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 Help needed for newbie with Philips RF780 RadioGram Repair
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 Return to top of page · Post #: 1 · Written at 10:44:21 AM on 21 September 2020.
Stockjg's Gravatar
 Location: Brisbane, QLD
 Member since 21 September 2020
 Member #: 2441
 Postcount: 5

Hi Guys/Gals,

I am just embarking on the repair of this old Philips radiogram that I picked up a few years ago. I have a basic understanding of electronics which has allowed me to keep my old Juke box and Pinball going (both electro-mechanical) but this is my first foray into 70's electronics with an intimidating amount of wires, resistors, caps, switches etc. I think I need some help.

1. Can anyone tell me where I can find a schematic/manual for this item
2. This selector switch (off/Gram/radio) appears to be damaged. Please see photo. The contacts nearest the knob seem to work OK but I'm not sure if turning it is supposed to close any switches at the other end where the live feed enters. Could this be the problem? If so can you advise on where to source replacements.

The radiogram powered up when I first plugged it in, the turntable worked but the sound from the needle was very quiet. The radio produced static and little more. All switches turned. Unfortunately after about 5 minutes there was a loud noise and the house circuit breaker tripped - I assume something burned/shorted out.

After some investigation online I made a 'current limiting device' to hopefully prevent this happening again. I again plugged in the radiogram and it made noise (static??) but then tripped the circuit again, weird because the light didn't come in on the limiter. I have tested the limiter by creating an intentional short and it lights up OK.

I have given myself a crash course on electronic components determined to work through this repair but I must admit to feeling a little daunted at the moment as I can't run power through it to see where the fault is. I have read that one solution is to diagnose using a lower voltage AC source. I can't seem to find an obviously burnt out component. I'd love to fix this.

Cheers John

Philips RF780 Radiogram
Philips RF780 Radiogram
Philips RF780 Radiogram
Philips RF780 Radiogram


 
 Return to top of page · Post #: 2 · Written at 11:03:21 AM on 21 September 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1987

I'd say you have an earth leakage. This could be anywhere in the mains side circuit, e.g. turntable mains switch, main unit switch, power cable. Only sure way to find it is by isolating things. Try unplugging the turntable mains connection first, since this is easier.

Do NOT disconnect the safety earth!

Low volume on records is probably due to the cartridge (the bit that holds the "needle"). By now this usually needs to be replaced. Does your unit have a BSR turntable or one of those plastic Philips ones?

Is this it here?

https://www.radiomuseum.org/r/philips_02rf780.html

Entry lists the turntable as a Philips GC035 but the one in the picture looks more like a BSR. I can recall seeing both used when these were new and under warranty. I hope yours has the BSR.


 
 Return to top of page · Post #: 3 · Written at 7:00:47 PM on 21 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 918

Good Luck John!

The radiomuseum page on the RF780 has a "schematic" you can download directly.

What Ian said, disconnect each item hooked to the mains and test for a line/neutral to ground leakage.
Like in a crappy power switch in the radio or changer.

Good Luck again!

Fred.


 
 Return to top of page · Post #: 4 · Written at 9:46:52 PM on 21 September 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6545

Photos uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 5 · Written at 11:06:55 PM on 21 September 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6148

The radiomuseum page on the RF780 has a "schematic" you can download directly.

Are we talking about the same page? I see a photo, but no schematic:

https://www.radiomuseum.org/r/philips_02rf780.html


 
 Return to top of page · Post #: 6 · Written at 7:08:00 AM on 22 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 918

Yep, click on the link in Ian's post.
That brings up the radiomuseum page.
Scroll down and 2 PDFs are available to click on in the text.
One of them is "flight deck" schematic.
Fred.


 
 Return to top of page · Post #: 7 · Written at 7:10:02 AM on 22 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 918

Oh, and those power switch modules can arc over internally with about 1 poofdeenth clearance between A, N and E!!!
Piece of crap.
Open it up and behold.
Fred.


 
 Return to top of page · Post #: 8 · Written at 9:36:06 AM on 22 September 2020.
Stockjg's Gravatar
 Location: Brisbane, QLD
 Member since 21 September 2020
 Member #: 2441
 Postcount: 5

Well as you suggested Fred the power switch module interior does look a tad unwell. I'm not sure it's salvageable and I'm not sure what it's supposed to look like anyway.
Are replacements easy to get?
I've submitted a photo of it.
John

Philips RF780 Radiogram


 
 Return to top of page · Post #: 9 · Written at 5:11:36 PM on 22 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 918

Hi, I have grafted a different type of switch wafer onto the spindle and made sure the insulation of the mounting was to my standard.
Used insulated pillars and an insulated spindle section to hold and turn the switch wafer.
Also only switched the active lead so kept neutral and earth right out of the switch area.
Fred.


 
 Return to top of page · Post #: 10 · Written at 5:15:21 PM on 22 September 2020.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6148

Well that's a first. Have never seen them attached like that. Makes them much easier to download. It's a wonder that the guy who rules over RM allows it.


 
 Return to top of page · Post #: 11 · Written at 8:31:48 PM on 22 September 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6545

Photo uploaded to Post 8.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 12 · Written at 9:01:47 PM on 22 September 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1987

Those switches are made of unobtainium. They were never safe, even when new IMHO.
The other switch contacts are not mains safe.
I suggest you bypass it, switch the unit on at the wall switch instead.


 
 Return to top of page · Post #: 13 · Written at 11:12:22 PM on 22 September 2020.
Stockjg's Gravatar
 Location: Brisbane, QLD
 Member since 21 September 2020
 Member #: 2441
 Postcount: 5

Thanks for the suggestions. I'm considering my options and will probably just bypass the switch and either turn it on at the wall or install a seperate on/off switch on the back. It would encourage me not to leave it turned on unattended anyway.
Would you suggest that I source some form of low voltage AC source to test it out so as not to damage anything else as I check the rest of it.
John


 
 Return to top of page · Post #: 14 · Written at 7:01:54 AM on 23 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 918

John for the moment just join the wires together (safely) and use an external switch to turn it on and off for testing.
Of course follow the normal safety practice, UNPLUG the set when handling or moving on the bench!

For a similar blow up and how I fixed it look in the "special projects" section scroll down the list and find "my STC Capeheart blew up".
Check out the para on fixing the blown up switch figs 4 to 6.

You may be able to do something similar or fit a non standard power switch somewhere in the cabinet (safely of course) or on the chassis or run the set from a switched power block/wall socket?

Fred.


 
 Return to top of page · Post #: 15 · Written at 10:49:51 AM on 24 September 2020.
Stockjg's Gravatar
 Location: Brisbane, QLD
 Member since 21 September 2020
 Member #: 2441
 Postcount: 5

Interesting story Fred. I think I'll probably end up with a seperate power switch on the cabinet (discretely), those old switches don't inspire much confidence.
Things are proceeding slowly as I am deciphering the schematic
One thing that is puzzling me is that the bulb didn't light on my home made isolator before the short on the Radiogram triggered the ELCB. I had previously tested it with a deliberate short and it worked ok.
Is it worth getting some kind of isolated power supply to protect everything in future?
Cheers John


 
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