Ekco TMB272. Patterning on picture. - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 1st Jun 2019, 12:59 pm

Been repairing an Ekco TMB272 mains-battery TV set.
One of the faults encountered was patterning on the picture. The fault was solved by replacing the screen grid decoupling capacitors in the sound IF amplifier. Strangely, the sound was OK with the faulty capacitors.

Last year I experienced a similar fault in a Murphy V410A.

https://www.vintage-radio.net/forum/...y+V410A&page=2

DFWB.

Peter.N. · 1st Jun 2019, 1:42 pm

Its very easy to be mislead, well done. I remember an early Murphy TV that if the focus control had reached the end of its travel - you replaced the sound output valve! Focus coil in series with the HT feed.

Peter

Jac · 1st Jun 2019, 2:28 pm

Excellent repair David.

These faults can be very misleading (at least for me).

Jac

FERNSEH · 1st Jun 2019, 5:13 pm

Peter.N wrote: "Its very easy to be mislead, well done. I remember an early Murphy TV that if the focus control had reached the end of its travel - you replaced the sound output valve! Focus coil in series with the HT feed."
The Murphy V180 is like that.

Hello Jac,
One could have easily been mislead into thinking the patterning fault was in the vision IF amplifiers and in fact the 6F1 valve screen grid decoupling capacitors also required replacement. The offending 0.003mfd capacitors were those brown ones made by Hunts.

DFWB.

Jac · 1st Jun 2019, 5:42 pm

Thanks David,

What did you use as replacement decoupling capacitors?
Someday I have to restore my TMB272 and TX275.

Jac

Tazman1966 · 1st Jun 2019, 7:47 pm

What a bright and pin sharp picture! Excellent CRT in that and nice linearity too.

FERNSEH · 1st Jun 2019, 11:11 pm

Jac wrote: "What did you use as replacement decoupling capacitors?
Someday I have to restore my TMB272 and TX275."
Hello Jac,
I've sent you a PM.

DFWB.

Malcolm G6ANZ · 4th Jun 2019, 7:54 pm

I rarely comment on TV's as my knowledge is minimal. A question though, did the wavey lines change with the sound? It looks like the photo was taken with a test tone would the lines be different with speech or music.

Malcolm

Restoration73 · 5th Jun 2019, 9:25 am

I'm doing two of these here. I've noted that it is important the 3.5MHz trap is set
correctly - manual says short trimmer C40 (V3 anode) and adjust L33 (V10 cathode)
for minimum dot pattern. Audio tone for sound modulation. Trimmer C67 will also
have some some effect.

1st Jun 2019, 12:59 pm	#1
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Ekco TMB272. Patterning on picture. Been repairing an Ekco TMB272 mains-battery TV set. One of the faults encountered was patterning on the picture. The fault was solved by replacing the screen grid decoupling capacitors in the sound IF amplifier. Strangely, the sound was OK with the faulty capacitors. Last year I experienced a similar fault in a Murphy V410A. https://www.vintage-radio.net/forum/...y+V410A&page=2 DFWB. Attached Thumbnails

1st Jun 2019, 1:42 pm	#2
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Ekco TMB272. Patterning on picture. Its very easy to be mislead, well done. I remember an early Murphy TV that if the focus control had reached the end of its travel - you replaced the sound output valve! Focus coil in series with the HT feed. Peter

1st Jun 2019, 2:28 pm	#3
Jac Heptode Join Date: Jun 2006 Location: Eindhoven, Netherlands. Posts: 642	Re: Ekco TMB272. Patterning on picture. Excellent repair David. These faults can be very misleading (at least for me). Jac

1st Jun 2019, 5:13 pm	#4
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco TMB272. Patterning on picture. Peter.N wrote: "Its very easy to be mislead, well done. I remember an early Murphy TV that if the focus control had reached the end of its travel - you replaced the sound output valve! Focus coil in series with the HT feed." The Murphy V180 is like that. Hello Jac, One could have easily been mislead into thinking the patterning fault was in the vision IF amplifiers and in fact the 6F1 valve screen grid decoupling capacitors also required replacement. The offending 0.003mfd capacitors were those brown ones made by Hunts. DFWB.

1st Jun 2019, 5:42 pm	#5
Jac Heptode Join Date: Jun 2006 Location: Eindhoven, Netherlands. Posts: 642	Re: Ekco TMB272. Patterning on picture. Thanks David, What did you use as replacement decoupling capacitors? Someday I have to restore my TMB272 and TX275. Jac

1st Jun 2019, 7:47 pm	#6
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: Ekco TMB272. Patterning on picture. What a bright and pin sharp picture! Excellent CRT in that and nice linearity too. __________________ All the very best, Tas

1st Jun 2019, 11:11 pm	#7
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ekco TMB272. Patterning on picture. Jac wrote: "What did you use as replacement decoupling capacitors? Someday I have to restore my TMB272 and TX275." Hello Jac, I've sent you a PM. DFWB.

4th Jun 2019, 7:54 pm	#8
Malcolm G6ANZ Octode Join Date: Feb 2006 Location: Bristol, UK. Posts: 1,042	Re: Ekco TMB272. Patterning on picture. I rarely comment on TV's as my knowledge is minimal. A question though, did the wavey lines change with the sound? It looks like the photo was taken with a test tone would the lines be different with speech or music. Malcolm

5th Jun 2019, 9:25 am	#9
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Ekco TMB272. Patterning on picture. I'm doing two of these here. I've noted that it is important the 3.5MHz trap is set correctly - manual says short trimmer C40 (V3 anode) and adjust L33 (V10 cathode) for minimum dot pattern. Audio tone for sound modulation. Trimmer C67 will also have some some effect.