Sparks inside the tube and cracking sounds

[Arm123]

Hey guys...

I just wanted to get a confirmation from the more experienced monitor people around here.

I was working on 5 of the same dead or dying chassis.  I got them all working and ready to use.  I was using the same known working tube to test them all.

I then proceeded to put them back in their cabinets and pair them off with the original tubes they came in with.  However, one of the five emits a cracking sound when powered up.  I don’t leave it on for more than 5 seconds.

I thought I would clean off the area around the anode cap and reseat it.  This did nothing.  I turned off the lights and tried it a few more times.  I noticed that there were sparks coming from inside the tube around the top corners.

This indicates a dead / faulty tube... ?  am I correct in assuming this ?

Thanks guys.

[grantspain]

is the earth braid present around the tube

[Arm123]

Indeed it is...

I believe i remember, when this monitor was first brought to me, that this tube did the same exact thing before going completely dead.

However, since removing the tube from the chassis, the guy said he kept it in his garage.  That was stupid, since it is winter.

So i was thinking that it may be moisture.  I left it indoors for three days.

Any thoughts on that ?

[grantspain]

3 days should be enough to dry out,
arcing from each corner inside the tube is not something i have ever seen and i have been in the coin op business for 22years
maybe ken or qrz have a view on this

[Arm123]

Its actually one top corner...   from the back and inside the tube that i see the spark.

[grantspain]

do you have access to an air compressor?

[Arm123]

i do...  you thiking its perhaps somthing inside the anode hole ?

[qrz]

under normal conditions there will not be ANY arcing inside the tube enclosure.

loosing the vacuum or a gassy tube can allow arcing to occur there.

an external arc from the anode cup to dag can be sealed w/silicone rubber or "corona dope"
arcing from tube exterior would be likely be due to an improper (defective) ground.

lastly , a 2nd anode short is where the anode is effectivly connected to the crt pins .
and yes , i have had a few like that -- quite the light show pulling an arc off the exposed pins
 
note:  typical anode voltages range 12-30kv  ( 13 - 27" +) 
x-production can occur above 32kv (a bad thing !)

qrz

[Arm123]

thanks qrz.

I just plugged that chassis into a known working tube and low and behold.  The chassis exhibits the same problems it had when it first came in.  So ill be replacing an IC and a resistor.

I 'think' i can assume that tube is shot ?

[SavannahLion]

an external arc from the anode cup to dag can be sealed w/silicone rubber or "corona dope"
arcing from tube exterior would be likely be due to an improper (defective)

"dag"?

Also, is that what the steel braid around the tube is for? I was puzzling over that when I realized arcade monitors don't have degaussers....

[qrz]

an external arc from the anode cup to dag can be sealed w/silicone rubber or "corona dope"
arcing from tube exterior would be likely be due to an improper (defective)

"dag"?

Also, is that what the steel braid around the tube is for? I was puzzling over that when I realized arcade monitors don't have degaussers....

sry, "dag" is slang for the conductive coating on the crt surface. the braid is the ground "conduit" .
and yes , they do have deguassing circuitry - (not needed on bw sets)

if the tube exhibs the same symptom on a known working chassis , it would be safe to assume the crt is at fault.

qrz

[SavannahLion]

and yes , they do have deguassing circuitry - (not needed on bw sets)

Then I must be confused. I thought those degauss wands are used because those monitors lacked a degaussing circuit. However, it's probably best I bow out of this thread to avoid a complete hijack.

[qrz]

confusion is purely optional .....
manual deguassing coils usually produce a stronger field than the internal coils.
meaning , it can remove "spots" the automatic circuits are unable to handle.
and the manual coil may be positioned to remove stray magnetism on framework, etc..

a "dumb" question is one that is not asked 

qrz

[Rickn]

Just show your post, first off the bad tube sounds like what is called an open Anode, very rare to find it in a tube that has been in service??

Here is a quick explanation:
The flyback produces the High voltage ( 25000 volts or so). This is the voltage that is on the anode cap ( that suction cup thing).

It needs a return path to ground, this happens inside the tube, then completes itself to that "silver ground braid" that has the black lead that plugs into the neckboard.

Gassey tubes, are normally caused by a couple things.
-as a manufacturer, brand new tube from the factory.... means insuffucient RF spot knocking ( a process where the tube is hit repeatedly with high voltage energy to clear particles)
- in the field, a particle of dust, glass ... inside the tube has find it's way to the neck of the tube.

This fault is characterized as a blue glow in the neck of the tube... clear it with a rejuvenator.

Alternatively if you are a good board tech and do not mind repairing the board (cause this one may cause faults)... plug the momitor in and crank up the G2 so that retarce is quite visible, let it run a while -after a number of arcs it may clear itself.

CAUTION DO NOT DO THIS WITH UNDERSTANDING THE COSEQUENCES.. TUBE IS NO GOOD AND NOW THE CHASSIS NEEDS TO BE FIXED.

Air tube is a tube that has a crack, air leak somewhere.... if there is a very bright orange in the neck with arcing... AIR tube throw it out.


yes I know I just said way more than what was asked, but thought it may help others.

Good Luck

Rick Nieman
Rick@Niemandisplays.com
www.niemandisplays.com