Hi Everyone /anyone .... I Have a problem with this amplifier/tuner units.... they both work together to control the system ( it has tape deck and cd units attached) when on low volume all works perfectly however if i increase the volume to a normal level the system cuts out into standby ....i can then turn it straight back on ... the fan is working well inside the SE-CH730 .... there is a problem with the display on the ST-CH730 ...some of the led's dont light up ... even when in standby (a clock is displayed) ... i suspect that it is possibly due to one or more of the electrolytic caps having dried out ... there are no obvious burst ones .. the units are getting quite old now and the clock display has been on for most of its life ....
the schematics for the two units can be found here
https://www.vintageshifi.com/repert....php?pdf=Technics-SECH-730-Service-Manual.pdf
https://www.vintageshifi.com/repert....php?pdf=Technics-STCH-730-Service-Manual.pdf
I've checked both units for dry solder joints and have found none
i found signs of overheating (darkening of the pcb ) in the Tuner unit around Q505 + c510
and around C615-618+C620 C251
my plan is to change these capacitors and the transistor Q505 if i can find one .... but i dont know if these are for the lcd ...
theres another post here for the technics CH7 and it turned out that it was probably just some bad capacitors
https://forum.allaboutcircuits.com/threads/technics-su-ch7-panasonic-sc-ch7-amplifier-issue.120179/
for the led the guy says for the ch7
"Then I replaced C702 and C713 and C714 in the tuner. That fixed the problem completely! Instant power-on from cold, no flickering on the tuner display. Everything works fine."
schematic for CH7
http://www.atipica.it/clienti/SU-CH7.zip
ive looked at this but the layouts seem quite different to me ....
I have a soldering iron and multimeter and am fine at dis-assembly re-assembly but not good at understanding schematics
.......... if anyone has any ideas for me on this one they'd be most welcome
all the best .... Andrew
the schematics for the two units can be found here
https://www.vintageshifi.com/repert....php?pdf=Technics-SECH-730-Service-Manual.pdf
https://www.vintageshifi.com/repert....php?pdf=Technics-STCH-730-Service-Manual.pdf
I've checked both units for dry solder joints and have found none
i found signs of overheating (darkening of the pcb ) in the Tuner unit around Q505 + c510
and around C615-618+C620 C251
my plan is to change these capacitors and the transistor Q505 if i can find one .... but i dont know if these are for the lcd ...
theres another post here for the technics CH7 and it turned out that it was probably just some bad capacitors
https://forum.allaboutcircuits.com/threads/technics-su-ch7-panasonic-sc-ch7-amplifier-issue.120179/
for the led the guy says for the ch7
"Then I replaced C702 and C713 and C714 in the tuner. That fixed the problem completely! Instant power-on from cold, no flickering on the tuner display. Everything works fine."
schematic for CH7
http://www.atipica.it/clienti/SU-CH7.zip
ive looked at this but the layouts seem quite different to me ....
I have a soldering iron and multimeter and am fine at dis-assembly re-assembly but not good at understanding schematics
.......... if anyone has any ideas for me on this one they'd be most welcome
all the best .... Andrew