Microvitec Cub 1431 repair

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mw0uzo
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Microvitec Cub 1431 repair

Post by mw0uzo » Thu Jan 26, 2017 2:00 pm

I got 1 of 2 working!! :D

Both of these monitors feeling very sorry for themselves.

1) Worked initially. Then horizontal lock collapse. Then vertical collapse. Then no line drive, PS ok, but otherwise dead.

Replaced TDA1180P horizontal processor and TDA1170 vertical driver. Replaced r235 10 ohm fusible and c224 1000uF 40V.

Got line drive back, but the LOPT was still damp from the monitor being stored out in a shed temporarily :shock: LOPT arced at the output terminal. #-o
Changed LOPT from the other monitor.
SV204819.JPG
SV204820.JPG
Focus isn't perfect, there's something wrong with the focus pot or tripler. Put switch cleaner in and allowed to dry, got some focus operation back but still not quite right. Seen it lose focus once. But it seems to be OK now, I'll leave it as it is.

mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Thu Jan 26, 2017 2:07 pm

Inspected the arced LOPT. It had arced under the first layer down to the bottom of the transformer.
Removed the label and terminal 'cover'
SV204822.JPG
Can you see the crack?
SV204824.JPG
Cleaned it all off with IPA and a toothbrush. Picked off the epoxy around the crack. Accidentally damaged the fine wire leading to the output terminal - repaired.
Covered the repair with epoxy and around the terminal and all over where it had arced before and between the base and the winding.
Glued back on the cover. Reinstalled the LOPT. Waiting for the glue to dry and I'll fire it up.

2) Vertical collapse. Then no line drive after 10 mins.

Replaced R226 10 ohm fusible and C224. Replaced TDA1180 and TDA 1170.

There's a stubborn vertical collapse problem with monitor #2 and also something wrong with the green driver circuit. Hopefully I'll get line drive back and be able to sort the additional problems.
Last edited by mw0uzo on Thu Jan 26, 2017 2:20 pm, edited 1 time in total.

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1024MAK
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Re: Microvitec Cub 1431 repair

Post by 1024MAK » Thu Jan 26, 2017 2:18 pm

I'm mobile, so don't have a schematic to hand, let alone the chance to look in mine, but if there are other electrolytic caps, it would be a good idea to renew those as well :wink:

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Thu Jan 26, 2017 2:45 pm

1024MAK wrote:I'm mobile, so don't have a schematic to hand, let alone the chance to look in mine, but if there are other electrolytic caps, it would be a good idea to renew those as well :wink:

Mark
Ok thanks, I never did find one for S3. Will probably need it for the vertical collapse problem, as the vertical driver has been replaced but still no worky

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danielj
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Re: Microvitec Cub 1431 repair

Post by danielj » Thu Jan 26, 2017 2:55 pm

Series 3?

d.

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1024MAK
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Re: Microvitec Cub 1431 repair

Post by 1024MAK » Thu Jan 26, 2017 5:05 pm

Err, sorry if there has been any confusion, I only have the same schematic as available on this forum...

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Thu Jan 26, 2017 5:06 pm

Haha! It works!
SV204825.JPG
It seems the arcing, has been fixed, so far.
I do get a curious 'tick' every 5 minutes or so though, hmmmm.
For reason unknown, the vertical frame came back and I have a full picture. It's not centre, but it works!
Focus OK. The green problem I thought had gone, but when I turn the lights off there is a slight green background, so it looks like the green gun maybe needs an adjustment.
For now I'll just leave it on and see if it dies.

On the first monitor, the focus problem came back.

mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Fri Jan 27, 2017 4:38 pm

The 'tick' had gone from the monitor :)
Readjusted the RGB settings on the CRT neck and now its picture perfect =D>

mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Mon Jan 30, 2017 7:51 pm

A few problems have occurred with the monitor so far
Brightness has gone funny - I'm hoping its a bad pot or something... Switches on bright but then fades and I have to turn it up at the back. Plus the brightness response isn't linear.
Monitor starts to lose focus after being on for a very long time.

mw0uzo
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Re: Microvitec Cub 1431 repair

Post by mw0uzo » Wed Feb 08, 2017 4:57 pm

Fixed. The problems were
Noisy/bad brightness pot.
Bad focus pot.
Switch cleaner on both and worked them for a minute, left to dry then reset.

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