NZ Murphy 23" TV Set

[Billy T]

I can't speak authoritively for Australian sets, but New Zealand and Australia do share a common set of standards for power generation, distribution and usage.

All our Philips CTVs: K9, K9II, KT2, KT3 etc used input bridge rectifiers, and even our Thorn TX574's (3500) were fitted with a mains transformer. No CTVs used half-wave rectification and the objective, presumably, was to keep DC off the mains and that in turn would have been to minimise damage to water mains etc.

Cheers

Billy

[AndrewM]

You're correct Billy about the reason for having full wave rectifiers - the authorities disliked the effects the half wave rectifiers were having on the grid. In Australia a few early imported colour sets used half wave rectifiers and many were issued modification kits to convert them to full wave rectifiers (early Blaupunkt models for example).

[GLENZ32]

Hi all here is an update on this one, some slow but steady progress has been made. The set now produces a full and bright picture, a rather big improvement on how it looked when I got first got a raster.

I've changed a handful of components in the line output section, the low value electrolytics and resistors were way past it, so no wonder I had a hard time getting reasonable EHT and width initially.

Treated the vertical to some new bits too which helped a lot but still have an issue with the top linearity, the control is hard at one end, no doubt there will be a resistor/cap thats gone wonky in there or the control itself has gone high, will come back to that later. There is still more work to do.

So that's it for now, some pictures of progress so far....

Cheers
Glen

[Billy T]

Ahh jeepers Glen!

All those neatly wound connections for replacement components!! I'm ashamed to say that I have never gone that far on any repair, but it sure does look nice.

It is great to see a picture up on the old girl again, and that CRT looks pretty good for its age too.

Cheers

Billy

[GLENZ32]

Hi Billy, thanks I thought I'd try doing this method for something different, in a way its actually quicker as you don't disturb the tag strip ends especially when there are multiple component legs and wires going into one hole, but then its the winding of the small lengths of solid wire then holding your mouth right as you carefully solder in the new component so either way its probably just as time consuming!

I did see this sort component installation in some old bit of Philips test equipment can't recall what it was but thats what gave me the idea to try. It does look neat and I'll be doing it again in various areas of the chassis.

Hope to have another go at the innards again this week.

Cheers

Glen

[daro]

Originally Posted by AndrewM

You're correct Billy about the reason for having full wave rectifiers - the authorities disliked the effects the half wave rectifiers were having on the grid. In Australia a few early imported colour sets used half wave rectifiers and many were issued modification kits to convert them to full wave rectifiers (early Blaupunkt models for example).

Ah! the old Blaupunkt KC chassis with half wave rectified phase controlled thyistor regulated power supplies & if you ran them on an mains isolation transformer they would soon get very hot because of the DC flowing back & causing the core to saturate & that was also a nightmare with the electricity supply authorities as they could damage pole transformers.

[GLENZ32]

Hi guys, this set is finally done! All cleaned up cabinet wise, fully re-capped and almost all the resistors too. The resistors that were in this were off and some of them had even drifted oddly enough to the next preferred value, which made me wonder if they were incorrectly marked while being manufactured...who knows? But at least they're out of there and won't cause any further problems.

The restoration took longer than expected, I just kept plugging away at it slowly so rather relieved that its come to an end.

But... I did have a couple of problems along the way...The first was intermittent hum bars that would come and go at will, at the time I thought it was just some of the old caps that were still in place, but after replacing all them and the rectifier diodes the hum bars were still there.

Scoping the B+ rails one of them clearly showed this 'blip' of noise moving along in time with the hum bar on the screen.

My next thought turned to the valves, thinking that maybe one of them had an internal short possibly due to the filament supply leaking AC across internally to somewhere it shouldn't be. As it turned out I found 'several' of them with multiple shorts the 6EB8 video output valve being the worst!
Once I replaced the cook valves and powered on again, the hum bars had vanished!

The next problem was towards the end of wrapping this up, I went through all the adjustments including the horizontal oscillator. Got that all done, had the picture all centered and locked nicely, powered the set on the next night from cold and found the sync to be way off.

After about 30 seconds the sync locked in again but the picture was way off to one side and I could see it slowly creeping back into line, after about 5 minutes it was normal again.

My thoughts about this turned to one of two things, faulty mica caps in the circuit as there were a couple and there was one in series with the hold control and the grid of the 6CG7 or the valve itself.

I changed that mica cap as it was well below its value of 330pf, this didn't really improve things so popped in another 6CG7 and problem solved!
So much for the original valve testing OK! I think in future I'll have some good know substitute ones handy for future niggly things like this.

So now its all back together and running very well, despite the CRT being on the weak side it still gives a very nice picture.

This is the first time I have overhauled one of these particular AWA/Murphy 34/35 series and have to say the contrast and definition is really good. I guess a good circuit design plays a part in this as well. If the picture tube was good the results would stunning I bet.
I've got two more variants of this to do so looking forward to getting to those eventually. They're both consoles

The End!

Some final pictures below and thanks for following this restoration. I've also done a video restoration series on you tube for those that can't sleep at night http://www.youtube.com/watch?v=8CThn6yz8fE

Cheers, all the best for the festive season.

Glen.

[Jonster]

Nice to see it finished. What's happened to the CRT face, is the bonded glass delaminating or is it a trick of the camera?

[GLENZ32]

Hi, thanks for the comment. Yes its the bonded glass delaminating away from the CRT, not much I can do about it really. When the set is running you don't notice it unless you look hard!

Cheers Glen.

Originally Posted by Jonster

Nice to see it finished. What's happened to the CRT face, is the bonded glass delaminating or is it a trick of the camera?