https://elektrotanya.com/kikusui_cos5040_sch.pdf/download.html
This is where i got it.
When page loads, there comes little link below preview picture where you can download it. You have to wait approx. 30sec (before there is ...processing...)
-welpester
So normally we'd look for V values on the schematic at various test points but there aren't any.
So the only option is to follow the signal path and compare readings with Ch 1.
Have you access to another scope ?
An appropriate signal input can be the probe Cal or some DC value, just make sure both channels are set the same and measure/compare at the same point in the signal path for each channel.
First point I would check is R115/215 as FET inputs can be damaged by overvoltage inputs.
Then junction of R114 and R120/R214 and R220 and so on............
Not sure if it's any help, but I have the cos 5060 model (nice CRO btw ) and these are the links for related files
http://www.kikusui.co.jp/manuals/index_e.php?GROUP=COS&skip=20
http://www.kikusui.co.jp/manuals/index_e.php?GROUP=COS&skip=0
I think the cos 50xx series are either the same circuit paths or very close in build
Best of luck sorting it out
I got a COS5060 of which one channel's vertical amplifier was playing tricks on me -- or so I thought. I opened it, didn't see anything obviously wrong (nothing burnt or smelly). Since there is no fan its pretty clean inside despite its age. While in it, I sprayed some contact cleaner on the contacts of the buttons and potentiometers of the front panel, turned them a bit in the hope to remove any dirt, closed the device again and that was it -- works fine again.
As far as I understand, it's quite common that user interface elements are the cause of malfunction on devices of this age (30+ years). Might be worth a shot to attempt to clean them again.
Found the email from Kikusui it might be worth following up for someone with a sad Kikusui scope
"Regarding the COS5060TM, this model is very old model.
So unfortunately we finished support this model.
However, we can provide the service manual of COS5060 to you.
Please let us know if you need it.
Thank you for your understanding.
Best regards,
Daisuke Tezuka
daisuke@kikusuiamerica.com
Kikusui America,Inc.
2975 Bowers Avenue, Suite 307
Santa Clara, CA95051
Toll-Free:1-877-876-2807
Phone:408-980-9433 ext.108
Fax 408-980-9409
"
Excellent straight up reply and options
here:
https://www.elektrotanya.com/kikusui_cos5040_sch.pdf/download.html
and
ftp://helpedia.com/pub/temp/service_manuals/bee.mif.pg.gda.pl/ciasteczkowypotwor/Kikusui/KIKUSUI%20COS%205040,%20COS%205041%20Instruction.pdf
top link is the schematics, that's about as close as you will get.