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Old 16th Mar 2023, 4:43 pm   #1
ben
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Default PTC replacement in Telefunken 712

I am working on a Telefunken 712 TV whose PTC is shorted, it is a round ITT branded gold coloured type. I forgot to take a close up and don't have the set to hand, but found images online showing the same chassis using a TDK type 350Y 7060. I have in my spares box a similar TDK one coded 500Y 6001. Can't seem to find data for them, though.

There seems to be a 220ohm resistor between the two disc parts on the schematic (which I assume to be integrated in the PTC) but that value does not coincide with any I have in the catalogue (attached).

Thoughts?
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Old 16th Mar 2023, 5:21 pm   #2
ms660
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Default Re: PTC replacement in Telefunken 712

So far as I can make out it could be a 270 Ohm 9W resistor in that schematic snippet, it appears to have a different component ref. number than the PTC, ditto on the board layout in the manual.

Lawrence.

Last edited by ms660; 16th Mar 2023 at 5:44 pm. Reason: extra info
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Old 20th Mar 2023, 3:46 pm   #3
Marconi_MPT4
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Default Re: PTC replacement in Telefunken 712

So far have not been able to locate any data on TDK PTC's but I believe there were Mullard/Philips parts that might work such as type 98003. Attached data for both 98003 and 98009. Both have similar thermal and peak current characteristics.

It appears that later PTC configurations favoured the parallel-series type as it did not require an additional large external resistor having to handle up to 25W peak. Instead the mains input PTC section on 98009 warms up to ensure the coil PTC resistance reduces and maintains a low residual degauss coil current. Note different pin connections!!

Does your PTC have an external resistor fitted?

Rich
Attached Files
File Type: pdf Mullard Philips 98003 and 98009.pdf (154.8 KB, 32 views)
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Old 21st Mar 2023, 3:18 pm   #4
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Default Re: PTC replacement in Telefunken 712

Thanks for the data, Rich. From what I could see after revisiting the set the other day, the TV has a large external ceramic resistor (R403), I suppose the TFK one is therefore a 98003 series type.

I tried the other TDK one I had and it seemed to work, so fingers crossed.
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