It is currently Sun Nov 19, 2017 1:22 pm

Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
Posts: 719
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Murphy V849U

Post by PYE625 » Fri Sep 25, 2015 1:36 pm

Hi Frank,

Thanks once again for the advice....I will check that 10k anode load resistor and replace it.

 
Posts: 231
Joined: Wed Jan 23, 2013 11:40 pm
Location: Swansea, South Wales

Re: Murphy V849U

Post by Alastair E » Fri Sep 25, 2015 4:49 pm

R233 10K pentode amp anode-load, and R235 15K Triode C.F. cathode resistor both worth replacing--Along with the PCF80 valve. Failing/weak valve gives low contrast, which can imitate a weak CRT in this chassis......

 
Posts: 719
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Murphy V849U

Post by PYE625 » Wed Nov 18, 2015 9:18 pm

Hi,

With very grateful thanks to Chris aka The Teleman, I now have a LOPT screening cover and dropper resistor!!
:aad
Cover in place, just need to replace the dropper....
Attachments
rsz_001.jpg

 
Posts: 3781
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Murphy V849U

Post by Terrykc » Thu Nov 19, 2015 1:29 pm

I don't think this has been mentioned before in this thread but do make sure the thermistor mod has been carried out.

TV125_Mod.png

TV125_Thermistor_Mod.PNG
TV125_Thermistor_Mod.PNG (41.28 KiB) Viewed 2011 times

If the CZ19 breaks in half because the mod hasn't been done, I doubt you'll find a replacement anywhere!

 
Posts: 5926
Joined: Sat Jul 23, 2011 8:19 pm

Re: Murphy V849U

Post by CTV » Thu Nov 19, 2015 1:34 pm

Terrykc wrote:I don't think this has been mentioned before in this thread but do make sure the thermistor mod has been carried out.

Andrew already addressed this back on the 4th September viewtopic.php?f=5&t=11844#p123162

 
Posts: 719
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Murphy V849U

Post by PYE625 » Thu Nov 19, 2015 4:24 pm

It's a very worthwhile modification....stops the thermistor running like an electric fire !!

 
Posts: 3781
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Murphy V849U

Post by Terrykc » Thu Nov 19, 2015 5:28 pm

CrustyTV wrote:Andrew already addressed this back on the 4th September http://forum.radios-tv.co.uk/viewtopic. ... 44#p123162

Ah! I did scan the thread - twice, in fact - but missed the vital line!

PYE625 wrote:It's a very worthwhile modification....stops the thermistor running like an electric fire !!

I don't know anything about the thermistor running like an electric fire - the reason for the mod is that, for some unknown reason (to me, at least) the DC component flowing through it causes it to crack neatly in the middle.

When the DC component is removed, there are no further problems.

 
Posts: 430
Joined: Sat Aug 20, 2011 3:59 pm
Location: Ilkeston, Derbyshire

Re: Murphy V849U

Post by Colourstar » Mon Nov 30, 2015 10:05 am

Andrew's excellent results in solving his LOPT problem have led me to taking another look at a later Rank set I have with a similar issue; i.e. width closing in and the picture gradually ballooning after only a few minutes operation. It was stored in a garage for some years before it came to me. The set is a Murphy V2015D (A640 chassis) in a very scruffy cabinet but with a really strong crt. Nothing to lose, but everything to gain in other words.

The LOPT construction looks broadly similar to Andrew's set with the 'inner core' clearly evident. Unfortunately the only psu I have to hand is a redundant one for a laptop, which is rated at 19v 6.3a. I'm not sure that would be man enough for the job of softening the overwind to enable withdrawal.

If I can successfully get the core out, I wondered about using some plumber's rubber repair tape I have in the toolbox. It's the width of 'standard' electrical masking tape, but designed for repairs to split pipes. It's non sticky, but very stretchy and, as such, self-binding, gripping itself tightly to form a seal as you wind it around.

Steve
Attachments
SANY0622.jpg

 
Posts: 5926
Joined: Sat Jul 23, 2011 8:19 pm

Re: Murphy V849U

Post by CTV » Mon Nov 30, 2015 10:59 am

Colourstar wrote:I wondered about using some plumber's rubber repair tape I have in the toolbox. It's the width of 'standard' electrical masking tape, but designed for repairs to split pipes. It's non sticky, but very stretchy and, as such, self-binding, gripping itself tightly to form a seal as you wind it around.
Steve

Steve why "spoil the ship for a hapeth of tar".

Plumbers tape is not designed for high voltage/high temperature electrical insulation application. Kapton transformer insulation tape is hardly expensive either. After Andrews success I bought myself a reel just in case one day I have to do likewise on my TV125CU

Kapton Tape
http://www.ebay.co.uk/itm/33MX-5-10-20m ... bs2W6YfGvg

 
Posts: 430
Joined: Sat Aug 20, 2011 3:59 pm
Location: Ilkeston, Derbyshire

Re: Murphy V849U

Post by Colourstar » Mon Nov 30, 2015 11:06 am

Good point Chris. I'd never heard of Kapton tape before. I'll follow the link and invest in some.

Many thanks!
Steve

 
Posts: 3028
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Murphy V849U

Post by Katie Bush » Mon Nov 30, 2015 7:36 pm

Colourstar wrote:Good point Chris. I'd never heard of Kapton tape before. I'll follow the link and invest in some.

Many thanks!
Steve



Same here! :elc: :aak :aad

 
Posts: 5926
Joined: Sat Jul 23, 2011 8:19 pm

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by CTV » Tue Apr 12, 2016 9:33 pm

I've made Andrews thread a sticky as it contains the cure for the dreaded Bush LOPT fault. I've also amended the thread title to reflect the LOPT cure info contain within this Murphy repair thread.

What's even better is we now have a further evidence that his method is a working solution. David has followed Andrews advice and it appears to have also now cured his failing TV115 LOPT .

Well done Andrew on a superb solution.

 
Posts: 430
Joined: Sat Aug 20, 2011 3:59 pm
Location: Ilkeston, Derbyshire

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by Colourstar » Tue Apr 12, 2016 10:12 pm

That's great news about David's set. As far as my own ailing Murphy LOPT goes, I can muster 30v from a Farnell bench PSU but although this does make the overwind good and warm, it's some way off being hot enough to ease it apart. Andrew did his with 35v across it, so I'm just that little bit short of volts!

Steve

 
Posts: 719
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by PYE625 » Wed Apr 13, 2016 7:53 am

Colourstar wrote:That's great news about David's set. As far as my own ailing Murphy LOPT goes, I can muster 30v from a Farnell bench PSU but although this does make the overwind good and warm, it's some way off being hot enough to ease it apart. Andrew did his with 35v across it, so I'm just that little bit short of volts!

Steve


30 volts should do it Steve, may take a little longer, but you'll know when you can feel slight movement of the overwind. :qq1
PS, my Murphy LOPT is still holding out after all this time so I can confidently say it does cure the problem.

 
Posts: 430
Joined: Sat Aug 20, 2011 3:59 pm
Location: Ilkeston, Derbyshire

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by Colourstar » Wed Apr 13, 2016 8:05 pm

Thanks Andrew, that certainly gives me hope! I'll leave it on a long simmer and see if there's any movement.

Steve

 
Posts: 19
Joined: Fri Jun 22, 2012 9:40 pm
Location: London/Norwich

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by davidh1041 » Thu Apr 14, 2016 8:39 pm

Steve, i used my 30 volt bench supply to cook the overwind, i had removed it from the former. I left it for a couple of hours and it softened up enough to carefully extract the tuning coil. I then carefully removed any lumps of tar in and around the core. Then wrap as many turns of tape around the coil so that it fits nice and snugly back into the core of the overwind. Its well worth the trouble, my TV115 seemed ok to start with using the tripler, but the primary ran hot. Since replacing the overwind, both primary and overwind run luke warm, (i think some of the heat is radiation from the PL36) and the set now has a lot more available width.
Good luck. David

 
Posts: 430
Joined: Sat Aug 20, 2011 3:59 pm
Location: Ilkeston, Derbyshire

Re: Murphy V849U ( Includes the RBM LOPT Overwind Cure)

Post by Colourstar » Thu Apr 14, 2016 10:06 pm

Success! :bba

It was a bit of a battle but after 3+ hours at 30v and a fair bit of squeezing/manipulating the warm overwind to break it's grip, the inner coil came out. A plastic solder dispenser tube was exactly the same diameter as the coil former and I used that to push it out through the overwind. It is wrapped in fabric tape just as the other examples have been.

Just need to order some Kapton tape now, then we'll see how things progress.

I'll keep you posted.

Steve

Previous

Return to Television



Who is online

Users browsing this forum: No registered users and 4 guests