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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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8th Jul 2020, 10:24 pm | #1 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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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 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,338
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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?
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Edward. |
9th Jul 2020, 4:10 pm | #3 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,927
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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 |
9th Jul 2020, 9:03 pm | #4 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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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
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21st Jul 2020, 8:16 pm | #5 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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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 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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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 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,338
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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.
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Edward. |
22nd Jul 2020, 5:54 pm | #8 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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Re: Faults on a Sony HMK70
Ok great, thanks. I'll do some investigating
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23rd Jul 2020, 10:47 am | #9 |
Triode
Join Date: Jul 2020
Location: Edinburgh, Scotland, UK.
Posts: 15
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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?
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23rd Jul 2020, 1:36 pm | #10 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,338
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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.
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Edward. |