Fixable???


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Fixable???

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Wiz
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Jan 31, 2006, 8:51 PM

Post #1 of 11 (1749 views)
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Fixable???	Can't Post

I have aquired a Grundig MW 82-2700 DPL/FT CUC2058. However, the TV will not turn on. It goes into stantdy, and when one of the prog buttons on the front is pushed there is a feint clicking sound from the rear of the main circuit board which is accompanied by a feint popping from the speakers. During this time the standby light dims slightly, but never turns green. After 2 or 3 seconds, the popping stops. There is 158 volts on the collector of the HOT when in standby, which varys when the popping occurs.

Any help much apprieciated

Oliver

techchris
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Jan 31, 2006, 9:08 PM

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Re: [Wiz] Fixable??? [In reply to]	Can't Post

check for short circuits across the lt diodes feeding off the power supply tx.also check no short circuit on vert scan ic and feed diode from fb tx

Wiz
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Feb 1, 2006, 1:54 AM

Post #3 of 11 (1736 views)
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Re: [techchris] Fixable??? [In reply to]	Can't Post

Thnks, I will try those tomorrow, if I have time. Do you happen to know the numbers of these diodes on the board - I don't have a schematic for this set yet.

techchris
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Feb 1, 2006, 6:55 PM

Post #4 of 11 (1724 views)
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Re: [Wiz] Fixable??? [In reply to]	Can't Post

sorry i have no circuit. the diodes all feed off the secondary of the smps tx. should be easy to see.some grundig tv's are vestel chassis and a favourite on these is corrupted nvm which prevents start up (assuming you have no short circuits anywhere), i would try the eeprom anyway if all else fails

Wiz
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Feb 2, 2006, 12:04 AM

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Re: [techchris] Fixable??? [In reply to]	Can't Post

I have narrowed down the clicking to the SMPS transformer (this where microphone showed the loudest sound). Does this back up the shorted diode theory? (not had a chance to test yet) and I presume that the problem is in the LT side of the transformer. However, there is 150v on the a+ line etc, and the flyback seems to be running, although the heaters and EHT not coming up.

Another observation is that the tv does seem to have been dropped, this may well have been after the tv was dumped, or could it be the cause of the problems?

rrobor
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Feb 2, 2006, 10:59 AM

Post #6 of 11 (1710 views)
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Re: [Wiz] Fixable??? [In reply to]	Can't Post

Cripes how can anyone tell. Your fault is in the high voltage stages not the supply. You hear the supply tick because it resorts to protect mode not that it has a clock going bad in there. If i were betting on it, it was dumped due to needing a transformer which proved to be costly, sorry my guess is you saved someone the bother of taking that to the tip.

Wiz
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Feb 2, 2006, 8:46 PM

Post #7 of 11 (1702 views)
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Re: [rrobor] Fixable??? [In reply to]	Can't Post

I have checked the circuit with an oscilloscope, and came to the conclusion that when the button is pushed, a sawtooth waveform is apparent on the base of the HOT (one click = one wave) but this stops once the clicking stops. To me this implies that the components that make the waveform are working correctly.

Techchris, You mentioned the feed diode from the flyback transformer, Is this the green module with a diode symbol on it that the EHT lead goes through?
This diode goes between the EHT lead and the chassis earth. this diode reads 600k ohms each way round. I removed the EHT lead to this module from the flyback and this made the flyback keep going. Is there any simple fix/bodge to make this work, or do I need to buy a new module?

(This post was edited by Wiz on Feb 2, 2006, 8:58 PM)

techchris
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Feb 2, 2006, 10:06 PM

Post #8 of 11 (1699 views)
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Re: [Wiz] Fixable??? [In reply to]	Can't Post

it def. sounds like its in protection mode.check for 5volts on the micro and check for short circuits on the vert scan lt feed(the diode i referred to off the flyback tx) it feeds about 26 volts to the scan ic. a short on any lt line will shut the set down. if you have 150 volts on the hot collector.unsolder emitter connection and check for base/emitter short circuit. failing that return it to the dump. it could be a hairline crack

Wiz
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Feb 4, 2006, 2:21 AM

Post #9 of 11 (1682 views)
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Re: [techchris] Fixable??? [In reply to]	Can't Post

Im now pritty much sure the problem is in the HV tripler. What is the use for this component , and where can I get a new one from?

Thanks

techchris
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Feb 4, 2006, 2:17 PM

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Re: [Wiz] Fixable??? [In reply to]	Can't Post

i have no idea. i dont know where you are but in the UK grundig went out of business a long time ago. the tv's you see now are only badged with the grundig name but are usually chinese or turkish origin generic chassis. the part you refer to supplies high voltage (30k) to the crt

Wiz
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Feb 8, 2006, 11:46 PM

Post #11 of 11 (1649 views)
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Re: [techchris] Fixable??? [In reply to]	Can't Post

Fixed!!!

I replaced the tripler and now working perfectly.

Thanks for all your help

Oliver

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