philips: BD284U (BD 284 U); Philetta 284 de Luxe

Hi all.....This is a great little radio. AM and SW work fine, Nothing on FM. The schematic is a bit difficult to read. Can someone tell me where to start trouble shooting FM?  All tubes are good, and contacts cleaned. Thanks    AL

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Hello Alfred,

1. Did you test the FM IF stages with a 10.7 MHz signal generator ?
2. Is the local oscillator working when FM is selected ?

What kind of test equipments you may use ?

I go and print the schematic to have a closer look.

Kind regards.

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Alfred,

Please don't feel offend if I give you obvious recommendations as I am not accurately aware about your knowledge in “electronics” (although I have read you have restored 100’s old radios).

1. First of all, for your own safety, please (!) : use an insulation transformer as the mains is connected to the chassis...

2. For the following tests 3 and 4, depress the FM key to be on FM mode.

3. FM local oscillator/mixer (“right” ½ UCC85) : verify the anode voltage.
If you have an oscilloscope, you may easily verify if the oscillator oscillates...

If this stage is working, you have to go from the loudspeaker to the antenna to verify the full FM line (an alternative method is to verify first the IF 10.7 MHz stages, as you want...).

Let us go from the loudspeaker to the antenna !

4. FM AF switching
u25 – u26 must be opened,
u26 – u 27 must be closed.

Touch the R41/C75 commun point with a screwdriver (or better : connect to this point a AF generator through a 0.1 µF capacitor) : you must hear some hum (or the signal tone) in the loudspeaker.

That are the very first tests.

Please give me your feeling and test results if any.

Kind regards.
Jean-Pierre

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Thanks Jean.....I gave up on this one...but with you on board, I will re-open the case. I will get to it, and let you know my findings...AL

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Ok AL,

In order to try to give you the more suitable advices, what test equipments do you own ?

Jean-Pierre

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I have been getting by with digital Meter....for voltages and ohms. Thanks  AL

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Ok AL for your digital multimeter.
If we are lucky, it will be fine...

Don't forget for your safety to use a real insulation transformer between mains and your radio set...

Jean-Pierre

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Hi Jean.....OK I got the radio back on the bench. All I get is a low buz on fm ( am works great) its diffiult to find the points you suggested to check what pin on the ucc85 is the anode? u25 26 27 where can I find these points along with r41 c75. I see them on schematic, but difficult to locate inside radio..very tight cramped set.....thanks  AL

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Hi AL,

Thank you for your answer.
May I suggest you to print the schematic ?
Or far better : put it on your disk, then you may easily widen it to save your eyes !

what pin on the ucc85 is the anode? 
Look at this fantastic schematic now on your screen :-) : pin 6.
This is for the "right" triode, the FM/UKW local oscillator.
You'll see on the schematic that the high voltage is switched by u15 - u16 :
in FM, this switch is closed in order for the FM local oscillator... to oscillate,
in AM, this switch is opened to stop this oscillator.

Generally speaking, the switches "uxx" are "active" in FM/UKW mode : "u" stands for UKW.

As you are near this tube, you may also verify if the VHF amplifier is well powered.
This is the very first stage, the "left" part of the UCC85.
The anode is pin 1.
The high voltage is always present even in AM as this VHF amplifier is not interfering in AM...

If you have again a look on the schematic, there are the nominal values :
156 V for the oscillator anode,
144 V for the VHF preamplifier anode.

u25 26 27 where can I find these points ?
All the points as uxxx (and axx for AUS [ON/OFF], lxx for LW, kxx for KW, mxx for MW) are "keyboard" points.
All the points like u25, u26, u27 are indicated in the schematic :
- in the drawing of the theorical schematic,
- in the drawing of the physical keyboard contacts : see the bank of contacts drawn with
"AUS", "LW", "KW", "MW" and "UKW" keys (more or less in the middle of the sheet, just at the left of the mains input, when you look in "landscape" format).
Particular case : for UKW, both MW and UKW banks are to be considered.
The u25, u26, u27 are included in the right column of the MW bank.

Switch off your radio.
Remove the power cable from the mains.
Depress down the UKW key.
Verify with your ohmmeter :
u25 – u26 must be opened,
u26 – u 27 must be closed.

r41 c75 : it's the u26 point on the keyboard.
Power on your radio via an insulation transformer (for your safety...).
Depress down the UKW key.
Put the metallic tip of an insulated screwdriver on u26 (if necessary, connect a long insulated wire to the metallic part of this tool...).
You must hear some hum...

Good luck and take care...
Jean-Pierre

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Hello....Its very difficult to make out the pin # because of the cluster surrounding the ucc85. I am getting 95v on one and 112v on another? What is USA # for ucc85 I don't see it in my book. A wax cap marked 470pf ...is that .05mf?....A white tubular with purple on tip, marked 120k ..is that a 120k resistor? Thanks for patience...This is a lot different than the sets I have worked on.....AL

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Hi Alfred !

Yes, I do believe it's not obvious to make out the pin # because of the cluster surrounding the ucc85.

UCC85
To find info about UCC85 :
- on the top of the screen, click the green/yellow link "Tubes + Tr",
- then in the first great box "Search for a tube/valve", type UCC85 in the yellow rectangle
  and finally click the red "GO" button.
Normally, you must reach :  http://www.radiomuseum.org/tubes/tube_ucc85.html
The pin number configuration is drawn at the bottom left, seen from pins side as usual.
Be careful : on the right, it's also seen from pins side !
I don't know the US # but you'll see 4 "Identical to" on the top of the page.
You say : "I am getting 95v on one and 112v on another" but I don't know what anode for
95 V (112 V for the other anode, of course).
Could you give me the anode pin for each voltage ?

Wax cap marked 470 pF
Say 500 pF for instance.
500 pF = 0.500 nF = 0.5 nF = 0.000500 µF = 0.0005 µF.
You may also write 500 µµF...
What do you mean with "mF" : millifarad ou microfarad ?
In the old radios, "mF" (or worst : "MF") is not millifarad (or Mégafarad !!!) but... µF !
You say "wax". I think that it's a mica cap or something like that which should be replaced
(if necessary) by a same type (mica) and also the "exact" same value (here : 470 and not 500)
as this cap may be placed into a tuned circuit.
Then question : where is this capa placed ?
Very often, this type of cap is rather reliable for years, but who knows ?!

A white tubular with purple on tip, marked 120k ..is that a 120k resistor ?
Only 2 colors : white body and one purple tip ? Nothing else ? Nothing written on, except 120k ?
"Tubular" : a full tube or a hollow tube ?
Where in the radio ?
Could you take a photo ?

u26
What about a metallic tip of an insulated screwdriver on u26 (if necessary, connect a long insulated wire to the metallic part of this tool...) ?
Did you find u26 ?

No problem for "patience" : it's a hobby...
I do understand this is a lot different than the sets you have worked on.

Have a good sunday.
Jean-Pierre

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The 120k is hollow, and goes to ucc85. I cleared the 'tar'/ wax cap....With the 2 feet of snow, and Christmas at our heels..I have to close down shop till 2010! Speaking of which...Merry Christmas...and Happy New Year!  All the best   AL  ( hopefully we can re-open this investigation in the near future)

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Hi AL !

120k component
I think it may be C19 in // (VHF point of view) with S19 as the cap of a 10.7 MHz tuned circuit.
120 = 12 followed by a 0 !
i.e. value = 12 multiply by 10^0 = 12 x 1 = 12 pF.
The purple tip may indicate the tolerance or the temperature coefficient or the service voltage for this cap !
Are you sure there are no other colored rings on this component ?

Wax cap marked 470 pF
Why did you remove ("clear" ?) the 'tar'/ wax cap ?
Did you remove the wax from the cap or did you remove the cap from the circuit ? (!)

Snow...
That's wonderful for Christmas, but 2 feet is a little bit high and leading to a lot of troubles in New York, I suppose...
Here, near Paris, there is only 1 inch of snow but some ice on the roads where I'm living.

Have also a Merry Christmas and a Happy New Year, for you and your family !
So long in 2010...

Jean-Pierre

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