Microcitec Cub 452 (Lack of) Display Issue

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dhoggan
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Microcitec Cub 452 (Lack of) Display Issue

Post by dhoggan » Fri Aug 17, 2018 3:11 pm

Hi,

I've managed to pick up a Cub 1431 in reasonably good condition, but it seems to have a bit of an issue. It powers on but all I get is the following, whether or not I have the RGB cable plugged in.
452 front.jpg
The front
What is interesting is that it has more options than other Cubs I've seen on the rear:
452 rear.jpg
Rear with unusual connector options
I've tried the switch in both positions - not really expecting it to work, but to see if anything changes. IN the TTL position I get the above output, in the 75ohm position, just a black screen. I have tried generating some output (*HELP) to see if it changes the display, but nothing obvious.

I've read a couple of other posts on Cub monitor issues, but they were more about rolling pictures, not no picture!

Any ideas what this might be/is is repairable/where to start?
BBC Model B Issue 7 with MMC Card implant, Microvitec Cub 653.

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1024MAK
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by 1024MAK » Fri Aug 17, 2018 3:33 pm

The other inputs are analogue red, green, blue and sync inputs (all terminated at 75 ohm). When using with a Beeb, you can ignore them. When using the DIN socket, the switch needs to be in the TTL position.

I'm on a phone at the moment, so can't see the photo very well. Is it showing a bright horizontal line at the top, but with no other illumination of the screen?

Does this line disappear or go dimmer if the Beeb is switched off or disconnected?

Mark
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by dhoggan » Fri Aug 17, 2018 4:07 pm

Hi Mark,

There's no obvious change in the lines with the BBC on or off, or even unplugged. And yes, you've described it exactly. The slight glow on the screen is simply as I've upped the brightness a bit, but the display is two or three fines lines - not a single line. It appears that these are scrolling horizontally. I did manamge to get them to stop scrolling when I unplugegd the RGB cable, but a power off/on and they were scrolling agian.

I wIsh I had an analogue RGB source - that way I could test the 75ohm side - I'm guessing that would prove the tube is OK. Unfortunatley I don't have anything to use as a source.

Thanks,

Dave
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1024MAK
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by 1024MAK » Fri Aug 17, 2018 5:21 pm

I don't think using the analogue inputs would make any difference. I think this fault may be a problem with the electron beam scanning system. It looks like the horizontal scan may be partly working, but it appears to me that vertical scan is not working.

Most CRT displays, when the brightness and contrast controls are cranked up to maximum, result in a glow across most of the screen. Sometimes this even works with no signal.

There are however other possible faults, but this looks most likely.

The good news is that the EHT circuit is working, as is the Tube, so this could well be repairable.

Mark
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by dhoggan » Fri Aug 17, 2018 6:22 pm

Ah, thanks. So, there is hope :-)

I guess the question then is: repairable by someone of average competence (me!) or by a specialist? As Microvitec no longer do repairs themselves (at least according to their web site), is there someone who repairs Cub monitors that anyone here could recommend?

Other than this it is in quite good condition, so it would be a shame to bin it.

Thanks,

Dave
BBC Model B Issue 7 with MMC Card implant, Microvitec Cub 653.

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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by daveejhitchins » Sat Aug 18, 2018 6:57 am

dhoggan wrote:
Fri Aug 17, 2018 6:22 pm
I guess the question then is: repairable by someone of average competence (me!) or by a specialist?
You need to find one of the remaining TV repair shops that's run by an old guy who has the experience of CRT sets (very rare these days!). I'm fortunate, here in Newton Aycliffe, as we have just such a person that meets all those requirements - and has made the transition to LCD/Plasma TV repairs . . .

Dave H :D
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by dhoggan » Sat Aug 18, 2018 11:28 am

Hi Dave,

Thanks for the info and sounds like he might be a good place to start. Do you have an email address for him? I’m hoping he would be happy for me to ship it - assuming that he’d be intested.

Would have sent a PM, but that feature is still disbaled :-(

Thanks,

Dave
BBC Model B Issue 7 with MMC Card implant, Microvitec Cub 653.

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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by Kazzie » Sat Aug 18, 2018 4:44 pm

dhoggan wrote:
Sat Aug 18, 2018 11:28 am
Hi Dave,

Thanks for the info and sounds like he might be a good place to start. Do you have an email address for him? I’m hoping he would be happy for me to ship it - assuming that he’d be intested.

Would have sent a PM, but that feature is still disbaled :-(

Thanks,

Dave
Click the "Contact Us" link at the bottom of the page and you can ask a moderator administrator to enable your PM abilities. They're usually very happy to do so for anyone who asks.
Last edited by Kazzie on Sun Aug 19, 2018 5:49 am, edited 1 time in total.
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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by daveejhitchins » Sat Aug 18, 2018 9:19 pm

dhoggan wrote:
Sat Aug 18, 2018 11:28 am
Thanks for the info and sounds like he might be a good place to start. Do you have an email address for him? I’m hoping he would be happy for me to ship it - assuming that he’d be interested.
Let me give him a ring on Monday . . . I'll report back here.

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by daveejhitchins » Sat Aug 25, 2018 8:34 pm

daveejhitchins wrote:
Sat Aug 18, 2018 9:19 pm
Let me give him a ring on Monday . . . I'll report back here.
Sorry, I did ring . . . He's on holiday - just forgot to let you know :?

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

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Re: Microcitec Cub 452 (Lack of) Display Issue

Post by dhoggan » Tue Aug 28, 2018 7:40 pm

Hi Dave,

No problem - right now I’m in the middle of building a log cabin so all my attention is on that. But I will then actually have a place to permanently setup the Beeb, so happy to wait. It’ll just be good to know whether he’s willing out not so I can add it to my options.

Thanks,

Dave
BBC Model B Issue 7 with MMC Card implant, Microvitec Cub 653.

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