Hello
I have the above minidisc with a strange fault
It powers on fine and stays powered on as long as you don’t play or record a minidisc
If play is selected the motor on the unit whirs and it starts playing fine. After around 2-3 mins the display shuts off, the motor whirs (not necessarily in this order) and the unit powers down. It sometimes resets and comes back on (display turns back on).
The power supply seems a linear design with a few windings on the secondary. Pin 16/17 on secondary go through a couple of diodes (see attachment)—- and through a filter capacitor (C701)(10000uF 16v). When working the filter capacitor has around 14v DC on it. This then connects to two 5v regulators (7805a). When the unit powers down upon pressing play the capacitor voltage drops to around 9v and the 5v regulated supply drops to around 1.8v.
I have no way of testing the capacitor as I only have a digital MM. The other supplies 7v regulated and 33v don’t drop. Issue only seems to be present on this line.
I disconnected the cable going to the main PCB which in turn connects to the playing unit and display. The supply remains constant on the filter capacitor and the two 7805s.
I’ve replaced a few 470uF capacitors around that area with no luck.
I don’t know what’s dragging the power supply down on the filter capacitor.
I also noticed the service manual suggests the filter capacitor (c701) should be a 4700/16v but the fitted one is 10000/16v? As far as I know this has never been replaced or changed before and the unit has been working fine before.
Any pointers would be handy
Thanks in advance
Jay.
I have the above minidisc with a strange fault
It powers on fine and stays powered on as long as you don’t play or record a minidisc
If play is selected the motor on the unit whirs and it starts playing fine. After around 2-3 mins the display shuts off, the motor whirs (not necessarily in this order) and the unit powers down. It sometimes resets and comes back on (display turns back on).
The power supply seems a linear design with a few windings on the secondary. Pin 16/17 on secondary go through a couple of diodes (see attachment)—- and through a filter capacitor (C701)(10000uF 16v). When working the filter capacitor has around 14v DC on it. This then connects to two 5v regulators (7805a). When the unit powers down upon pressing play the capacitor voltage drops to around 9v and the 5v regulated supply drops to around 1.8v.
I have no way of testing the capacitor as I only have a digital MM. The other supplies 7v regulated and 33v don’t drop. Issue only seems to be present on this line.
I disconnected the cable going to the main PCB which in turn connects to the playing unit and display. The supply remains constant on the filter capacitor and the two 7805s.
I’ve replaced a few 470uF capacitors around that area with no luck.
I don’t know what’s dragging the power supply down on the filter capacitor.
I also noticed the service manual suggests the filter capacitor (c701) should be a 4700/16v but the fitted one is 10000/16v? As far as I know this has never been replaced or changed before and the unit has been working fine before.
Any pointers would be handy
Thanks in advance
Jay.
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