Tired CRT symptoms that aren't a tired CRT?

[lnx64]

Hey so I've been preparing to try and open my own arcade, and visited a local one to get some ideas on how they are laid out, and I saw that a Ms. Pac-Man machine was down because it was broken. I spoke with the owner and found that they explained the CRT is busted because it got necked by the previous owner and they didn't know until it was setup on the floor.

Knowing that my 80's Samsung TV, C911OMA (which has a K20 chassis) actually uses the same exact CRT, though tired, I offered a temporary solution so the machine could work. I brought my TV in (since I haven't used it often much anymore), and we did a CRT swap (and deflection yoke because we weren't sure if the yoke would be the same), found that the tabs were slightly in different places where it mounts, but it still fit behind the bezel of the arcade cabinet just fine.

Powered it up, and um, I got fairly confused fast. On the TV itself, the CRT smears when too bright or the colors up too high, it's blury and just all around appears tired. On the Ms. Pac-Man machine? It was bright, vibrant, sharp and doesn't actually seem tired at all!!

What's going on here, how could the CRT have tired symptoms in the set, but in the arcade cabinet appear like an entirely different CRT? I know it's RGB but even with the contrast cranked, no smearing at all, no blooming, it just looks good. The TV's K20 chassis however, cannot do anything even remotely close to this.

Is it possible to have perhaps a fault on the TV chassis causing symptoms of a tired CRT? I did when I originally got the TV years ago when I joined this forum, needed to change out the flyback to an HR Diemen as the original was internally shorting, but the picture quality did not change between flybacks. What else on the CRT's chassis should I be looking at?

Currently the TV is without a CRT but still with me, as the CRT is currently being used in the arcade as we speak and racking in quarters which is nice, so it's getting use. They are planning to source a proper replacement and give me my CRT back (I didn't charge, it was a favor to help out a local business), but I'm still at a loss, I've never seen this CRT appear so good before, and the Ms. Pac-Man cabinet does have a tinted glass, and yet is still brighter than if the CRT was in the TV with no tinted glass in front of it.

Ideas? I know this TV ain't worth saving, but it appears the CRT is actually VERY good on it's own, but the chassis is garbage.

[jbattles]

Tube is probably tired in the TV, but in the arcade it's not. In the arcade they're driven harder than a set. Look at the screen burn they get. Usually if the picture is moving like a computer screen saver it does not burn, but an arcade is driven so hard that just the normal display burns the screen.

[lnx64]

There was burn on the old CRT but not stationary objects. What was burnt in was the game play field, some bits of the score, and other stationary elements. Player sprites appear to suffer no burn.

I might just let them keep the CRT as a donation and get myself a new CRT for myself if I can even source one. Since I don't use this set much anymore since even though it's "woodgrain" it's truly a BPC at heart, I can certainly find something better and worth it anyway. The TV had maybe the worst notch filter I had ever seen, and lacks a proper color killer circuit (or it never worked) so monochrome sources always had color fringing as if it was trying to decode color from something without a color burst.

[old_tv_nut]

Are you sure the color killer didn't work? There were some sources, particularly analog cable systems, that kept the color burst on all the time, even on monochrome content.

[JohnCT]

Originally Posted by lnx64

Is it possible to have perhaps a fault on the TV chassis causing symptoms of a tired CRT?

Yes, possible but unlikely. The filament voltage is what's most picky when it comes to "zip". If your filament voltage was low on your Samsung, then the tube would look tired. Since the filament is derived from the flyback, then low HV could cause that, but there are usually other symptoms besides a tired look of the picture.

I've seen the kine source bypass filter cap (typically low value like 10uf and high voltage like 250V) go bad and cause excessive brightness. When the G2 adjustment is lowered to compensate, the cutoff of the guns is wrong and the tube can flare out like it's weak, but the other symptom of the bad filter cap is that the brightness would be higher on the right side of the picture. Since you didn't mention that, I don't think the kine source cap is weak/bad in the Samsung.

It's possible (likely really) that your Samsung tube has different impedance on the filament so when installed in the game monitor, you're filament is running brighter (hotter) because the filament winding of the monitor flyback is different than the filament winding on the Samsung.

John

[lnx64]

Originally Posted by JohnCT

Yes, possible but unlikely. The filament voltage is what's most picky when it comes to "zip". If your filament voltage was low on your Samsung, then the tube would look tired. Since the filament is derived from the flyback, then low HV could cause that, but there are usually other symptoms besides a tired look of the picture.

I've seen the kine source bypass filter cap (typically low value like 10uf and high voltage like 250V) go bad and cause excessive brightness. When the G2 adjustment is lowered to compensate, the cutoff of the guns is wrong and the tube can flare out like it's weak, but the other symptom of the bad filter cap is that the brightness would be higher on the right side of the picture. Since you didn't mention that, I don't think the kine source cap is weak/bad in the Samsung.

It's possible (likely really) that your Samsung tube has different impedance on the filament so when installed in the game monitor, you're filament is running brighter (hotter) because the filament winding of the monitor flyback is different than the filament winding on the Samsung.

John

Sorry for late reply, but I had to verify the filament voltage, and you are correct, the arcade monitor board is producing a higher voltage than that of the TV (and I did plug the TV into the tube as a test so it had a proper load as well).

Which one would be correct though, because both used the same CRT part number make and model, and both use monitor boards built by Samsung. So in that case, I'm not sure which is right or wrong.

[JohnCT]

Originally Posted by lnx64

Sorry for late reply, but I had to verify the filament voltage, and you are correct, the arcade monitor board is producing a higher voltage than that of the TV (and I did plug the TV into the tube as a test so it had a proper load as well).

Which one would be correct though, because both used the same CRT part number make and model, and both use monitor boards built by Samsung. So in that case, I'm not sure which is right or wrong.

Using a TRMS meter**, the correct voltage is 6.30VAC.

Often there is a dropping resistor (5W typically) that will be used to fine tune the filament winding of the flyback to the CRT filament impedance - perhaps one in either monitor was replaced and the value is off.

Also, make sure someone didn't add a filament winding to the flyback of either in order to "float" the filament from ground. We used to do this to kludge a heater to cathode short. Floating the filament with an external and isolated winding around the flyback's ferrite core would hide the short on screen, but a lot of guys didn't pay much attention to the turns or even placement of the winding on the core.

If the voltage is a couple of tenths bellow 6.3, the picture would look weak on a tube with a bunch of hours on it that otherwise would still be serviceable (a strong tube will run at 6.0 volts fine however). If the voltage is a couple of tenths above 6.3, the tube will look great but will have a shorter life.

**TRMS meter.. Since the AC voltage of the filament is sourced from the flyback, it's not a 60hz AC but a 15Khz AC, and a meter that isn't a TRMS will not read accurately at 15Khz. Another poster on VK used a TRMS meter and still got an erroneous reading, so apparently any TRMS meter may not be the solution. I do know the 80 series of Fluke works on TV scan derived AC voltages.

John

[lnx64]

In lieu of a TRMS meter, I brought my Tek oscilloscope to measure with (and since I don't know if I'm dealing with an open chassis or not I used an isolation transformer on the scope to not get hurt or the scope hurt).

The TV in circuit is actually only producing 5.9v, the arcade board peak to peak is around 6.16v on the filament voltage. I did notice on the arcade board this seems fairly consistent, but on the TV board this varies based on what's on the screen. The more white the picture gets, the more the voltage drops (by about .2v). I'm going to take a guess that the TV is having some issues in the power supply section since I did replace this flyback with a high quality replacement 10 years ago, and the original flyback produced the same visual tired clues before the original flyback went in a blaze of glory.