Technics SL PG490 - "no disc" error

[N Cook]

Sometimes (rarely) plays a CD.
Sometimes spins up at half cock a few times followed by "no disc" on
display.
Or fails to spin at all , then "no disc". Checked connections & solder of
ICs etc
Sledge servo and focusing servo and laser work always. M(otor)DATA line from
main micro to servo processor
changes state at start always but no platter driver output to input to the
platter motor driver.
Inverse RFDET, pin 17 of the AN8805 stays at 5V. Before delving into
waveform symmetry or focus, anything simple to check first ?

electronic hints and repair briefs , schematics/manuals list on
http://homepages.tcp.co.uk/~diverse

 

[James Sweet]

Sometimes (rarely) plays a CD.
Sometimes spins up at half cock a few times followed by "no disc" on
display.
Or fails to spin at all , then "no disc". Checked connections & solder of
ICs etc
Sledge servo and focusing servo and laser work always. M(otor)DATA line from
main micro to servo processor
changes state at start always but no platter driver output to input to the
platter motor driver.
Inverse RFDET, pin 17 of the AN8805 stays at 5V. Before delving into
waveform symmetry or focus, anything simple to check first ?

electronic hints and repair briefs , schematics/manuals list on
http://homepages.tcp.co.uk/~diverse

My guess would be that the optics are dirty and/or the laser has gone weak
with age.

 

[N Cook]

My guess would be that the optics are dirty and/or the laser has gone weak
with age.

I forgot to ask the owner the usual question
Did the trouble start gradually and then over months get worse or happened
all of a sudden?