shmups.system11.org

hi all

wanted to see if people here can venture a diagnosis for the following issue on a bvm-d20f1 model.

the monitor works normally, shows a nice picture and everything works as expected, except that every minute or so there's an audible snapping sound coming from the back of the monitor, with a simultaneous twitch of the whole picture.
then after a minute this will repeat again.

the snapping sound is audible but not incredibly loud or anything, probably lower than the snap you hear when degaussing.


here's a recording of the fault:

https://dl.dropbox.com/s/8lezyfgb24husos/bvm-snap.mov


any ideas as to what could be causing this will be very welcome.

thank you.

Have not checked your video yet (no speakers accessible at the moment) but your description makes it most likely sound like a cold solder joint - easy fix, as long as you can track down the bad solder! Hopefully that is the case.

thank you!

I have a little good news and quite a lot of bad news.

The good news I have had exactly this fault on a D24 back in the day and managed to repair it. It would crack intermittently and the screen would wobble when it did.

The bad news is that it was a faulty flyback. I had to use a spare one recovered from a dead old d24 which had a faulty tube.

You might struggle to locate this part but Savon Pat would be a good start. Also, changing this is INCREDIBLY dangerous if you don’t know what you are doing. You could seriously injure or kill yourself if you don’t discharge everything properly. You might want to find a professional to do this for you, but good luck finding an engineer still qualified or willing to work on a crt.

Hello,

This is very likely a fault on your D20’s PA board. Do guy have a multimeter?

If you can, please PM me.

Thanks

hello, thanks everyone for chiming in, had a friend look into this.

he checked and recapped the PA board, then fixed some cold solder joints in the flyback, and applied vaseline to the cap.
we thought the monitor was fixed because the fault was seemingly gone.
but as I found out later, it still has the same fault, it's just that instead of doing it every minute it does it every 15 minutes or so.

an improvement but not quite there yet.
my friend things the PA board wasn't related to the fault.

I have zero technical skill when it comes to electronics so I can't really give a more in depth update.

any ideas would be more than welcome.

One important thing: you should have dielectric grease applied to the anode cap. Vaseline isn’t a suitable replacement as far as I’m aware.

will try to clean up the vaseline and apply this instead, thank you



is this the right stuff?

https://www.amazon.com/Permatex-81150-D ... 000AL2RI2/



should I wipe off the vaseline and clean any left overs with isopropyl alcohol?

(I understand you can only do this with a discharged tube)



thanks

Wipe it clean with a dry cloth, water or iso can dissolve the aquadag if you are not careful.

thanks

is this the correct thing to replace the vaseline with?
https://www.amazon.com/Permatex-81150-D ... 000AL2RI2/

EDIT you already know that you should discharge the tube, moving on

https://www.youtube.com/watch?v=2YaElaoPTBk

This is a video related to the PA board and over loading. Does yours go into overload? Maybe you could try what happens if you crank up brightness on an all white screen.

yeah thanks I did watch that video, the overload indicator does light up occasionally when showing an overly bright picture, but never really shuts down like in the video.
I took this to be normal behaviour even after watching the video.

maybe I should put 25 ohm terminators? It's pretty bright but doesn't bloom in weird ways.

Yup, that one works!

many thanks

The flyback that was mentioned is a high voltage step up transformer, there are no solder joints in it. It must be replaced.

yeah I'm rereading the explanation and I got this wrong. the cold solder joints he fixed where not in the flyback, I got that jumbled up, sorry.

thanks everyone for chiming in, any ideas on what to look for is appreciated.

I've recorded a new video of the issue:
https://dl.dropbox.com/s/u8jgvchv9girol9/bvm-snap.mov 

There doesn't seem to be any sparks or anything, it's just that the screen twitches and there's a quiet snapping sound, about every 15 minutes.

Regards