TRIO Kenwood CS 1022 dual channel Oscilloscope 20Mhz 1980 repair

I got this cool scope for free at a locan fleamarked, i was told it was a little bit defective, so i checked it all and fixed it all, now the scope is super nice again.
---
#oscilloscope
#repair
#teardown
--
I use auto generated subs, I go thru them my self, but i am far from perfect at finding all errors, so if you find errors worth fixing, please comment (or PM) with the TIME in the video you saw the error, i will be happy to fix it. This also apply to the Danish version.
--
(Thanks to all my Sponsors / Traders / Swappers / Sellers / Buyers, without your support and constant flow of cool items in/out, none of this would be possible)

[@grantwills5421]

Thanks Thomas for this video. I have just inherited an identical CS1022 with a non functional CH1. I suspected that someone had fried the input and so it turned out to be. The input stage uses an obsolete M47F dual fet and one of the two was faulty. I was able to replace the faulty section with an MPF102 selected to match the remaining fet. I did notice the same "hum" component superimposed on the Y channel inputs. I was able to determine that this was caused by a dodgy grounding of the power/Y amp board. There is only one self tapping screw that provides a ground for the entire board. The screw was loose and corrosion evident. I removed it, cleaned the contacts and added two more screws that were not in place. The hum completely disappeared. EDIT: I also discovered that the timebase board had a similar issue - intermittent high frequency noise on the signal due to bad contacts on the two grounding screws. Removing them and cleaning them and the attached clips and the underside of the lid cleaned up the noise.

[@TeardownOZ2CPU]

thanks a lot for sharing your results and findings, this can help others.

[@velox__]

Thanks for such a detailed overview! I own this scope (got it for €30 , not quite as good of a deal as yours) and it's worked great so far, but this will be a great help if it ever starts acting up :)

[@incucinaconklea.]

Tanks for your interesting video. I have an oscilloscope like this and one of the channel is wrong, but i have no scheme. I think that the component i have to change is M47F-C, but i can't find it. Can you help me? Do you know where may I find it or how may I substitue it? Where may I find the scheme? Thanks for you answer and sorry for my terrible English.

[@Edisson.]

Hi, that's a great purchase, you can't not buy it for that money 😂 we don't have flea markets like that here 😭
I'm looking at the modified PCB, so either they made a mistake in the design of the board, or other transistors than were originally intended were installed and have different terminals, or someone already repaired it with a replacement with swapped terminals.
I've been looking at the source diagram for about ten minutes and I don't see a design error there, I'm probably tired after the second sleepless night anyway, so I looked at what kind of strange DPS it is, the paths are kind of moldy and then I just realized that it's screen printing way from the other side 🤦‍♀
Transistor Q304 will open based on the voltage drop across R304 even if it were to open completely the power dissipated in R306 would be dissipated assuming Q306 is open also if Q306 does not open then Q308 will not start to open either the voltage drop across R304 and Q304 will remain closed and he's fine again. A slightly modified current mirror.
I know the worn path of the potentiometer, the faulty connection to the pin as well, but this is the first time I see such degradation.
The CRT draws beautifully, it will serve you for a long time 👍
Nice day 🙂 Tom

[@TeardownOZ2CPU]

noisy potentiometer is clearly a thing, specially in audo music kind of equipment, but I have not seen anything as crasy as this before, so it was super I was able to document it

[@renepedersen7141]

Thanks for another interesting video! :)
Would it be possible to make a video about how you make your logo on oscilloscopes? Just a suggestion.

[@TeardownOZ2CPU]

thanks, you are not the first to ask, so YES it is planned

[@renepedersen7141]

@@TeardownOZ2CPU Great! :)

[@Omegaman1969]

Great! What are you driving the graphics with ? PC and a sound card ?

[@TeardownOZ2CPU]

arduino and 2 x 8 bit DAC and 2 opamps, my logo is too complex, many points need very fast update, so i can not use a soundcard
I will release a video about how it was made.

[@Omegaman1969]

@@TeardownOZ2CPU Ah I see, neat. Look forward to that video.