Mystery TV (Philips 485U) - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

AidanLunn · 18th Oct 2013, 7:45 am

I am very shortly going to be undertaking this TV (at last!)

I have worked out how to remove the chassis by pure luck. Unscrew the base, then speaker and then bezel, and reverse the chassis out.

Let's hope I can get it done in time for the 50th anniversary of Doctor Who on November 23rd! :P

AidanLunn · 20th Oct 2013, 12:20 pm

Well, I've worked out how to remove the chassis - one thing that I didn't notice was the knobs even have their own screws to release them! :O

There are many rusting panels, including valve holders, and the coating of the sound output transformer is peeling/crumbling, so pretty normal fare for a TV set this age.

There is healthy heater continuity (showing 003 on my meter), the tone of my multimeter was music to my ears when I was dreading the worst.

Cheers for any help offered

AidanLunn · 13th Apr 2014, 10:33 am

Update: The chassis is now out. After all the usual switch-on scares, I found that the TV intermittently kept on melting the secondary mains dropper (the anode bias pair for the PZ30). The valve heaters would only light up when said heater wasn't doing an impression of a bright orange light bulb! I think this is down to C3, which was intermittently either s/c or o/c. It's certainly crumbling in any case. It seems this capacitor was only o/c when the set was powered through a 100W lamp limiter first. If full mains was applied from cold without the lamp switched in, C3 would go s/c and melt the secondary dropper. Obviously, it shouldn't do this, provided the fuse is the correct rating, so I will be checking both fuses are the correct rating after any faults in the PSU are cleared up, just so the higher fuse value can tell me more about what's going on. A blowing fuse couldn't tell me much and the nature of the fault would mean the lamp limiter would be useless in this case.

On a related note, in a moment of stupidity, I did damage the top section of the primary mains dropper (R2), otherwise both droppers are working OK. I did effect my own repair for this.

Thread available at http://www.forum.radios-tv.co.uk/vie...=3716&start=25

(linked to the page where things began to get interesting)

18th Oct 2013, 7:45 am	#21
AidanLunn Heptode Join Date: Jan 2010 Location: Killamarsh, Sheffield, South Yorkshire, UK. Posts: 746	Re: Mystery TV I am very shortly going to be undertaking this TV (at last!) I have worked out how to remove the chassis by pure luck. Unscrew the base, then speaker and then bezel, and reverse the chassis out. Let's hope I can get it done in time for the 50th anniversary of Doctor Who on November 23rd! :P

20th Oct 2013, 12:20 pm	#22
AidanLunn Heptode Join Date: Jan 2010 Location: Killamarsh, Sheffield, South Yorkshire, UK. Posts: 746	Re: Mystery TV (Philips 485U) Well, I've worked out how to remove the chassis - one thing that I didn't notice was the knobs even have their own screws to release them! :O There are many rusting panels, including valve holders, and the coating of the sound output transformer is peeling/crumbling, so pretty normal fare for a TV set this age. There is healthy heater continuity (showing 003 on my meter), the tone of my multimeter was music to my ears when I was dreading the worst. Cheers for any help offered Last edited by AidanLunn; 20th Oct 2013 at 12:49 pm.

13th Apr 2014, 10:33 am	#23
AidanLunn Heptode Join Date: Jan 2010 Location: Killamarsh, Sheffield, South Yorkshire, UK. Posts: 746	Re: Mystery TV (Philips 485U) Update: The chassis is now out. After all the usual switch-on scares, I found that the TV intermittently kept on melting the secondary mains dropper (the anode bias pair for the PZ30). The valve heaters would only light up when said heater wasn't doing an impression of a bright orange light bulb! I think this is down to C3, which was intermittently either s/c or o/c. It's certainly crumbling in any case. It seems this capacitor was only o/c when the set was powered through a 100W lamp limiter first. If full mains was applied from cold without the lamp switched in, C3 would go s/c and melt the secondary dropper. Obviously, it shouldn't do this, provided the fuse is the correct rating, so I will be checking both fuses are the correct rating after any faults in the PSU are cleared up, just so the higher fuse value can tell me more about what's going on. A blowing fuse couldn't tell me much and the nature of the fault would mean the lamp limiter would be useless in this case. On a related note, in a moment of stupidity, I did damage the top section of the primary mains dropper (R2), otherwise both droppers are working OK. I did effect my own repair for this. Thread available at http://www.forum.radios-tv.co.uk/vie...=3716&start=25 (linked to the page where things began to get interesting)