Fidelity HF45 has started buzzing

[harleyford]

Folks

I'm new to UK Vintage Radio. I am the owner of a Fidelity HF45 record player and am respectively seek advice from knowledgeable forum members...

I acquired the unit a few weeks back. It was a gift for teenage daughter fascinated with vinyl. Myself, I'm personally of the age where we used to throw these in the skip. I'm astounded they're now collectable. Anyway it was working faultlessly until recently when it started producing a continuous buzzing sound:

https://youtu.be/mPs9PZ6F-LA

Attached are images of the circuitry which seems simplistic. I can only presume there is a failure in one of the components; capacitor, rectifier, IC, but have no idea. Any help to diagnose would really be appreciated.

What I know is before it failed, my kids had left it switched on for a couple of weeks (they hadn't switched off at the plug and hadn't realised the volume control was a dual function power switch). I noticed it had been left on when I heard background hum. Perhaps this extended loading finally killed off an electronic component that hadn't been used in two decades.

If it's a simple matter of replacing a capacitor, or other, I have enough soldering skills, but don't know if diagnosis can be that straightforward that forum members can suggest a fix.


Any help greatly appreciated.

[Clydeuk]

It looks like the electrolytic on the right has been replaced in the past. I'm normally not one to just replace capacitors without some fault finding, but this is such a basic circuit that it would probably be beneficial to replace the other 2 electrolytics. The 1000uF may be the culprit (sorry I've not checked the youtube link as I can't put the volume on at the moment)

[Edward Huggins]

Yes, a good old 100Hz hum. Replace the big electrolytic caps and advise your Daughter as to these!

[crackle]

The volume sounds like it is very low, check to see if a wire has not come off the back of the pickup cartridge.

Mike

[Techman]

From the looks of the video the hum is regardless of volume control setting, so is unlikely to be anything to do with the cartridge or its connections, although it would be worth just visually checking these for soundness. The fault will be due to the failure of the large smoother as has already been said.

[harleyford]

Thanks people for fast response, brilliant, I'll let you know how I get on.

[Techman]

It's likely to be that large smoothing electrolytic capacitor. Make sure that you fit a replacement of the same type, ie, of a similar value in capacitance and of a working voltage the same or a little higher than the original. You must also make sure that this type of capacitor is connected the correct way round, ie, the same way as the original, if you get this wrong it will explode with an almighty bang!

[Michael Maurice]

It is probably worth replacing the rectifier (the blue rectangle at the left of the capacitor) as well but note that you must get all the connections correct.

[kevinaston1]

I agree that the capacitors are probably open circuit; but those old TBA800 output devices can also give the same symptoms .


Regards.


Kevin

[harleyford]

I've replaced the big 1000uF smoothing cap. No result, and then the old bridge rectifier with a W005M, no result. I'll work through the other three electrolytic caps and consider the SN76013ND IC.

It's a shame to be butchering the PCB with my poor soldering skills. I know these early 70's players were base-quality commodity consumer items, but its kind of time-locked. Some poor lady in a factory in north London was probably the last person to have put a soldering iron to it, working up to her tea break on a Friday afternoon, little knowing the whole UK electronics industry was just about to collapse.

I'll let you know how I get on.

[harleyford]

Okay cracked it...

It was the capacitor equivalent to C5 on the schematic for the R314 HF45 circuit from Radio Museum. Note, this record player, with the older IC (SN76013ND) has a slightly different circuit to that. Although it's a HF45 model, the PCB with this one actually has 'HF43 Mk II/I' marked on the back.

The 47uF 25VDC capacitor cost 40p from Maplins at lunchtime (although £23 spent on other junk by the time I walked out of the shop).

One thing is, the sound is significantly better that before, much louder. Presumably swapping out 40 year old components has helped!

Marked up image attached if it helps someone.

[unitaudio]

Another one snatched from the jaws of landfill! Does landfill have jaws? It does now. Nice one, good effort!

Regards,
Paul