Something strange happens in this Philips TV
 

Hi,

I'm having a strange problem I've never had before in any vintage TV I have restored.

A friend of mine found a Philips TV identical to the one I posted some photos on this forum, but I found the LOPT overwind damaged in the last layer, as someone poked with the screwdriver on the winding and damaged it. I fixed it removing about 10 turns from the overwind that were damaged and I got the continuity again (430 Ohms).

I fitted a new EY51 and I have the following problem: with all the right voltages at the CRT, it shows a very dim raster you could only see in a dark room and with the brightness and contrast controls turned fully up.


The EY51 is lit and I could draw a 1,5cm spark (but I have to put the screwdriver at about 6-7 mm to start the arc)from its plate. The ion trap is correctly adjusted, as to obtain maximum light and the CRT tests as new (over the full scale of my B&K465, that is 1000 and the cutoff voltage test is right). When you crank the brightness fully up, the image blooms in the vertical direction..

The boost voltage is in the range of 560-600V, as my own TV (mine has boost voltage going up to 640-650V with a blank screen) and the PL81's control grid is at -17V (about as mine), the line whistle is barely audible when you are near the EHT cage. You do hear the sound of the CRT charging, so I think there is at least some EHT...

Could it be that the LOPT is not resonating? The spacers for the gap are still present

What else could cause this problem? If it could be of any help, I could post the schematic

Best Regards

Giulio Maiocco

LOPT? Is that the flyback?

Hi,

Yep, that is the "small bastard" :yes: :D

Thanks

Giulio Maiocco

I would not expect 10 turns to make a huge difference. Perhaps there is damage (a short?) that you cannot see. Did you have to remove any insulation that was not replaced? Can you post a picture of the transformer?

Hi,

If it could be of any interest, I could post a photo I took after the fix to the transformer, I haven't any taken before the "surgery"... I am quite convinced that the fault is the EHT winding, as I measured today the resistance again and the "guilty" one measures 416 Ohm, the good one mounted in my TV measures 425-426 Ohms, I couldn't believe that 10 or 20 turns could make a 9-10 ohm of difference....

Today I also discovered that one of the power rectifier, a PY82, exploded... There is no short in the B+ path...

This model of TV was also sold in Brazil, so, if a very kind soul has a good flyback transformer for this TV, it would be very appreciated! The tubes used in the horizontal section are: ECL80 (hor. oscillator), PL81 (Hor output), PY81 (Damper) and EY51 (EHT rectifier)

Many thanks

Giulio Maiocco

Hi,

did you measure the high voltage at the anode connector of the crt with a hv probe? Does the high voltage has it's correct value? What happens if you turn on or off the brightness control? Does the high voltage change values?

I don't believe that the LOPT is faulty.

Kind regards,
Eckhard

Hi Eckhard,

At the moment I don't have an EHT probe, so I don't know how much EHT I have... I think it could be very low, as I don't need to discharge the CRT when I have to remove the EHT cup, you don't hear the tipical sound of the CRT charging.

You could only see a very dim raster on the screen if you turn almost fully up the brightness and contrast control, otherwise the screen is completely blank... When you crank the brightness and/or the contrast fully up, you notice a blooming in the vertical direction.

I have the width control set to the minimum and the screen is completely filled in the horizontal direction....This tells me that the EHT is quite low, on mine I must keep the width control at the maximum to have the raster fill completely the screen...

Best regards

Giulio Maiocco

In these cases I have taken the high voltage from another well-operating set to test the crt.