NEC K-537 cassette deck speed fault - UK Vintage Radio Repair and Restoration Discussion Forum

crudmeister · 5th Oct 2014, 8:01 pm

Hi Guys.

I have here a decent 3 head tape deck that seems to work great - except it runs way too fast in play mode. I don't have a service manual and have looked everywhere online with no luck.
The main motor is rated 12V but I noted close to 14V across it, which may explain the high speed. Even having adjusted the on motor pot to slowest, its still much too fast, probably double speed or thereabouts.

Does anyone out there have a service manual.circuit diagram for the NEC K-537 ?
I know it's a long shot.. but finding a service manual always seems to be a good start - tracing and circuits takes a lot of time!

Any general suggestions and responsible faults regarding too fast faults also glady received.

Cheers guys
Rob

ben · 6th Oct 2014, 11:09 pm

Check that the speed does not vary at all. A common fault symptom with many technics/panasonic units is that you get generally faster speed - 20% or so - but if you listen closely, it is also unstable. The motor regulator IC (often a part of the motor) is at fault in such cases.

If the speed is permanently fast, check that the belt is sitting on the right part of all pulleys. Also that the pinch roller engages fully. Try playing a tape at the end of a side and compare with the start of side. If the pinch is not engaging properly, it will stall at the end of the tape.

Presumably this is a single well tape deck, if so I cannot see how a 2v increase in supply would cause it to run at double speed . A dual well deck will have motors with an extra winding on for high speed copy.

hsbhachu3d · 7th Oct 2014, 3:32 pm

Interesting.. I had 2 decks, a Hitachi and a Pioneer. they both had the same problem. I don't really know why. I fixed the pioneer by replacing a couple of capacitors in the speed adjustment that was on the board but the Hitachi, nothing really worked. It had a 9 volt motor and it was running 10.2 volts across the line. I tried a resistor to slow it down but it didn't work so I wouldn't suggest because, even though your multimeter will give you a correct reading, the amps will have decreased and that will reduce the torque of your motor making you surprised that even 12 v hasnt brought it to speed. Also the resistor will get hot of the tolerance isn't right. I fixed it by replacing the motor with a similar one. I have nearly 10 lying around at home. Motors like the ones you describe always have a transistor to regulate the speed and as soon as that burns out, maybe due to being started after a long time or a sudden surge of current, the transistor shorts. it's cheap to replace them with similar ones. I've added pictures for example. Mabuchi and Sankyo made ones are quite reliable and I have my decks working until now. Just replace the motor. everything will be sorted. they can take -/+ 12% so 14 volts is perfectly fine. I'm guessing in your motor the transistor is gone. just replace it.

crudmeister · 18th Oct 2014, 9:25 pm

Thanks guys for those tips, however the speed seems stable and the pinch roller does seem to engage fully. The belt (there's only one) has been changed for a new one (slightly smaller) and the result is the same, so it must be an electronic issue regarding speed control - wish I had a service manual!! , but this seems a fairly scarce deck - but it's really nice and I'd love to fix it.

If you have any new ideas, please let me know, helps me to eliminate possible causes at least... cheers chaps!

5th Oct 2014, 8:01 pm	#1
crudmeister Retired Dormant Member Join Date: Jan 2012 Location: Middlewich, Cheshire, UK. Posts: 237	NEC K-537 cassette deck speed fault Hi Guys. I have here a decent 3 head tape deck that seems to work great - except it runs way too fast in play mode. I don't have a service manual and have looked everywhere online with no luck. The main motor is rated 12V but I noted close to 14V across it, which may explain the high speed. Even having adjusted the on motor pot to slowest, its still much too fast, probably double speed or thereabouts. Does anyone out there have a service manual.circuit diagram for the NEC K-537 ? I know it's a long shot.. but finding a service manual always seems to be a good start - tracing and circuits takes a lot of time! Any general suggestions and responsible faults regarding too fast faults also glady received. Cheers guys Rob

6th Oct 2014, 11:09 pm	#2
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: NEC K-537 cassette deck speed fault Check that the speed does not vary at all. A common fault symptom with many technics/panasonic units is that you get generally faster speed - 20% or so - but if you listen closely, it is also unstable. The motor regulator IC (often a part of the motor) is at fault in such cases. If the speed is permanently fast, check that the belt is sitting on the right part of all pulleys. Also that the pinch roller engages fully. Try playing a tape at the end of a side and compare with the start of side. If the pinch is not engaging properly, it will stall at the end of the tape. Presumably this is a single well tape deck, if so I cannot see how a 2v increase in supply would cause it to run at double speed . A dual well deck will have motors with an extra winding on for high speed copy. __________________ Regards, Ben.

7th Oct 2014, 3:32 pm	#3
hsbhachu3d Pentode Join Date: Nov 2013 Location: Coventry, West Midlands, UK. Posts: 199	Re: NEC K-537 cassette deck speed fault Interesting.. I had 2 decks, a Hitachi and a Pioneer. they both had the same problem. I don't really know why. I fixed the pioneer by replacing a couple of capacitors in the speed adjustment that was on the board but the Hitachi, nothing really worked. It had a 9 volt motor and it was running 10.2 volts across the line. I tried a resistor to slow it down but it didn't work so I wouldn't suggest because, even though your multimeter will give you a correct reading, the amps will have decreased and that will reduce the torque of your motor making you surprised that even 12 v hasnt brought it to speed. Also the resistor will get hot of the tolerance isn't right. I fixed it by replacing the motor with a similar one. I have nearly 10 lying around at home. Motors like the ones you describe always have a transistor to regulate the speed and as soon as that burns out, maybe due to being started after a long time or a sudden surge of current, the transistor shorts. it's cheap to replace them with similar ones. I've added pictures for example. Mabuchi and Sankyo made ones are quite reliable and I have my decks working until now. Just replace the motor. everything will be sorted. they can take -/+ 12% so 14 volts is perfectly fine. I'm guessing in your motor the transistor is gone. just replace it. Attached Thumbnails Last edited by AC/HL; 7th Oct 2014 at 3:41 pm. Reason: Images uploaded

18th Oct 2014, 9:25 pm	#4
crudmeister Retired Dormant Member Join Date: Jan 2012 Location: Middlewich, Cheshire, UK. Posts: 237	Re: NEC K-537 cassette deck speed fault Thanks guys for those tips, however the speed seems stable and the pinch roller does seem to engage fully. The belt (there's only one) has been changed for a new one (slightly smaller) and the result is the same, so it must be an electronic issue regarding speed control - wish I had a service manual!! , but this seems a fairly scarce deck - but it's really nice and I'd love to fix it. If you have any new ideas, please let me know, helps me to eliminate possible causes at least... cheers chaps!