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

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

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!