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Grundig TV and DVD problems

 
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PostPosted: Tue Jun 03, 2008 8:10 am    Post subject: Grundig TV and DVD problems Reply with quote

Hi all!

I have two problems with Grundig products. A TV and a DVD.

1)Grundig CUC 7303 (20” CRT).
When I power it on the led starts blinking and I am hearing a tick-tick-tick from the loudspeaker. Nothing more. I took some measurements:
Main filter capacitor = 302 to 291 V.
UC3842 pin 7 = 11 to 14V.
I have replaced Chopper transistor, LOPTr (S2055), UC3843. I have also the service manual but I can’t understand what is going on. Any opinions?

2)DVD Grundig GDP-1100. When I power it on I am hearing tick-tick-tic. Not spinning disk, no display, nothing. It has the TNY268P in the power supply. I can’t find a service manual or a schematic.

I would be very grateful for any help or opinions.
Have a nice summer!
Manos
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Tue Jun 03, 2008 12:07 pm    Post subject: Reply with quote

In both cases, the fault is most likely a short somewhere on the secondary side of the power supply.
Check all output voltages for shorts. In the tv, a common cause for this kind of problem is a shorted line output transistor, possible as a consequence of other faults in the line output stage (flyback capacitors, bad solder joints, open circuit somewhere in the deflection coil circuit). Also, shorted rectifier diodes or filter capacitors in the power supply are common causes.

For the TNY268, check out its datasheet and application notes at www.powerint.com . Most power supplies using TNY chips use to adhere closely to the schematic examples.

If the UC3842 power supply has a small resistor in series with the emitter/source of the switching transistor, make sure that it has not changed value.

A good primer on general troubleshooting of switched mode power supplies can be found at http://focus.ti.com/lit/an/slva085/slva085.pdf
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PostPosted: Wed Jun 04, 2008 9:00 pm    Post subject: Reply with quote

1) TV
I think it’s the flyback transformer. I disconnected it then power the set on. The led is now flashing, no more tick tick tick, secondary voltages are there .I also hearing a bzzzzzgzzgzzg from the chopper transformer.
How can I be sure that the flyback (031.54B or HR6572) is faulty? Is it expensive?

2) DVD
I have checked the secondary parts and everything seems ok.
BTW the 1N5822+ a coil(mark as 100K, the plastic is half melted) + two 220μF for 3V3 and +5V, goes very hot!
Tick tick is still there….
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Thu Jun 05, 2008 7:33 am    Post subject: Reply with quote

1) Before blaming the flyback transformer, check the line output transistor and other components in the line output stage as i mentioned before. Grundig's flyback transformers generally seem to be very reliable, at least as compared to some other european manufacturers. A good way of checking a flyback transformer is to measure the inductance of the primary winding with an RCL meter and compare to another similar transformer. A clear sign of shorted turns is that the inductance is low and that you get very different inductance readings when measuring at various frequencies. Usually, it is good to test at 1 kHz and 10 kHz.

2) Does the DVD power supply work if you disconnect the loads on +3,3V and +5V ? Are you absolutely sure that the 1N5822 and the 220 uF capacitors are ok? In some cases - but seldom - a diode can have a high leakage current although it tests ok with a multimeter's diode test. Also, check the coil and make sure that it has no shorted turns. 100K probably means 10 uH.
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PostPosted: Thu Jun 05, 2008 4:58 pm    Post subject: Reply with quote

Hi torbjorn!

1) The line output transistor is new and ok also the line output stage.
Unfortunately I don’t have an RCL meter so im gonna buy it…
2) the DVD power supply does not work if i disconnect the loads on +3,3V and +5V.But when I disconnect only the 3.3v, the front panel start blinking. After 10 s, smoke come out from inside the laser! That’s it I burned it…..
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