the measurement did say that it was a problem there. I've resoldered it and now the startuptime is down to around 2.5 min for a picture, and yes, it is much but i guess that the CRT have got some damage when testing this fault and now have a relativly large diff between the R G B cannons and therefore the 4680 think it isn't ready to turn on the video to the CRT before that time. The picture is WERY good when working so i just have to accept the long startup time because i can't find any more problems with the unit when examine it deeply.

If some have the same problem i can give the the exact componenet name if you whant, contact me by mail then, hopefully decipering of my mailadress would not be that difficult.

Anyone that have any moore sudgestions to the startuptime?

Thanks for all the sudgestions i have got on this problem.

Reply to
Janne G

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