Faults on a Sony HMK70 - UK Vintage Radio Repair and Restoration Discussion Forum

stiggyd · 8th Jul 2020, 10:24 pm

Hi,

I've had an old Sony HMK70 music centre for a while and it has a few problems.
Firstly (and least importantly) the section for the radio frequencies does not light up apart from the bar indicating the current frequency, is this fixable?

The most problematic issue is that there is the sound of what sounds like static that seems to build up, sounds like classic static sound or a scratchy untuned radio that culminates in a loudish pop when I flick the on switch a few times then it slowly builds up again. What could cause this?

My last question is: if these issues are too difficult to diagnose or fix, how doable is it to remove the turntable section and install into a custom housing (turntable only)? I really like the sound of this TT and it would pain me to get rid of it

Edward Huggins · 9th Jul 2020, 7:41 am

In terms of removing the TT you may well show up its inherent deficiences when used with more demanding ancilliary equipment. It will also render the rest of the unit basically worthless. The components of these Music Centres were designed to be mutually compatible. What you are calling "static" is probably down to old capacitor problems. The lights should be an easy fix. The HMK70 is a classic product of its period and is well worth restoring per se. If you feel this may be beyond you, there are Members of ths Forum nearby to you that might be prepared to give it a look over?

Welsh Anorak · 9th Jul 2020, 4:10 pm

This sort of mush is often caused by dirty switches. With the machine off, work the switchbank in and out, then put a cassette in and do the same with the the record and play buttons. Might help.
I agree with Edward - you could remove the turntable, but I have a feeling the motor is an unusual voltage. Far better to get this going if you can

stiggyd · 9th Jul 2020, 9:03 pm

Ok, thank you both. I'll give cracking it open a go and check/replace capacitors and clean contacts etc

stiggyd · 21st Jul 2020, 8:16 pm

Thanks, cleaning out the pots and switches fixed the issue.

Now I just need to figure out how to sort out the platter's 4% speed increase!

stiggyd · 22nd Jul 2020, 11:06 am

OK, pots are clean and no longer scratchy, the noise is back though. Before I start getting in too deep and replacing capacitors etc. (this thing is quite complicated to take apart) can anything be diagnosed from this recording?

https://voca.ro/4ydDVX7r0vI

About half way through you can hear me turn it off and on again. This sound happens intermittently, sometimes worse, sometimes better and for all sources and in both channels.

Edward Huggins · 22nd Jul 2020, 1:25 pm

Sounds like a capacitor failing and then being re-charged again upon switch on. This fault is quite common on many units. If I'm right, this will need tracing and measuring. It could be the large value capacitors in the power supply.

stiggyd · 22nd Jul 2020, 5:54 pm

Ok great, thanks. I'll do some investigating

stiggyd · 23rd Jul 2020, 10:47 am

One last question, if the sound doesn't happen if a small AUX speaker is connected to the tape Rec output on the back can I assume that the issue is in the power amp section?

Edward Huggins · 23rd Jul 2020, 1:36 pm

You need to use the TAPE PLAYBACK socket. It will need to be an active speaker for your test, not just a passive (non-amplifed) speaker.

8th Jul 2020, 10:24 pm	#1
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Faults on a Sony HMK70 Hi, I've had an old Sony HMK70 music centre for a while and it has a few problems. Firstly (and least importantly) the section for the radio frequencies does not light up apart from the bar indicating the current frequency, is this fixable? The most problematic issue is that there is the sound of what sounds like static that seems to build up, sounds like classic static sound or a scratchy untuned radio that culminates in a loudish pop when I flick the on switch a few times then it slowly builds up again. What could cause this? My last question is: if these issues are too difficult to diagnose or fix, how doable is it to remove the turntable section and install into a custom housing (turntable only)? I really like the sound of this TT and it would pain me to get rid of it

9th Jul 2020, 7:41 am	#2
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Faults on a Sony HMK70 In terms of removing the TT you may well show up its inherent deficiences when used with more demanding ancilliary equipment. It will also render the rest of the unit basically worthless. The components of these Music Centres were designed to be mutually compatible. What you are calling "static" is probably down to old capacitor problems. The lights should be an easy fix. The HMK70 is a classic product of its period and is well worth restoring per se. If you feel this may be beyond you, there are Members of ths Forum nearby to you that might be prepared to give it a look over? __________________ Edward.

9th Jul 2020, 4:10 pm	#3
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: Faults on a Sony HMK70 This sort of mush is often caused by dirty switches. With the machine off, work the switchbank in and out, then put a cassette in and do the same with the the record and play buttons. Might help. I agree with Edward - you could remove the turntable, but I have a feeling the motor is an unusual voltage. Far better to get this going if you can __________________ Glyn www.gdelectronics.wales

9th Jul 2020, 9:03 pm	#4
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Re: Faults on a Sony HMK70 Ok, thank you both. I'll give cracking it open a go and check/replace capacitors and clean contacts etc

21st Jul 2020, 8:16 pm	#5
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Re: Faults on a Sony HMK70 Thanks, cleaning out the pots and switches fixed the issue. Now I just need to figure out how to sort out the platter's 4% speed increase!

22nd Jul 2020, 11:06 am	#6
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Re: Faults on a Sony HMK70 OK, pots are clean and no longer scratchy, the noise is back though. Before I start getting in too deep and replacing capacitors etc. (this thing is quite complicated to take apart) can anything be diagnosed from this recording? https://voca.ro/4ydDVX7r0vI About half way through you can hear me turn it off and on again. This sound happens intermittently, sometimes worse, sometimes better and for all sources and in both channels.

22nd Jul 2020, 1:25 pm	#7
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Faults on a Sony HMK70 Sounds like a capacitor failing and then being re-charged again upon switch on. This fault is quite common on many units. If I'm right, this will need tracing and measuring. It could be the large value capacitors in the power supply. __________________ Edward.

22nd Jul 2020, 5:54 pm	#8
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Re: Faults on a Sony HMK70 Ok great, thanks. I'll do some investigating

23rd Jul 2020, 10:47 am	#9
stiggyd Triode Join Date: Jul 2020 Location: Edinburgh, Scotland, UK. Posts: 15	Re: Faults on a Sony HMK70 One last question, if the sound doesn't happen if a small AUX speaker is connected to the tape Rec output on the back can I assume that the issue is in the power amp section?

23rd Jul 2020, 1:36 pm	#10
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Faults on a Sony HMK70 You need to use the TAPE PLAYBACK socket. It will need to be an active speaker for your test, not just a passive (non-amplifed) speaker. __________________ Edward.