Sony HMK-40 - UK Vintage Radio Repair and Restoration Discussion Forum

george1960 · 18th Jun 2016, 9:51 pm

Sorry if this is in the wrong section. I know it's a music Centre but I have a tape problem. Every time I put a tape in press play and the button won't stay down .but if I wind the tape on till the end. Turn over to the other side it plays perfect. Anyone got any ideas please

TonyDuell · 19th Jun 2016, 7:38 am

I am not sure quite what you mean. Are you saying that side one of every cassette trips the end-of-tape mechanism so that the play button is released but side two of all cassettes plays correctly?

I assume this fault does occur with all cassettes and that the problem is not a defective cassette.

This does sound as though the unit thinks it's at the end of the tape and is activating the auto-stop mechanism. I have come across 3 types of such mechanism in cassette recorders :

1) By far the most common. There is a sensor lever, normally plastic tipped, and normally between the erase head and record/playback head. Normally this is sprung towards the rear of the unit. At the end of the tape, the tape gets taut and forces the lever forwards. This then engages another lever under the deck with a cam on the flywheel, Said second lever then releases the operating keys.

2) Similar, but the tape-taut sensor operates an electrical switch, which then operates a solenoid to release the keys.

3) Not common in simple home machines, but more common in auto-reverse and car units. End of tape is detected by the spools stopping turning. Often a switch contact on one of the spool turntables changes state several times per revolution. A electronic circuit detects this. If the switch doesn't change for more than a certain time the thing determines that the spools have stopped and either reverses (auto-reverse machines) or operates a solenoid to release the keys (or eject the tape on some car units).

Assuming it's a tape-taut sensor one, perhaps the tape _is_ too taut. Maybe the supply side spindle is sticking. If not, then check the levers to make sure they are moving freely. One advantage of mechanical problems is that you can often see the problem area (once you have dismantled the casing, etc).

sp10mk11 · 19th Jun 2016, 9:27 am

Hello these tape decks have a sort of tension sensor for the auto stop, at this age I would think the belts will need replacing and maybe the mech could do some cleaning and re-greasing.
Worth doing though as this range was well built and very serviceable
Gary

18th Jun 2016, 9:51 pm	#1
george1960 Pentode Join Date: Apr 2016 Location: Southampton, Hampshire, UK. Posts: 103	Sony HMK-40 Sorry if this is in the wrong section. I know it's a music Centre but I have a tape problem. Every time I put a tape in press play and the button won't stay down .but if I wind the tape on till the end. Turn over to the other side it plays perfect. Anyone got any ideas please

19th Jun 2016, 7:38 am	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony HMK-40 I am not sure quite what you mean. Are you saying that side one of every cassette trips the end-of-tape mechanism so that the play button is released but side two of all cassettes plays correctly? I assume this fault does occur with all cassettes and that the problem is not a defective cassette. This does sound as though the unit thinks it's at the end of the tape and is activating the auto-stop mechanism. I have come across 3 types of such mechanism in cassette recorders : 1) By far the most common. There is a sensor lever, normally plastic tipped, and normally between the erase head and record/playback head. Normally this is sprung towards the rear of the unit. At the end of the tape, the tape gets taut and forces the lever forwards. This then engages another lever under the deck with a cam on the flywheel, Said second lever then releases the operating keys. 2) Similar, but the tape-taut sensor operates an electrical switch, which then operates a solenoid to release the keys. 3) Not common in simple home machines, but more common in auto-reverse and car units. End of tape is detected by the spools stopping turning. Often a switch contact on one of the spool turntables changes state several times per revolution. A electronic circuit detects this. If the switch doesn't change for more than a certain time the thing determines that the spools have stopped and either reverses (auto-reverse machines) or operates a solenoid to release the keys (or eject the tape on some car units). Assuming it's a tape-taut sensor one, perhaps the tape _is_ too taut. Maybe the supply side spindle is sticking. If not, then check the levers to make sure they are moving freely. One advantage of mechanical problems is that you can often see the problem area (once you have dismantled the casing, etc).

19th Jun 2016, 9:27 am	#3
sp10mk11 Octode Join Date: Feb 2009 Location: Cornwall, UK. Posts: 1,275	Re: Sony HMK-40 Hello these tape decks have a sort of tension sensor for the auto stop, at this age I would think the belts will need replacing and maybe the mech could do some cleaning and re-greasing. Worth doing though as this range was well built and very serviceable Gary