Ferguson Model 34574.

[Woody1963]

Hi just purchased a Ferguson music system type 34574. The on-off rotary switch produces loud crackle during rotation and the crackle continues when turned off for a short time. I’m Thinking this is a capacitor based problem but thought I would see if anyone has experience of this issue and Could provide some guidance.

Thanks Dave

[Michael Maurice]

I’ve had this switch fail completely, it will need to be replaced.

[Woody1963]

Hi All

After some help, looking over the board of a Ferguson 34574 I have spotted a blown capacitor but I’m not sure what type as the casing is damaged and also not sure where this sits in the circuitry. The volume/on-off switch has loads of crackle even for a period when switched off so wondered if this could be causing this.

Thanks Dave

[Station X]

Which capacitor has blown?

I suggest shorting out the contacts of the OFF/ON switch and checking how the player performs.

[Edward Huggins]

It sounds like you may have a combination of a capacitor discharging upon switch off and a dirty volume control potentiometer track. Spray cleaning with a contact cleaner may improve the latter.

[Woody1963]

Hi all the capacitor that has blown is visible in the photo at the top right of the metal cover that has the holes in, you can see the foils.

[Station X]

A close up picture may help, but in the absence of a circuit diagram, I don't think we're going to be able to determine the capacitor's value short of reverse engineering the player.

Perhaps someone has a similar player and they could check for you.

[Woody1963]

Hi Graham I have removed the blown capacitor but the uF rating is missing it is a 16v callins capacitor and has a diode connected to one side (the end without the grey band), would that be the positive or negative terminal of the capacitor? I do not have a schematic so not sure what capacitor to fit, can you help?

[Station X]

A diode suggests the detector circuit. Does the radio work?

[Woody1963]

Hi Graham, yes all working just had that crackle in the speakers when touching the on-off volume knob. There does not appear to be any polarity markings on the cap uploaded photo

[AC/HL]

As best as I can see from the photo, this is a record player only version of the Ferguson Studio 6 audio centre. The only 16v electrolytic I can see in the parts list is C68, 250 uf, decoder supply smoothing. Positive to ground.
All Callins black capacitors are replace on sight now.

PS replace with 220 uf 15V or higher.

[Woody1963]

Hi Bill, this system is the Ferguson Unit Audio and has a record player, radio and an input for a separate tap player. This cap is the only Black Callins one I can see so hopefully you are correct. As mentioned in a previous post it also has a diode connected to one side of the cap so does that match your data? Thanks Dave

[Station X]

Is this it?

https://www.radiomuseum.org/r/thorn_...ntre_3463.html

If you download the schematic you''ll see that C68 is indeed connected to a diode.

[AC/HL]

Yes, It's a zener diode, it's across the capacitor in fact. Thorn used a lot of these capacitors back then, any others may have already been changed.

[Woody1963]

Hi Graham superb yes that looks like the one, checked the board and located next to the R68 resistor. I have two caps to choose from 220uF or 450uF, Both 16v ones, should I go for the higher value?