UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - JVC HR-D750 FF Trips: Requires Reel Motor Repair?

G6ONEDave · 9th Dec 2022, 3:26 pm

The 4.7uf cap is probably a bit too large in value to respond fast enough to the spike pulses, that's why I suggested a 10nf cap. My next suggestion was to try the 10nf across the reel motor drive, or to fit a 10nf cap from each side of the reel motor drive and chassis (0v).

However I now think that the problem is actually power supply related. Try scoping the motor 12v supply output to see if you have all those spikes at that location. I'm tipping that they will be there and of a higher amplitude. You could try the 10nf across the power supplies motor supply output to see if it cures the problem. If it does dramatically improve things then it suggests that the actual problem is being caused by the STK5490. This regulator chip is probably a switch mode design internally as opposed to a linear design. I've not checked the data sheet to confirm this yet but feel that this may well be the case.

Dave

9th Dec 2022, 3:26 pm	#26
G6ONEDave Octode Join Date: Dec 2019 Location: Owston Ferry, North Lincolnshire, UK. Posts: 1,701	Re: JVC HR-D750 FF Trips: Requires Reel Motor Repair? The 4.7uf cap is probably a bit too large in value to respond fast enough to the spike pulses, that's why I suggested a 10nf cap. My next suggestion was to try the 10nf across the reel motor drive, or to fit a 10nf cap from each side of the reel motor drive and chassis (0v). However I now think that the problem is actually power supply related. Try scoping the motor 12v supply output to see if you have all those spikes at that location. I'm tipping that they will be there and of a higher amplitude. You could try the 10nf across the power supplies motor supply output to see if it cures the problem. If it does dramatically improve things then it suggests that the actual problem is being caused by the STK5490. This regulator chip is probably a switch mode design internally as opposed to a linear design. I've not checked the data sheet to confirm this yet but feel that this may well be the case. Dave __________________ Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica)