Murphy V114 Saga - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Heatercathodeshort · 7th Dec 2020, 3:09 pm

I'm not sure how relevant these Murphy notes are to the transformer you fitted but they may explain the odd display. John.

em536716 · 12th Dec 2020, 4:29 am

Quote:

Originally Posted by Heatercathodeshort

First the good news. The Mazda CRM92 looks to be in excellent condition.

What a strange effect! The raster[?] appears to be correct on the extreme left side. The first thing I would check is the frequency of the line oscillator T41 Thyratron generator.
Is the replacement LOPT from a V114? Check scan coil and the timebase panel for incorrect connections.

Replace C58 .25uf, C59 .02uf also C53 8uf, C55 .001uf, C56 .005uf, C60.02uf and C67 25uf if you have not already done so. This will eliminate all the trouble spots. The coupling capacitor C54 is probably a silver mica and should be OK. John.

Hi John, and thanks for the reply. All the timebase oscillator capacitors have been changed. I’ve had to use variations of the original capacitances, such as .22s instead of .25s, and .01s instead of .02s, however I haven’t ever seen this as an issue before, surly they are all in tolerance anyway.

All the resistors have been checked and any high ones have been changed. I’ll have a look at the document you’ve provided for trouble shouting and try and see if this solves any issues I have.

The height pot is faulty however this will be addressed as soon as I can find a suitable replacement.

Regards
Ed

em536716 · 12th Dec 2020, 4:30 am

Quote:

Originally Posted by Heatercathodeshort

I'm not sure how relevant these Murphy notes are to the transformer you fitted but they may explain the odd display. John.

To add as well, yes the output transformer is from the spares chassis

em536716 · 12th Dec 2020, 4:50 am

As I haven’t got an original line output transformer here to measure the D.C. resistance of the primary, I am unable to compare it to the new one fitted (the original was O/C), however this one does measure around 140 ohms which may suggest these modifications need to be made. I will use it as a troubleshooting guide.

I’ll sort out the height pot first, then get on with this to see if any improvements can be made.

Heatercathodeshort · 12th Dec 2020, 11:17 pm

A .01uf in place of .02uf Not good in timebase circuits. Better to fit the correct values. .22uf is correct for .25uf, .47uf for .5uf etc but a .01uf should be used for a .01uf and a .022uf for a .02uf.

Problem is you end up with a chassis full of incorrect components creating obscure faults and frustration. Better to start with a clean plate. Hope you get it sorted. John.

murphyv310 · 13th Dec 2020, 3:40 pm

Just parallel two 0.01 caps together in the meantime which gives 0.02uf.

em536716 · 14th Dec 2020, 4:15 pm

Thanks for the advice guys, you learn something new everyday - funny enough I know about value substitution, but yes, it’s always best to have correct values in timebase circuits, they are the most sensitive to change - especially in my experience the Frame timebase, lower frequencies and all...

I’ve sourced the web and found a supplier for .02 values and similar which I’ll purchase. This could be a man made fault...

Also regarding those height and amplitude reopots, I removed each of them to test from the circuit, and the fixing of the chassis, I tested them weeks ago and they appeared fine apart from flaky contacts, but now I can see they are pretty much shorted To earth. A little frustrated as this could be the cause of the excessive foldover.

But some positives at least. I cleaned the frame hold control, and put in a 180 ohm resistor to substitute the height control, to my surprise, I could see what looks like test card C!

Does anyone know of any replacement wire wound 500ohm and 200ohm pots I could purchase?

You do really learn a lot with each step of a restoration, don’t you!

em536716 · 2nd Jan 2021, 12:07 pm

Happy new year everyone!

Just a few updates with the Murphy.

So, I have now reconditioned all wirewound controls, including the correct contrast control, I’m able to get test card C to appear quite well, however the tube doesn’t appear to be THAT bright. There’s slight line fold over. I’ll follow the modifications given to me by John to see if this improves things.

Will try and post photos soon!

After this I’ll be taking a short break from the Murphy, to make way for new projects. I’m also a full time university student, so since studies are starting up again, I may need to move my focus onto assignments

Thanks for the advice everyone.

7th Dec 2020, 3:09 pm	#21
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Murphy V114 Saga I'm not sure how relevant these Murphy notes are to the transformer you fitted but they may explain the odd display. John. Attached Thumbnails

12th Dec 2020, 4:50 am	#24
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Murphy V114 Saga As I haven’t got an original line output transformer here to measure the D.C. resistance of the primary, I am unable to compare it to the new one fitted (the original was O/C), however this one does measure around 140 ohms which may suggest these modifications need to be made. I will use it as a troubleshooting guide. I’ll sort out the height pot first, then get on with this to see if any improvements can be made.

12th Dec 2020, 11:17 pm	#25
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Murphy V114 Saga A .01uf in place of .02uf Not good in timebase circuits. Better to fit the correct values. .22uf is correct for .25uf, .47uf for .5uf etc but a .01uf should be used for a .01uf and a .022uf for a .02uf. Problem is you end up with a chassis full of incorrect components creating obscure faults and frustration. Better to start with a clean plate. Hope you get it sorted. John.

13th Dec 2020, 3:40 pm	#26
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Murphy V114 Saga Just parallel two 0.01 caps together in the meantime which gives 0.02uf. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

14th Dec 2020, 4:15 pm	#27
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Murphy V114 Saga Thanks for the advice guys, you learn something new everyday - funny enough I know about value substitution, but yes, it’s always best to have correct values in timebase circuits, they are the most sensitive to change - especially in my experience the Frame timebase, lower frequencies and all... I’ve sourced the web and found a supplier for .02 values and similar which I’ll purchase. This could be a man made fault... Also regarding those height and amplitude reopots, I removed each of them to test from the circuit, and the fixing of the chassis, I tested them weeks ago and they appeared fine apart from flaky contacts, but now I can see they are pretty much shorted To earth. A little frustrated as this could be the cause of the excessive foldover. But some positives at least. I cleaned the frame hold control, and put in a 180 ohm resistor to substitute the height control, to my surprise, I could see what looks like test card C! Does anyone know of any replacement wire wound 500ohm and 200ohm pots I could purchase? You do really learn a lot with each step of a restoration, don’t you!

2nd Jan 2021, 12:07 pm	#28
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	Re: Murphy V114 Saga Happy new year everyone! Just a few updates with the Murphy. So, I have now reconditioned all wirewound controls, including the correct contrast control, I’m able to get test card C to appear quite well, however the tube doesn’t appear to be THAT bright. There’s slight line fold over. I’ll follow the modifications given to me by John to see if this improves things. Will try and post photos soon! After this I’ll be taking a short break from the Murphy, to make way for new projects. I’m also a full time university student, so since studies are starting up again, I may need to move my focus onto assignments Thanks for the advice everyone.