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Old 5th May 2020, 5:54 pm   #1
mancunian69
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Default Philips B5X44A stereo

Hi all,
I have the above mentioned Philips set that works in stereo but the stereo light does not come on. I suspect it is the driver PCB that sits on top of the decoder.
Does any member have one lying around that you could donate to me or buy it a low cost.

I think the problem is the trimmer pot, which was very loose and I'm not sure it was making good contact.
I tried to repalce it with a new 10k item. Those blue things with one brass screw on top that seemingly just keep turning with no stop.
Unfortunately, that did not work and I ended up damaging the board in the process.

The decoder is fine.

Michael.
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Old 5th May 2020, 6:58 pm   #2
orbanp1
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Default Re: Philips B5X44A stereo

Hi Micheal,

That is certainly a nice radio!
That circuit sitting on top of the decoder must be the stereo light driver circuit, it is transistorized bi-stabil multivibrator.
elektrotanya has the manual with the schematics in it:
https://elektrotanya.com/philips_b5x.../download.html

The nice thing with such an old radio is that the circuits are not miniaturized, it is easy to work on them. That driver board surely can be fixed!
If anything it would be C301 that 2.5uF electrolytic capacitor that would be suspect.
If you have an ESR-meter do check out the cap, otherwise just replace it.
(That is probably true for the other low voltage electrolytic caps in the transistorized circuits!)
If the decoder is working fine, tune to a strong stereo station, and adjust R302 that 10k trim-pot that the stereo light would be on.

Regards, Peter
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Old 5th May 2020, 8:59 pm   #3
ekjdm14
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Default Re: Philips B5X44A stereo

If you've personally given up hope of repairing the PCB, perhaps you'd post it to me & let me take a look? I'll attempt to repair the damage & replace any components found out of spec or faulty & post it back for the price of any parts I might have to purchase (as opposed to what I already have in stock new/used). I must be a masochist, but I like repairing damaged PCB's haha!
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Old 6th May 2020, 2:56 am   #4
mancunian69
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Default Re: Philips B5X44A stereo

Hi, That's finw with me.
Please PM me your details.
Michael
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Old 6th May 2020, 3:01 pm   #5
Yendornerraw
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Default Re: Philips B5X44A stereo

Greetings from Ireland,
Michael, -I had this exact same problem with a Aristona 5213A which is a clone of your Philips model, using the same decoder and separate bulb driver board.
Apart from the bulb blown, ( be careful it's rated as a 50mA part), on measuring the incoming 38KHz signal from the decoder, the level was around 6 volts peak to peak. On feeding a separate signal from a wave generator, I found that it needed at least around 7V to make the stereo bulb glow. I eventually got around this by replacing the 10k pot on the small pcb with a 20K one and Bingo it now works beautifully. In the meantime I had built a new pcb complete, as I thought the fault was in this area as the print was looking dodgy, but in the end didn't need to use this, -- so if you want a new pcb (complete except for the pot) P.M me and I'll send it to you gratis.

Cheers,
Rodney Warren
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Old 7th May 2020, 12:06 am   #6
ekjdm14
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Default Re: Philips B5X44A stereo

Interesting note on the required signal level to the driver, If/when I get the driver board working I'll look into the level required to switch it on.

I'd have to wonder though, was the signal level for switching-:

A) higher on your board because of component degradation on the driver board requiring higher signal level?

Or B) lower from the MPX decoder unit due to component degradation in that side of the circuit?


Either way, it must have worked when new so something other than the 10k pot is causing either reduced drive from the decoder or lower sensitivity in the driver. I'll bear this in mind when testing and see what level is required on the Philips board.
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Old 8th May 2020, 6:18 am   #7
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Default Re: Philips B5X44A stereo

Quote:
Originally Posted by Yendornerraw View Post
on measuring the incoming 38KHz signal from the decoder, the level was around 6 volts peak to peak. On feeding a separate signal from a wave generator, I found that it needed at least around 7V to make the stereo bulb glow.
Cheers,
Rodney Warren
I would say there's a really good chance that the low signal level is due to reduced amplification in the previous stages.
De-coupling capacitors C204 & C207 are prime suspects and if they indeed are the culprits you should consider replacing all electrolytic cap's in the stereodecoder.
Time takes it's toll.
I've recently come across a NOS Philips stereodecoder that had just been stored and never used. It's a bit newer than the one in this radio but not much (belongs in a fully transistorized set 22RH786, late 60'ies). I intended to use it in another radio but had to do repairs before it worked. Among other problems one blue Philips electrolytic cap' had completely given up. Your decoder being even older there's a good chance that the two mentioned cap's have developed problems as well.

rgds,

/Torben
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Old 8th May 2020, 12:49 pm   #8
mancunian69
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Default Re: Philips B5X44A stereo

Hi, Thanks for info Tri comp.

While I have the lamp driver sent away for repair I will take a look inside the decoder and replace any electrolytic that I see fit.
Michael.
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Old 8th May 2020, 1:31 pm   #9
ekjdm14
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Default Re: Philips B5X44A stereo

Torben, that pretty much confirms my thoughts. The set must have worked properly when new so chances are, Rodney's set at least, there's lower gain prior to the lamp driver.

Michael, if you have a 'scope perhaps you could check the level of this drive signal from your decoder & see what sort of P-P voltage yours is putting out?
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Old 8th May 2020, 4:13 pm   #10
mancunian69
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Default Re: Philips B5X44A stereo

I have replaced all lthe electrolytics in the decoder today. Yes, I have an OWON digital scope but am not sure where to probe it or what to look for.
It may be better if I drop off the whole chassis to you
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Old 8th May 2020, 6:09 pm   #11
ekjdm14
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Default Re: Philips B5X44A stereo

Possibly, if there's still problems after I've had a go at the lamp driver boards then you'd be welcome to do so as you're not a million miles away but I'm hopeful that the decoder itself will be functioning properly & (touch wood) the driver board may just work when it's repaired.

Will have a look over the service manual when I get a minute and try to let you know where to 'scope and what to look for on it.
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Old 8th May 2020, 6:59 pm   #12
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Default Re: Philips B5X44A stereo

file:///C:/Users/User/Documents/philips_b5x44a.pdf
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Old 8th May 2020, 9:22 pm   #13
ekjdm14
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Default Re: Philips B5X44A stereo

I've got a copy of the service manual from elektrotanya, thanks. I learned a little Dutch when working on my Philips 'scope as the only manual I could find for that was in Dutch too! I wonder, has/will an English version for this set be added to the VRSD database any time? It's not present, on my 2019 disc at least.
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Old 1st Jun 2020, 6:24 pm   #14
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Default Philips stereo indicator board.

Just attaching a photo of the repaired traces on this board, for Mancunian69 (Michael) since can't work out how to attach it in PM.

Good quality copper. Even as thin as the lifted trace was (probably <25 thou wide!) I only had one fracture to bridge, after untwisting and manipulating it back into place, and even that was not from fatigue but due to it snagging on the hard skin on my thumb after securing the end!
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