Fidelity HF45 Tone Control Not Working

[Daggerfan]

Hi there

I have recently acquired a Fidelity HF45 and have a problem in that the tone control on the front panel does not seem to be working. The volume control is working fine but when I turn the tone control fully clockwise and then fully anti-clockwise there is no difference in the sound. Does anybody have any idea what maybe wrong?

Thanks Daggerfan

[Daggerfan]

Dear all
If anybody could help me with this issue I would really appreciate it. I have attached pictures of the circuit board to help. I’m not sure if I should replace the Tone Control Potentiometer or if another component is faulty and needs to be replaced.
Regards Daggerfan

['LIVEWIRE?']

The tone control pot. is, IMHO, unlikely to be faulty. Check first for things such as dry solder joints or cracked printed tracks where the control is soldered to the PCB. Another possibility is that the associated capacitor is either faulty or D.S. joints are present around it.

[leslie5555]

Cleaning the pot by Spraying Servisol inside the pot though the gap where the connections are and then turning it back and forth it may get it working.

[stevehertz]

Originally Posted by 'LIVEWIRE?'

The tone control pot. is, IMHO, unlikely to be faulty.

Well, you just never know, in this day and age where mechanical parts are often badly constructed (mentioning no country names), it could be that the wiper and track are not making contact or some other electromechanical problem (eg poor crimping/riveting of the connection tag to the track end) in the pot itself. I agree, not so common a fault, but it could be the case. If nothing else is found, I'd remove the pot, remove its back and take a look inside, checking connections with an ohmmeter as I go.

[Daggerfan]

Dear all

Many thanks for your replies I will try these suggestions and let you know how I get on.

Regards Daggerfan

[slidertogrid]

These pots are notorious for not working, the wiper corrodes and goes black or green on the contact ends . You can test it with a meter or just try shorting the wiper connection (centre pin) to each end connection in turn. One end should change the tone if the circuit is otherwise working.
The pot is easily dismantled the end contacts will usually clean up OK. I put a tiny smear of silicone grease on the contacts before re assembly.

Rich.

[defender]

Looks same as I have and slidertogrid is spot on, I had the same problem.

[Stylo N M]

I've had the same problem in the very same record player, the connecton at the centre spindle in the pot failed. Although mine looked a bit as if it had been twisted about by someone.

I set about replacing it with a new pot, as the connection was split internaly beyond repair. I used very thin insulated wire, to take the connections from the tone control to the board, very time consuming and fiddley.

The 10nF 10,000pF 0.01uF bass capacitor is a C280 type, colour coded Brown, Black, Orange then a further black band indicating 20% tolerence, or if it's a white band 10% tolerence. Anyway as it's only a top cut trebble control this isn't anything to worry about. Neather is the last band wich you might not even beable to see, wich is red and indicates the voltage that the capacitor is capable of handling. In the case of this capacitor it's 200 volts, but don't worry there's little to vertually no voltages that you need to worry about at this stage in the circuit.

The capacitor is unlikely to be faulty, but they do tend to split a little with fine cracks apearing down the sides, so maybe worth just checking whilst you have it all in bits.

Keep safe and keep your fingers away from the back of the on/off switch, and volume control, if your intending to plug the unit in with the front cover down. And do not attempt to do any soldering or work on the circuit board, unless the unit is unpluged, and completely dissconected from the mains.

Paul

[Daggerfan]

Dear all

It was an easy fix after all, I sprayed the pot with contact cleaner and it started working. The only problem I have with it now is that there seems to be some play in the spindle the knob is attached to if it’s moved upwards slightly the sound goes tinny. I’m guessing this means that the pot is wearing out and needs to be changed. My thanks to everyone for their help.

Regards Daggerfan

[ekjdm14]

Sounds like it could be on it's way out yes. a replacement shouldn't be too gadawful hard to fit if you're careful not to lift any tracks off the board, you'd be looking for a 50k Logarithmic pot (as opposed to Linear type).

[Daggerfan]

Dan
Many thanks for that last piece of advice.
Regards Daggerfan

[plaka78]

The only real cure for this type of pot is to take it apart and fully clean the contacts as they suffer a green type of corrosion, then slightly retension the all wiper contacts, I have had 100% success by doing this and they work like new with no hint of a crackle.