UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Help! Problem with my Technics Amp cutting out .

PJL · 6th Jul 2020, 10:27 pm

This is a very complex system. The power relay is controlled by IC801 (System Control) but that has a datalink to the ST-CH730 unit where there is a microcomputer. The ADI connection to the ST-CH730 serves multiple purposes by using different sink resistance values and includes the buttons and the fan/DC offset fault signal.

Lifting one end of R391 (47K) will tell you if the error is coming from the fan/DC offset fault signal, otherwise the fault must be detected in the ST-CH730 unit.

There is also a link you can short (TP701) that will force the power to remain on to help with fault finding.

I suggest you check all power supply voltages marked up on the circuit, particularly the output of the regulators, -15V and 14.8V.

6th Jul 2020, 10:27 pm	#42
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Help! Problem with my Technics Amp cutting out . This is a very complex system. The power relay is controlled by IC801 (System Control) but that has a datalink to the ST-CH730 unit where there is a microcomputer. The ADI connection to the ST-CH730 serves multiple purposes by using different sink resistance values and includes the buttons and the fan/DC offset fault signal. Lifting one end of R391 (47K) will tell you if the error is coming from the fan/DC offset fault signal, otherwise the fault must be detected in the ST-CH730 unit. There is also a link you can short (TP701) that will force the power to remain on to help with fault finding. I suggest you check all power supply voltages marked up on the circuit, particularly the output of the regulators, -15V and 14.8V.