Microvitec Cub: Is it a 653 or 895?

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dhoggan
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Microvitec Cub: Is it a 653 or 895?

Post by dhoggan »

Hi all,

I while ago I picked up a Microvitec monitor but didn't get a chance to play with it as my Cub 653 (MS4 variety) has just come back from being recapped and looked glorious (an still does)!

I'm now looking at the other Cub in more detail and I'm not actually sure what it is. I though it was an 895 as it was legible in mode 0 and is the structural foam casing, not the metal shield one, and I thought that only the 895 came in LS form. Now I know I'm wrong, so this is either a 653LS or a 895LS.

The label on the front simply state "Microvitec Cub" with no number and the rear has a blank model number field above the filled in serial number. And that's it! The screen looks much lighter (when off) compared to the 653MSm, which appears almost inky black. As for 80 column mode, text looks fine on both, but I'm not sure that's a good was to tell if one it is a medium resolution (like my 653MS) or a high resolution monitor?

Can anyone think of a conclusive way to tell what it is? Would the lightness of the screen be an indicator?

As mentioned elsewhere, the 895s have surprisingly little info on them.

Thanks,

Dave
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VectorEyes
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Re: Microvitec Cub: Is it a 653 or 895?

Post by VectorEyes »

I have an 895 but I've never had a chance to test it!

I seem to recall reading somewhere that the 895 has a noticeably blue tint, owing to the different CRT tube it contains. If you put them next to each other, does white on one screen look noticeably 'bluer' on the other?
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dhoggan
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Re: Microvitec Cub: Is it a 653 or 895?

Post by dhoggan »

It maybe a daft question, but you mean the text displayed as opposed to the overall screen colour when off? If so, I don't think so. I'm trying to righ up a second Beeb so I can have both monitors on side-by-side as I wouldn't rely on my memory in the time it takes to change a cable!

Also, a Google found someone suggesting (copied below) a green tint, not blue, but again, I'm not sure if they mean when off or the white text when displayed.

The 1431-MS is the bog-standard low-res one (0.32dp IIRC), and this was
by far the biggest seller.

The 1451-MS had the higher-resolution tube. If you place one of those
next to a standard res tube model, you'll see the phosphor is a darker
grey. 0.29dp IIRC. Very nice when used with a Beeb.

The 1441-MS had the very high res tube, and as mentioned above, the
phosphor appears green when placed next to standard tube. Think this is
0.25dp. Overkill for a BBC.


I just dug out the orignal email from when I bought is a couple of years ago and it was sold as an 895 and I've no reason to doubt the seller, but thinking it is and knowing it is are different things.
Model B Issue 7 - Dual Gotek/5.25"; IFEL Sideways board; RetroClinic Co-Pro; VideoNuLA
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1024MAK
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Re: Microvitec Cub: Is it a 653 or 895?

Post by 1024MAK »

If you can take the cover off, it’s likely the tube will have a label or other marking with the tube manufacturers markings/part number on it.

Mark
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dhoggan
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Re: Microvitec Cub: Is it a 653 or 895?

Post by dhoggan »

Simple solutions are always the best :-)

There is not much to go on that's printed but there is a hand-written label that states either "1441 HIRES CIV" or "1441 H/RES CIV" depending on how you read it. I suspect the 1441 is the answer I was after so it does appear to be a 895 version. There is also printed on the blue PCB "Microvitec LCCD03".

I guess my next thought/question is whether it is worth using that or the 653. The image on the 895 has a vertical 'shimmer' so I suspect the caps need redoing, but not sure (1) the place I used a couple of years ago is still there and (2) it's worth what they charge. I like to darker screen (not sure what you call it, but the darkness when off" - as the blacks look, well black. But, I like the look of the structural foam case over the metal one, so I'm torn between the two.

Is there is a compelling advantage in using the 895 over the 653 on a model B or is going to be down to personal taste?

Thanks,

Dave
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Re: Microvitec Cub: Is it a 653 or 895?

Post by philpem »

I've scanned the service manual for the early Cubs - this includes the low-res and hi-res, but not the 653: https://archive.org/details/microvitec-cub-service.

The part number on the CRT tube should give away the model -- as would the part number on the CRT neck board ("HRTB 01" or similar for high res). The high-res (895 pixel) units have a different neck board and CRT.

Sadly the CRT part number label might be on the underside or one of the sides, and may be hard to see.

The shimmering is probably caused by a broken degauss PTC (at least it was on my 653). Does it stop after the monitor has been switched on for a while?


Cheers
Phil.
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dhoggan
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Re: Microvitec Cub: Is it a 653 or 895?

Post by dhoggan »

The shimmering appears more pronounced on mode 0 than mode 7 although both have it. Once the monitor has been on a while it's almost unnoticeable on mode 7 (almost, but just very feint if you look from a close range), but still there on mode 0 although, again, less so than when just powered uo.

Thanks,

Dave
Model B Issue 7 - Dual Gotek/5.25"; IFEL Sideways board; RetroClinic Co-Pro; VideoNuLA
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Re: Microvitec Cub: Is it a 653 or 895?

Post by philpem »

dhoggan wrote:
Sun Aug 23, 2020 11:38 pm
The shimmering appears more pronounced on mode 0 than mode 7 although both have it. Once the monitor has been on a while it's almost unnoticeable on mode 7 (almost, but just very feint if you look from a close range), but still there on mode 0 although, again, less so than when just powered uo.
That's almost certainly the degauss PTC. It contains two parts - a low-resistance PTC and a higher-resistance heater. The PTC's resistance increases as it warms up. The idea is that the degauss coil is on at full power for the first few seconds of the screen being powered on, then tails off over time to demagnetise the tube.

It's a white, blue or black component with three legs which connects to the degauss connector. It's easy to replace and fairly inexpensive, I used one of these: https://www.ebay.co.uk/itm/PTC-1-PTC962 ... 1896277441

Cheers
Phil.
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