Restauration of Sanyo VM 4209 & Sanyo VM 4092

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Restauration of Sanyo VM 4209 & Sanyo VM 4092

There is always something new to do.

 

At the moment, I am getting my hands on Sanyos (VM 4209 and 4092) and want to bring them back to their former glory. I have managed to buy two of those each on eBay. Obviously, I will not restore the electrical parts of them myself, but have a pro looking at them. I have the service manual of the 4209 that can guide them.

 

It is not easy to find an old-school repair shop for CRTs, but I am pretty sure there are still some old masters in the area, I just need to find them.

 

These are the things I want to achieve:

 

Regarding optics

1. Repaint the housing (done by a pro – I expect first results end of the week)

2. Recreate the Sanyo logo plaque (there is one missing). I have ordered aluminium plaques in the right shape and have them powder coat painted, then the logo will be lasered – looking forward to that one as I have a Laser Pecker 2 which should be up for this task. 

3. Recreate the dials (four in total are missing). Will try to 3D render those (they consists of two parts; black plastic and a metal (?) top. I will print the plastic part and CNC the top part (a friend's son has a CNC machine. Maybe that works – let's see!)

 

Regarding function

1. Adjust/Optimize the picture geometry

2. "Unburn" the tube – I have heard that in the past there has been a special kind of equipment that was able to "refreshen" a CRT's tube – not sure if that information is accurate, but I will research that. Any insights are appreciated!

3. "Unwobble" the picture. Two of the monitors have a minor "wobble" in the picture. Not dramatic, but maybe this can be healed by someone experienced.

 

Why do I do this? 

 

There is still the plan that I want to initiate a special exhibition at the Deutsches Museum in Munich in 2026 (Apple's 50th birthday) where I want to (temporarily) donate a few fully working replicas for people to actually sit down and experience the Apple-1 for themselves. I had initial contact with the museum in 2022 and they were responding positively to the idea.

 

I will post updates on this from time to time if you don't mind.

 

Best

 

Armin

 

 

 

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what rejuvenators can and can't do

Hello Armin.

When a CRT tube has "burn-in", it means that the phosphor coating on the inside of the tube face has worn out from long use. Once this happens, it will no longer glow evenly: the areas that have had the most use will be dimmer than other areas, leaving a kind of "negative image" superimposed on whatever the monitor displays. This burned-in image can even be seen when power to the monitor is off.

The only way to "cure" burn-in is by replacing the tube, or rebuilding it. CRT tubes are not being made any longer, so there are not many left as spares for replacements. The shops capable of rebuilding tubes have all closed.

Other problems are treated differently. If there is no burned-in image, but the picture from the display is simply too dim or blurry, then "rejuvenating" the tube is sometimes helpful. It is really the cathode that rejuvenation fixes, by heating it so that the surface begins to boil. At this point, the atoms on the surface get remixed which can help a worn out cathode to emit more electrons.

The only thing that can be done now about burn-in is to prevent it. This is what so-called "screen saver" software was meant to do. By replacing an idle, motionless image with a black screen or an animation, wear is spread out over the whole screen area. Later, when CRT displays were made with energy saving sleep modes, "display sleep" settings also helped prevent burn-in.

 

Regarding the knobs, you may be able to find a matching set from various suppliers. Knobs were rarely made by the OEM, they were usually bought off the shelf.

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Yup, I did a bit of more

Yup, I did a bit of more research. While you can "rejuvenate" the cathode, burned-in stuff isn't really curable.

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How to mitigate burn-in pictures in CRTs

In post #3, retroplace_1 wrote:

 

" Yup, I did a bit of more research. While you can "rejuvenate" the cathode, burned-in stuff isn't really curable.  "

 

Uncle Bernie comments:

 

Unless it is a very severe case of burn-in, you can greatly mitigate the issue by dialing down the brightness control.

 

The usual, "correct" setting for brightness is such that in the "black" areas of the screen here still is a faint glow of the phosphor. However, this exposes the burn-in.  I have one old Shibaden monitor which still shows the static picture of the driveway it once was pointed to for decades. Came from a security system. But with the brightness dialed down, the burned-in picture is barely noticeable. The fact that the characters for text only display (Apple-1) have less "white dots" than "black area" helps, too.

 

A modern desktop would suck and expose the burned-in picture in a nasty way.

 

- Uncle Bernie

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Some pictures (work in progress)

Here are some pictures, first the 4092. The Sanyo logo is still missing, though:

 

 

And here comes the 4209:

 

 

What has been done so far?

The housing has been painted, making sure that the structure of the paint resembles the original paint. This turned out just wonderful. The guys at the paint shop obviously where spot on when they said "this was not structured paint, it was just a 'bad' paint job", ie. the case was just spray painted without any finishing afterwards (like sanding or similar). 

 

The rest has been cleaned as well as possible. The chrome parts have been polished (they had a bit of surface rust, nothing dramatic, though). Next steps: I am waiting for the alumium blanks for the brand logo plaque (they will be powder coated and the logo lasered). And finally: I have managed to buy a special tool that might be able to regenerate the cathode tube.So far, I am pretty happy with how it turned out.To be continued …

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Cathode regeneration with Müter BMR 95

Little update: I stumbled across a nifty little device called "Müter BMR 95". It was used to regenerate/rejuvenate CRT tubes. I got it for 80 Euro and thought it was worth trying if it did anything to the Sanyo tubes. So I read a bit about how to do the process and tried it.

 

The results have been mixed:

 

My 4092 seems to have a pretty weak/worn heating element which hardly glows at all. During regenration I could see that there were a lot of sparking going in the tube (which is a good sign as that means the oxide layer breaks off the surface thus allowing the barium (?) to release electrons easier. The picture was way brighter and more in focus afterwards. So that worked. The heating element is still very, very dim in operation, but I am not sure whether my expectation of how bright it should glow is simply wrong.

 

My 4209, on the other hand, showed basically no change, but it was pretty good already. Unfortunately, there must be a little issue with it because when I kick in the contrast, the lower lines of characters get extended to the right. This is something I have seen in the past when either the trimmer on the Apple-1 was far to the right or with very high contrast boost on the monitor. But in this case, I hardly crank the contrast up and this symptom already shows. It is still acceptable, but probably I will replace the tube in that one … let's see …

 

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The structure of a CRT

The structure of a CRT cathode is something like a hollow tube with the heater coiled up inside it. So even though the heater is glowing like a filament, it does not shine out like a light bulb from the neck of the tube. The amount of visible light has nothing to do with the cathode emissivity.

 

If the raster width increases with beam current, see http://www.repairfaq.org/sam/monfaq.htm#monbloom

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Thanks for that.  I was

Thanks for that. 

 

I was wondering because the heating element in my 4902 looks way brighter than the one in the 4092 despite them having the same tube.

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Sanyo Logo Plaque Replica

Another milestone in restoring the VM 4092 has been achieved. Today, I received the powder-coated blanks, which I then lasered the logo in. Here is the result with which I am really, really happy.

 

 

If you compare side by side, there is a slight chance, you will spot tiniest differences, but it is very close

 

 

Judge for yourself: Which one is the original?

 

Best

 

Armin

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Well done, Armin. Looks great

Well done, Armin. Looks great!

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Hi Armin,Would you happen to

Hi Armin,

Would you happen to know what the color code for the VM-4209 is?  I'd love to repaint mine.

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CRT rebuilding

I thought I would link to some videos about CRT rebuilding since it has interest to collectors of antique computers.

 

This is a video taken at RACS in southern France. It shows the steps used to separate the gun assembly from the bell of the tube, phosphor removal and cleaning, the application of fresh phosphor, metal sputtering, cleaning and assembly of a new gun assembly, welding the new assembly to the bell, and air evacuation and flashing the getter. (actually I think the later stages were in another video I cannot locate)

The Early Television Museum has pages describing the rebuilding process. There is a video of the first tube they successfully rebuilt.

The last professional rebuilders retired a decade ago, but some experimenters have made progress since. I don't know of any who currently offer rebuilding as a service, but you could make inquiries at the ETM or on videokarma.org which seem to be abreast of most activity in this space.

This type of rebuilding is possible for monochrome tubes; for color CRTs, only electron gun replacement is practical, which means that burn-in on color tubes has no remedy.

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Not on top of my head. But I
Shilmover wrote:

Hi Armin,

Would you happen to know what the color code for the VM-4209 is?  I'd love to repaint mine.

 

Not on top of my head. But I will repaint another one soon and then I can tell you the color exactly (the painter has it).

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