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

Perfect video clip for the circumstances.

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

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 😊

Yes. Adjust L2 in the modulator slightly.

You will need a thin plastic knitting needle, filed down to a screwdriver point.

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

The PL series was one of the few models of HMV that were not directly coupled between the video amp & CRT cathode. Instead it uses DC restoration. check the OA81. make sure it is inoperative order. a Philips or Kriesler would out perform it . PS some HMVs have a counter weight in the bottom the set. UNsure its secure. If the tuner is mounted on the CRT holding band make its tight & secure,.If loose it can crack the CRT. Douglas