noise from the CRT (Color Classic)

[mraroid]

Hi...

I installed a re capped logic board and a re caped analog board in my color classic. When I booted, I got the happy chime, but nothing on the screen. It was as if the computer was turned off.  After another disassembly and assembly I checked everything and could find nothing wrong. Same issue.  I swapped out hard drives, and tried to boot to a SCSI boot CD.  Nothing.

Yet another tear down. I pulled off the metal box that plugs into the back of the CRT.  When I removed the metal lid, I found 4 solder points that looked a bit off- maybe rusty looking? Using a very soft tooth brush, I brushed the 4 solder points, lightly used a little compressed air, and then re assembled. I inspected my CRT with a hand lens under good light.  No cracks, or anthing looking bad. 

My computer will boot now, and the screen looks good, but I now have another issue.

When I boot the CC, I get a buzzing and humming noise from the metal box that is plugged into the rear of the CRT.  And when I turn the CC off, I get some snap, crackle and pop from that box.

You can hear the sound the metal box makes when I boot in this video.  You can down load the  627MB video from my google cloud here:

https://drive.google.com/file/d/0B5MQG-qmz1DLOGE4WHBuYVU5VVk/view?usp=sharing

Sound is good, video is off. Sorry.  I did it in a rush.

What you can not hear in the above video is the snap, crackle and pop when I shut down the computer.  I will make a short video of that noise (I did a reboot not a shut down in the above video).  I do not know this stuff like all of you, but the buzzing sound, and snap crackle and pop dose not sound normal to me.  Is it?

Enclosed are some photos of the rear of the metal box that plugs into the rear of my CRT.  It has the cover taken off.  On the left of the photo are the 4 points of solder that I cleaned with a soft tooth brush.  I just bought a can of contact cleaner.  Should I dis assemble this box further and spry a little on the top or bottom of the circuit board of this box?

Leave it as it?  Do more work?  I am leaving the country soon (I live in the USA).  I am moving to Ecuador.  Shipping a analog board out of Ecuador would be easy, but I would pay one hell of a duty to get it back.  So if I have a problem, I need to fix it now, not later.

Thanks for your opinions.

jack

 

[uniserver]

the sound in the video is completely normal, i mean you are right up on a naked crt,  there is a gun right there firing electrons at 24KV.

 

[uniserver]

when you power down a crt there is static like snapping noises as the field collapses.  

 

[mraroid]

OK.  If that is all it is, then I am a happy camper.  I did put the case back on the CC, but I can still hear the noise.  Maybe it is because I am listening for it?  I don't recall ever hearing it before. 

But after my tooth brush cleaning, I see a great image on my CRT.

I bought a can of contact cleaner.  Can I (or should I) dis assemble the metal box, spray the circuit board inside and re assemble?  It looks kind of grody inside. 

Or, leave well enough alone?

Also, can I use silicone caulk to go around the CRT neck and that metal box? It had some gray stuff I had to cut away to remove the box in the first place.

jack.

 

[uniserver]

yeah there might be a little bit more output cap ringing from the SMPS, than before, just because I don't goop the new caps down with hot glue like they did from the factory... but yeah,  it sounds like a normal CC to me.  I'm sure it's less with the case on vs right up on the back of the tube with the cam.

'

i'd leave her be and use it,  with the CC and 5XX, contact cleaner is very useful on the edge connectors of the AB/MB  all it takes is one little hunk of crap in one of those connections and issues appear.

 

[techknight]

This is normal. 

There are little spark gaps in the neck PCB that bleed off excess voltage, and thats the hiss you hear. Also, if the CRT tube itself is a little bit gassy, it will do that. 

 

[mraroid]

Ah!  OK.  Well if you two think it is normal, I think I will silicone the metal box in place tonight and let it dry.  I took a chance and sprayed contact cleaner on the bottom of the circuit board and some of the end tabs that had turned brown or discolored.  That cleaned them up. I dried it out, put the metal cover over it, and fired up the CC.  It booted fine.  Colors on the CRT are perfect.

I found extremely small wires on the bottom of this small circuit board in the metal box that attaches to the CRT.  They are *really small*.  I found them when I was using a hand lens.  What is that all about?  After market fix, or is that factory?

I hope my CRT is not going bad.  So far, it looks perfect.  About 6 months ago I found what was said to be a NOS CRT on ebay and bought it. It came in what looked like old factory wrapping. I double boxed it and it is going to Ecuador with me.  So if this one is going south, I can swap it out. I saw that China is selling rebuilt Sony trinitron CRTs (M23JVK12X).  I almost bought a rebuilt one, when I found the NOS one on ebay.  I have no idea if it is any good or not.

Guess I will forget about the noise after a bit.  The good news is that I can take this CC apart in the dark with one hand now.

Thanks gentleman for the good feedback.

jack
 

 

[mraroid]

Good news!  I have been working on my CC for maybe  8 or 9 hours per day (trying to format a CF card).  My CRT seems just fine.  So I guess you guys were right - noise or no noise, the CC is working just great, colors on the CRT are perfect. That very soft tooth brush fixed the bad solder points and the contact cleaner cleaned it up even better.Thanks again. I am sure glad I have both my CC II logic board and the analong board re caped. 

jack

 

[uniserver]

awesome!