Goodmans HiFi Casseiver 4000 - huge hum - UK Vintage Radio Repair and Restoration Discussion Forum

michaelevwalker · 22nd Jan 2017, 8:35 pm

We've just salvaged this from my sister-in-law's loft as part of an effort to equip my son with a starter hifi system on little to no budget.

The unit works in the sense that everything lights up, the tuner picks up radio stations on all wavebands, the cassette player plays and the phono input appears to work. However, there are very high levels of what I assume is mains hum on all inputs. It's worst on phono (you can only just make out the signal from the record deck in amongst the hum), very bad on cassette (unlistenable, though the music at least comes through clearly) and least bad on FM radio - with a strong station, it seems to cease altogether.

There's also a dynamic element to it: every time we switch input there's a brief momentary increase in the level of hum, even with the volume turned way down. Switching the Dolby NR on the cassette section on or off produces this effect too, regardless of which input is selected.

There's also some rushing/crackling and some very low frequency output at switch on (you can see the bass speakers move in and out at around 1 or 2 Hz for a cycle or two) but this settles down in two or three seconds. The volume, balance and tone controls all crackle quite a lot when adjusted but we know how to fix that.

Apart from that, we're pretty much novices at this sort of thing. We can identify components on a circuit board and have successfully made simple repairs / alterations to guitar amps and effects pedals. We're hoping that this is something we might be able to tackle ourselves and would welcome any help. The unit dates from 1978 or thereabouts; it seems very solidly made and it would bring pleasure to several people if we could restore it to its original capability.

Thanks in advance for any suggestions,

Michael and James

paulsherwin · 22nd Jan 2017, 8:47 pm

It's likely that the power supply electrolytic capacitors have had it. These will have a value of 1,000uF or more and probably be located near the mains transformer. Note that these are polarised, and any replacements must be fitted the correct way round.

poppydog · 22nd Jan 2017, 9:06 pm

That looks remarkably like the Ferguson stereo casseiver that I have languishing in an upstairs wardrobe that has probably not seen the light of day for 20 years (maybe not so many bells and whistles on the Ferguson). I take it they came out of the same stable?

Regards
Poppydog

michaelevwalker · 24th Jan 2017, 12:48 pm

Thanks Paul.

We have identified two 2200uF capacitors in the location you suggest (and noting else with a value that large) with ratings of 80V and 50V. Should we replace both?

Grubhead · 24th Jan 2017, 1:05 pm

Quote:

Originally Posted by michaelevwalker

Should we replace both?

I would after all that time.

michaelevwalker · 29th Jan 2017, 5:54 pm

We replaced both the 2200uF capacitors and nothing has changed at all. Any other suggestions, please?

On testing last night, the meter/tuner dial lights did flicker a fair bit after power-up (and some audio 'grumbling' / throat clearing through the speakers) so could it be a transformer/power supply issue?

paulsherwin · 29th Jan 2017, 6:55 pm

Does the hum vary with the volume control?

Assuming it doesn't, one of the diodes in the power supply may have failed. It's unlikely to be a transformer fault.

Double check that you have fitted the new electrolytics the right way round. Old electrolytics often have their positive connection marked; most current ones have the negative marked.

michaelevwalker · 30th Jan 2017, 12:25 am

The hum does vary with the volume control, though there is some even when it's turned to minimum.
We thought we had the capacitors the right way round but haven't kept the old ones (taken to school for controlled explosion in physics class...). There's a capacitor symbol printed on the top face of the circuit board under each, presumably showing the correct orientation. One of the parallel bars is thin and the other is thick. We assumed the thick bar was the positive and the thin one negative but I can't find any circuit diagram symbols that look quite like this to compare against.

AC/HL · 30th Jan 2017, 1:19 am

British equipment used to identify the positive with a red mark or a +, but now the norm is to to highlight the negative, so the broad marking on the component is probably that. The PCB may have both marked, but not obviously so.

Grubhead · 30th Jan 2017, 1:54 am

As the hum varies with the volume it's not the power supply. I assume the hum is in both channels, so unless you have two identical failures in both channels, we are looking for something that feeds the main amp, but covers both channels. I wonder if there is a voltage regulator circuit on the main power amp board? Look for something on it's own, that doesn't have a twin. Say a transistor or IC. It could have another capacitor connected to it.

22nd Jan 2017, 8:35 pm	#1
michaelevwalker Retired Dormant Member Join Date: Jan 2017 Location: Tunbridge Wells, Kent, UK. Posts: 4	Goodmans HiFi Casseiver 4000 - huge hum We've just salvaged this from my sister-in-law's loft as part of an effort to equip my son with a starter hifi system on little to no budget. The unit works in the sense that everything lights up, the tuner picks up radio stations on all wavebands, the cassette player plays and the phono input appears to work. However, there are very high levels of what I assume is mains hum on all inputs. It's worst on phono (you can only just make out the signal from the record deck in amongst the hum), very bad on cassette (unlistenable, though the music at least comes through clearly) and least bad on FM radio - with a strong station, it seems to cease altogether. There's also a dynamic element to it: every time we switch input there's a brief momentary increase in the level of hum, even with the volume turned way down. Switching the Dolby NR on the cassette section on or off produces this effect too, regardless of which input is selected. There's also some rushing/crackling and some very low frequency output at switch on (you can see the bass speakers move in and out at around 1 or 2 Hz for a cycle or two) but this settles down in two or three seconds. The volume, balance and tone controls all crackle quite a lot when adjusted but we know how to fix that. Apart from that, we're pretty much novices at this sort of thing. We can identify components on a circuit board and have successfully made simple repairs / alterations to guitar amps and effects pedals. We're hoping that this is something we might be able to tackle ourselves and would welcome any help. The unit dates from 1978 or thereabouts; it seems very solidly made and it would bring pleasure to several people if we could restore it to its original capability. Thanks in advance for any suggestions, Michael and James

22nd Jan 2017, 8:47 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Goodmans HiFi Casseiver 4000 - huge hum It's likely that the power supply electrolytic capacitors have had it. These will have a value of 1,000uF or more and probably be located near the mains transformer. Note that these are polarised, and any replacements must be fitted the correct way round.

22nd Jan 2017, 9:06 pm	#3
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Goodmans HiFi Casseiver 4000 - huge hum That looks remarkably like the Ferguson stereo casseiver that I have languishing in an upstairs wardrobe that has probably not seen the light of day for 20 years (maybe not so many bells and whistles on the Ferguson). I take it they came out of the same stable? Regards Poppydog

24th Jan 2017, 12:48 pm	#4
michaelevwalker Retired Dormant Member Join Date: Jan 2017 Location: Tunbridge Wells, Kent, UK. Posts: 4	Re: Goodmans HiFi Casseiver 4000 - huge hum Thanks Paul. We have identified two 2200uF capacitors in the location you suggest (and noting else with a value that large) with ratings of 80V and 50V. Should we replace both?

29th Jan 2017, 5:54 pm	#6
michaelevwalker Retired Dormant Member Join Date: Jan 2017 Location: Tunbridge Wells, Kent, UK. Posts: 4	Re: Goodmans HiFi Casseiver 4000 - huge hum We replaced both the 2200uF capacitors and nothing has changed at all. Any other suggestions, please? On testing last night, the meter/tuner dial lights did flicker a fair bit after power-up (and some audio 'grumbling' / throat clearing through the speakers) so could it be a transformer/power supply issue?

29th Jan 2017, 6:55 pm	#7
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Goodmans HiFi Casseiver 4000 - huge hum Does the hum vary with the volume control? Assuming it doesn't, one of the diodes in the power supply may have failed. It's unlikely to be a transformer fault. Double check that you have fitted the new electrolytics the right way round. Old electrolytics often have their positive connection marked; most current ones have the negative marked.

30th Jan 2017, 12:25 am	#8
michaelevwalker Retired Dormant Member Join Date: Jan 2017 Location: Tunbridge Wells, Kent, UK. Posts: 4	Re: Goodmans HiFi Casseiver 4000 - huge hum The hum does vary with the volume control, though there is some even when it's turned to minimum. We thought we had the capacitors the right way round but haven't kept the old ones (taken to school for controlled explosion in physics class...). There's a capacitor symbol printed on the top face of the circuit board under each, presumably showing the correct orientation. One of the parallel bars is thin and the other is thick. We assumed the thick bar was the positive and the thin one negative but I can't find any circuit diagram symbols that look quite like this to compare against.

30th Jan 2017, 1:19 am	#9
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Goodmans HiFi Casseiver 4000 - huge hum British equipment used to identify the positive with a red mark or a +, but now the norm is to to highlight the negative, so the broad marking on the component is probably that. The PCB may have both marked, but not obviously so.

30th Jan 2017, 1:54 am	#10
Grubhead Heptode Join Date: Dec 2016 Location: Sheffield, South Yorkshire, UK. Posts: 539	Re: Goodmans HiFi Casseiver 4000 - huge hum As the hum varies with the volume it's not the power supply. I assume the hum is in both channels, so unless you have two identical failures in both channels, we are looking for something that feeds the main amp, but covers both channels. I wonder if there is a voltage regulator circuit on the main power amp board? Look for something on it's own, that doesn't have a twin. Say a transistor or IC. It could have another capacitor connected to it.