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Dead colour guns on crt

Printed From: ukVac.com
Category: Technical
Forum Name: Tech, Maintenance & Repairs
Forum Description: Need Help? Ask Here
URL: http://www.ukvac.com/forum/forum_posts.asp?TID=385710
Printed Date: 20 Sep 2021 at 6:07pm


Topic: Dead colour guns on crt
Posted By: virtvic
Subject: Dead colour guns on crt
Date Posted: 14 Sep 2021 at 9:25pm
I have tested my 28” tube with a rejuvenator, kindly on loan from Porchy and initial tests show that the guns weren’t showing up on the needle range or with the cut off voltages slowly increased.

I rejuvenated the Red and got a small light show for 20 seconds with the neck glow going on and off etc.
Tried the green next after waiting a minute or so. It glows, but no light show and don’t seem to end the rejuvenation
Same with the blue.

I’m thinking that the guns are knackered and this time is useless?

When I reinstalled the chassis, the red was much improved, but no blue and only a very faint bit of green on the 19 in 1 test pattern.

Any thoughts?

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THE PENCE IS MIGHTIER THAN THE SWORD!

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Replies:
Posted By: FinalFight
Date Posted: 15 Sep 2021 at 10:40am
I know this is not helpful to your post vic but i remember being told once a tube is rejuvenated its only temporary and they seem to go back the same after a few months i dont know how true that is?


Posted By: Macro
Date Posted: 15 Sep 2021 at 12:03pm
My understanding is that the rejuvenator works by heating up the gun which makes the metal expand and the accumulated oxidisation then (hopefully) cracks off, leaving a nice clean (but thinner) gun.

This does mean it can only be performed so many times, as the crud that it removes is oxidised gun, so eventually there is not enough left or putting an increased voltage through simply burns it out.

usually with home use though it can last a fair while.

I only ever had one done, and that was about 15 years ago - still working OK in my Atari System 1 cab.





Posted By: FinalFight
Date Posted: 15 Sep 2021 at 5:39pm
Originally posted by Macro Macro wrote:

My understanding is that the rejuvenator works by heating up the gun which makes the metal expand and the accumulated oxidisation then (hopefully) cracks off, leaving a nice clean (but thinner) gun.

This does mean it can only be performed so many times, as the crud that it removes is oxidised gun, so eventually there is not enough left or putting an increased voltage through simply burns it out.

usually with home use though it can last a fair while.

I only ever had one done, and that was about 15 years ago - still working OK in my Atari System 1 cab.





Ahh that makes sense its good to know yours worked out and its lasted all them years


Posted By: robotech
Date Posted: 15 Sep 2021 at 6:47pm
I thought the same sure I have read that it burns a layer of oxidisation off of the cathode

My set has gun tracking and clean and balance short
removal ect rather than going strait for the heavy re juvinate
I've only ever used this set though so don't know what other sets offer and I'm still learning too the manual that comes with the set misses a few important bits out that I managed to get pointers on through other people's you tube videos

I've had tubes that have shown very low on the test scale
That have had to have the clean and Ballance carried out a few times to get the guns up on the scale
I can do indervidual guns on this set but it takes seconds to clean each gun I wouldent want to leave it on for longer than that if you've been leaving it on for minutes you might have cooked it
If your guns are showing nothing it's not going to hurt to keep trying it a few more times if the tubes knackered anyway
The grid voltage and heater voltage need to be set right for the tube you have though you can't just connect it and rejuvinate
Run the tube number through the tubular website to find correct voltages for your tube

As for the clean only lasting so long dosent the tube naturally build oxidisation on the cathodes through normall usage anyway so is allways degrading gradually
It's not like there on 24hrs a day in your house I would imagine it would last year's in a home environment



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Daytonaaaaaaaaaaaaaaaaaa lets go away


Posted By: Retroman839
Date Posted: 15 Sep 2021 at 7:28pm
all depends on how much a tube was used
if it had a life in a jap arcade circa 1980 -1990

was most likely never switched off so could be cooked
it’s like office crt monitors always burned to a crisp.

basically they just go dim… phosphors degrade too lowering brightness

look all over for tell tale signs of how much usage
normally lots of old crusty flux around hot area of chassis that have been well used
baked pcb plastic again in hot areas discolouration on pcb..

but flyback does the brightness too so maybe it’s not right?
is b+ voltage correct
has it had a cap kit caps will help colours if the caps are knackered
   


Posted By: robotech
Date Posted: 15 Sep 2021 at 7:53pm
All I know is that every tube I've done so far has looked like a new tube beautiful vibrant colours ect
So they can't be all that bad

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Daytonaaaaaaaaaaaaaaaaaa lets go away


Posted By: Bods
Date Posted: 15 Sep 2021 at 8:11pm
Interesting and i was going to ask what it actually does, used them at work when they boosted the knackered tubes before they had a sale selling all the old crap out warehouse and gave 3 months guarantee

Was also under impression they would last 3-6 months but obviously depends how much its used, some people have TV on half the day everyday

Still haven't tried the ones i have yet, nice to have them though, did have a couple of tubes that looked poor, hopefully i still have em and will try it out

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Posted By: Retroman839
Date Posted: 15 Sep 2021 at 8:21pm
good tips on using the website tubular
and short bursts eliminating shorts
thanks robotech

i nearly picked up my first rejuvenator last week.
i will eventually get one.. and have a few tubes that i think may benefit

hope vic sorts his tube out
or at least gets it somehow verified as it’s a pain
you want to know either way if it’s a keeper
or for the scrap heap


Posted By: Vamino
Date Posted: 15 Sep 2021 at 8:28pm
Originally posted by robotech robotech wrote:

All I know is that every tube I've done so far has looked like a new tube beautiful vibrant colours ect
So they can't be all that bad


The MS9 you serviced for me still looks fantastic mate. I've soak tested it for hours and hours and it still looks as vibrant as it did when I first dialed in the colours + geometry. Your rejuve box is a really nice piece of kit. Smile

On this MS9 I think the blue gun was showing as bad when we first tested it. You noticed that the blue pot on the chassis was turned up to the max which would make sense. Once you had cleaned the blue gun I think it briefly showed a short, but, after another quick blast the readings were then all showing good.

With the blue pot on the remote set to the middle, the blue pot on the chassis is now set to approx the middle and I'm getting nice blues. Way better than the sh*tshow before tinkering with it!

Here's a picture from a Groovymame setup running at 15khz on the same MS9.
Some PCB's tend to look a bit nicer from my experience, but the results we got speak for themselves.




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Insert Coin[s]


Posted By: robotech
Date Posted: 15 Sep 2021 at 8:34pm
I have a bandk 476 it's a really nice set came from a TV repair shop and looks to have been really well looked after
It Has a selection of different sockets and all the manuals booklets and paperwork from The TV shop over the years
There's a few videos on you tube explaining how to use this model correctly without them and just the manual I would of been confused as it's not explained too well

It's a tool worth having even if the effects turn out to be short term
if your boosting a tube with 20 years plus of dayly arcade useage and it already has poor emissions to get any kind improvement over its current status is a bonus
It's not like your going to get hold of a new tube any time soon


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Daytonaaaaaaaaaaaaaaaaaa lets go away


Posted By: virtvic
Date Posted: 16 Sep 2021 at 1:11pm
The one I’m using came from Porchy and automatically sets the correct voltage with the adapter that you use.
When I rejuvenate, it does a little light show in the neck if it’s doing it correctly. When I do (what I think) is a dead gun, it just keeps going and doesn't automatically finish it’s thing.

When I test them after and do the ? Test the needles are way down, where a healthy tube should read circa 0.7 mA

-------------
THE PENCE IS MIGHTIER THAN THE SWORD!

Check out the podcast

http://tenpencearcade.co.uk

Got cabarets? > CALL ME!



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