Sony TC-K7B-II - UK Vintage Radio Repair and Restoration Discussion Forum

Steveatbath · 31st Oct 2025, 2:28 pm

Hi to experts!
I bought this heavyweight cassette machine new in January 1981 for £129 (maybe a special offer). It weighs 10kg and wa made in Japan. It worked well for over 30 years, with one service and new belts. The sound quality of tapes recorded from FM was remarkable. I have not used it for several years and it has been carefully stored. Testing it now the play function is fine, with a good audio output. However FF/RR seems stuck. There is a brief whirring noise and then auto switch off. How can this be remedied? I can only see one main drive belt which looks fine. Incidentally why was this machine made so heavy?
Thanks for any guidance. Steve

knobtwiddler · 2nd Nov 2025, 12:37 pm

I have a later 777 Sony deck that uses an idler drive for FF / RW. I suspect that your transport is a predecessor to the 777 mechanism. Because your belts were changed, the PB side seems to be ok. Idlers can harden and lose their grip over time, which will explain the FF / RW issue. I would have a look at the idler tyre condition. If you search the web for "Sony TC-K7B-II idler" you will see firms selling replacements.

The decks were heavy (as is my 777) on account of them being released in the peak era of cassette OEM competition. The titans of Japan were slugging it out against each other, with Sony, Nak, Technics and Aiwa in a corporate battle. Sony were unique, in that along with Nak, they made their own heads (others fitted Alps, Canon etc). The 1978 Technics RS-9900US illustrates this perfectly, whereby the transport and audio path amps were put in separate enclosures, making a deck that weighs aroun 25Kg in total (I don't recommend buying one - the ferrite heads are always shot)

Steveatbath · 2nd Nov 2025, 8:49 pm

Thanks Twiddler. I have replaced belts and cleaned heads etc but my tech knowledge is limited. I need to identify the idler tyre; is it readily visible? I only have the user manual and maybe I need to find servicing guides to print and study.

knobtwiddler · 3rd Nov 2025, 9:55 am

You should be able to get the SM here: https://www.hifiengine.com/manual_library/sony/tc-k7.shtml

I've attached a photo of what to look for. Having pointed the finger at the idler, note that it could be something else. The idler is the most obvious culprit as rubber of this age often has issues (you replaced the belts, but not idler), but do be sure to look at all potential factors.

Dried grease is a big problem for Sony decks of this age. It can literally turn into glue, seizing arms and carriages, whereby they cannot move into position for tensioning or making contact with the heads (head carriage seizure is a classic problem, but if you can play ok it's unlikely an issue here).

The idler drives the reels. You say that the deck plays ok, which could suggest that maybe the idler's ok, but it's not being actuated correctly during FF / RW... This could be dried grease...or something else.

You will need to figure out how much investment you want to make here, in terms of time and cost. A pro would have a W+F test tape (Google 'Hans Peter Roth test tape - he sells a set of 6 for around 50 Euros) and meter (you can get free software meters, but you'll need an audio input to the PC or laptop). Do you want to restore other machines and make a hobby of it? Do you listen to enough tapes to warrant paying a pro? (Peter Dolman would be my UK recommendation if so, but you're looking at 3-6 months lead time as he is busy).

edit = photo is from MK1 deck. I suspect MK2 will have same mechanism, but cannot find many photos of the MK2.

Steveatbath · 4th Nov 2025, 12:13 pm

Many thanks, I will get the SM and maybe enlist help from someone with more expertise in renovation. I will report in due course. Meanwhile I can wind tapes on another machine and even use a little plastic winding device, if I can find it; I think Metrosound made that.

31st Oct 2025, 2:28 pm	#1
Steveatbath Triode Join Date: Nov 2014 Location: Bath, Somerset, UK. Posts: 42	Sony TC-K7B-II Hi to experts! I bought this heavyweight cassette machine new in January 1981 for £129 (maybe a special offer). It weighs 10kg and wa made in Japan. It worked well for over 30 years, with one service and new belts. The sound quality of tapes recorded from FM was remarkable. I have not used it for several years and it has been carefully stored. Testing it now the play function is fine, with a good audio output. However FF/RR seems stuck. There is a brief whirring noise and then auto switch off. How can this be remedied? I can only see one main drive belt which looks fine. Incidentally why was this machine made so heavy? Thanks for any guidance. Steve

2nd Nov 2025, 12:37 pm	#2
knobtwiddler Octode Join Date: Mar 2016 Location: London, UK. Posts: 1,383	Re: Sony TC-K7B-II I have a later 777 Sony deck that uses an idler drive for FF / RW. I suspect that your transport is a predecessor to the 777 mechanism. Because your belts were changed, the PB side seems to be ok. Idlers can harden and lose their grip over time, which will explain the FF / RW issue. I would have a look at the idler tyre condition. If you search the web for "Sony TC-K7B-II idler" you will see firms selling replacements. The decks were heavy (as is my 777) on account of them being released in the peak era of cassette OEM competition. The titans of Japan were slugging it out against each other, with Sony, Nak, Technics and Aiwa in a corporate battle. Sony were unique, in that along with Nak, they made their own heads (others fitted Alps, Canon etc). The 1978 Technics RS-9900US illustrates this perfectly, whereby the transport and audio path amps were put in separate enclosures, making a deck that weighs aroun 25Kg in total (I don't recommend buying one - the ferrite heads are always shot)

2nd Nov 2025, 8:49 pm	#3
Steveatbath Triode Join Date: Nov 2014 Location: Bath, Somerset, UK. Posts: 42	Re: Sony TC-K7B-II Thanks Twiddler. I have replaced belts and cleaned heads etc but my tech knowledge is limited. I need to identify the idler tyre; is it readily visible? I only have the user manual and maybe I need to find servicing guides to print and study.

3rd Nov 2025, 9:55 am	#4
knobtwiddler Octode Join Date: Mar 2016 Location: London, UK. Posts: 1,383	Re: Sony TC-K7B-II You should be able to get the SM here: https://www.hifiengine.com/manual_library/sony/tc-k7.shtml I've attached a photo of what to look for. Having pointed the finger at the idler, note that it could be something else. The idler is the most obvious culprit as rubber of this age often has issues (you replaced the belts, but not idler), but do be sure to look at all potential factors. Dried grease is a big problem for Sony decks of this age. It can literally turn into glue, seizing arms and carriages, whereby they cannot move into position for tensioning or making contact with the heads (head carriage seizure is a classic problem, but if you can play ok it's unlikely an issue here). The idler drives the reels. You say that the deck plays ok, which could suggest that maybe the idler's ok, but it's not being actuated correctly during FF / RW... This could be dried grease...or something else. You will need to figure out how much investment you want to make here, in terms of time and cost. A pro would have a W+F test tape (Google 'Hans Peter Roth test tape - he sells a set of 6 for around 50 Euros) and meter (you can get free software meters, but you'll need an audio input to the PC or laptop). Do you want to restore other machines and make a hobby of it? Do you listen to enough tapes to warrant paying a pro? (Peter Dolman would be my UK recommendation if so, but you're looking at 3-6 months lead time as he is busy). edit = photo is from MK1 deck. I suspect MK2 will have same mechanism, but cannot find many photos of the MK2. Attached Thumbnails

4th Nov 2025, 12:13 pm	#5
Steveatbath Triode Join Date: Nov 2014 Location: Bath, Somerset, UK. Posts: 42	Re: Sony TC-K7B-II Many thanks, I will get the SM and maybe enlist help from someone with more expertise in renovation. I will report in due course. Meanwhile I can wind tapes on another machine and even use a little plastic winding device, if I can find it; I think Metrosound made that.