Marconiphone 4616

Looks like a Thorn 950 to me, I recognise the little fly-wheel sync unit with the EF80 on top.

Hi Chris
That was very quick!
just had a look at the service data for the 950 a it looks like your spot on

Thanks
Frank

Thorn 950 MkII chassis. What a stunning set, very similar in style to the 19" HMV 2635 I worked on last year.

viewtopic.php?f=5&t=5145

Look forward to hearing how you get on with it.

Cheers,
Brian

Hi Brian
I had a read or your thread, it is a interesting read.

I just powered it up slowly with a variac, there is a picture of the results below. It looks promising.

Frank

Promising indeed! The system switch will probably be found to have ceased up so exercise care when applying full mains and changing standards. Usually lubrication and moving the sliders by hand, (set unplugged from the mains of course), a few times frees the mechanism.
Nice to know another example of this chassis has survived.

I spotted an error on re-reading my HMV 2635 thread. R50 is 1M5, not 680K. Apologies for that.

Look forward to hearing more.
Cheers,
Brian

I spotted an error on re-reading my HMV 2635 thread. R50 is 1M5, not 680K. Apologies for that.

Please disregard this- R50, the PFL200 sync separator section grid leak resistor is indeed 1M5 in the Thorn 950 and 960 chassis, it's 680K in the Thorn 950 MkII chassis which of course applies to your Marconiphone 4616.

Brian

Hi Brian
Thanks for the heads-up on the system switch. This is the first dual standard that I have seen since my childhood so not familiar Territory for me.
I will have a play with it as time permits.

Frank

Progress so far.
After changing a few components in the Frame timebase I have what appears to be both frame and line fold over.
There is ample height, I just have it reduced as the picture needs to be shifted up.
The picture below was taken in a mirror.

Frank

Spent some time on this set earlier today lack or width was down to R133 being over double its value. The 625 contrast control had no effect due to R145 being open, and eventually found that C43 0.1uF on the grid of the sync separator was the cause of the field and line fold over.
It had gone leaky measuring 2meg on the 250V range of a megger.
I found some out of tolerance resistors and dodgy cap's along the way which were changed.

I have to center the picture yet and the focus control needs looking at as it has no effect, but that's for another day.

Frank

Great work so far. C43 is certainly troublesome in these sets, interesting how the fault symptoms were different between your set and the HMV 2635. The lack of focus control is probably due to the R125 (820K) at the earthy end of the pot.

Cheers,
Brian

Good work indeed and a real lucky find

Thanks Taz

Brian you were right R125 was open.

The voltage on the wiper now varies between 200V and 700V aprox.
This voltage is reaching the focus pin on the tube base but I can see no change on the screen when varied from min to max, though the focus is pretty good as it is.

The width could not be adjusted to fill the screen. R133 and R130 were gone high in value and were changed.
It now fills the screen but just about, the width control is at one end.

Frank

Hi Trevor
Thanks for that tip, will check it out first chance I get.

Frank

R131 (1M8) may also be in need of replacement. It's looking really good now. Well done.

Further to my previous comments re R50 I see it was changed from 1M5 to 680K to reduce the effects of cogging on 405-lines. R47 was also changed from 5K6 to 10K.

Cheers,
Brian

Trevor
I checked out the width sleeve, the adjustment lever on was broken so I took off the scan coils and moved the sleeve by about 5mm towards the base and it has helped a little. the nylon screw of the clamp on the scan coils was seized a good squirt of silicone oil freed it up.

Brian
I totally overlooked R131, I checked it today and it is OK. It was changed before in the very distant past.

I tried it today on 405 and it is working pretty well the picture is allot wider.
It sounds good too on 405, even though I was only listening to the test tone. The sound on 625 is poor to say the least.

Frank

Trevor
I checked out the width sleeve, the adjustment lever on was broken so I took off the scan coils and moved the sleeve by about 5mm towards the base and it has helped a little. the nylon screw of the clamp on the scan coils was seized a good squirt of silicone oil freed it up.

Brian
I totally overlooked R131, I checked it today and it is OK. It was changed before in the very distant past.

I tried it today on 405 and it is working pretty well the picture is allot wider.
It sounds good too on 405, even though I was only listening to the test tone. The sound on 625 is poor to say the least.

Frank

In what way poor? Quite? Off-tune? Vision on sound?

Hi Aidan
The sound quite and distorted with some vision on sound.
I didn't get a chance to get back to it yet, when I do C69 in the ratio detector will be one of the first things I will check.

Frank