Repair help needed on Trio CS1022 Oscilloscope

[hadihf]

trio cs1022

Hi,

I have a Trio CS1022 Oscilloscope which has a problem that trace is very bright. I cannot control the briliance control and when i turn it full there is noise comming from inside..like a low hiss. Anybody please give hint on repair. Scope is very old and have to diy. Please help.

 

[jacklim]

cs1022

Hi,

I am new here. I was also trawling the net for answers to the same problem until I came upon this nice forum.

I fixed the problem on my 20 year old scope by soldering a spare resistor of 42Ω 3W rating in series with the CRT heater. The heater pins are on either side of the key at the CRT base.

My idea to reduce the heater current worked to reduce the uncontrolled trace intensity, which I heard is a common problem for this scope. I am thinking of mounting at the chassis back a potentiometer of around 50 - 100Ω to enable intensity adjustment.

Do let me know if you succeed.

 

[hadihf]

manufacturer of trio oscilloscopes

I replaced two diodes D4 & D5 in the HV power supply with 1N4007 and it worked ok.

Regards

 

[jacklim]

osciloscope trio manual

I changed the 2 diodes mentioned, one of which was found shorted. Now the scope works like new.

Thanks for the tip and the schematic, which I made a copy to put inside the scope in case of future trouble!

Regards.

 

[E-design]

triooscilloscopeรุ่นcs1022

It may be a good idea to replace D4,5 with a better faster diode than a 4007 which will be lossy at high frequency and may over-heat. Also it can't harm to change C12,13 as it is part of the restoring circuit and subjected to high voltage stress.