CRT Repair Question (Bang & Olufsen MX7000) - Page 1
Forum section: electronics / repair

author: gameboy0101
author_rank: Newbie
timestamp: July 07, 2020, 10:21:30 am
content: Hi,I have just brought a 20+ year old CRT and its in pretty good condition, except for 2 small black shapes showing just at the bottom of it. I have confirmed they are there on all inputs. Im not really sure where to start with CRT's tbh and was wondering if anyone might know what these symptoms might point towards and if its worth attempting a repair. (Im not an electronics expert, but do like to tinker so assume my skill level is not super high when it comes to repairing electronic components).Appreciate any advice!Thanks

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 07, 2020, 01:24:09 pm
content: In plenty of years repairing CRT TV's it's the first time I see that, it looks as if there is a loose part inside the CRT.It could be the ceramic disc and metal strip that are normally attached behind the EHT connection have broken.In any case if there are loose parts inside the CRT you can't repair it.You could get them to slip out of the way by tilting TV back about 30° (I know they're heavy...) And giving it a good whack that may get the parts to rest in the bottom of the glass rather than on the shadow mask.You don't want to tilt too far back either, if the floating parts get stuck in the CRT neck then you have no picture at all.

author: mzacharias
author_rank: Frequent Contributor
timestamp: July 07, 2020, 02:44:45 pm
content: I think it's damage to the internal CRT mask.No fix short of a new picture tube.

author: gameboy0101
author_rank: Newbie
timestamp: July 07, 2020, 03:16:29 pm
content: Quote from: shakalnokturn on July 07, 2020, 01:24:09 pmThat seems to have fixed it! I just leant it back and dident even need to give it a whack! Maybe just the car journey made something come loose?Thanks for your help!

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 07, 2020, 05:36:27 pm
content: Should be fine as long as it sits, just remember the risk is there each time you move it.A bunged CRT neck or dent in the shadow mask and you'll definitely be in need of a new CRT or TV.May I ask why you went for this model specifically?

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 07, 2020, 05:56:35 pm
content: For the youngsters who have never shattered a CRT to a jagged heap...The shadow that was visible on gameboy0101's photo is the "getter" holder that has come un-clipped from the back of the final anode connection. Not many photos around internet.https://www.researchgate.net/figure/Process-of-getter-firing-The-getter-container-is-inductively-heated-by-a-rf-coil-First_fig4_240668339For general view of colour CRT internals:http://www.earlytelevision.org/images/26_inch_crt-cutaway-hd.jpg

author: gameboy0101
author_rank: Newbie
timestamp: July 07, 2020, 08:05:03 pm
content: Quote from: shakalnokturn on July 07, 2020, 05:36:27 pmI wanted to get a CRT for some old consoles (I have yet to also get). I had experience of B&O TV's as my granddad used to have them and I always thought the picture looked great so decided to see what I could get. I ended up buying 3 different models as they are so cheap now. Dangers of Ebay.One is really great (Avant 32"), the other is this one, and the third..... well seems to have some issues.

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2020, 08:55:25 pm
content: Hmm, that does look like the image of a fallen-off getter.Irrc, B&O were reputed to use 'Southern Hemisphere' CRTs in their European TVs, so that they could place the EHT cap underneath the CRT and produce a very thin looking looking upper case profile. Maybe the whole Northern Hemisphere / Southern Hemisphere CRT thing is an old wives tale - I've never been able to make up my mind.

author: gameboy0101
author_rank: Newbie
timestamp: July 07, 2020, 09:53:28 pm
content: Quote from: Gyro on July 07, 2020, 08:55:25 pmOther then being careful when moving is there anything I should be concerned about if it is that which has fallen?

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2020, 10:01:43 pm
content: Probably not. It was always at the same potential as the bulb inner coating, the shadowmask and the final anode. It looks too big to get further down the neck than the final anode.The biggest risk is that it gets lodged somewhere where it can't easily be freed, for instance the shadowmask mounting springs or between the final anode and the glass.

author: james_s
author_rank: Super Contributor
timestamp: July 07, 2020, 10:11:17 pm
content: That looks like the getter has come un-welded from the electron gun and fallen down into the funnel. It is a ring on the end of a strap that hangs it against the inside of the bell where it can be heated by an induction coil when the tube is being pumped down. I've never seen one fall off before but I can't think of anything else that would create a shadow of that shape.I love CRTs, it makes me sad to think how many of them have gone to landfills and recyclers in recent years. They were absolutely everywhere and yet soon they will be gone. They have some unique properties that no other display technology has, especially for classic games, the light guns require a CRT display.

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 08, 2020, 02:13:23 am
content: Quote from: gameboy0101 on July 07, 2020, 09:53:28 pmNow I ponder at it, has the whole history of CRT discussion ever asked how sensitive they are to impactfrom the inside?

author: james_s
author_rank: Super Contributor
timestamp: July 08, 2020, 05:14:29 am
content: Quote from: shakalnokturn on July 08, 2020, 02:13:23 amThey certainly are prone to damage, I had a Tek 2215 with a loose piece of metal rattling around inside the CRT which would occasionally short something. It was also common for CRTs used in cocktail table arcade games to develop faults from debris falling down into the electron gun which was pointed up in that application.

author: Gyro
author_rank: Super Contributor
timestamp: July 08, 2020, 09:52:23 am
content: It's entirely possible that this was faulty manufacture and the getter fell off almost immediately. After all, a large screen CRT isn't something that you pick up and shake to see if it rattles!It could well have spent all of its working life like that. It would take quite a bit of jiggling to get it to settleinsidethe deep metal frame that the shadowmask foil is welded to, it would normally just drop to the bottom of the bulb.