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HMV PL chassis
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Return to top of page · Post #: 1 · Written at 8:40:48 PM on 22 December 2024.
	Ian Robertson Location: Belrose, NSW Member since 31 December 2015 Member #: 1844 Postcount: 2549
Is anyone here old enough to have worked on the HMV PL or PN chassis? This was one of the least reliable B&W TVs made by a major manufacturer. It was released in 1963 and has the dubious distinction of having the most service bulletins released for it. My collector friend Pete in Albury was asked to fix one of these. He was ignorant of its legendary status! Issues with the PL and PN were mainly due to the designer(s) not doing the sums on component parameters or running a worst case analysis. The situation with the vertical circuit (which meant that a 6GV8 rarely lasted longer than 3 months) was the most egregious. We replaced the vertical output transformer with one from a later model to fix this. I won't bore you with the entire restoration story, just an example of why it turned out to be so difficult. One of the faults was intermittent horizontal pulling. An 18k resistor in the video path to the sync separator sets the slicing level for the sync. When tested, it measured 20k so it was left in place. But that extra 10% turned out to be the cause of the intermittent bad sync! A 10% shift in a resistor should NOT break the circuit. But it did. The MSP horizontal output transformer failed after an hour's running. It was resurrected by a soak in Prepsol to dissolve the wax, which was replaced with polyester lacquer using several long soaks. This method was very successful, the transformer now runs barely warm. And here is the end result! https://youtu.be/6xMNPG1OtHE?si=NF4xiboy4-ObJXCJ

Return to top of page · Post #: 2 · Written at 10:37:27 PM on 22 December 2024.
	GTC Location: Sydney, NSW Member since 28 January 2011 Member #: 823 Postcount: 6834
Perfect video clip for the circumstances.

Return to top of page · Post #: 3 · Written at 8:22:22 AM on 23 December 2024.
	Johnny Location: Hobart, TAS Member since 31 July 2016 Member #: 1959 Postcount: 575
Yes Ian I worked on many of these. Cannot remember them as being anymore troublesome than a brand/model using 6Y9 and 6X9 's with a high attrition rate and burnt components. And the shop I worked for sold these, but would have been a few years old by the time I started. 1966. Maybe the service bulletins were adhered to. JJ

Return to top of page · Post #: 4 · Written at 12:27:53 AM on 29 December 2024.
	Pitchersj Location: Albury, NSW Member since 2 July 2017 Member #: 2134 Postcount: 181
Hi Ian This is my set and Pete has done a fantastic job with it. Just a question. I am using the modulator you built with it which is giving an excellent picture however I am getting distortion in the sound no matter how much I adjust the gain ? Is there a solution to this ? Regards Steve 😊

Return to top of page · Post #: 5 · Written at 7:56:21 AM on 29 December 2024.
	Ian Robertson Location: Belrose, NSW Member since 31 December 2015 Member #: 1844 Postcount: 2549
Yes. Adjust L2 in the modulator slightly. You will need a thin plastic knitting needle, filed down to a screwdriver point.

Return to top of page · Post #: 6 · Written at 4:39:27 PM on 29 December 2024.
	Pitchersj Location: Albury, NSW Member since 2 July 2017 Member #: 2134 Postcount: 181
Hi Ian Thank you Pete has shown me how to adjust the L2 So I have gently adjusted it. Strangely it was screwed right down I now have crystal clear sound and picture https://youtu.be/br68gG9L0jQ?si=sRbB6_Wvap4ZYadA

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