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Old 17th Mar 2017, 1:50 am   #121
karesz*
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Default Re: Philips PM5544 Faulty

Hi Stan,
HTML Code:
The only position this modification will not work... as the lamp is fed with 6.3V ac.
Sorry, I do`t agree; why dont we apply an rectifier diode to solute it please?
Best regards- Karl

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Old 17th Mar 2017, 4:53 pm   #122
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Default Re: Philips PM5544 Faulty

Hello Karl
If an E5 LES 6V 40-50mA lamp can be found and fitted it keeps things simple. I agree a 1/8W 330R resistor and a small diode, for example a 1N4148 could be fitted into the base of the original lamp and a small LED soldered to the resistor and diode and glued to hold everything together. This replacement could be used on all the units without any internal modifications and without the need to worry about anyone fitting any lamp or replacement LED in the wrong place and causing all sorts or power supply problems. Sometimes it is better to keep things simple.
Regards Stan.
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Old 18th Mar 2017, 12:00 am   #123
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Default Re: Philips PM5544 Faulty

Hello Stan,
"Sometimes it is better to keep things simple."_I agree...
A simple way should be; spar lamps from model train supplier, but I can see (15mA) AC-LED-lamps only for AC/DC 12-22V, possibly it has enough light on 6V too?
Regards Karl
PS; I found just an 6V,50mA E5,5 source for -€21,70/pocket -for 100 pcs., or 10 pcs 6V (current unknowed) for €19,82...

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Old 18th Mar 2017, 11:54 am   #124
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Default Re: Philips PM5544 Faulty

Hello Karl
I think either of your suggestions would be suitable, I am sure the LED would give enough light output at 6 volts and the 6V 50mA E5 lamp is the correct replacement. I will also know who to ask for a few spares should I ever need any.
Regards Stan.
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Old 18th Mar 2017, 1:07 pm   #125
Alistair D
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Default Re: Philips PM5544 Faulty

Bipolar LEDs for AC operation are now available at reasonable prices.

https://www.rapidonline.com/kingbrig...olar-led-29359

Only a current limiting resistor would be required.

Al
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Old 5th May 2017, 10:26 am   #126
skysat2
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Default Re: Philips PM5544 Faulty

I have now installed a similar formfactor of the Bulb, with the same Voltage and mA. It works fine.

I installed the Unit in a 19''-Rack with Temperature Sensor connected to two Fans at the Top inside of the Rack


Regards SkySat
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Old 5th May 2017, 11:43 am   #127
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Default Re: Philips PM5544 Faulty

PM5544 on Flatscreen
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Old 5th May 2017, 8:41 pm   #128
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Default Re: Philips PM5544 Faulty

Hello Skysat2
I am pleased to see your PM5544 up and running and displaying a colour picture. I think your characters are set to produce dots and this can be adjusted by means of links on the Teletext board (AB CD and DE), see diagram. The dot width can be adjusted by R6 on the current gate board from 0.2 to 0.5 micro seconds.
Please see the attached picture of a BBC PM5544 Test card and note the difference in the width of the text characters. There are also six frequency gratings and the 250 kHz blocks at white and mid grey.
Regards Stan.
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Old 6th May 2017, 3:09 pm   #129
skysat2
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Default Re: Philips PM5544 Faulty

Hi Stan.
Thank you. What do you for modifications for the special multiburst on your Testcard?

Regards skysat
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Old 8th May 2017, 11:20 am   #130
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Default Re: Philips PM5544 Faulty

Hello Skysat2
There are modifications to several PCB’s and wiring changes to the back plane wiring, I would not recommend doing it. I have only modified one unit and it took me weeks to sort it out and get it working correctly. I have attached some photos of some of the modifications to the boards, which included adding TTL chips, dual transistors and different value weighting resistors and wiring changes to the back plane wiring.
Regards Stan.
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