Analog oscilloscope ONLY working for a split second when restarted

[osmax_br]

I have a goldstar (LG) 9020g oscilloscope, its problem that it doesn't give any output , so I turn it off and then immediately on and it flashes for a brief second and then no output again

I am suspecting the hv circuit is malfunction , the problem is that I have a medical condition call HighVolt-Phobia and I don't know for sure how to test it without getting killed

My question

1- sources on the internet where someone explains how to deal with crt high voltage circuit (I want him still alive just to make sure 😀)

2- do you have any suggestions for the malfunction cause (maybe it is not the hv circuit) ?

3- channels where people fix similar things

4- general advice

5- THX A LOT <3

*There is 2 photos for my little device and the fast flash

[tggzzz]

Might be HV, might be the LV PSU, might just need a good internal clean.

Is the fault a new fault?

A 10s gurgle reveals the service manual https://gepengser.weebly.com/uploads/9/6/3/5/9635683/os_9020_g_lg-goldstar_1.pdf

[osmax_br]

Yup it is a new fault
Before that it was working but with dim display and then it  stopped working , I don't think it is a crt problem because the crt is flashing on startup
And side note , six months ago it returned working suddenly and I still dont know how it worked , however it worked a few times
I have the service manual , just need to see someone on yt working on similar HV circuit just to know that I am not risking myself

+ All the functions of the oscilloscope are working perfectly fine (function gen , and the xy functions ) and as far as I know they use the same low voltage psu as the crt (maybe I am wrong but that's what I believe )
Thanks for your reply

[tggzzz]

Yup it is a new fault
Before that it was working but with dim display and then it  stopped working , I don't think it is a crt problem because the crt is flashing on startup
And side note , six months ago it returned working suddenly and I still dont know how it worked , however it worked a few times
I have the service manual , just need to see someone on yt working on similar HV circuit just to know that I am not risking myself

+ All the functions of the oscilloscope are working perfectly fine (function gen , and the xy functions ) and as far as I know they use the same low voltage psu as the crt (maybe I am wrong but that's what I believe )
Thanks for your reply

The service manual ought to indicate the "interesting" areas.

Certainly the connections at the other end of the tube could bite, and the other one could be a "sticking plaster" on the side of the next with a thick cable coming from it. The latter takes a long time to discharge.

[Analog Kid]

[...] the problem is that I have a medical condition call HighVolt-Phobia and I don't know for sure how to test it without getting killed

I'll just say that that is a good condition to have. You'll live longer.

[George Edmonds]

Hi

First you need part 3 of the online service manual to get the schematics.

If you are not trained or experienced with HV circuits, DO NOT work on them to avoid personal injury and possibly death. There is some 1.9KV on the CRT Cathode/1st Grid

I have had a quick look at the HV/CRT circuits in the service manual, the design is at best very poor.  My best guess is that the fault is in the CRT high voltage circuitry.

A quick look on a certain auction site shows numerous faulty such LG scopes for sale, I wonder why.

I have been repairing, and back in the day designing CRT scopes, for the last sixty five years so I do know what I am doing with them.  Plus I am still very much alive still.

G Edmonds