Tape deck too fast on Sony HMK-77 - UK Vintage Radio Repair and Restoration Discussion Forum

hopefortape · 5th Aug 2016, 7:35 pm

Hi, I've inherited a Sony HMK-77 and the cassette deck plays well but too fast. I've seen that there is often a small hole so you can adjust the speed of the motor on a tape deck but I've got no idea where to find it! I'd really appreciate any suggestions... Many thanks! H

paulsherwin · 5th Aug 2016, 7:37 pm

It's normally on the back of the motor. If yours doesn't have a hole, then either the speed is set by a preset on one of the circuit boards, or it's not adjustable at all.

vidjoman · 5th Aug 2016, 9:43 pm

Don't fiddle until you know it's the motor. Might be the belt riding on the edge of the pulley because it's stretched and needs replacing.

paulsherwin · 5th Aug 2016, 10:49 pm

Yes, check the mechanism carefully before doing anything else, especially if the speed is a long way out.

Marconi_MPT4 · 6th Aug 2016, 3:17 pm

As previous posts, first check drive belts and associated idlers and clean where required, presuming the speed had been previously correct.

However, it was nearly 40 years ago and I do recall a batch stock problem with these with regard to tape speed stability in that it varied easily with temperature! The motor drive system is FG (frequency generator) servo type with external control circuitry. Note the use of thermistor TH1101 for temperature compensation.

If memory serves, I think the issue was a motor fault. But first there are a number of electrolytic capacitors that could have dried up. Sony used good quality Elna, but over time even these deteriorate. Check and clean the switch contacts of S106. RV1104 adjusts speed.

Rich

Clydeuk · 7th Aug 2016, 1:08 am

Another thing worth checking is the capstan, this kind if thing can happen when a tape gets chewed up and the remains wrap around the capstan, effectively increasing it's diameter. Used to be quite common on cheaper mechanisms.

camtechman · 8th Aug 2016, 8:44 am

If it helps, you can download the service manual, free from here:

http://elektrotanya.com/sony_hmk77_7.../download.html

5th Aug 2016, 7:35 pm	#1
hopefortape Retired Dormant Member Join Date: Aug 2016 Location: London, UK. Posts: 1	Tape deck too fast on Sony HMK-77 Hi, I've inherited a Sony HMK-77 and the cassette deck plays well but too fast. I've seen that there is often a small hole so you can adjust the speed of the motor on a tape deck but I've got no idea where to find it! I'd really appreciate any suggestions... Many thanks! H

5th Aug 2016, 7:37 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	Re: Tape deck too fast on Sony HMK-77 It's normally on the back of the motor. If yours doesn't have a hole, then either the speed is set by a preset on one of the circuit boards, or it's not adjustable at all.

5th Aug 2016, 9:43 pm	#3
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Tape deck too fast on Sony HMK-77 Don't fiddle until you know it's the motor. Might be the belt riding on the edge of the pulley because it's stretched and needs replacing.

5th Aug 2016, 10:49 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	Re: Tape deck too fast on Sony HMK-77 Yes, check the mechanism carefully before doing anything else, especially if the speed is a long way out.

6th Aug 2016, 3:17 pm	#5
Marconi_MPT4 Heptode Join Date: Mar 2011 Location: Dorset, UK. Posts: 521	Re: Tape deck too fast on Sony HMK-77 As previous posts, first check drive belts and associated idlers and clean where required, presuming the speed had been previously correct. However, it was nearly 40 years ago and I do recall a batch stock problem with these with regard to tape speed stability in that it varied easily with temperature! The motor drive system is FG (frequency generator) servo type with external control circuitry. Note the use of thermistor TH1101 for temperature compensation. If memory serves, I think the issue was a motor fault. But first there are a number of electrolytic capacitors that could have dried up. Sony used good quality Elna, but over time even these deteriorate. Check and clean the switch contacts of S106. RV1104 adjusts speed. Rich Attached Thumbnails __________________ To an optimist a glass is half full; a pessimist half empty; an engineer twice as big as need be!

7th Aug 2016, 1:08 am	#6
Clydeuk Hexode Join Date: Mar 2012 Location: Liverpool, Merseyside, UK. Posts: 453	Re: Tape deck too fast on Sony HMK-77 Another thing worth checking is the capstan, this kind if thing can happen when a tape gets chewed up and the remains wrap around the capstan, effectively increasing it's diameter. Used to be quite common on cheaper mechanisms.

8th Aug 2016, 8:44 am	#7
camtechman Nonode Join Date: Jan 2008 Location: Milton Keynes, Bucks. UK. Posts: 2,552	Re: Tape deck too fast on Sony HMK-77 If it helps, you can download the service manual, free from here: http://elektrotanya.com/sony_hmk77_7.../download.html __________________ When I die, please don't let my Wife sell my collection for the amount I told her I paid for it!